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20 1:250000 geological map Geology of the Murihiku Area I. M. Turnbull A. H. Allibone (compilers) BIBLIOGRAPHIC REFERENCE Turnbull, I.M.; Allibone, A.H. (compilers) 2003: Geology of the Murihiku area. Institute of Geological & Nuclear Sciences 1:250 000 geological map 20. 1 sheet and 74 p. Lower Hutt, New Zealand. Institute of Geological & Nuclear Sciences Limited. Edited, designed and prepared for publication by P.J. Forsyth, P. L. Murray, P. A. Carthew and D.W. Heron. Printed by Graphic Press & Packaging Ltd, Levin ISBN 0-478-09800-6 © Copyright Institute of Geological & Nuclear Sciences Limited 2003 FRONT COVER The most prominent geological feature in the Murihiku area is the Southland Syncline. The north limb, seen here looking southeast from south of Lumsden, is outlined by prominent strike ridges trending away through the Hokonui Hills. The axis of the syncline lies to the south (right) and passes under the area of cloud in the far distance. The syncline is formed in Permian to Jurassic Murihiku Supergroup sedimentary rocks, with these strike ridges in Early to Middle Triassic North Range Group. The active Hillfoot Fault separates the Hokonui Hills from the extensive Quaternary gravels of the Waimea Plains (left), underlain by Permian Maitai Group sedimentary rocks. Photo CN43841/16: D.L. Homer ii CONTENTS ABSTRACT .................................................................. v Keywords ...................................................................... v INTRODUCTION .......................................................... 1 THE QMAP SERIES ....................................................... 1 The Geographic Information System ............................. 1 Data sources .................................................................. 1 Reliability ....................................................................... 1 REGIONAL SETTING .................................................... 2 GEOMORPHOLOGY ...................................................... 6 Northern ranges and basins ........................................... 6 Southland Syncline ........................................................ 7 Te Anau and Waiau basins ............................................ 7 Southland and Waimea Plains...................................... 12 Takitimu Mountains and Longwood Range ................. 12 Stewart Island .............................................................. 12 Offshore physiography ............................................... 12 STRATIGRAPHY ........................................................ 14 SILURIAN TO DEVONIAN ......................................... 14 Takaka terrane ............................................................ 14 CARBONIFEROUS TO CRETACEOUS ....................... 14 The Median Batholith ................................................. 14 Median Batholith from Longwood Range to Ruapuke ............................................................ 14 Permian Brook Street terrane intrusives within the Median Batholith ................................................. 16 Triassic- Jurassic intrusives ........................................ 16 Median Batholith on Stewart Island ............................ 19 Carboniferous ............................................................. 19 Middle Jurassic ........................................................... 19 Late Jurassic to earliest Cretaceous ........................... 19 Early Cretaceous ......................................................... 22 Plutonic rocks of Fiordland and offshore islands ........ 22 PERMIAN TO JURASSIC ............................................ 23 Brook Street terrane ................................................... 23 Unassigned mélange units ........................................... 26 Murihiku terrane ......................................................... 26 Willsher Group ............................................................. 28 Dun Mountain-Maitai terrane .................................... 29 Caples terrane ............................................................. 31 Paterson Group ............................................................ 33 CRETACEOUS SEDIMENTARY ROCKS ................... 34 EOCENE TO PLIOCENE ............................................... 35 Eocene non-marine sedimentary rocks ........................ 35 Oligocene to Pliocene sedimentary rocks .................... 36 Te Anau and Waiau basins (Waiau Group) ................. 36 Winton Basin and Southland shelf .............................. 36 Late Miocene to Pliocene non-marine sediments ........ 39 QUATERNARY ............................................................ 41 Early Quaternary deposits ........................................... 41 Middle Quaternary deposits ........................................ 41 Late Quaternary deposits ............................................ 42 OFFSHORE GEOLOGY ................................................ 46 TECTONIC HISTORY ................................................ 48 Eastern and Western provinces ................................... 48 Mesozoic deformation within the Median Batholith .... 49 Late Cretaceous tectonics ............................................ 49 Cenozoic tectonics and basin development ................. 49 Quaternary tectonics ................................................... 50 ENGINEERINGGEOLOGY ......................................... 51 Paleozoic to Mesozoic rocks ........................................ 51 Late Cretaceous and Tertiary sedimentary rocks ......... 51 Quaternary sediments .................................................. 51 GEOLOGICAL RESOURCES ..................................... 52 METALLIC RESOURCES ............................................. 52 Hard-rock gold mineralisation ...................................... 52 Alluvial gold ................................................................ 52 Silicon and ferrosilicon ................................................ 52 Other metallic minerals ................................................. 53 NON-METALLIC RESOURCES ................................... 54 Coal .............................................................................. 54 Peat .............................................................................. 55 Hydrocarbons .............................................................. 55 Aggregate .................................................................... 55 Limestone .................................................................... 56 Silica sand .................................................................... 56 Serpentinite .................................................................. 56 Clay .............................................................................. 56 Building stone and riprap ............................................ 56 Groundwater ................................................................ 56 GEOLOGICAL HAZARDS ......................................... 57 Earthquakes (by G. L. Downes) .................................... 57 Tsunami (by G. L. Downes) .......................................... 60 Landslides .................................................................... 60 Volcanic hazard ............................................................ 62 Subsidence due to mining ............................................ 62 Groundwater contamination ......................................... 62 AVAILABILITY OF QMAP DATA ............................... 63 ACKNOWLEDGMENTS ............................................. 63 REFERENCES ............................................................. 64 APPENDIX 1 Nomenclature of units mapped on Stewart Island ....... 72 iii Te Puka o Taakitimu - Monkey Island This rocky knob near Orepuki, which becomes an island at high tide, has significance to Maaori as Te Puka o Taakitimu – the anchor stone of the legendary Taakitimu waka/canoe which was wrecked in Te Waewae Bay. It is said that the waka was turned to stone as the Taakitimu Mountains, and the bailer of Taakitimu became the Hokonui Hills. iv ABSTRACT The Murihiku 1:250 000 geological map covers 18 000 km2 of south Otago and Southland, in the South Island of New Zealand, and includes Stewart Island (Rakiura). Topography varies from flat-topped ranges and intervening basins in northern Southland, to prominent strike ridge topography of the Kaihiku, Hokonui, and North ranges, the jagged Takitimu Mountains, the lower bushclad Longwood and Twinlaw massifs, and the extensive Southland Plains. Stewart Island has generally subdued bush and scrub-covered topography, with rolling hills and the swampy Freshwater Depression in the centre. Numerous other offshore islands dot the shallow waters of Foveaux Strait and the fringes of Stewart Island. The Waiau Basin lies in the far southwest, on the eastern edge of Fiordland. The map area covers a wide range of Paleozoic to Mesozoic rocks which form parts of several tectonostratigraphic terranes. The Paleozoic to Cretaceous Median Batholith comprises gabbroic to granitic plutonic rocks that intrude metamorphic rocks of the Takaka terrane on Stewart Island and the Permian oceanic volcanic island arc sequence of the Brook Street terrane in the Takitimu and Longwood ranges, and at Bluff. Late Permian to Jurassic Murihiku terrane sedimentary rocks separate Brook Street and Dun Mountain-Maitai terranes and underlie most of the map area, thrust over Brook Street terrane in the west and faulted against Dun Mountain Maitai terrane along the northeastern limb of the regional Southland Syncline. The Dun Mountain-Maitai terrane is in turn faulted against the Caples terrane in the northeastern corner of the map area. Dun Mountain - Maitai terrane rocks represent an Early Permian ophiolite complex, overlain by metasediments of Permian to Triassic age. The Caples terrane is probably of Permian to Triassic age in the map area. Except on Stewart Island, these basement terranes are overlain by discontinuously preserved Cretaceous and more extensive Eocene and younger sedimentary rocks of the Ohai, Nightcaps, Waiau and East Southland groups. The contact is the widespread Late Cretaceous to Cenozoic Waipounamu Erosion Surface in northern Southland. The fault-controlled Cenozoic Waiau Basin contains up to 5 km of marine and non-marine clastic sedimentary rocks; coeval but much thinner shelf sedimentary rocks, typically limestones, extend beneath the Winton and Eastern Southland basins and the Waimea Plains. Quaternary glaciation in Fiordland and northern Southland produced large volumes of gravel which accumulated in the Waimea and Southland Plains, the latter also influenced by marine sedimentation during interglacial high sea levels. Cirque glaciation affected the Takitimu and probably Longwood ranges, and glaciers also formed on Mt Anglem and Mt Allen on Stewart Island. In northern Southland, at Gore and at Orepuki, Quaternary deposits (including beach placers at Orepuki) have produced at least 8000 kg of alluvial gold. Lode systems are preserved in the volcanic rocks around the Longwood Range but few have been mined. Platinum group metals have been mined and prospected for in the Longwood Range. Non-metallic minerals include limestone, subbituminous coal at Ohai, and large reserves of lignite in the East Southland Group. The Murihiku map area is subject to seismic hazard from the Alpine Fault west of Fiordland, and active faults in Central Otago and Western Southland, with associated earthquake shaking, landsliding, ground rupture, liquefaction and delta collapse. Landslides and rockfalls, both during and independent of major rainstorms, are minor but ongoing hazards. Tsunami, mine collapse and flooding are more localised hazards. Keywords Murihiku; Southland; Stewart Island; Invercargill; Foveaux Strait; 1:250 000 geological map; geographic information systems; digital data; bathymetry; Brook Street terrane; Caples terrane; Dun Mountain - Maitai terrane; Murihiku terrane; Takaka terrane; Median Batholith; plutons; Pegasus Group; Paterson Group; Caples Group; Maitai Group; Willsher Group; Dun Mountain Ultramafics Group; Livingstone Volcanics Group; Dun Mountain Ophiolite Belt; Brook Street Volcanics Group; Takitimu Subgroup; Productus Creek Group; Barretts Formation; Greenhills Group; Greenhills Ultramafic Complex; Bluff Intrusives; Pahia Intrusives; Holly Burn Intrusives; Tin Hut mélange; Letham Ridge mélange; Murihiku Supergroup; Kuriwao Group; North Range Group; Taringatura Group; Diamond Peak Group; Ferndale Group; Mataura Group; Park Volcanics Group; Ohai Group; Nightcaps Group; Waiau Group; Clifden Subgroup; East Southland Group; Forest Hill Formation; marine terraces; alluvial terraces; alluvial fans; moraines; till; outwash; landslides; peat swamps; sand dunes; oysters; Livingstone Fault; Hauroko Fault; Blackmount Fault; Tin Hut Fault System; Letham Ridge Thrust; Gutter Shear Zone; Hillfoot Fault; Escarpment Fault; Freshwater Fault System; Southland Syncline; Taieri - Wakatipu Synform; Quaternary tectonics; active faulting; economic geology; alluvial gold; platinum; sub-bituminous coal; lignite; Ohai Coalfield; Eastern Southland Coalfield; peat; limestone; groundwater; hydrocarbons; engineering geology; landslides; regolith; natural hazards; seismotectonic hazard; volcanic eruptions; new stratigraphic names. v 170° E Ne w 35° S Ca le do 175° E 35° S Kaitaia a Ba 00 Whangarei m 0m 200 ni 20 sin Auckland Waikato Challenger Plateau Rotorua 47 mm/yr Taranaki Basin Raukumara Hawkes Bay Taranaki 40° S h ug Australian Plate 20 00 ik H m Haast t ul Fa ne i p 38 Al Kaikoura 41 mm/yr mm/yr Christchurch Wakatipu Puys 165° E Pacific Plate Chatham Rise Aoraki Waitaki 45° S Fiordland r 37 mm/y Bounty Trough Dunedin egur Tren ch n a ur Greymouth 45° S o Tr i g Wairarapa Wellington Nelson 40° S 2000 m QMAP Murihiku Campbell Plateau 170° E 175° E 0 100 200 Kilometres 180° E Figure 1 Regional tectonic setting of New Zealand, showing the location of the Murihiku geological map and other QMAP sheets, major offshore features (as illustrated by the 2000 m isobath) and active faults. The Murihiku sheet lies on the Pacific Plate, east of the Alpine Fault which marks the Australian-Pacific plate boundary west of Fiordland. The relative rates and directions of plate movements are shown by the arrows. Adapted from Anderson & Webb (1994). vi INTRODUCTION THE QMAP SERIES This map is one of a national series known as QMAP (Quarter-million MAP; Nathan 1993; Fig. 1), and supersedes the previous 1:250 000 geological maps of the Murihiku area which were published in the 1960s (Wood 1966; McKellar 1966; Watters et al. 1968). Since then, Stewart Island has been mapped in detail for the first time (see Appendix 1), and there have been numerous detailed onshore and offshore geological and geophysical studies of parts of the area by government, university and industry geologists. The need for geological information has increased as a result of the Resource Management Act, demands for geological resources, a new educational curriculum, and greater awareness of natural hazards and their mitigation. In the Murihiku area, changes in land use have expanded the demand for geological information, especially on groundwater. The increase in environmentfocused tourism, boosted by the creation of Rakiura National Park, has also resulted in a demand for more detailed information on local geology. The geology shown on the map has been generalised for presentation at 1:250 000 scale. Rock types are shown primarily in terms of their age of deposition, eruption or intrusion. The colour of the units on the map face thus reflects their age, with overprints used to differentiate some lithologies. Letter symbols (in upper case, with a lower case prefix to indicate early, middle or late if appropriate) indicate the predominant age of the unit. Metamorphic rocks are mapped in terms of age of the parent rock (where known), with overprints reflecting the degree of metamorphism and deformation. The last lower case letter (or letters) indicates either a formal lithostratigraphic unit or the predominant lithology. A time scale showing the correlation between international and local time scales, and ages in millions of years (Ma) or thousands of years (ka) (Cooper 2004), is inside the front cover. This accompanying text is not an exhaustive description or review of the various rock units mapped. Except for some units on Stewart Island, names applied to geological units are those already published; the nomenclature has not been revised where anomalies are present. For more detailed information on individual rock units, specific areas, natural hazards or minerals, see the references cited throughout the text. The Geographic Information System The QMAP series uses computer methods to store, manipulate and present geological and topographical information. The maps are drawn from data stored in the QMAP Geographic Information System (GIS), a database built and maintained by the Institute of Geological and Nuclear Sciences (GNS). The primary software used is ARC/INFO®. The QMAP database is complementary to other digital data sets maintained by GNS, e.g. gravity and magnetic surveys, mineral resources and localities, fossil localities, active faults and petrological samples. Background topographic data were purchased from Land Information New Zealand. The QMAP series is based on detailed geological information, plotted at 1:50 000 scale on NZMS 260 series topographic base maps. These record sheets are available for consultation at GNS offices in Lower Hutt and Dunedin. The detailed geology has been simplified for digitising, with linework smoothed and geological units amalgamated to a standard national system based on age and lithology. Point data (e.g. dips and strikes) have not been simplified. All point data are stored in the GIS, but only representative structural observations are shown. The procedures for map compilation and data storage and manipulation are given by Rattenbury & Heron (1997). Data sources This geological map includes data from many sources, including published geological maps and papers, unpublished data from University theses, unpublished GNS technical and map files, mining company reports, field trip guides, the New Zealand Fossil Record File (FRED), and GNS digital databases of geological resources and petrological samples (GERM, PET). Field mapping of poorly known areas, undertaken between 1999 and 2001, ensured a more even data coverage over the map area. Landslides were mapped from air photos, with limited field checking. Offshore data were obtained from published and unpublished surveys by NIWA, GNS, and the University of Otago Geology Department. Types of data sources used are shown in Fig. 2; data sources used for map compilation are identified by * in the references. Reliability This 1:250 000 map is a regional scale map only, and should not be used alone for land use planning, planning or design for engineering projects, earthquake risk assessment, or other work for which detailed site investigations are necessary. Some of the data sets which have been incorporated with the geological data (GERM, for example) have been compiled from old or unchecked information of lesser reliability (Christie 1989). 1 1 3 59 2 5 6 40 4 48 30 57 7 8 11 39 9 14 10 12 51 49 13 28 52 29 34 35 31 36 32 41 16 15 54 44 43 17 53 18 37 42 50 58 51 27 26 25 33 38 24,47 20 19 22 45 47 56 23 55 21 Student theses 46 Published papers Published 1:250 000 map sheets Student theses 1. Hall 1989 2. Kirby 1989 3. Pringle 1975 4. Scott 1974 5. G. Hyden 1979 6. Meder 1963 7. McOnie 1969 8. Houghton 1977 9. Griffith 1983 10. Willsman 1990 11. Begg 1981 12. Gass 1998 13. Arafin 1982 Published papers 14. Boles 1971 15. Forsyth 1992 16. Banks 1977 17. Rombouts 1994 18. Macfarlane 1973 19. Waddell 1971 20. Allibone 1986 21. Peden 1988 22. Frewin 1987 23. Cook 1984 24. Webster 1981 25. Graham 1977 26. Elder 1994 27. Mossman 1970 28. Morton 1979 29. Griffin 1970 30. Clough 1987 31. Ryder-Turner 1977 32. Ritchie 1977 33. Holden 1993 34. Stenhouse 2002 35. Bishop 1962 36. Becker 1973 37. Simpson 2002 38. Bosel 1981 39. Landis et al. 1999 40. Coombs 1950 41. Mortimer et al. 1999a 42. Cahill 1995 43. Price & Sinton 1978 44. Willett & Wellman 1940 45. Allibone & Allibone 1991 46. Allibone & Tulloch 1997 47. Watters 1978a 48. Cawood 1986 49. McIntosh et al. 1990 50. Campbell et al. 2001 51. Coombs et al. 1992 52. Cawood 1987 53. Macpherson 1938 54. Campbell & Force 1973 55. Bishop & Mildenhall 1994 56. Allibone 1991 Published 1:250 000 map sheets 57. McKellar 1966 58. Watters et al. 1968 59. Wood 1966 Figure 2 Types of geological data sources used in compiling the Murihiku map. Over 150 sources are represented; details of individual sources can be obtained from the references, where they are indicated by an asterisk. REGIONAL SETTING The Murihiku geological map area extends from eastern Fiordland to the Pacific coastline at the Catlins, and south across Foveaux Strait to Stewart Island and its offshore islands. The area lies entirely within the Pacific Plate, east 2 of the active Australian-Pacific plate boundary which in southern New Zealand is the Alpine Fault, west of Fiordland (Fig. 1). The Pacific Plate beneath Murihiku is largely composed of fault-bounded terranes of regional extent with different geological histories – the Paleozoic to Mesozoic Takaka, Brook Street, Dun Mountain-Maitai, 60 76 70 80 79 98 99 61 86 77 87 92 81 77 100 101 71 73 63 62 87 88 89 82 102 65 78 64 83 79 103 90 80 97 67 68 87 72 106 66 91 93 87 104 105 84 74 94 95 107 69 96 85 71 75 Other published maps Reports Unpublished maps Other published maps 60. McKellar 1973 61. Mutch 1964 62. Wood 1969 63. Bowen 1964 64. Turnbull 1992 65. McKellar 1968 66. Lindqvist 1992 67. Wood 1956 68. McIntosh 1992 69. Speden 1971 70. Mortimer 1993a 71. Isaac & Lindqvist 1990 72. Marshall 1918 Reports 73. Patchell 2002 74. Mutch 1976 75. Watters 1994 76. Ritchie 1994 77. Beanland & Berryman 1986 78. Mutch 1977 79. Bishop & Macfarlane 1984 80. Thomson & Read 1996 81. Stewart & Glassey 1993 82. Glassey et al. 1996 83. Liggett 1979 84. Liggett 1972 85. Purdie 1970 Unpublished maps 86. Carter & Norris 1980 87. Willett 1939 88. Willett 1950 Murihiku and Caples terranes – which were amalgamated along the margin of Gondwana during the Mesozoic (Fig. 3). During and after terrane amalgamation, Brook Street and Takaka terrane rocks were intruded by the Median Batholith which is represented in the map area by the plutonic rocks of Stewart Island and the Longwood 89. Mutch 1960 90. Harrington & Wood 1947 91. Mutch 1967 92. Chandler 1964 93. Wood 1965b 94. Bluck 1998 95. Wood & Hitt 1964a 96. Wood & Hitt 1964b 97. Liggett 1973b 98. Healey 1938 99. Wood 1965a 100. Isaac & Lindqvist 1978 101. McPherson 1973 102. Watters 1947a 103. Watters 1947b 104. Speden 1957 105. Speden 1958 106. McKellar & Mutch 1967 107. Liggett 1973a Range. The terranes, and the Median Batholith, were overlain by Cretaceous to Cenozoic sedimentary rocks which are now thin or absent over much of the map area but thicker within the Te Anau and Waiau basins. Quaternary deposits are widespread and include the extensive gravels of the Waimea and Southland Plains. 3 SEDIMENTARY AND D VOLCANIC ROCKS Northland and East st Coast allochthons Pahau Caples terrane Rakaia Dun Mountain - Maitai aitai itai terrane Murihiku terrane ovince Province Hunua-Bay of Islands nds ds terrane Eastern Morrinsville-Manaia a Hill-Waioeka assemblage g (Waipa Supergroup) p) Torlesse composite terrane (eastern NZ) Brook Street terrane rane ne e estern Western e ovince Province Takaka kaka terrane Buller ler terrane NIC IC ROCKS KS S PLUTONIC Median edian Batholith h Karamea, aramea, Paparoa roa a and Hohonu ohonu batholiths thss ORPHIC OCKS RPHIC ROCKS CKS S AND METAMORPHIC NIC IC RPRINTS RINTS C OVERPRINTS INTS TS TECTONIC Esk k Head and Whakatane hakatane akatane katane ne mélanges g Haast aast st Schist Gneiss neiss ss N 200 km FA A LP IN U LT E Murihiku Figure 3 Pre-Cenozoic basement rocks of New Zealand, subdivided into tectonostratigraphic terranes; the extent of the Northland and East Coast allochthons is also shown. Chrystalls Beach Complex (Coombs et al. 2000) is shown here as part of the Caples terrane. Pale yellow (inset) shows covering Cenozoic sediments. Adapted from Mortimer 2004 4 TAKITIMU MOUNTAINS TH EA U IM O A S W TE A NA BAS U IN NORTHERN RANGES AND BASINS LA N D PL AIN S Cluth MURIHIKU ESCARPMENT a WAIAU BASIN Rive r SOUTHLAND r NC LI NE PLAINS Mataura Waiau R River o aR F arim LONGWOOD RANGE ve Ri Oreti Ap SY v e a u x S t r a i t STEWART ISLAND Figure 4 Shaded topographic relief model of the Murihiku map area, derived from 20 m contour data supplied by Land Information New Zealand, and illuminated from the northeast. North- to northeast-trending ranges and basins in the northeast of the map area are separated from the northwest-trending strike ridges of the Southland Syncline by the Murihiku Escarpment. 5 GEOMORPHOLOGY The Murihiku map area includes several distinct physiographic regions (Fig. 4), which are controlled by underlying geology and influenced by erosion and late Cenozoic tectonics. Northern ranges and basins The northern edge of the map sheet, between the Clutha and Mataura rivers, lies at the southern limit of the Central Otago region of tilted fault block ranges separated by faultangle depressions. Ranges up to 1500 m in elevation include the Blue Mountains (Fig. 5) and the Black Umbrella Range (Fig. 6). The ranges generally trend north to northeast, with some trending northwest. Most range front faults are Late Cenozoic in age, and the Blue Mountain No 1 Fault is active (Beanland & Berryman 1986). The fault blocks comprise massive to weakly foliated Caples Group sandstone and semischist. The blocks become lower southward as the northeast-trending fault systems die out toward the Murihiku Escarpment. In the map area, large scale landsliding typical of Central Otago range fronts (McSaveney & Hancox 1996; Turnbull 2000) is present only in the Black Umbrella Range. The flat surfaces of the ranges, and the downlands beside the Clutha River in the northeast of the map area, are inherited from the Cretaceous to Cenozoic Otago Peneplain or Waipounamu Erosion Surface (WES) (LeMasurier & Landis 1996; Youngson & Landis 1997). This broadly planar surface originally extended across much of the South Island and beyond. It has a complex fluvio-marine origin, and is of early to mid Cenozoic age in the map area. The surface can be used as a structural marker for determining Late Cenozoic deformation, such as folding and vertical fault displacement (Fig. 6). The southern ends of the Mataura, Black Umbrella and Blue Mountains ranges are cut by the antecedent gorges of the Mataura, Waikaka, and Pomahaka rivers (Fig.7), formed during initial uplift of the ranges in Late Pliocene to Quaternary time. Extensive high terraces lie between these major valleys, with flights of lower terraces and fans near the modern flood plains of these rivers. The upper eastern slopes of the Black Umbrella Range contain small cirques of glacial origin, strongly modified by landsliding. Figure 5 The Blue Mountains and adjacent Tapanui depression, looking south. The range front fault (Blue Mountain No 1 Fault) has active traces, although none are visible in this picture. The Blue Mountains form one of the southernmost fault blocks in the northeast-trending Otago range and basin province. The Murihiku Escarpment, parallel to the trend of the Southland Syncline, lies in the distance. Photo CN43993/9: D.L.Homer 6 Southland Syncline Te Anau and Waiau basins The most conspicuous and well-known geomorphic feature within the Murihiku map area is the Southland Syncline (see front cover). Alternating harder sandstone and softer mudstone have been eroded to form strike ridges, which define the north limb of the syncline from the Catlins coast northwest through the Kaihiku, Hokonui, North and Taringatura ranges. The syncline ends abruptly at the Murihiku Escarpment, the geomorphic expression of the Hillfoot Fault (Fig. 4). In the Catlins, these strike ridges, crossed by northeast-trending faults, joints and lineaments, form a trellised landscape. Strike ridges are a less obvious feature of the landscape on the south limb, but form prominent bluffs in the southwestern Hokonui Hills and the Venlaw Forest, and define subsidiary folds (Fig. 8). Strike ridge topography is less well-developed on the western limb in the foothills of the Takitimu Mountains (Fig. 9). The western margin of the Murihiku map area, between Fiordland and the Takitimu Mountains and Longwood Range, includes parts of the Te Anau and Waiau basins. These depressions have existed since middle Cenozoic time, and are controlled by subsidence along the northeasttrending Moonlight Fault System. Both are infilled with Cenozoic sedimentary rocks (Turnbull & Uruski 1993), within which sandstone and limestone units form prominent strike ridges. The Cenozoic sedimentary rocks are overlain by extensive flights of Quaternary terraces, deposited by the Waiau River draining the former Te AnauManapouri piedmont glacier and other Fiordland glaciers. Moraines are not extensively preserved within these basins in the Murihiku map area. Extensive alluvial fans extend west from the Takitimu Mountains into the basins. 800 0 ge 110 1000 900 60 0 40 0 0 40 0 30 nt ou M ue Bl 200 TO ive NE r FA 600 40 0 500 M R ra R GS FO tau 900 800 700 600 500 400 Tapanui N Ma N 0 60 0 50 0 10 VI 30 0 00 10 SY 0 20 LI 20 0 ai 50 0 0 40 ns 60 0 50 0 70 0 0 30 0 30 0 50 300 200 400 500 80 700 0 30 0 20 0 7 60 00 0 300 400 0 40 50 0 40 0 0 50 0 50 0 40 U 300 60 0 100 IP 500 50 0 0 30 AT 30 0 0 60 500 0 40 500 AK 60 0 5 40 00 0 30 0 0 70 - W B la ck U m b r e l l a R a n 30 0 0 0 80 0 0 30 I 0 90 40 0 40 IER 20 0 30 00 11 00 10 100 TA 0 70 Waikaia 0 80 700 00 12 0 60 0 70 0 60 0 50 0 40 20 0 0 30 0 20 30 0 UL T 0 40 0 10 0 20 Clu 0 30 200 tha Riv 100 er 200 Gore HIL Waipounamu Erosion Surface (WES) LF OO TF AU 100 LT WES eroded along fault scarps and in gorges WES concealed by Cenozoic sediments 100 fault fold in foliation contour on WES (100 m interval) Figure 6 Structure contours on the Waipounamu Erosion Surface (WES), north of the Hillfoot Fault in the eastern part of the Murihiku map area. Major faults and folds in foliation are shown. 7 Figure 7 The Pomahaka River forms an antecedent gorge cutting through the southern Blue Mountains, seen here looking north-northwest. The higher flat-topped surfaces in the middle distance are underlain by Gore Piedmont Gravels of Early Quaternary age. The forested area to the right is underlain by Caples Group rocks, separated from Livingstone Volcanics Group (centre) by the northwest-trending Livingstone Fault (arrowed). Photo CN43913/10: D.L.Homer Figure 8 Ridges underlain by steeply dipping Jurassic sandstone and conglomerate strike inland from the Catlins coast near Teahimate Bay, on a subsidiary fold of the southern limb of the Southland Syncline. Gold has been mined from the Teahimate beach sands. Photo CN27259/18: D.L. Homer 8 Figure 9 Looking north along the Takitimu Mountains (left), which rise to 2000 m west of the upper Wairaki valley (foreground). The mountains are formed of resistant Permian Takitimu Subgroup volcanic rocks; less resistant Late Permian Productus Creek Group and Mesozoic Murihiku Supergroup sedimentary rocks form lower and less rugged country. Murihiku Supergroup rocks underlie Mt Hamilton, the isolated peak on the skyline right of centre. Photo CN43782: D.L. Homer Figure 10 The Southland Plains, seen here looking north over the mouth of Waimatuku Stream west of Invercargill, are underlain by Quaternary gravels of both alluvial and marine origin. An extensive 20 m marine bench (of OI stage 5 age) is truncated by a younger (6000 yr) sea cliff (arrowed) inland from the present coastline. Alluvial sediments from the Oreti River and other streams merge imperceptibly onto the OI stage 5 marine bench from the north. Wind-blown dunes trend diagonally across the back-beach lagoons in the foreground. Photo CN43805/8: D.L. Homer 9 Figure 11 Mt Hamilton, at the northern end of the Takitimu Mountains, is underlain by a thick sequence of Murihiku Supergroup sedimentary rocks. In this view to the south, bedding can be seen cutting across the west face of the peak. Faults of the Tin Hut Fault System (right foreground) separate Mt Hamilton from the main Takitimu Mountains. Figure 12 Port Pegasus and southern Stewart Island, looking to the west. The prominent domes of Bald Cone (B), Gog (G) and Magog (M) rise above the drowned valley system occupied by Port Pegasus, and are formed of the particularly quartz-rich granitic Gog Pluton. Denser vegetation grows on the adjacent granodioritic Easy Pluton. Photo CN43767: D.L. Homer 10 Figure 13 The lower Freshwater valley on Stewart Island is filled by a sand plain which extends from Paterson Inlet (distant), west to the Ruggedy Mountains. Longitudinal dune ridges overlie the sand plain. Thomsons Ridge (upper left) lies along the northern side of the Freshwater Fault System; the southern edge of the fault system lies along the hills to the south, and beyond to the south side of Paterson Inlet. Photo CN44055/15: D.L. Homer 11 Southland and Waimea Plains Stewart Island Over half the onshore part of the Murihiku map area consists of flat to gently rolling terrain between the Aparima, Oreti, and Mataura rivers, known as the Southland and Waimea Plains (Figs 4, 10). The terrain comprises Quaternary alluvial plains and terraces built of gravel derived from the Paleozoic and Mesozoic rocks of the river catchments. The older terraces are mantled with windblown loess and have been subtly dissected. Younger surfaces are flat with well-preserved meanders and low terraces. Terrace and paleodrainage systems are complex, as there has been considerable channel switching in response to aggradation, stream capture, and local tectonism. The topography of much of Stewart Island is dominated by a gently east-sloping plateau that rises from c. 20 m above sea level at the east coast to between 400 and 500 m elevation midway across the island. This gently sloping surface may be a stripped peneplain, an inference supported by the deep weathering typical of the underlying rocks. Isolated peaks such as Mt Anglem (980 m), Mt Allen (750 m) and the Tin Range (640 m) may represent remnant Cretaceous hills that have survived Cenozoic erosion. The Freshwater and Rakeahua river systems dissect the east-sloping surface. During higher interglacial sea levels, inundation of the Freshwater valley west to Mason Bay may have divided Stewart Island into two or three separate islands. Marine benches and paleoshorelines are present parallel to the modern coast (Fig. 10; see also Figs 36, 37). The benches formed during interglacial high sea levels, with subsequent tectonic uplift increasing to the west. A marine bench is also conspicuous east from Riverton, cut off from the present coastline by a younger sea cliff (Fig. 10), and extends intermittently eastwards. Older paleoshorelines further inland are indistinct, being partly obscured by peat mounds up to 10 m high and many hectares in extent. Takitimu Mountains and Longwood Range Dominating the landscape in the west of the Murihiku map area are the Takitimu Mountains (Fig. 9) and Longwood Range. The Takitimu Mountains consist of deeply eroded Permian Brook Street terrane volcanic rocks uplifted between the Moonlight Fault System, which follows the Waiau valley, and the Tin Hut Fault System in the Wairaki and upper Aparima valleys. As these bounding faults are active, the Takitimu Mountains are probably still rising. The range was extensively glaciated during the Quaternary, and cirques, U-shaped valleys and down-valley outwash plains are well developed. The volcanic rocks are jointed and prone to frost shattering, so steep prograding fan surfaces and active screes are extensively developed (see Fig. 38). Mt Hamilton (Fig. 11) is a fault-controlled massif separated from the main Takitimu Mountains by the active Tin Hut Fault System, and is still rising, with tilted Quaternary surfaces on its northern flank (Force et al. 1970). Mt Hamilton is underlain by Triassic sedimentary rocks of the Murihiku Supergroup, forming one of the thickest continuous sections of Murihiku rocks in New Zealand. Twinlaw and Woodlaw hills south of Ohai, and the lower Riverton peninsula, are also fault-controlled uplifted blocks of Permian volcanics. As they have not been glaciated and the rocks are typically deeply weathered, their profiles are much more rounded than the Takitimu Mountains. The Longwood Range, underlain by deeply weathered Paleozoic to Mesozoic plutonic rocks, may have been glaciated, but no glacial erosional features remain. 12 Steep cliffs reflecting active marine erosion characterise much of the west coast, interrupted by beaches such as Mason Bay (see back cover). Beaches are backed by large sand dunes that extend into the scrub- and bush-covered hinterland, reflecting the strong prevailing westerly winds. The east coast, in contrast, is dominated by the drowned valleys of Paterson Inlet, Port Adventure, Lords River and Port Pegasus (Fig. 12). The drowned valleys, the easterly slope of the topography, and the generally eastward drainage direction are consistent with gentle tilting of the island towards the east, probably during the late Cenozoic. Extensive sand plain deposits form gently east-dipping flights of terraces throughout the Freshwater River catchment (Fig. 13). These terraces are overlain by longitudinal and parabolic dune fields that have modern analogues at Mason and Doughboy bays, where dunes are actively advancing eastward under the prevailing westerly winds. Extensive modern and fossil peat swamps are interbedded with the dune fields and sand terraces. Evidence of Quaternary glaciation is preserved at Mt Allen (Allibone & Wilson 1997), and cirques and moraines are common features of the Mt Anglem massif (Fig. 14). Offshore physiography Foveaux Strait from Te Waewae Bay east to Slope Point in the Catlins is a shallow seaway with a relatively flat floor draped in gravel and sand and punctuated by hard rock knobs, some of which reach the surface as islands, rocks and intertidal reefs (Cullen 1967). Areas of sandy to gravelly bottom host the world famous Bluff oyster banks (Cullen 1962). At the western entrance of the strait, the sea floor remains shallow (Fig. 4) to the head of the Solander Trough, beyond the mapped area. The sea floor deepens rapidly west of Stewart Island into the Solander Trough. At the east end of the strait, there is some relief on the sea floor to depths of 40-50 m but the slope does not steepen until east of Ruapuke Island. Southeast of Stewart Island the sea floor is irregular and may be a continuation of the exhumed erosion surface studded with granite hills seen onshore (Figs 4, 12). Figure 14 The Mt Anglem massif on Stewart Island, with well-developed cirque topography, moraine ridges (dashed lines) and a glacial tarn (foreground). Jointing in quartz monzodiorite of the North Arm Pluton dips subvertically above the tarn. Photo CN2715/17: D.L. Homer 13 STRATIGRAPHY The Murihiku map area includes significant areas of many of New Zealand’s major Paleozoic to Mesozoic “basement” rock units and, in particular, the Permian to Jurassic clastic sedimentary rocks. Late Cretaceous to Cenozoic “cover” sedimentary rocks occur in the fault-controlled Te Anau and Waiau basins and beneath the Southland Plains. Fluvioglacial and alluvial deposits of Quaternary age are widely preserved, mainly in basins and lowlands. Sedimentary and volcanic basement rocks are primarily subdivided into tectonostratigraphic terranes (Figs 3, 15; Bradshaw 1993; Mortimer et al. 1999b). Within each terrane the rocks are described in terms of their age and lithology, related to traditional lithostratigraphic units at formation or group level. Several terranes have been affected by regional metamorphic and structural events and schistose rocks are also subdivided in terms of their textural development. In the west the terranes have been intruded by, or are dominated by, plutonic rocks of the Median Batholith. Where plutonic rocks are a minor part of a terrane they are described under that terrane. Median Batholith plutonic rocks are described in order of age, subdivided into plutons and intrusive complexes but only allocated to petrogenetic suites where these are known. Much of the mapping and subdivision of Stewart Island basement rocks is new and is based on work by Allibone & Tulloch (see Appendix 1). SILURIAN TO DEVONIAN Takaka terrane Metasediments of the Pegasus Group (SDp) (Watters et al. 1968; Henley & Higgins 1977) form rafts, xenolith screens and narrow elongate belts associated with Median Batholith plutons on Stewart Island. The group consists of micaceous schist rich in biotite and muscovite, quartzofeldspathic psammitic schist, laminated metaquartzites with traces of biotite and pyrite, calcareous psammitic schists rich in Ca-plagioclase, amphibole and clinozoisite, and hornblende-biotite amphibolites. Micaceous schists commonly contain minor sillimanite but garnet and cordierite are both rare. Primary sedimentary features have been destroyed by deformation and metamorphism, although transposed lithologic layering is still present (Fig. 16). In the Kopeka River catchment, Pegasus Group rocks are pervasively intruded by dikes from the adjacent Blaikies Pluton (shown by an overprint). At least three phases of ductile deformation and metamorphism have affected the Pegasus Group (Williams 1934b; Henley & Higgins 1977; Watters 1978b; Allibone & Tulloch 1997; Tulloch 2003). The earliest predates emplacement of granitoid rocks at 344 ± 2 Ma while later phases occurred between c. 344-305 Ma and during movement on the Gutter Shear Zone between c. 128120 Ma (Fig. 17). The youngest detrital zircons from the Pegasus Group, dated by single-crystal U-Pb TIMS (Walker et al. 1998), are 420 Ma, suggesting a maximum Late Silurian to Devonian sedimentation age and correlation with Takaka terrane. 14 CARBONIFEROUS TO CRETACEOUS The Median Batholith Plutonic rocks in Fiordland, in the Longwood Range, at Pahia Point and Bluff, beneath Foveaux Strait, and on Stewart Island are part of the Median Batholith (Mortimer et al. 1999b). Eastern parts of the batholith have previously been interpreted as a zone of dismembered fault-bounded volcanic arc fragments with likely allochthonous relationships to both the Eastern and Western Provinces, and referred to as the Median Tectonic Zone (Bradshaw 1993; Kimbrough et al. 1992; Kimbrough et al. 1994; Muir et al. 1998). The batholith was formed between the Late Devonian (c. 380 Ma) and mid Cretaceous (c. 100 Ma) along the paleoPacific margin of Gondwana (Mortimer et al. 1999b) with the intrusion of several distinct suites of I, S and A-type granitoids at different times (e.g. Tulloch 1983, 1988; Muir et al. 1998). Paterson Group volcanic and sedimentary rocks on Stewart Island are likely to be coeval with plutonism in the Median Batholith and were regarded as part of the Median Batholith by Mortimer et al. (1999b). Numerous plutons have been mapped on Stewart Island (Fig. 17) and in the Longwood Range. They are inferred to represent single or several closely related intrusions of magma that form contiguous mappable bodies, except where dismembered by younger plutons. Units such as the Bungaree, East Ruggedy and Pahia Intrusives comprise numerous small plutons, plugs and dikes that generally cannot be shown separately at 1:250 000 scale, or which have not been mapped to a level where boundaries between individual bodies have been established. Suite and source affinities of plutons are discussed where applicable. Median Batholith from Longwood Range to Ruapuke Permian to Jurassic plutonic rocks on the mainland lying west and south of the Brook Street Volcanic Group from the Longwood Range to Bluff are included in the Median Batholith (Mortimer et al. 1999a, 1999b; Fig. 18A). These intrusives are divided into an older Permian to Triassic suite of mafic to ultramafic rocks, and younger Triassic to Jurassic mafic, intermediate and felsic plutons (Mortimer et al. 1999b). The older intrusives represent the roots of the adjacent Brook Street terrane volcanic arc while the younger suite was emplaced after accretion of the Brook Street terrane arc to the margin of Gondwana (Mortimer et al. 1999a, 1999b). The Longwood - Pahia Point area has been investigated by Wood (1966), Challis & Lauder (1977), Price & Sinton (1978), Bignall (1987), Rombouts (1994) and others. Previous work has been summarised and supplemented with isotopic data by Mortimer et al. (1999a), with several new plutons and intrusive units described. The Bluff Intrusives have been intensively studied by Service (1937), Harrington & McKellar (1956), Watters et al. (1968), Mossman (1970, 1973), Graham (1977), Bosel (1981), O’Loughlin (1998) and Spandler et al. (2000). to gs Mo on Sy light ste F m ault in Liv Letham Ridg Thrust ne e Fault Hil lfo ot Fa ult FWFS E N G 20 km Tectonostratigraphic unit Terrane boundary and other major faults Late Cretaceous to Recent sediments Lithostratigraphic unit Caples terrane Caples Group Dun Mountain Maitai terrane Maitai Group Livingstone Volcanics Group Dun Mountain Ultramafics Group Murihiku terrane Murihiku Supergroup (see Fig. 23) Brook Street terrane Productus Creek Group Brook Street Volcanics Group (Takitimu Subgroup) Greenhills Group Brook Street terrane intrusives Median Batholith Many plutons (see Figs 17 and 18), including some in Brook Street terrane Takaka terrane Pegasus Group Figure 15 Major fault systems, and basement tectonostratigraphic units of the Murihiku area related to their lithostratigraphic framework. FWFS - Freshwater Fault System; E - Escarpment Fault; G - Gutter Shear Zone. 15 Permian Brook Street terrane intrusives within the Median Batholith In the Longwood Range, Permian intrusives form two large plutons: Pourakino Trondhjemite (Ybj) and Hekeia Gabbro (YTh) (Cowden et al. 1990; Mortimer et al. 1999a). Trondhjemite dikes and a small stock intrude adjacent Takitimu Subgroup rocks, which are altered to hornfels. The trondhjemite may be a composite earliest to Middle Permian unit, intruded between 292 Ma (Mortimer et al. 1999a) and 261 Ma (Tulloch et al. 1999). Hekeia Gabbro also intrudes Takitimu Subgroup. It includes gabbro, olivine gabbro, norite, troctolite, and anorthosite. A dioritic phase is differentiated in places and cumulate textures occur locally. On the coast between Pahia Point and Riverton, Brook Street intrusive rocks include the informal Colac granite (eTc) and Oraka diorite (eTo) units (Bignall 1987; Mortimer et al. 1999a). Isotopic data show these Permian intrusives to be petrologically primitive, with no crustal contamination, and genetically related to Brook Street terrane island arc rocks. Ar-Ar spectra from Hekeia Gabbro suggest minimum cooling ages of 249-245 Ma (latest Permian to earliest Triassic) (Mortimer et al. 1999a). Figure 16 Raft of Pegasus Group metasediments within Kaninihi Pluton quartz monzodiorite at South West Cape, Stewart Island, showing pervasive folding of lithologic layering. Lithologies include quartz-muscovite schist and amphibolite. 16 The Bluff Intrusives (Ybz) include the layered Greenhills Ultramafic Complex (Mossman 1970, 1973) which intrudes the Permian metasedimentary Greenhills Group. The ultramafic complex has a concentrically zoned dunitewehrlite core more than 750 m thick, surrounded by an upper olivine clinopyroxenite portion 650 m thick, and an outer gabbroic ring dike system. The zoned core has welldeveloped cumulate layering, modified by magma flow and mixing. Cogenetic dunite, wehrlite, gabbro, anorthosite, trondhjemite, and hornblende pegmatite dikes, and younger basalt and ankaramite dikes cut the complex. Associated gabbro and norite (Fig. 18B), and diorite, granodiorite and quartz diorite occur at Bluff itself. Similar norite, tonalite, and diorite with inclusions of hornfels and tonalite outcrop on Ruapuke Island (Webster 1981). Bluff Intrusives are dated at 265 Ma (Middle Permian) (U-Pb TIMS age; Kimbrough et al. 1992). Triassic- Jurassic intrusives Mesozoic intermediate to silicic plutonic rocks are more widespread than Brook Street intrusives, and form the western side of the Longwood Range and much of the 17 Lords Pluton Easy Pluton Doughboy Pluton ca. 128-116 Ma Knob Pluton ca. 305 Ma Tikotatahi Pluton Mason Bay Pluton Smoky Pluton Freshwater NE Pluton Walkers Pluton microdiorite dikes Kopeka South Pluton Adventure South Pluton Gabbro dikes Table Hill Orthogneiss Pegasus Group Tobin Ridge Folding, foliation development, amphibolite facies metamorphism------------------------------------------------------------------- Ridge Orthogneiss Foulwind Ruggedy Granite Freds Camp Pluton ca. 308-294 Ma ca. 340-345 Ma Rakeahua Pluton ca. 168 Ma Codfish Granite ca. 152 Ma Median/Darran Neck Granodiorite Big Glory Pluton Euchre Pluton Saddle Pluton ca. 140 Ma South West Arm Pluton Cow & Calf Gabbro North Arm Pluton ca. 130 Ma ca. 167 Ma Rollers Pluton Tarpaulin Pluton ca. 125 Ma Forked Pluton Paterson Group Richards Pt Porphyry Separation Point Bungaree and East Ruggedy Intrusives Figure 17 Age ranges and geochemical suite affinities of plutons within the Median Batholith on Stewart Island, related to major tectonic episodes. Modified after Tulloch (2001, 2003), Tulloch & Kimbrough (in press), and unpublished information. Uncoloured boxes denote plutons not assigned to any suite. ca 420-345 Ma Kaninihi Pluton Tight to isoclinal recumbent folding, foliation development, amphibolite facies metamorphism--------------------- Deceit Pluton Escarpment Pluton ca. 145 Ma ca. 340-345 Ma Campsite Pluton Development of the Gutter Shear Zone----------------------------------- Foliation development, shearing north of Freshwater valley-- Upper Kopeka Pluton Blaikies Pluton ca. 127-120 Ma Gog Pluton Movement on the Escarpment Fault ------------------------------------------------------------------------------------------------------ Upper Rakeahua Pluton ca. 116 Ma ca. 105-110 Ma Plutons north of the Escarpment Fault Movement on the Freshwater Fault System -------------------------------------------------------------------------------------------------------------------- Plutons south of the Escarpment Fault Suites coast from Pahia Point to Colac Bay (Challis & Lauder 1977; Price & Sinton 1978; Mortimer et al. 1999a). Mafic intrusions along the coast are termed Pahia Intrusives (Challis & Lauder 1977). Holly Burn Intrusives (Thb) (Mortimer et al. 1999a) in the western Longwoods include diorite, mela- and leuco-diorite, quartz monzodiorite, granodiorite and rare monzogranite and syenogranite, and the informal Austin quartz monzodiorite along the coast (Bignall 1987; Mortimer et al. 1999a). Larger areas of diorite and quartz diorite are differentiated. On the western margin of the Holly Burn Intrusives, steeply west-dipping foliation outlined by quartz, biotite and epidote defines the Grindstone Gneiss (shown by an overprint) (Wood 1969; Mortimer et al. 1999a). Pahia Intrusives (Jpi) include layered gabbronorite, norite and hornblende gabbros, and minor peridotite, with cumulate layering (Price & Sinton 1978). Layering was accompanied by flow and deformation and is highly irregular. Orbicular texture is rarely developed. Centre Island is composed of layered gabbro with numerous mafic dikes (Bignall 1987) and although undated is included in the Pahia Intrusives. Diorite, quartz diorite and granite are present along the Pahia Point coast (Challis & Lauder 1977; Price & Sinton 1978; Bignall 1987) (Fig. 18C). The informal units Boat Harbour diorite and Ruahine granite are differentiated (Mortimer et al. 1999a). Mesozoic intrusives of the Median Batholith are not known at Bluff. Late Triassic tonalite, quartz monzonite and diorite (lTq) occur on Ruapuke Island, where they have been dated by Rb-Sr (Devereux et al. 1968; Webster 1981). Holly Burn Intrusives and coastal equivalents range in age from Middle Triassic to earliest Jurassic, and the Pahia Intrusives are slightly younger (Devereux et al. 1968; Kimbrough et al. 1994; Mortimer et al. 1999a; Tulloch et al. 1999) based on a variety of dating methods. These Triassic - Jurassic Median Batholith rocks are isotopically more evolved than the Permian Brook Street plutons they intrude. TRIASSIC Mackinnon Peak Intrusives LONGWOOD RANGE to COLAC BAY PERMIAN Oraka diorite Colac granite Productus Creek Group White Hill Intrusives Takitimu Subgroup Brook Street Volcanics Group Brook Street Volcanics Group Brook Street intrusives TAKITIMU MOUNTAINS BLUFF and RUAPUKE Hekeia Gabbro diorite Pourakino Trondhjemite Granodiorite, Bluff Intrusives quartz diorite, diorite (includes Greenhills Ultramafic Complex) Norite and gabbro Dunite and other ultramafics Greenhills Group A B Figure 18 (A) Nomenclature of Brook Street terrane plutonic rocks (included in the Median Batholith) in relation to Brook Street Volcanics, Productus Creek and Greenhills groups in the Murihiku map area, from Bluff to the Longwood Range. Units in italics are informal. (B) Norite on the foreshore at Bluff. Bluff norite has been extensively used for dimension stone, as well as for reclamation work in Bluff Harbour. (C) Diorite of the Pahia Intrusives at Monkey Island near Pahia Point. 18 C Median Batholith on Stewart Island The plutonic rocks that comprise c. 90% of the Stewart Island basement were previously mapped as the granitoiddominated Rakeahua Granite in southern and western Stewart Island, and the diorite-dominated Anglem Complex in northeastern Stewart Island. Both units were inferred to comprise numerous individual intrusions (Watters et al. 1968). Subsequent mapping has delineated many of the plutons initially included in these (superseded) units, and each is briefly described below in order from oldest to youngest. Field relationships and radiometric dates have been used to determine the ages of different plutons. Radiometric dating indicates that the various plutons that comprise the Median Batholith on Stewart Island were emplaced between c. 344 and 105 Ma (Tulloch 2003). Dikes of diorite and gabbro, whose age is unknown, are intercalated with Pegasus Group schist and orthogneiss within the Gutter Shear Zone. These dikes form a diffuse swarm that extends for about 35 km along strike between the catchments of Doughboy Creek and the Lords River. Cretaceous deformation between c. 130 and 100 Ma resulted in development of the Gutter Shear Zone, Escarpment Fault and Freshwater Fault System within the Median Batholith on Stewart Island (Allibone & Tulloch 1997; Tulloch 2003) (Fig. 17). Cataclasis along some faults within the Freshwater Fault System may have occurred during the Cenozoic. Carboniferous Carboniferous intrusive rocks comprise c. 12% of the Median Batholith on Stewart Island. Individual plutons include the Ridge Orthogneiss (eCr) (344 ± 2 Ma), Ruggedy Granite (eCg) (342 ± 2 Ma), Table Hill Orthogneiss (eCt) (c. 340 Ma), Knob Pluton (Cmk) (305 ± 10 Ma), the Freds Camp (lCf) (294 ± 5 Ma), Big Glory (lCb) and Forked (lCk) plutons (308-294 Ma) (Allibone 1991; Allibone & Tulloch 1997; Tulloch 2003) and the Neck Granodiorite (eCn) (c. 340 Ma; T.R. Ireland and N.J.D. Cook pers. comm. 2003). The undated Adventure South Orthogneiss (Þv) and Kopeka South Pluton (Þk) may also be Paleozoic in age (Tulloch 2003). The Ridge (Fig. 19A), and Adventure South orthogneisses comprise foliated, locally K-feldspar megacrystic biotite granodiorite and subordinate granite, while the Table Hill Orthogneiss comprises foliated and often lineated biotite ± muscovite-bearing granite and leucogranite. These gneissic intrusions form tabular bodies intercalated with each other and with Pegasus Group schist in central and southern Stewart Island. The Ridge Orthogneiss also forms isolated blocks within and between younger plutons south of the Gutter Shear Zone. Massive equigranular granite and granodiorite dominate the Ruggedy Granite and Neck Granodiorite respectively, with deformation restricted to those parts of both plutons within and adjacent to the Freshwater Fault System. The Freds Camp, Big Glory and Forked plutons comprise massive quartz monzonite, syenogranite, granite and alkali feldspar granite with variable amounts of biotite. Variably foliated, distinctly peraluminous biotite ± muscovite ± garnet granodiorite and granite comprise the Knob and Kopeka South plutons. Aligned K-feldspar megacrysts (Fig. 19B), tabular xenoliths of Pegasus Group schist, and zones of compositional banding define fabrics in many parts of the Knob Pluton which are related to both magma flow and later ductile deformation. Tulloch et al. (2003) assigned the Ruggedy Granite to the dominantly I-type Tobin Suite and cited the Ridge Orthogneiss as the type pluton of the S-type Ridge Suite. The alkaline nature of the Freds Camp, Big Glory and Forked Creek plutons suggests correlation with the A-type Foulwind Suite (Tulloch et al. 2003). The c. 305 Ma U-Pb monazite age of the Knob Pluton also suggests correlation with the A-type Foulwind Suite, although the peraluminous and potassic nature of this intrusion distinguishes it from other members of that suite. Suite affinities have not been assigned to the other Carboniferous plutons. Middle Jurassic Middle Jurassic rocks form about 22% of the Median Batholith on Stewart Island and include the Rakeahua (mJk) (c. 169-166 Ma), South West Arm (mJs) (c. 167 Ma), and Euchre (eJe) plutons. The Euchre Pluton is assigned a Middle Jurassic age on the basis of its geochemical similarity to the South West Arm Pluton. The Rakeahua Pluton (Allibone & Tulloch 1997) includes gabbro, anorthosite, diorite, a late quartz monzodiorite phase, and minor dolerite. A particularly large body of layered anorthosite and gabbro within the Rakeahua Pluton forms the prominent Mt Rakeahua. The South West Arm (Allibone & Tulloch 1997) and Euchre plutons comprise relatively homogenous biotite granodiorite and granite. K-feldspar megacrysts occur locally within the South West Arm Pluton but are absent from the finer grained Euchre Pluton. Late Jurassic to earliest Cretaceous Late Jurassic and earliest Cretaceous rocks emplaced between c. 145 and 130 Ma form about 28% of the Median Batholith on Stewart Island. Principal units include the Codfish Granite (lJc) (c. 152 Ma), Saddle (eKx) and Deceit (mJd) plutons (c. 145 Ma), Bungaree (eKa) and East Ruggedy (eKy) Intrusives (c. 140-130 Ma), North Arm and Rollers plutons (eKn, eKz) (c. 132-130 Ma), Richards Point Porphyry (eKr) (c. 130 Ma), Tarpaulin Pluton (eKt) (c. 125 Ma), and Freshwater Northeast (eKf) and Smoky (eKs) plutons (less than c. 130 Ma). North of the Freshwater Fault System a progression from dominantly mafic (Saddle Pluton) through intermediate (Bungaree and East Ruggedy Intrusives, North Arm and Rollers plutons) to granitoid plutonism (Tarpaulin, Freshwater Northeast and Smoky plutons) is apparent during Late Jurassic to earliest Cretaceous time. The Saddle Pluton (Frewin 1987; Tulloch 2001) comprises gabbro and diorite, with minor dunite and norite (Fig. 19C), and includes gabbro at Cow and Calf Point (Watters et al. 1968). These mafic rocks form Little Mt Anglem, The Paps, and the northeastern slopes of Mt Anglem. The Bungaree and East 19 A B C D F 10 – 100 m E pegmatite dike transposed contact Table Hill Orthogneiss intrusive contact Pegasus Group Ridge Orthogneiss leucogranite dike Figure 19 Typical Median Batholith rocks on Stewart Island (A) Foliated potassium-feldspar megacrystic Ridge Orthogneiss within the Gutter Shear Zone, cut by an Upper Rakeahua Pluton leucogranite dike, on Adams Hill. (B) Aligned megacrysts of potassium feldspar in the Knob Pluton at the mouth of Seal Creek, southeast coast of Stewart Island. (C) Steeply dipping primary igneous layering in gabbro and anorthosite of the Saddle Pluton on The Paps. (D) Compositional banding and associated foliation (schlieren), probably related to magma flow, in the Doughboy Pluton on the west face of Mt Allen. (E) Rafts of coarse biotite leucogranite and smaller amphibolite xenoliths in the Mason Bay Pluton at the south end of Little Hellfire Beach. (F) Schematic view of field relationships in the Gutter Shear Zone. Intercalated layers of Pegasus Group, Table Hill Orthogneiss and Ridge Orthogneiss are cut by a swarm of aplite, leucogranite and pegmatite dikes associated with the Upper Rakeahua, Campsite and Lords plutons. Dike rocks may form up to 50% of outcrops and dominate float within the dike swarm, giving a false impression of bedrock geology. 20 Ruggedy Intrusives comprise numerous small plutons and dikes of diorite, quartz monzodiorite and granodiorite with subordinate granite, gabbro, and amphibolite (Waddell 1971; Frewin 1987). Similar diorite, quartz monzodiorite and granodiorite form the large North Arm and smaller Rollers (Frewin 1987) plutons. Dioritic rocks of the Bungaree Intrusives and North Arm Pluton form the summit region of Mt Anglem. The Tarpaulin (Cook 1987, 1988) and Freshwater Northeast plutons comprise biotite granodiorite and granite, while the more aluminous Smoky Pluton comprises biotite-muscovite ± garnet granodiorite and granite. Both the Freshwater Northeast and Smoky plutons intrude the c. 130-132 Ma North Arm Pluton. A widespread but not pervasive foliation is developed in the North Arm, Tarpaulin and Saddle plutons, and in older rocks within the Bungaree and East Ruggedy Intrusives. This foliation is cut by younger plutons within the Bungaree and East Ruggedy Intrusives and by the Freshwater A Figure 20 Northeast and Smoky plutons. The intense foliation developed in southern parts of the North Arm and Tarpaulin plutons, and in the East Ruggedy Intrusives on the northern side of the Freshwater valley, marks the northern edge of the Freshwater Fault System. South of the Freshwater Fault System, Late Jurassic-Early Cretaceous plutonism is represented by the Codfish Granite, Deceit Pluton, and Richards Point Porphyry. The Codfish Granite comprises massive biotite granite in which primary magmatic minerals are extensively retrogressed to chlorite, sericite and epidote. The Deceit Pluton comprises massive unfoliated, biotite ± muscovite granodiorite, granite and leucogranite. The granodioritic Richards Point Porphyry (Allibone 1991) is characterised by a prominent chilled margin indicating emplacement at a shallow depth. No suite affinity has been assigned to any of these rocks, although their age is similar to rocks included in the Darran Suite of Fiordland by Muir et al. (1998). B Deformation fabrics associated with major Stewart Island faults. (A) Strongly foliated diorite and quartz monzodiorite of the Walkers Pluton within the Gutter Shear Zone at the Ernest Islands. (B) Strongly foliated granitoid rocks derived from either Southwest Arm Pluton or Tikotatahi Pluton within the Escarpment Fault at Port Adventure. 21 Early Cretaceous Plutons emplaced between c. 125 and 105 Ma comprise about 38% of the Median Batholith on Stewart Island and only occur south of the Escarpment Fault. Four generations of intrusions are recognised within this time span; the second and fourth generations in particular are probably part of the Separation Point Suite. Pluton definitions are given in the Appendix. The plutons include, from oldest to youngest: 1. The dioritic to quartz monzodioritic Walkers Pluton (eKw) (c. 127-120 Ma) (Peden 1988; Tulloch 2003) and the heterogeneous quartz monzodioritic-granodioritic Escarpment Pluton (eKv) (c. 126 Ma). Foliations in both plutons are inferred to have formed during movement on the adjacent Gutter Shear Zone (Fig. 20A) and Escarpment Fault (Fig. 20B). 2. The Easy (eKe) (c. 128 Ma), Tikotatahi (eKi) and Doughboy (eKd) (Fig. 19D) plutons comprise texturally similar hornblende, biotite quartz monzodiorite and granodiorite with minor granite (Peden 1988) and may represent apophyses of a single larger body. Rafts of diorite and gabbro occur within the Easy Pluton at Port Pegasus (Þd). Field relationships and geochemical data suggest the Mason Bay Pluton (eKm) (Allibone 1991) is related to these three plutons. It includes biotite quartz monzodiorite, biotite granodiorite and granite plus numerous amphibolite rafts (Fig. 19E). 3. The Blaikies (eKb) (c. 116 Ma) and Upper Kopeka (eKp) plutons largely comprise peraluminous biotite ± muscovite ± garnet granite and granodiorite, mineralogically distinct from other mid Cretaceous plutons on Stewart Island (Allibone & Tulloch 1997; Tulloch 2003). Muscovite and garnet are particularly common in the southern part of the Blaikies Pluton which contains numerous rafts of Pegasus Group schist. Foliation development is inferred to reflect the 22 effects of both magma flow and subsequent postcrystallisation ductile shear. Peraluminous S-type granitoids elsewhere in New Zealand are Paleozoic in age and these two plutons have no known correlatives. 4. The Gog (eKg) (c. 105 Ma), Lords (eKl) , Campsite (eKc), and Upper Rakeahua (eKu) plutons comprise fine-grained leucocratic biotite granodiorite and granite with subordinate quartz monzodiorite, leucogranite, pegmatite and aplite, with related dikes (Fig. 19F) (Allibone & Tulloch 1997; Tulloch & Kimbrough in press). No sharp contact exists between the Gog and more mafic Kaninihi Pluton (eKk), suggesting that the two plutons are closely related, with the former representing the evolved core of the latter. The extensive swarm of related aplite, leucogranite and pegmatite dikes (outlined on the map face), and similarities between these four plutons, imply that they are apophyses of a major body that underlies much of southern and central Stewart Island. Plutonic rocks of Fiordland and offshore islands Biotite granodiorite and biotite-hornblende tonalite (eKh) form much of Paddock Hill at the northwest corner of the map, and are overlain by Cenozoic sedimentary rocks along the Hauroko Fault (Carter et al. 1982) and toward Lake Manapouri (cf. Wood 1966). A c. 500 m2 area of massive epidotised diorite (eKh), cut by a fine-grained amphibolite dike, underlies Cenozoic rocks along the Blackmount Fault (Carter & Norris 1980) and is inferred to be an outlier of Fiordland basement rocks. These rocks are undated, and are tentatively included in the Median Batholith. Some of the numerous islands off Stewart Island and in Foveaux Strait have not been visited because of access difficulties, and are mapped as undifferentiated Median Batholith (Þu). PERMIAN TO JURASSIC Brook Street terrane In the Murihiku map area the Brook Street terrane forms the Takitimu Mountains, the eastern Longwood Range, the Riverton and Bluff peninsulas, some of the islands and reefs in northern Foveaux Strait, and underlies much of the southern Southland Plains. The terrane is intruded in places by the Median Batholith, and in the eastern Takitimu Mountains it is overthrust by the Murihiku terrane (Landis et al. 1999). A 20 km As well as Permian plutonic rocks, described above under the Median Batholith, the Brook Street terrane includes several other lithostratigraphic units. The oldest is the Brook Street Volcanics Group, which in the map area is represented by the Early Permian Takitimu Subgroup. The Early to Late Permian Productus Creek Group rests conformably on the Takitimu Subgroup. Jurassic Barretts Formation unconformably overlies both units. Permian Greenhills Group metasediments and Bluff Intrusives represent the Brook Street terrane at Bluff. B Letham Ridge Thrust PRODUCTUS CREEK GROUP Caravan Formation 15 TAKITIMU SUBGROUP 10 Elbow Formation * Maclean Peaks Formation * Heartbreak Formation Chimney Peaks Formation * 5 Brunel Formation * 0 (Base not seen) Breccia C Conglomerate Sandstone Mudstone Pillow lava C Andesite Basalt Rhyodacite Tuff Figure 21 (A) Composite stratigraphic column through the Takitimu Subgroup in the Takitimu Mountains, after Houghton (1981) and Landis et al. (1999). Formations indicated by * are not differentiated on the map. (B) Pillow lava of the Takitimu Subgroup in a quarry on Twinlaw. (C) Volcanic breccia cut by dikes within Takitimu Subgroup at Riverton. Photo CN44044/10: D.L. Homer 23 In the central Takitimu Mountains the Takitimu Subgroup (Ybt) consists of an eastward-younging homoclinal sequence (Mutch 1964; Houghton 1981), striking N-S and dipping vertically. To the south and north the strike changes, although some of the central Takitimu formations can still be recognised. Takitimu Subgroup is predominantly volcaniclastic and includes mudstone, sandstone, conglomerate and breccia, and subordinate basaltic, rhyolitic, and andesitic flows and pillow lavas (Houghton 1977, 1981, 1982, 1985; Houghton & Landis 1989; Landis et al. 1999). It is subdivided into 6 formations (Fig. 21A). Only the predominantly volcanic Heartbreak Formation (Ybt) (Houghton 1981) of microgabbro, basaltic rocks, pillow lava and volcaniclastic breccia, and the youngest Caravan Formation (Ybt) (Willsman 1990; Landis et al. 1999) of volcanic breccia with distinctive ankaramitic dikes and tuffs, are differentiated on the map face. The rocks are folded about steeply to gently plunging axes in the south (Nebel 2003) and are gently southeast-dipping in the north (Pringle 1975; Scott 1974). The rocks contain zeolite and prehnite-pumpellyite facies mineral assemblages (Houghton 1982). Undifferentiated Takitimu Subgroup, comprising flow rocks, dikes, pillow lavas (Fig. 21B, C) and intercalated sedimentary rocks including breccias, conglomerates, sandstones and tuffs, forms Woodlaw and Twinlaw, the eastern Longwood Range, and the hills west from Riverton. Bedding in these areas strikes generally north to northwest and is gently folded (Harrington & Wood 1947; Macfarlane 1973; Banks 1977). Takitimu Subgroup rocks at the confluence of the Makarewa and Oreti rivers (Wood 1966) comprise altered and veined basalt and andesite flows (Watters 1961). The Takitimu Subgroup is interpreted to be the remains of a calc-alkaline volcanic arc and adjacent sedimentary basins (Houghton & Landis 1989; Landis et al. 1999), deposited by subaerial and submarine arc volcanism with closely associated turbidite sedimentation. Macrofossils in the Takitimu Subgroup are Early Permian in age (Waterhouse 1958, 1964). Figure 22 Productus Creek Group limestone in a branch of the Waterloo Burn, northern Takitimu Mountains, immediately below the Letham Ridge Thrust. Slightly deformed macrofossils are visible; the outcrop is veined with calcite. Field of view is 0.5 m across. 24 The Productus Creek Group (Ypg) lies east of the Takitimu Mountains within a structurally complex area. It has been redefined by Landis et al. (1999), following earlier work by Mutch (1972), Force (1975) and Waterhouse (1982, 1998) among many others. The Group rests conformably on the Caravan Formation and comprises the Mangarewa Formation and Glendale Limestone (not differentiated at 1:250 000 scale). Mangarewa Formation includes richly fossiliferous limestone (Fig. 22), pebbly conglomerate, volcaniclastic sandstone and mudstone. Lenses of conglomerate occur at the top of the formation. The overlying Glendale Limestone comprises atomodesmatinid limestone with minor bioturbated sandy, tuffaceous and muddy horizons. Productus Creek Group sedimentary rocks are dated as latest Early to early Late Permian, based on macrofossil evidence (Waterhouse 1998; Landis et al. 1999). Leaves of the Gondwanan fern Glossopteris ampla are preserved in Mangarewa Formation (Mildenhall 1970) and basal Glendale Limestone (H.J. Campbell, pers. comm.). The Takitimu Subgroup is intruded by gabbro, diorite, microgabbro and microdiorite of the White Hill Intrusives (Ybl; Houghton 1981), and andesitic and microdioritic dikes of the Mackinnon Peak Intrusives (mTm; Houghton 1987). Larger monzodiorite and olivine monzodiorite dikes up to 5 km long (Wether Hill Dikes) (Douglas 1997; Willsman 1990; Landis et al. 1999) and minor sills intrude both Takitimu Subgroup and Productus Creek Group. White Hill intrusions are concordant, increasing in thickness with stratigraphic depth toward the west; they are altered and crosscut by younger granophyric phases and by basaltic dikes, and are inferred to overlap in age with the final stages of Takitimu Subgroup volcanism. Mackinnon Peak Intrusives are considerably younger (Middle Triassic; Houghton 1987). None of these intrusives are contiguous with the Median Batholith. Barretts Formation (Jub), mapped by Landis et al. (1999) in the upper Wairaki River, unconformably overlies Takitimu Subgroup, Productus Creek Group, and various intrusives QMAP Murihiku NZ stage Late several metres in diameter, include granitoids, basaltic to andesitic volcanics, and rare limestone. The matrix is zeolitised (Landis et al. 1999). The formation is a fluvial unit deposited on an irregular paleotopography; it has been dated as Early to Middle Jurassic from pollens and molluscs (Landis et al. 1999). Plutonic clasts within it range in age from Jurassic to Triassic (c. 180 to 237 ± 3 Ma; Tulloch et al. 1999). QMAP Dunedin and is included within the Brook Street terrane. This formation replaces numerous conglomeratic units previously assigned to Productus Creek Group and Murihiku Supergroup (Landis et al. 1999). Barretts Formation is dominated by quartzofeldspathic to volcaniclastic sandstone, with coarse conglomerate and minor tuff, coal and mudstone. Conglomerate clasts, up to Ko Late Mataura mJf # Ferndale Catlins Ha Bw Bm Br Murihiku Supergroup Middle mJc eJd eJg Glenomaru# Diamond Peak lTs lTt u Warepan Taringatura Middle Gk Middle Late Early Triassic New Haven # Kt Bo Permian mJm mJn Hu Early Jurassic Kh Kaihikuan u mTs mTn Ge North Range Gm Gn u YDm Yu Kuriwao lTs code on map face Warepan group name mapped stage Kuriwao u # Superseded group name Unconformity Figure 23 Subdivision of the Murihiku Supergroup, after H.J. Campbell et al. (2003). Note that the map units used for QMAP Murihiku supersede those used on the adjacent Dunedin QMAP sheet (Bishop & Turnbull 1996). New Zealand stage names are given in full on the time scale (inside front cover). 25 The Greenhills Group (Yg) is generally attributed to the Brook Street terrane and consists of interbedded volcaniclastic breccia, dolerite, spilitic tuff, sandstone and rare limestone adjacent to the Bluff Intrusives at Mokomoko Inlet near Greenhills (Service 1937). Macrofossils from Mokomoko Inlet indicate a late Early Permian age (Mossman & Force 1969). The Mokomoko rocks are of prehnite-pumpellyite facies. Higher grade hornblende hornfels, garnet hornfels and hornblende and hornblendepyroxene bearing schist at Bluff, together with basalt, keratophyre, altered diorite, albite-actinolite schist, and granite from Tiwai Point, are included in the Greenhills Group (Mossman 1970). Similar volcaniclastic rocks occur on Ruapuke Island (Webster 1981) and also form Dog Island. The foliation and shearing seen in the higher grade Greenhills Group rocks may be related to the deformational event that produced the Grindstone Gneiss in the Longwood Range (see above). of central and eastern Southland, and the area from the Mataura River east to the Catlins coast, are underlain by Murihiku terrane. The northern contact with the Dun Mountain - Maitai terrane is the Hillfoot Fault. In the west the terrane is thrust over Brook Street terrane (Landis et al. 1999). Rocks within the Murihiku terrane form the lithostratigraphic Murihiku Supergroup (Campbell & Coombs 1966; H.J. Campbell et al. 2003). The Supergroup comprises 6 groups (Fig. 23), most of which include numerous formations (generally not differentiated on the map face). Murihiku Supergroup rocks are also involved in the Tin Hut mélange in the Wairaki River area (Landis et al. 1999). The map area includes the type sections for the following local biostratigraphic units of Triassic age: the Gore and Balfour series, and the Malakovian, Etalian, Kaihikuan, Oretian, Otamitan, Warepan and Otapirian stages. Mapping of Jurassic strata for this map was completed prior to Hudson’s (2003) revision of the Ururoan and Temaikan local stages. Unassigned mélange units In the upper Wairaki River area (see Fig. 9), Landis et al. (1999) re-assigned several formations previously included in the Productus Creek Group (sensu Mutch 1972) to two tectonic units, the Tin Hut and Hawtel - Coral Bluff mélanges. Another unit, the Wairaki Breccia, occurs as fault-bounded slices of pebbly andesitic breccia (too small to map at 1:250 000) containing a rich Late Permian macrofauna (Landis et al. 1999). Hawtel - Coral Bluff mélange (Yer) is composed of blocks of black mudstone, sandstone and limestone in a highly sheared grey calcareous mudstone. The blocks are pervasively disrupted, and veined by zeolites and calcite. The limestone contains conspicuous corals and is distinct from those of the Glendale and Mangarewa formations in being rich in bryozoans rather than atomodesmatinids. The macrofaunas in the Hawtel - Coral Bluff mélange are of early Late Permian age, and the mélange is inferred to result from tectonic deformation of olistostromes. Both Hawtel Coral Bluff mélange and Wairaki Breccia lie along the Letham Ridge Thrust, which separates Murihiku terrane from underlying Brook Street terrane. Early and Middle Triassic fossils occur in both sandstone and limestone blocks in the Tin Hut mélange (eTt) in the upper Wairaki River (Landis et al. 1999). The mélange consists of sheared, zeolitised and veined volcaniclastic sandstone with blocks of limestone and conglomerate. It lies along the Tin Hut Fault System (see Fig. 45), and is probably derived from Murihiku Supergroup. The mélange was probably emplaced during Late Cretaceous to Cenozoic faulting (Landis et al. 1999). Murihiku terrane The Murihiku terrane consists of Permian to Jurassic volcaniclastic sedimentary rocks in the Southland, Northwest Otago, Nelson, and Auckland - Waikato areas. In the map area, the terrane extends from the northern Takitimu Mountains south to Ohai, and throughout the Taringatura Hills, North Range, and Hokonui Hills. Much 26 Kuriwao Group (Yu) forms inliers south of Wyndham on the south side of the Southland Syncline (Campbell et al. 2001) and near Pukerau on the north limb (Wood 1956), both overlain by Triassic North Range Group. The Wyndham inlier consists of volcaniclastic sandstone, rare granule conglomerate and several limestone bands (Yul), the lowest including rare tuff. Plant and atomodesmatinid fragments are scattered throughout. The fault-bounded Kuriwao inlier consists of blue-grey sandstone containing atomodesmatinid fragments, limestone, and conglomerate (Wood 1956). The Wyndham sequence is ca. 850 m thick; the base is not seen and the top is unconformably overlain by North Range Group. Although of Permian age and unconformably overlain by North Range Group sedimentary rocks, lithostratigraphic and petrographic evidence supports inclusion of the Kuriwao Group within Murihiku Supergroup (Campbell et al. 2001; H.J. Campbell et al. 2003). The North Range Group (mTn) (Coombs 1950; Campbell & Coombs 1966; H.J. Campbell et al. 2003) includes rocks previously assigned to Malakoff Hill and North Etal groups, and ranges in age from Early to Middle Triassic. Equivalent strata to the east of the Murihiku map area were mapped as Middle Triassic (mTs) by Bishop & Turnbull (1996), where the older North Range Group strata are probably excised by the Hillfoot Fault. The group consists of up to 3500 m of well-bedded siltstone and fine sandstone (Fig. 24A), with subordinate vitric and lithic tuff, tuffaceous sandstone, and minor shellbeds and volcanic conglomerate (Coombs 1950; Mutch 1964; Boles 1974; Begg 1981). North of Ohai and at Mt Hamilton, siltstone is the dominant lithology; sandstone becomes more abundant to the east. The oldest North Range rocks are unfossiliferous, but macrofossils and shellbeds become more abundant upward (Begg 1981). Although six formations were defined within the group in the Hokonui Hills by Boles (1974), with probable equivalents in the upper Wairaki River and at Mt Hamilton, only the Stag Stream Siltstone is mapped at 1:250 000 scale. A B C E D Figure 24 Murihiku Supergroup lithologies. (A) North Range Group thick-bedded sandstone and thin-bedded siltstone on the north limb of the Southland Syncline, on State Highway 6 in the western Hokonui Hills. (B) Monotis shellbed within Taringatura Group in Dipton Stream, Taringatura Hills. Photo: H.J. Campbell (C) Mudstone and siltstone in the Ferndale Group east of Wyndham. (D) Conglomerate of the Ferndale Group east of Tokanui. Clasts are harder than the zeolitised matrix, and conglomerates are preferentially quarried for road metal. (E) Silicified logs and stumps of the fossilised forest at Curio Bay occur on an intertidal platform of flat-lying Jurassic sediments of the Ferndale Group. Photo CN34670: D.L. Homer 27 The Taringatura Group (lTt) (Coombs 1950) overlies North Range Group unconformably and consists of up to 5400 m of predominantly tuffaceous sandstone, with abundant conglomerate, tuff and siltstone. McKellar (1968) and Boles (1974) erected several formations within the group in the Hokonui Hills, as did Force & Campbell (1974) on the western limb of the Southland Syncline. Equivalent rocks to the east were mapped as undifferentiated Late Triassic sedimentary rocks (lTs) by Bishop & Turnbull (1996). Taringatura Group rocks also occur in the Catlins and north of Wyndham (Campbell et al. 1987; Campbell et al. 2001). Fossils are widespread (Fig. 24B) and indicate an age range of Middle to Late Triassic. Conglomerates are conspicuous, and the appearance of granitic clasts in conglomerates, along with distinctive Kaihikuan faunas, marks the base of the group. The Kaihikuan and Warepan stages have been mapped separately (mTt, lTt) where possible; Kaihikuan strata include conglomerate horizons. The depositional environment of the Taringatura Group was probably shallow marine, and local and regional unconformities are known. Rocks containing Warepan faunas, for example, are locally absent but in other places are up to 400 m thick (Campbell 1959). Diamond Peak Group (eJd) was introduced by Wood (1956) for up to 1300 m of predominantly coarse tuffaceous sandstone, with minor mudstone and arkosic tuffaceous sandstone, that conformably overlies Taringatura Group. Conglomerate horizons are prominent in places. McKellar (1968) described the group in the Hokonui Hills as consisting of blue-grey fossiliferous mudstone with minor sandstone, coarsening upward into sandstone and thin but continuous conglomerate, in turn overlain by coarse sandstone. Marine shelf and slope environments are represented. Macrofaunas are of Early Jurassic age. Ferndale Group (mJf) (Wood 1956) conformably overlies Diamond Peak Group and marks the incoming of shallow water, near-shore conditions. Sandstones predominate, with cross bedding, abundant plant material and scarce marine macrofossils, and mudstone units are also mapped (Fig. 24C). Discontinuous but locally thick conglomerate includes the distinctive McPhee Cove Conglomerate (Speden 1971). In the Waikawa area, fluvial environments are indicated by conglomerate (Fig. 24D) and repeated fining-upward cycles (Noda et al. 2002). The Curio Bay fossil forest (Fig. 24E) grew on a fluvial plain subject to flash flooding, adjacent to volcanic hills (Pole 2001; Thorn 2001). Ferndale Group macrofaunas indicate an early Middle Jurassic age. Mataura Group (mJm) sedimentary rocks overlie Ferndale Group conformably and are of late Middle Jurassic age, the youngest preserved in the Murihiku Supergroup in the mapped area (H.J. Campbell et al. 2003). Mataura Group was described by Wood (1956) as consisting of tuffaceous arkose, blue-grey siltstone, feldspathic sandstone and minor but persistent conglomerate. Plant fossils and fragments are common; tuffs are rare compared with older sequences. 28 Murihiku Supergroup sedimentary rocks were deposited in a very long-lived back-arc or possibly fore-arc basin, adjacent to an active volcanic island arc marginal to Gondwana. A wide range of environments is represented, from submarine fans with typical turbidite deposits and channel-filling conglomerates, through outer and inner shelf, to deltaic and non-marine at the top, where conglomerates become more common (Fig. 25) (Carter 1979; Carter et al. 1978; Ballance & Campbell 1993; Noda et al. 2002). Paleocurrent and petrological data imply southwest to northeast sediment transport (Carter 1979; Ballance & Campbell 1993; Pole 2001; Thorn 2001; Noda et al. 2002; Roser et al. 2002), although a possible northeasterly-derived component has also been suggested (Boles 1974). Regionally extensive unconformities (Fig. 25) and disconformities occur within the supergroup and sedimentary (formation) boundaries may be slightly timetransgressive. Provenance changed from basaltic - andesitic in the Late Permian to highly felsic (rhyolitic) in the Middle to Late Triassic; an upper continental crust (granitic) component was significant from Middle Triassic to Jurassic time (Roser et al. 2002). Contemporaneous andesitic to rhyolitic volcanism is indicated by widespread tuffs and tuffaceous sandstones, especially in the Triassic, but lavas are only known from two areas. Shallow intrusive rocks, extrusive volcanics, and some sedimentary rocks of Triassic – Jurassic age, the Park Volcanics Group (TJp) (Coombs et al. 1992) are intercalated with Murihiku Supergroup north of Ohai and southeast of Wyndham. Several areally restricted formations have been defined (Coombs et al. 1992). Park Volcanics Group includes porphyritic two-pyroxene andesite, trachydacite and rhyodacite, conglomerate, and autobrecciated trachydacitic extrusives including ignimbrite. All are modified by lowgrade zeolite facies metamorphism with albitisation of feldspars and assemblages of laumontite, pumpellyite, celadonite and chlorite. These rocks have medium to highpotassium andesitic chemistry, suggestive of back-arc or intra-arc settings. They were largely intruded at very shallow depths, although some are extrusive (cf. Grindley et al. 1980). The volcanics have been dated by Rb-Sr and K-Ar methods as Late Triassic to Early Jurassic (Gabites 1983; Coombs et al. 1992). Willsher Group A zone of sedimentary rocks characterised by laminated siltstone and volcaniclastic sandstone, of Early to Late Triassic age, lies north of the Hillfoot Fault at the northeastern margin of the map area and has recently been redefined as Willsher Group (mTw). It was previously mapped as the Kaka Point fold belt (Coombs et al. 1976) or Structural Belt (Bishop & Turnbull 1996). It has been divided into numerous formations, based on a coastal section further east (J.D. Campbell et al. 2003). Inland exposure is poor and the group is mapped here as undifferentiated, although some conglomerate units can be traced. Willsher Group is dominated by thick sequences of laminated siltstone to very fine-grained sandstone, with conspicuous tuffs and common calcareous concretions. Conglomerates are up to several hundred metres thick, with clasts ranging from andesite and felsic tuff to tonalite, gabbro and granitoids. The group is structurally complex on the coast and probably inland, and is inferred to be fault-bounded. The metamorphic grade is zeolite facies, although lower than the adjacent Murihiku Supergroup. A rich macrofauna indicates an age range from Early Triassic into the earliest Late Triassic. In spite of intense study, its terrane affinities are still uncertain; it may be a lower grade equivalent of the Murihiku Supergroup (Campbell et al. 2003), a Maitai Group equivalent (Bishop & Turnbull 1996), or a separate terrane. Dun Mountain-Maitai terrane The Dun Mountain-Maitai terrane comprises two major units. The Dun Mountain Ophiolite Belt, comprising Dun Mountain Ultramafics and Livingstone Volcanics groups, represents a slice of Early Permian oceanic crust. The overlying sedimentary Maitai Group was deposited on these mafic igneous rocks (Coombs et al. 1976). In the Murihiku map area the terrane is extensively disrupted, thinner, and less well-exposed than in the adjacent area of northwest Otago (Coombs et al. 1976; cf. Turnbull 2000). A conspicuous magnetic anomaly associated with the ophiolite belt delineates its position between areas of outcrop (Woodward & Hatherton 1975). The Murihiku segment of the ophiolite belt has almost no ultramafic rocks, N 20 km Southland Syncline Form lines Unconformable contacts Conglomerate units Tuffaceous units Mataura Group Ferndale Group Diamond Peak Group Murihiku Supergroup Taringatura Group North Range Group Kuriwao Group Figure 25 Murihiku Supergroup within the map area, showing distribution of conglomerate and tuffaceous units, and unconformities. Form lines are drawn on strike ridges and represent bedding. 29 and an increasing quartz and potassium feldspar content eastward suggests that it may not be derived from typical oceanic crust. U-Pb TIMS dating of rocks from the ophiolite belt gives ages spanning 275-285 Ma (Early Permian; Kimbrough et al. 1992). The Dun Mountain Ultramafics Group forms two areas within the map sheet. Northeast of Mossburn, sheared serpentinite includes blocks of gabbro and peridotite (Coleman 1966; G. Hyden 1979) in a fault-bounded mélange (Yds). A larger area of outcrop, lacking serpentinite, forms the Otama Complex (Coombs et al. 1976), northeast of the Mataura River between Riversdale and Waikaka. The complex includes tonalite, albite granite, granophyre, norite, two-pyroxene olivine gabbro and hornblende gabbro (Yda), and rare anorthosite (McPherson 1973). The rocks are extensively brecciated and inter-faulted with Livingstone Volcanics Group (Coombs et al. 1976). The Livingstone Volcanics Group comprises spilitic and keratophyric volcanics, dikes, dolerite, and volcaniclastic sedimentary rocks. In the Lintley Range northeast of Lumsden, the group was subdivided by Cawood (1986) into mafic and silicic igneous associations, dominated by spilite (Yl) and quartz keratophyre and plagiogranite (Ylq) respectively. Small areas of undifferentiated Livingstone Volcanics Group form isolated knobs on the Five Rivers Plain. In the Otama area, the group includes extensively brecciated keratophyre, quartz keratophyre and keratophyric breccia but spilite is rare (Coombs et al. 1976). Locally, diorite and tonalite with some trondhjemite (Ylp) are differentiated (McPherson 1973). North of Waipahi the group is faulted into Maitai Group (Wood 1956; Coombs et al. 1976; Cawood 1987) and includes spilite, basalt, keratophyre and quartz keratophyre, and rare plagiogranite. Shearing, brecciation, and mylonitic contacts with the Maitai Group are common (Coombs et al. 1976; Cawood 1987). The Livingstone Fault separates spilite from Caples terrane in the southern Blue Mountains (Stenhouse 2002; see Fig. 7). Both the Dun Mountain Ultramafics and Livingstone Volcanics groups have a complex metamorphic history (Coombs et al. 1976); they are of pumpellyite-actinolite, prehnite-pumpellyite and zeolite facies. Brecciation and mélange formation are likely to be early deformational processes, but the infaulting of Dun Mountain ophiolites into Maitai Group is thought to be related to obduction and terrane amalgamation in Cretaceous time. Maitai Group rocks unconformably overlie, or are faulted against, Livingstone Volcanics Group. They are exposed northwest of Mossburn, and form a semi-continuous strip along the western Lintley Range (McOnie 1969; Cawood 1986). Poorly exposed Maitai Group is mapped adjacent to Murihiku Supergroup from Mossburn southeast to Gore. It underlies the rolling hills of Kaiwera between the Hillfoot Fault and the Livingstone Fault, from east of Gore to Balclutha (Bishop 1965; Cawood 1987; Bishop & Turnbull 1996). The group consists of well-bedded sedimentary rocks of low metamorphic grade, subdivided into one 30 subgroup and several formations. Because of structural complexity, faulting and poor exposure, thicknesses of individual units are unknown; the group is up to 6500 m thick (Campbell & Owen 2003). Equivalent units are mapped from northern Southland to the Alpine Fault, reappearing in Nelson, where most of the formations were named (Landis 1974). The basal Upukerora Formation (Ymu), a distinctive coarse red and green volcaniclastic breccia with a hematised sandy matrix, occurs only as thin, mostly fault-bounded slivers in the Lintley Range (Cawood 1986). In one outcrop, vesicular spilite is interbedded with breccia. Upukerora Formation clasts are derived from the adjacent Livingstone Volcanics Group. Wooded Peak Limestone, normally overlying Upukerora Formation, is apparently absent from the Murihiku map area. Tramway Sandstone (Ymt) consists of well-bedded grey fossiliferous sandstone and siltstone, rare atomodesmatinid limestone, and distinctive lenses of volcaniclastic breccia. It underlies much of the Lintley Range near Lumsden (Cawood 1986) and is also present northwest of Mossburn (G. Hyden 1979).Tramway Sandstone rests either on Upukerora Formation, or on Livingstone Volcanics Group. Blocks of keratophyre and plagiogranite within Tramway Sandstone at Lumsden are inferred to be olistoliths (Cawood 1986), and breccia lenses resemble Upukerora Formation. The Little Ben Sandstone (Tml) conformably overlies Tramway Sandstone and is dominated by distinctive green or rarely red, hard, fine- to coarse-grained volcaniclastic sandstone. The formation is unfossiliferous, and contains characteristic yellow-green and red mudstone chips. Minor siltstone, volcaniclastic conglomerate (Tml) and breccia units were recorded by Cawood (1987). East of Gore, Little Ben Sandstone is massive to graded, grey or red, less commonly green volcaniclastic sandstone, typically with red hematitic mudstone chips (Cawood 1987). Rare volcaniclastic conglomerate, and interbedded grey sandstone with black, rather than red/green mudstone is present east of Clinton. The overlying Greville Formation (Tmg) at both Lumsden and Clinton consists of laminated to thin-bedded grey quartzofeldspathic sandstone and mudstone, with rare tuffs. Volcaniclastic sandstone and rare conglomerate and redeposited atomodesmatinid limestone occur near Clinton (Cawood 1987) but not at Lumsden. The overlying Waiua Formation (Tmw) differs from the Greville Formation in the red or reddish-purple colour of finer grained beds. At Clinton it contains interbedded volcaniclastic sandstone and pebble conglomerate. Rare atomodesmatinid limestone lenses are entirely redeposited (Cawood 1987; Campbell & Owen 2003). Little Ben, Greville and Waiua formations are poorly exposed east of Clinton, and contacts are inferred to be faulted. The Stephens Subgroup (Tms) of the Maitai Group conformably overlies Waiua Formation northwest of Mossburn (Hyden et al. 1982) but has not been recognised southeast of Lumsden. It consists of thick-bedded greygreen sandstone and subordinate red siltstone and intraformational breccia, with a conspicuous ridge-forming conglomerate toward the top. Stephens Subgroup is of Early Triassic age; Permian macrofossils in a quarry north of the Oreti River are from an allochthonous block within the conglomerate (Hyden et al. 1982; Campbell & Owen 2003). Undifferentiated, poorly exposed Maitai Group (YTm) rocks north of the Hillfoot Fault between Gore and Mossburn consist of siltstone and thinly laminated sandstone, and resemble both Greville and Waiua formations. Conglomerate containing pebbles and cobbles of sandstone, granite and diorite is exposed south of Lumsden. McKay (1892) noted red mudstone, possibly Waiua Formation, beneath Cenozoic coal measures in a drillhole on the Waimea Plains near Riversdale. Most of the Maitai Group has been metamorphosed to zeolite and prehnite-pumpellyite facies (Cawood 1986, 1987), but lawsonite, present in northwest Otago and Nelson, has not been recognised in the map area. The metamorphic grade is lower than in the adjacent Dun Mountain Ophiolite Belt rocks, and similar to that of the Caples (prehnite-pumpellyite) and Murihiku (zeolite) terranes. The depositional settings of the Maitai Group ranged from initial fault-bounded basins, to a complex of submarine fans in a large elongate basin (Landis 1980; Aitchison & Landis 1990). The group is largely volcaniclastic in origin, with subordinate silicic volcanic and metamorphic debris in the Tramway Formation. The age of the Maitai Group is constrained by macrofossils, including ammonoids, as Late Permian to Early Triassic; the Permian - Triassic boundary lies at the base of the Little Ben Sandstone (Campbell & Owen 2003). Caples terrane The northeastern part of the Murihiku map area is underlain by rocks of the Caples terrane, with non-schistose sandstone and mudstone adjacent to the Livingstone Fault in the west grading northeast into semischists of the Haast Schist. The Caples terrane is a volcaniclastic sequence, predominantly andesitic but with more felsic material in the east (Chrystalls Beach Complex of Coombs et al. 2000). In the type area of northwest Otago, the Caples terrane includes the Caples Group of several formations, as summarised by Turnbull (2000). In the Murihiku map area, formations have not been established although several lithologic units, particularly characteristic red and green sandstone with red and green mud flakes, have been mapped. Caples terrane rocks are subdivided in terms of their foliation development (see text box). The semischist zones on the map face differ slightly from those in the adjacent Dunedin QMAP sheet (Bishop & Turnbull 1996), because of revision of the textural zonation system (Turnbull et al. 2001). Most of the Caples Group (Yc) in the Murihiku map area is undifferentiated and consists of massive to thickly bedded fine- to medium-grained grey sandstone with thin disrupted black mudstone interbeds. More uniformly bedded, often graded, sandstone and mudstone are less common. Large areas in Tomagalak Stream, northeast of Lumsden, are underlain by massive to metre-bedded dark green and/or red sandstone with subordinate red and green Textural zones Textural subdivision is a useful method for mapping low grade metamorphic rocks and major structures within the Haast Schist. The textural zonation system established by Bishop (1974) has been revised by Turnbull et al. (2001). Textural zones (t.z.) separated by “isotects” are independent of metamorphic facies boundaries, and can cut across isograds or foliation. Characteristics of these revised textural zones are: t.z. I: Rocks retain their sedimentary (primary) appearance. Detrital grain texture is preserved, and bedding (when present) dominates outcrops. Metamorphic minerals may be present, but are very fine-grained (<75 µm), and there is no foliation. t.z. IIA: Rocks retain their primary appearance and sedimentary texture, although detrital grains are flattened. Metamorphic minerals are fine-grained (<75 µm), and impart a weak cleavage to sandstones. Mudstones have slaty cleavage. Bedding and foliation are equally dominant in outcrop. Rocks are termed semischist. t.z. IIB: Rocks are well foliated, although primary sedimentary structures may still be seen. Bedding is transposed or flattened. Clastic grains are flattened and metamorphic overgrowths are visible in thin section. Metamorphic mica grain size is still <75 µm and metamorphic segregation appears. Mudstone is changed to phyllite; meta-sandstone is well foliated and forms parallel-sided slabs. Rocks are termed semischist. t.z. III: Planar schistosity identified by metamorphic micas is developed in all rocks. Bedding is barely recognisable, and is transposed and parallel to foliation. Clastic grains may still be recognisable in sandstones, but are recrystallised and overgrown, and metamorphic segregation laminae are developed. Rocks are termed schist. Quartz veins develop parallel to foliation, or are rotated and flattened. Metamorphic micas are typically about 75-125 µm long (very fine sand size). t.z. IV: Primary sedimentary structures and clastic grains are destroyed at a mm-cm scale, although primary sedimentary units may be discernible in outcrop. Schistosity tends to be irregular due to porphyroblast growth. Metamorphic mica grain size is 125-500 µm. Schistosity and segregation are ubiquitous and rocks are termed schist. Gneissic textures may be developed. Quartz veins are abundant in most lithologies. 31 mudstone (Ycy), identical to Kays Creek Formation mapped further north (Turnbull 2000). Similar red and green sandstone and siltstone occurs in the lower Clutha valley (Becker 1973), and in the Clinton - Pomahaka area where it was named Watties Sandstone by Cawood (1987). Cawood speculated that it was either a separate unit (terrane) or part of the Maitai Group, but on the basis of geochemistry, including trace elements, Stenhouse (2002) has included it in the Caples Group. direction of schistosity in rocks of t.z. IIA or IIB (Fig. 26). The trace of the axial plane is offset in places by Cenozoic faults. Kink folds in schistosity are also commonly associated with Cenozoic faults. Mesoscopic folds in bedding occur throughout the Caples terrane, with axial plane schistosity in the more foliated parts, but no macroscopic folds in bedding have been mapped. Transposition of bedding increases with increasing metamorphic and textural grade, from prehnite-pumpellyite facies, t.z. I adjacent to the Livingstone Fault to t.z. III, pumpellyite-actinolite facies in the northeastern corner of the map area. A belt of rocks 1 to 5 km wide adjacent to the Livingstone Fault in the Lintley Range and the southern Blue Mountains is less indurated and deformed, and more varied, than typical Caples Group and includes black and red mudstone units up to 100 m thick (Yci), decimetre-bedded graded sandstone sequences in the Blue Mountains (Stenhouse 2002), and massive grey sandstone. In the Lintley Range, laminated siltstone with plant fragments is interbedded with mudstone. Minor Caples lithologies include metavolcanic rocks forming greenschist bands (Ycg) with rare chert (Yct) (Clough 1987), and granule to pebble conglomerate (Ycc) (Becker 1973). The Chrystalls Beach Complex (Coombs et al. 2000) is characterised by broken formation with volcanic and radiolarian chert fragments, and geochemistry intermediate between “typical” Caples and Torlesse terranes. In the map area the presence of Chrystalls Beach Complex is based on a geochemical analysis from near Tuapeka Mouth; no structural or lithologic contact has yet been mapped bounding the Chrystalls Beach Complex and it is included in the Caples terrane. An enigmatic regional fold in foliation in the Caples terrane, the Taieri-Wakatipu Synform (Mortimer & Johnston 1990; Mortimer 1993a), trends northwest across the map area. The synform hinge is marked by a gentle change in dip Caples terrane rocks mainly accumlated in submarine fans in depositional settings ranging from trench slope, to trench-slope basins, and possibly trench floor (see summary in Turnbull 2000). Mélanges and zones of broken Figure 26 Gently south-dipping foliation in t.z. IIA semischist of the Caples terrane defines the northern limb of the Taieri-Wakatipu Synform in the Black Umbrella Mountains. The valley of the Argyle Burn follows the Argyle Fault, in the foreground. Photo CN43910/3: D.L. Homer 32 formation may have formed during subduction-related accretion. No fossils are known from the map area. Elsewhere, the Caples Group includes redeposited Permian limestone blocks (Turnbull 1979; Ford et al. 1999), detrital zircons of Triassic age (Adams et al. 2001), and Middle Triassic radiolaria in the Chrystalls Beach Complex (Coombs et al. 2000). A Late Permian to Triassic age is inferred for the Caples terrane in the Murihiku area. The Caples terrane was metamorphosed during Early Jurassic to Cretaceous time (Graham & Mortimer 1992). Little et al. (1999) suggested that metamorphism peaked at c. 170-180 Ma (Middle Jurassic), followed at 135 Ma (Early Cretaceous) by rapid uplift and cooling. Paterson Group Paterson Group (eJp) comprises andesitic, dacitic and rhyolitic volcanic, volcaniclastic, tuffaceous and related sedimentary rocks (Fig. 27) in the West Ruggedy, Freshwater valley, Paterson Inlet, and Little Hellfire areas of Stewart Island (Watters et al. 1968; Waddell 1971; Cook 1984; Allibone 1991). Smaller fault-bounded slices of Paterson Group occur on the west coast of Stewart Island between Waituna Bay and the northern end of the Ruggedy Mountains, and at the eastern end of Codfish Island (Allibone 1986; Allibone & Allibone 1991; Watters 1994). Paterson Group may be part of a volcanicsedimentary sequence which formed the “cover” to the Median Batholith, but is still considered to be “basement” beneath Cretaceous and Cenozoic sedimentary sequences. The coastal section between Little Hellfire and Richards Point is dominated by andesitic flows, whereas other parts of the Paterson Group are dominated by dacitic and rhyolitic volcaniclastic and related sedimentary rocks. Clasts in the coarser grained volcaniclastic rocks include dacite and rhyolite with subordinate granitoid material and rare schist. The widespread occurrence of granitoid detritus, coupled with the calc-alkaline geochemistry and predominance of felsic material, imply that the Paterson Group formed in an active continental margin setting (Allibone 1991). Foliation is widely developed in the Paterson Group, particularly within and adjacent to the Freshwater Fault System and northern splays of the Escarpment Fault. Greenschist facies metamorphic assemblages characterise the majority of Paterson Group rocks — chlorite zone in the Freshwater valley and Paterson Inlet, and biotite zone at West Ruggedy and in the hills northeast of Little Hellfire. Lower amphibolite facies contact metamorphic assemblages occur in the vicinity of intrusive contacts with the Codfish Granite, Richards Point Porphyry and larger felsic porphyry dikes (Allibone 1991). U-Pb TIMS zircon dating of a stratigraphically concordant banded rhyolite flow within the Paterson Group at The Neck gave an age of 146 ± 2 Ma (Kimbrough et al. 1994), while TIMS zircon dating of a rhyolite tuff at Abrahams Bay gave an age of c. 142 Ma (Tulloch 2003). The Paterson Group is thus latest Jurassic in age, similar to the older parts of the adjacent Bungaree Intrusives. Codfish Granite intruding Paterson Group south of Richards Point has an age of c. 152 Ma, suggesting that western, andesitic parts may be about 10 Ma older than other parts of the Paterson Group. U-Pb TIMS zircon dating of a granitoid clast within the Paterson Group at Abrahams Bay gave an age of c. 340 Ma (Tulloch 2003), similar to some of the older granitoids in the adjacent basement and implying a relatively local provenance for the group. Figure 27 Coarse tuff (left) and tuffaceous siltstone (right) of the volcaniclastic Paterson Group at West Ruggedy Beach on northwest Stewart Island (see back cover). 33 CRETACEOUS SEDIMENTARY ROCKS Conglomerate, sandstone, mudstone and coal of the Ohai Group (lKo) are mapped in the Ohai depression (Bowen 1964) (Fig. 28), and as outliers in the upper Wairaki River (Landis et al. 1999). From seismic data, Cretaceous sedimentary rocks, possibly Ohai Group equivalents, are inferred beneath the Waiau Basin (Turnbull & Uruski 1993). The Group has been intensively investigated by mapping, drilling and geophysical prospecting in the Ohai Coalfield (Bowen 1964; Bowman et al. 1987). Sykes (1988) and Turnbull & Uruski (1993) interpreted the depositional and tectonic environments. Ohai Group consists of up to 50 m of basal sandstone, carbonaceous mudstone, and impure coal (Wairio Formation, not differentiated) resting unconformably on Murihiku Supergroup, Takitimu Subgroup or (locally) Barretts Formation (Bowen 1964; Landis et al. 1999). The basal sequence is overlain by up to 120 m of New Brighton Conglomerate (lKo). Clasts are derived from Takitimu Subgroup and Murihiku Supergroup and include Median Batholith plutonics. Conformably overlying the conglomerate are up to 210 m of interbedded sandstone, carbonaceous mudstone, and sub-bituminous coal (Morley Coal Measures, not differentiated). Ohai Group outliers in the upper Wairaki River consist of basal conglomerate overlain by sandstone and carbonaceous mudstone (Landis et al. 1999). The Ohai Group is overlain unconformably by the Eocene Nightcaps Group (see below). The Ohai Group was deposited in a fault-controlled fluvial basin or basins, with ongoing tectonism indicated by facies and thickness changes (Sykes 1989). Pollen indicates a latest Cretaceous age (Raine in Turnbull & Uruski 1993). Coarse, thick-bedded sandy conglomerate and minor sandstone (lKc) form Black Rock, off Stewart Island, (Tulloch 1998) and two islands known as The Sisters (Fig. 29) (Fleming & Watters 1974). Bedding dips east on Black Rock, and NNW on The Sisters toward a fault adjacent to the coast of Stewart Island. Clasts are subangular to well rounded and match lithologies on Stewart Island (Fleming & Watters 1974), although rare volcanic clasts occur on Black Rock (Tulloch 1998). The Sisters conglomerate matrix is zeolitised. No datable material has been recovered, and these conglomerates are inferred to be of Late Cretaceous to possibly Cenozoic age. Figure 28 The town of Ohai in the down-faulted Ohai depression. Twinlaw and Woodlaw hills lie beyond (upper right) with the Longwood Range in the far right distance. Coal seams in the Late Cretaceous Ohai Group are worked in open cast and underground mines north of the town. Photo CN43931/2: D.L. Homer 34 Figure 29 Northwest-dipping conglomerate of inferred Late Cretaceous age forming the northernmost of The Sisters islands east of Port Pegasus, southeastern Stewart Island. EOCENE TO PLIOCENE Eocene to Pliocene sedimentary rocks once blanketed much of the Murihiku map area, resting unconformably on older rocks. A sequence over 8 km thick is preserved in the central Waiau and Te Anau basins, partly exposed around the deformed basin margins (Turnbull & Uruski 1993). The sequence is thinner to the east (e.g. F. Hyden 1979, 1980; Isaac & Lindqvist 1990; Cahill 1995) and largely concealed beneath the gravels of the Waimea and Southland plains, with outcrops on river banks and in stream beds. Limestone strike ridges protrude through the gravels, and limestone quarries are a feature of the Southland landscape (Fig. 30). Cenozoic sedimentary rocks are mapped in several groups; lithostratigraphic nomenclature of the various formations and groups is summarised in Fig. 31. Eocene non-marine sedimentary rocks Nightcaps Group (En) overlies fresh to slightly weathered basement rocks on the margins of the the Takitimu Mountains and is intermittently exposed around the Longwood Range. It is inferred to extend beneath the western Winton Basin (Cahill 1995). Two formations are mapped. The basal Beaumont Coal Measures (Enb), up to 250 m thick, include arkosic sandstone in channelled and cross-bedded units, subordinate carbonaceous mudstone, rare coal seams and, at Orepuki, oil shale (Willett & Wellman 1940). Beaumont Coal Measures are conformably overlain by up to 350 m of Orauea Mudstone (Eno), a lacustrine to lagoonal carbonaceous mudstone with rare graded sandstone interbeds. Orauea Mudstone is overlain by Oligocene Waiau Group, but the contact has not been seen. The Nightcaps Group reflects regional subsidence and formation of an extensive fluvial then lacustrine system over much of western Southland (Turnbull & Uruski 1993). The Eocene Mako Coal Measures (Em) formation is preserved along the southwestern side of the Hokonui Hills (Rout 1947; McKellar 1968). It rests unconformably on Murihiku Supergroup and consists of about 20 m of silty mudstone, claystone and sandstone overlain by 15-20 m of sandstone with thin seams of sub-bituminous coal. Eocene lignite measures (Elm) are poorly exposed in a shallow basin in the lower Pomahaka Valley west of Clydevale (Liggett 1979). Mapping and drilling confirm a maximum preserved thickness of 20 m. The unit consists of lignite, white to brown variably carbonaceous clay, and rare fine-grained sand. It rests on leached Caples terrane basement and is unconformably overlain by Early Quaternary Clydevale Gravel. Tiny remnants of quartz sandstone and mudstone (lEh), in places silica-cemented, are preserved adjacent to the Tuapeka Fault Zone, and are correlated with the Hogburn Formation of Central Otago. 35 Oligocene to Pliocene sedimentary rocks Thick Oligocene to Pliocene marine sedimentary rocks are preserved in the deep Te Anau and Waiau basins in western Southland. Thinner sequences are present in central and eastern Southland. Sedimentary rocks in the southern Te Anau Basin are zeolitised (Landis 1974) but zeolitisation is less apparent in the Waiau Basin. There are numerous folds within the Cenozoic rocks, and basin margins are complexly faulted (Carter & Norris 1980; Isaac & Lindqvist 1990). Te Anau and Waiau basins (Waiau Group) At the northern end of the Takitimu Mountains in the Te Anau Basin, Eocene Nightcaps Group is conformably overlain by undifferentiated lower Waiau Group rocks (eOw) comprising graded sandstone with olistostromes, channelised breccia and conglomerate and local limestone, overlain by graded sandstone and mudstone (Carter & Norris 1977a; Turnbull & Uruski 1993; Turnbull 2000). The older sandstone and conglomerate is locally derived from Takitimu Subgroup and the younger graded sandstone from Fiordland granitoids. Lower Waiau Group thins out locally and the overlying Waicoe Formation, of massive, sometimes concretionary calcareous mudstone (Oww), rests on Nightcaps Group (or possibly basement, east of Mt Hamilton). Waicoe Formation hosts numerous other named formations in the Waiau Basin; it encloses graded limestone beds (Muf) of a submarine fan sequence in the upper Aparima River (Mutch 1972). A tiny but important outcrop of Tunnel Burn Formation limestone (lOw), at the foot of Paddock Hill west of the Hauroko Fault (Carter et al. 1982), represents a condensed shelf sequence on the margin of the Te Anau Basin (Norris & Turnbull 1993; Turnbull & Uruski 1993). Southwest of the Takitimu Mountains, the Blackmount Fault separates two further Waiau Group sequences of predominantly submarine fan sediments (Carter & Norris 1977a, 1977b, 1980; Turnbull & Uruski 1993, 1995) (Fig. 31). West of the fault, near Monowai in the southernmost Te Anau Basin, Miocene graded sandstone and mudstone of the Borland Formation (Mwb) overlie Waicoe Formation. Borland Formation is overlain by northward-derived Middle Miocene conglomerate and sandstone of the Monowai Formation (Mwm), succeeded in turn by graded sandstone and mudstone and rare conglomerate of the Duncraigen Formation (Mwd) submarine fan. East of the Blackmount Fault, a westerly-derived submarine fan sequence (Blackmount Formation, Owb) with a locallyderived basal dioritic breccia (Ligar Breccia) rests on dioritic basement and grades up through thick-bedded lithic sandstone into graded sandstone and mudstone, and then into Waicoe Formation. An easterly-derived Oligocene redeposited graded limestone - mudstone facies, Birchwood Formation (Owi) (Arafin 1982) is enclosed within Waicoe Formation mudstone west of Ohai. A younger easterly-derived submarine fan of graded limestone beds isolated within Waicoe mudstone, the 36 Miocene McIvor Formation (Mwv), was probably derived from the westward-prograding limestone-dominated Clifden Subgroup (Turnbull & Uruski 1993). In the southeast of the Waiau Basin around the Longwood Range, shallow marine facies overlying basement include conglomerate, fossiliferous sandstone, limestone and mudstone of the Waihoaka Formation (Owk), limestone (Oul, Mul); and conglomerate and sandstone (Oc) in the Pourakino Valley and near Otautau (Harrington & Wood 1947; Forsyth 1992). The Clifden Subgroup of the Waiau Group represents the western part of a shallow marine shelf which covered much of Southland in the Late Oligocene to Middle Miocene (F. Hyden 1979, 1980), extending into the Waiau Basin through the tectonically-controlled Ohai depression. Clifden Subgroup includes several formations and the type localities of several New Zealand stages (Fig. 32A) and is described in detail by Wood (1969). Two informal subdivisions are mapped: a lower Clifden Subgroup (Mwc) of basal sandstone overlain by pebbly conglomeratic limestone (Hyden 1980), and thick limestone of the Forest Hill Formation (Ouf) (Fig. 32B); and an upper Clifden Subgroup (Mwc) of laminated siltstone and mudstone, shellbeds, massive fossiliferous bioturbated sandstone, and locally lignite at the top of the sequence. The Clifden Subgroup is unconformably overlain by further Waiau Group rocks, including massive shallow marine sandstone with minor shellbeds (Late Miocene Rowallan Sandstone, Mwa; Turnbull & Uruski 1995). Overlying Rowallan Sandstone is the very shallow marine Pliocene Te Waewae Formation (^wt) (Turnbull & Uruski 1995), composed of laminated siltstone, cross-bedded sandstone and local shellbeds and conglomerate, forming the cliffs behind Te Waewae Bay. Orepuki Formation (^Qa) is slightly younger, very shallow to marginal marine and possibly fluvial sandstone, lignite, and conglomerate, in paleovalleys and dissected high terraces on the southern Longwood Range near Orepuki (Willett & Wellman 1940; Willett 1946a; Wood 1969). Winton Basin and Southland shelf East of the Takitimu Mountains and Longwood Range, Cenozoic subsidence was less than along the Moonlight Fault System and sedimentary rocks are thinner, although the Winton Basin is up to 2800 m deep (Cahill 1995). Basal Eocene non-marine sedimentary rocks are overlain by massive calcareous mudstone of the Oligocene Winton Hill Formation (Owh), the lateral equivalent of the Waicoe Formation. The Winton Hill Formation lenses out beneath the Eastern Southland Coalfield (Isaac & Lindqvist 1990). It is overlain by the Chatton Formation (part of the East Southland Group; see below) and then by distinctive scarp-forming bioclastic bryozoan limestone of the Late Oligocene to Early Miocene Forest Hill Formation (see Figs 30, 31, 32B). Forest Hill Formation commonly has a basal conglomeratic facies (not mapped) (F. Hyden 1979, 1980). In the Winton Basin, neither Forest Hill nor Winton Hill formations are assigned to any group. Non-marine East Southland Group rocks overlie Forest Hill Formation west of Forest Hill (Isaac & Lindqvist 1990). The East Southland Group (Isaac & Lindqvist 1990) underlies the area east of the Oreti River, and the Waimea Plains and basins north of Gore, and is time-equivalent to both Chatton and Forest Hill formations. The group consists of discontinuous basal marine and estuarine facies (Chatton and Pomahaka formations), conformably overlain (and in places underlain) by non-marine Gore Lignite Measures. Chatton Formation (Mec) as mapped includes the Castle Downs Formation of Hyden (1980), following Isaac & Lindqvist (1990). It consists of up to 150 m of fossiliferous sandy limestone and variably glauconitic sandstone, representing inner to mid-shelf environments. In the west it overlies Winton Hill Formation; elsewhere it either overlies basement, or rests on and interfingers with East Southland Group coal measures. At Bluff, Chatton Formation rests unconformably on basement and is locally derived, conglomeratic and cemented by authigenic zeolites (Bosel & Coombs 1984). Chatton Formation varies in age from Late Oligocene in the north to late Early Miocene in the south (Isaac & Lindqvist 1990). Pomahaka Formation (Mep), between the Blue Mountains and a basement high northeast of Gore, consists of interbedded fossiliferous claystone, sandstone, lignite and carbonaceous mudstone. It was deposited in a Late Oligocene-Early Miocene estuary. The Gore Lignite Measures (Meg) contain economically significant lignite deposits in eastern Southland, hosting numerous seams up to 18 m thick. Oil shale occurs in the Waikaia Valley (Wood 1966). Three lithofacies were differentiated by Isaac & Lindqvist (1990): a lower sandstone-dominated unit, a middle unit hosting thick coal seams (Fig. 33), and an upper sandstone-siltstonecarbonaceous mudstone unit with little coal. The Gore Lignite Measures were deposited in lower coastal plain, delta plain and alluvial plain environments, in a progradational setting. On Landslip Hill the quartz gravel and sand facies are silica-cemented and form extensive horizons (Wood 1956; Lindqvist 1990); scattered boulders of very hard, silica- and limonite-cemented quartz sand and gravel in the Kaihiku Range, on the southern Blue Mountains, and in the Waipahi district are inferred to be equivalents. Scattered silcrete boulders in the Millers Flat basin (mMm; Wood 1966) are correlated with the equivalent Miocene Manuherikia Group of Central Otago. Figure 30 Quarries in Oligocene to Miocene Forest Hill Formation limestone, at Castle Rock north of Winton. LImestone is down-faulted into Triassic rocks in the axis of the Southland Syncline. The North Range lies beyond, to the north. The active Castle Rock Fault lies parallel to the line of pine trees (arrowed) in the centre middle distance. Photo CN43901/21: D.L. Homer 37 Figure 31 Paddock Hill Mwb Mwm Mwd p Duncraigen Fmn Monowai Fmn Borland Fmn Waicoe Fmn Tunnel Burn Fmn Waiau Group (undifferentiated) Orepuki Fmn Te Waewae Fmn Rowallan Sandstone Clifden Subgroup Forest Hill Fmn limestone McIvor Fmn Waicoe Fmn Birchwood Fmn Waihoaka Fmn Blackmount Fmn Mwd Mwm Mwb Oww lOw eOw Qa wt Mwa Mwc Ouf Muf Mwv Oww Owi Owk Owb wt Owb Mwa Owb Oww Mwa Ohai Group Nightcaps Group En Qa lKo En Owk Eno Oww Mwc Enb Ouf Owi Ouf lKo Winton Oc Mul En Meg S GAP F A U LT Owh Oul Range En Ouf Mec Mec Meg Winton SCOTT Owh Longwood Orauea Mudstone Beaumont Coal Measures Mwc Enb Eno Oww Mwv Oww Muf Ohai lKo Ohai Group (undifferentiated) lKo New Brighton Conglomerate Eno Enb En Mwc Mwc Oww Oww Oww Mountains En Oww Ta k i t i m u En eOw Basin ungrouped East Southland Group Em Owh Mec Meg Mec Mul Oul Ouf Owh Oc Em Meg Mec Mep Gore n si Mep Wyndham limestone limestone Forest Hill Fmn Winton Hill Fmn conglomerate Mako Coal Measures Gore Lignite Measures Chatton Fmn Pomahaka Fmn Mec Meg Meg Broken fence diagram illustrating lithostratigraphic nomenclature of Cretaceous and Cenozoic sedimentary rocks in the Murihiku area. Not to scale. Prospect Fmn Pp H AU FA R O U K LT O Waiau Group lOw T Oww au lOw W eA n T N Ba Basin Te A n a u B BL A FA C K UL MO T U Waiau Basin Blackmount au ai in as u ia Wa n si Ba Oww Clifden W Orepuki 38 E Figure 32 (A) The type locality of the Clifden Subgroup at Clifden, western Southland, extends along the southern bank of the Waiau River from the Clifden bridge (centre left) upstream into the trees (right centre). This is also the type locality for the Southland Series, and for the Clifdenian, Waiauan, Lillburnian and Altonian stages. (B) Forest Hill Formation limestone on the banks of the Waiau River at Clifden. Photo CN44048/22: D.L. Homer Palynology indicates the Gore Lignite Measures are of Late Oligocene to Early Miocene age (Pocknall & Mildenhall 1984), although the youngest measures may be Middle Miocene (Isaac & Lindqvist 1990). Late Miocene to Pliocene non-marine sediments In the Te Anau Basin, the Waiau Group marine sequence is truncated by the Late Miocene to Pliocene Prospect Formation (^p) (Fig. 34), preserved in the core of the Monowai Syncline north of Blackmount (Carter & Norris 1977a). The formation consists of clast-supported conglomerate with subordinate cross-bedded sandstone. Apart from local Takitimu Subgroup and Fiordland input, Prospect Formation is largely derived from the Caples terrane, reflecting Late Miocene to Pliocene uplift and eversion of the Te Anau Basin along the Livingstone and other faults (Turnbull & Uruski 1993; Manville 1996). Pebbly Hill Gravels (M^q) consists of up to 150 m of Late Miocene to Pliocene sandy pebbly quartz conglomerate with a clayey matrix, interbedded with rare claystone, quartz sand and lignite. The unit appears to overlie Gore Lignite Measures unconformably near Gore (Wood 1956), where McKellar (1968) called it Waimumu Quartz Gravel. Similar quartz and quartz-lithic gravel and sand north of Gore, inferred to be slightly younger, were named Waikaka Quartz Gravels by Wood (1978). Pliocene lignite offshore in Toetoes Bay (Wood 1966), and quartz sand and lignite in drillholes southeast of Invercargill (Mutch 1975), may be laterally equivalent to the Pebbly Hill Gravels. 39 Figure 33 Weathered woody lignite in the Gore Lignite Measures of the East Southland Group in the Goodwin mine, near Waimumu. Photo: M.J. Isaac Figure 34 Steeply dipping Late Miocene to Pliocene Prospect Formation gravels, largely derived from sandstones of the Caples terrane, in the axis of the Monowai Syncline at Redcliff Stream. 40 QUATERNARY The widespread Quaternary deposits of the Murihiku map area rest unconformably on older units, and have been subdivided using both geomorphology and lithology. They have been given a variety of formation names in the past (e.g Wood 1966; McKellar 1968). On the map, deposits are coded by age expressed in terms of their assessed Oxygen Isotope (OI) stage, prefixed by “Q”, with a letter code and overprint for their depositional environment. Radiometric age control is lacking for most deposits, although McIntosh et al. (1990) and Berger et al. (2002) have used luminescence and tephrochronology to date alluvial terrace sequences in the Mataura valley. Radiocarbon dates are available for some younger deposits, particularly on Stewart Island; nevertheless most age assessments are based on geomorphic correlation with dated sequences, degree of weathering and preservation of landforms, and by “counting back” through glacial events. Although deposits are assigned a “best guess” OI stage (e.g. Q4a) on the map face, the ages recorded in the GIS database reflect any uncertainty (e.g. Q2-6). Deposits of unknown age are mapped as undifferentiated Quaternary (uQa). These include alluvium on Stewart Island and alluvial fans in numerous places. Early Quaternary deposits The Maitland and Clydevale - Pomahaka areas are underlain by Gore Piedmont Gravel (eQa) and Clydevale Gravel (eQa) (Wood 1956; Liggett 1979; Barrell & Glassey 1994b). No type localities or formal definitions have been introduced for these units and neither has been dated. Both lie in structural depressions and form a broad rolling to flat landscape (see Fig.7). The gravels are deeply weathered with clasts of quartz, greywacke, argillite, semischist and schist; lithic clasts are usually intensely weathered. Gore Piedmont Gravel is gently deformed against the Dunsdale Fault System. Both units are interpreted as probably Early Quaternary alluvial plain deposits from the proto-Waikaka, Pomahaka and Clutha rivers; Clydevale Gravel remnants extend as far as Balclutha (Barrell et al. 1998). Undifferentiated Early Quaternary deposits (eQa) underlying very high terrace remnants adjacent to the Clutha River (Thomson & Read 1996) are younger than the adjacent Clydevale Gravel. Deeply weathered gravels (eQa) forming dissected terrace surfaces near Ohai include plutonic, volcanic and greywacke clasts and are almost completely weathered. They may represent deposits of a proto-Waiau River flowing east through the Ohai depression and into the Aparima catchment (see below). Small terrace remnants underlain by deeply to moderately weathered gravels in the lower Waiau valley are also mapped as Early Quaternary, but are probably younger than the Ohai gravels. Middle Quaternary deposits Middle Quaternary glacial and fluvioglacial deposits are preserved in the Waiau catchment. Weathered, sandy to bouldery, Fiordland-derived till (mQt) occurs on Paddock Hill. Glacial outwash gravel (mQa) up to 100 m thick, with some interbedded till and ice-contact deposits, underlies high terrace remnants between Redcliff Creek and Blackmount (Fitzharris 1967; Carter & Norris 1980). Outwash is also mapped south of Monowai, and forms more extensive terraces east of the Waiau River above Clifden. The gravels are weathered, sandy, pebbly to bouldery, planar to cross-bedded, and overlain by up to 3 m of loess. Slightly to moderately weathered, Fiordland- and locallyderived outwash gravel also underlies terraces northeast of Mt Hamilton. Associated contemporaneous fan remnants (mQa) are dominated by Murihiku Supergroup debris from nearby Mt Hamilton. High, loess-covered terrace remnants on the Waimea Plains and in the Waikaia valley are underlain by moderately to strongly weathered sandstone-dominated (Caples-derived) gravels (mQa). On the eastern Southland Plains, the Middle Quaternary Kamahi Terrace (Wood 1966; Mutch 1975) which extends from Gore to Invercargill, was deposited by a proto-Mataura River and has a well-developed fan morphology with an apex at Gore. The Kamahi surface is mantled by sand dunes and loess and underlain by weathered greywacke-quartz sandy gravels up to 50 m thick. Locally-derived fans (mQa) grade onto the surface west of Gore. A dissected fan of very similar weathered alluvial gravels (Fig. 35) of inferred Middle Quaternary age lies adjacent to the lower Aparima River. Remnant terraces of weathered greywacke-schist gravel, and gently sloping fan surfaces (mQa) with a very thin veneer of gravel, are mapped along the Clutha River from Millers Flat to Figure 35 Deeply weathered gravels, composed of sandstone and volcanic clasts, in a road cut south of Otautau. Similar brown to orange-weathered gravels of Middle Quaternary age underlie many fan surfaces in Southland, including the extensive Kamahi Terrace of the eastern Southland Plains. 41 Clydevale (Thomson & Read 1996) ; they are inferred to be Middle Quaternary in age. On the north side of the Freshwater valley, Stewart Island, a sequence of locally derived basal gravel overlain by cross-bedded sand and variably carbonaceous silt (mQa) rests on granitic basement and underlies an extensive Late Quaternary sand plain. Palynology indicates an Early to Middle Quaternary age (Mildenhall 2003). Q8 Till inferred to date from OI stage 8 (Q8t) is mapped on Paddock Hill, with remnants of moderately weathered glacial outwash gravel terraces (Q8a) mapped south of Paddock Hill, near Redcliff Creek, and along the southern margin of the Takitimu Mountains. On the eastern side of the Waiau catchment, extensive alluvial fans (Q8a) derived from the screes of the Takitimu Mountains have built out over older terraces and moraines. OI stage 8 terraces mapped in the Mataura catchment, following McIntosh et al. (1990) and Berger et al. (2002), are underlain by moderately weathered greywacke gravels with subordinate quartz, and overlain by loess. McIntosh et al. (1990) and McIntosh et al. (1998) attributed these terraces to an ancestral “Lumsden River”, when the Oreti River flowed east from Lumsden rather than south as it does now (Fig. 36). Terraces mapped as Q8a in the lower Mataura and Oreti catchments may be degradational surfaces eroded into older (mQa) gravels. Q7 Flat to gently rolling and dissected surfaces (Q7b) between 20 and 40 m ASL northeast of Riverton, around Orepuki, and west of the Waiau River at about 100 m ASL, are interpreted to be of marginal marine origin and assigned to OI stage 7 (185 - 248 ka). The coastline east from the Mataura River is backed by terraces a few metres to tens of metres wide, at heights of 7 - 9 m ASL. These inferred OI stage 7 marine benches are overlain by up to 4 m of loess comprising several horizons, and underlain by weathered and iron-stained, locally derived gravels. OI stage 7 terraces at 10-20 m ASL with an up-river slope of 4° were mapped near Balclutha by Barrell et al. (1998). This profile projects up the Clutha River to meet OI stage 6 terraces mapped down-valley by Thomson & Read (1996). The apparent mis-match between the alluvial terraces and the marine surfaces mapped at the coast may indicate that the alluvial terraces are slightly older than shown, and have been partly stripped of gravel (perhaps by marine incursions up the Clutha River). Q6 The Waiau and upper Oreti catchments contain outwash gravel terraces consisting of Fiordland-derived rocks (Q6a). The associated till occurs north of the map area, in the southern Te Anau Basin (McKellar 1973). In the lower 42 Waiau valley, Q6a deposits are mostly eroded and only narrow terrace treads remain, above a more extensive OI stage 4 aggradational terrace surface. Q6a terraces in the Clutha are also eroded (see above). Alluvial fans (Q6a) building out from the Blue Mountains, the Taringatura Hills and the hills north of Ohai are dated on the basis of profiling onto major catchment terrace sequences. The fans merge onto wider, flatter alluvial terraces with no distinctive fan morphology. The fan gravels are generally sandier or siltier than the better sorted gravels of the major rivers. Late Quaternary deposits Q5 A flat-topped marginal marine bench (Q5b) is intermittently preserved along the coast from west of the Waiau River (Fig. 37) to east of the Mataura River, decreasing in height from 25-60 m ASL in the west, to 12-25 m at Riverton and 57 m in the east. The bench is underlain by gravel and sand, with peat in places, resting on a flat to undulating erosion surface cut in both Cenozoic sedimentary rocks and older basement rocks. It is overlain by dunes at Waipapa Point. East of Invercargill the bench is obscured by thick mounds of peat formed over both the deposits and the marine cliff behind it. Marginal marine deposits on the bench can be distinguished from nearby (possibly coeval) fluvial gravels by their plane-parallel or inland-dipping tabular cross bedding, rather than trough cross bedding, and by containing a higher proportion of reworked quartz gravel (Liggett 1976). These marginal marine deposits are inferred to date from OI stage 5 (70 - 130 ka), with an intermediate step (Fig. 37) representing a fluctuation in sea level during this interglacial period. Q4 Fiordland-derived fresh bouldery sandy till (Q4t) forms hummocky ground in the upper Waiau River adjacent to the Mararoa weir (McKellar 1973). A down-valley outwash gravel train (Q4a) forms the widest terraces preserved along the Waiau River, including the extensive flats north and south of Clifden. Several degradational terrace surfaces have been cut into these gravels. Terrace gravels (Q4a) are preserved throughout the Aparima, Oreti, Mataura and Clutha catchments. The gravels are relatively fresh and greywacke-dominated; the proportion of Fiordland material decreases away from the Waiau catchment and schist, quartz and semischist debris increases toward the Clutha catchment. In the lower Mataura valley, the gravels underlie loess dated by thermoluminescence as being older than 44 ka ±3 ka (Berger et al. 2002). Loess dunes (Q4e) are mapped north of Gore (McIntosh et al. 1990). Fan gravels (Q4a) derived from local ranges, mapped south of Ohai and beside the Blue Mountains, are assigned to OI stage 4 on the basis of down-valley profiling and their il lf o o tF Oreti Wa i a Mataura ti 2 ti 1 Ore Ore H "Lu u1 msd au en R iver " lt W aia u a rew Ma a ura 1 a ur M a ta rima a2 rim ka rim Apa Apa A pa M a at Invercargill Coastline N Present-day rivers Shorelines: Q7 Q5 20 km Figure 36 Southland Plains Quaternary paleogeography, showing present-day river systems and inferred paleodrainage, together with inferred paleoshorelines behind marine terrace remnants. There has been considerable channel switching of the major rivers throughout the Quaternary. The Waiau River may have drained via Ohai into the Aparima in the Early Quaternary (Waiau 1). In the late Middle Quaternary the upper Oreti River (Oreti 1) drained south into the Aparima catchment at Mossburn. Diversion of the Oreti 1 stream to the east (to its present position) was probably influenced by movement on active faults near Mossburn (see Figs 40 and 44). Drainage from the Five Rivers plain (and possibly the upper Mataura) flowed east into the present-day Mataura (Oreti 2) - the “Lumsden River” (McIntosh et al. 1990, 1998). The Aparima and upper Oreti rivers combined formed the wide plains between the two present-day river channels, and drained southeast into the present-day lower Oreti (Aparima 1). Probable stream capture saw this Aparima-Oreti river drain through a limestone ridge southeast of Otautau to reach the sea at Waimatuku (Aparima 2) (see Fig. 10). The lower Oreti, north of Winton, may have captured the east-flowing Oreti (the “Lumsden River”) south of Lumsden to bring it into its present route. The present-day Aparima River, minus the upper Oreti, was probably captured by a stream draining from the Otautau area to Riverton. During the Middle Quaternary the lower Mataura River built an extensive fan from Gore into the Makarewa and lower Oreti catchments. 43 Figure 37 Raised marine benches (Q5b) west of the Waiau River are underlain by gravel and sand. The prominent dark line (left centre and upward) is a former sea cliff inferred to date from a minor sea level fluctuation during OI stage 5. Gold was concentrated in beach sand at the foot of this cliff, and was sluiced in the Tunnel Claim; sludge channels (dark gullies) run from the old cliff to the modern cliff above the beach ridges behind the modern shoreline. The mouth of the Waiau River is in the distance, marked by a boulder bar. Photo CN44029/24: D.L. Homer height relative to younger deposits. These gravels are generally sandier and siltier than the better sorted gravels of the major rivers; their ages are poorly constrained. 44 Q2 Q3 Probable OI stage 2 tills occur throughout the Takitimu Mountains, but some may be older and as there is no age control, they are mapped as undifferentiated till (uQt). The only deposits of this age are laminated and crossbedded sands and silts in the upper Waiau River (Q3a) (McKellar 1973). This unit was deposited on a sand plain, probably associated with a pro-glacial stream system. Fresh sandy pebbly to bouldery glacial outwash (Q2a) forms inner terraces above the modern flood plain in the Waiau River, but its associated till is only preserved north of the Murihiku map area. Q2 outwash derived from the Monowai glacier forms wide terraces west of Blackmount, but no till from the OI stage 2 advance is known (Fitzharris 1967). OI stage 2 alluvial and fan deposits (Q2a) are widespread in most catchments. Many are probably of wider age range than OI stage 2. A large area of Q2a alluvium between the Oreti and Aparima rivers northwest of Winton was deposited following channel switching of the Aparima River into the Oreti (see Fig. 36). On Stewart Island, parallel-laminated sand underlies much of the Freshwater valley, and forms terraces along the west coast between the Ruggedy Mountains and Mason Bay. Radiocarbon ages of 24 802 ± 196 years and > 48 000 years have been obtained from peat within this sand. Field relationships suggest this sand covers a wide age range and consequently it is mapped as Late Quaternary (lQ). Peat within the sand at Little Hellfire has a cold climate Last Glaciation palynoflora (Mildenhall 2003). The sand terraces along the west coast include breccia lenses and beds derived from the adjacent granite basement (Bishop & Mildenhall 1994). Longitudinal and parabolic dunes in the Freshwater valley overlie fluvial sands of Late Quaternary age (see above), and although undated are likely to be OI stage 2 (Q2d). Winds from both westerly and easterly quarters are indicated by the dune patterns (F.J. Brook, pers. comm. 2002; see Fig. 13). carbonaceous mud may be interbedded. Several terrace levels may be present. Alluvial fans (Q1a) with clearly defined radial drainage and steeper slopes grade downstream onto terraces. Fans are composed of locally derived, commonly angular gravel, and may include debris flows as well as stream deposits. Sand dune deposits Dune fields (Q1d) occur on the mainland, along the south coast, and on Stewart Island. The mainland dunes are well preserved behind modern sandy beaches such as Oreti Beach and east of Waipapa Point. Some dune fields may predate OI stage 1, and have since been remobilised. Most are longitudinal dunes, with shore-parallel back-beach dune ridges closer to the coast. Active dune fields are indicated by a red overprint. Dunes are widely preserved behind bays and beaches on the western coast of Stewart Island. Bishop & Mildenhall (1994) reported radiocarbon ages of 7-10 000 yrs from peat (including a fossil forest) beneath the Mason Bay dune field. Liggett (1973c) reported, but did not map, widespread dune sands overlying Kamahi Terrace gravels (mQa) northeast from Invercargill, up to 35 km inland from the present coastline. Silcrete boulder ventifacts around Gorge Road (probably derived from silica-cemented sand within the Gore Lignite Measures) have been faceted by these wind-blown sands. Holocene deposits Peat deposits Cirque moraines Cirque morphology is widely preserved in the Takitimu Mountains, and there are small cirques on Mt Allen (Allibone & Wilson 1997) and Mt Anglem on Stewart Island (see Fig. 14). Most cirques date from OI stage 4 and earlier glacial events, but are commonly floored or fronted by bouldery angular till (Q1t), typically with well preserved terminal moraine topography. In the Takitimu Mountains, successive moraine loops are preserved in some cirques and some occur well down-valley from their headwaters. In the absence of radiometric dating, these are mapped as undifferentiated Quaternary till (uQt). Scree On Mt Hamilton and in the Takitimu Mountains, scree and slopewash derived from Brook Street and Murihiku terrane rocks is extensive enough to be shown on the map (Q1s; Fig. 38). Most scree is reactivated from deposits formed during Quaternary glacial periods when vegetation cover was suppressed, and may be up to 50 m thick. Scree deposits commonly grade downslope into fan and alluvial deposits. Alluvial terraces and fans Alluvium (Q1a) infills most valleys and underlies modern flood plains, and consists of locally derived, often bouldery, unconsolidated gravel, sand, and mud; peat and Significant areas of the Southland Plains are covered by fibrous to woody peat deposits (Q1a) (Fig. 39), some of which form mounds above the surrounding terraces; the base of these thick peats is probably older than OI stage 1. The Awarua Plains east of Invercargill in particular have well-developed and actively growing peat mires, and the peat beneath the Awarua deposit is at least 15 m thick. Some peat swamps are ponded behind gravel barriers, or limestone bands such as the Isla Bank - Otautau ridge. In the Blue and Takitimu Mountains, peat swamps are still forming in poorly drained valley heads and on ridges, impounded by vegetation in string bogs. Peat is widespread on Stewart Island, forming paleosols within fluvial and dune sands, underlying large areas in the Freshwater valley, and accumulating over much of the island beneath modern vegetation. Landslide deposits Landslides are most common in areas underlain by Caples Group semischist in the north of the map area, influenced by unfavourably oriented joint and foliation surfaces. Only those over 1 km2 in area are shown on the map, by an overprint. Smaller landslides occur within Murihiku Supergroup rocks, mainly as bedding plane dip slope failures in steeply dipping interbedded sandstonemudstone units. Minor landslides affect areas of Winton Hill and Waicoe formation mudstones. Although landslides in the semischist were probably initiated at various times 45 Figure 38 Looking southward from the central Takitimu Mountains to Telford Peak (centre). The extensive partly vegetated scree slopes are developed on Permian volcanic rocks of the Takitimu Subgroup. during the Early Quaternary (McSaveney et al. 1988) and so predate OI stage 1, many are still partly active. underlying rocks, and debris from small landslides and solifluction lobes. Beach deposits Loess is widespread throughout Southland up to 300 m ASL, and has been extensively investigated by Bruce (1973, 1984), McIntosh (1992, 1994), McIntosh et al. (1988,1990) and Berger et al. (2002). Loesses have been dated using tephra (volcanic glass) (Eden et al. 1992) and luminescence, and date back to at least 350 ka (Berger et al. 2002). In some localities up to four loess sheets are preserved, separated by paleosols (Berger et al. 2002), in a sequence up to 6 m thick (Bruce 1973). Loess dune fields mapped by McIntosh et al. (1990) north of Gore reflect strong westerly wind reworking older loess deposits, some as old as 250 000 years. Loess dunes are also reported from the older terraces in the Blackmount region by Carter & Norris (1980). Although a significant landforming lithology, loess is too variable in thickness and in outcrop to be shown on the 1:250 000 geological map, although the loess dunes north of Gore are shown. An extensive area of beach gravel (Q1b) with welldeveloped ridges underlies the Tiwai peninsula east of Bluff. An area of gravel with ridge topography beside the lower Oreti River is also mapped as a beach deposit. Some beach sands preserved behind modern beaches along the Catlins coast are large enough to be shown; generally modern beach sands (Q1b) are quite narrow and grade into dune fields above high water mark. Deposits of human origin Tailings (Q1n) from gold dredging operations are widespread in the Waikaia and Waikaka catchments. Smaller areas (not mapped) occur at Waimumu, west of Gore. Tailings also infill valleys between Round Hill and Orepuki, west of Riverton. Parts of Bluff Harbour consist of land reclaimed (Q1n) during port expansion in the 1950s (Wood 1958) and 1960s. Unmapped surficial materials Surficial materials, or regolith, include loess, weathered rock, and soils. While important in interpreting the underlying geology, and significant for human activities such as agriculture and construction, they are too thin, diffuse, and complex to be shown on the map. On flat to gently sloping older Quaternary surfaces in Central Otago and in northern Southland, the regolith is dominated by silty loess which, where remobilised on steeper slopes, grades into loess colluvium. Elsewhere and on higher and steeper slopes, the regolith is predominantly slopewash and locally derived scree, weathered material derived from 46 OFFSHORE GEOLOGY The submarine geology and surficial sediments of Foveaux Strait have been described by Cullen (1967) and Cullen & Gibb (1965). Information on the deeper sedimentary rocks and structures came from a seismic reflection profile in eastern Foveaux Strait (Mortimer et al.2002). Turnbull & Uruski (1993) re-interpreted oil company seismic data from the Solander Basin, in the western approaches to the Strait. Eastern Foveaux Strait and part of the shelf offshore from Stewart Island lie within the Great South Basin, described by Cook et al. (1999). The basement geology of Foveaux Strait can be inferred from regional geophysical data (Woodward & Hatherton 1975) supplemented by information from the scattered islands.Offshore basement southeast of the Catlins is assumed to be Murihiku Figure 39 Strip mining of a Sphagnum-dominated peat swamp east of Winton; much of this peat is exported for horticultural uses. The peat has formed a raised mound over alluvial gravels, which show subdued terrace edge morphology (upper right). Photo CN43917/19: D.L. Homer Supergroup, following Cook et al. (1999) and Mortimer et al. (2002). Murihiku rocks thin to the southwest, overlapping Brook Street terrane on an inferred thrust contact - the extension of the Letham Ridge Thrust (cf. Landis et al. 1999) (see cross-section A-A’). The Brook Street - Median Batholith contact, inferred to be intrusive, lies beneath northern Foveaux Strait just south of Ruapuke Island, where Median Batholith rocks are exposed. Mafic plutonics of the Median Batholith underlie central Te Waewae Bay, off the Waiau River mouth (Bishop et al. 1992). Mid Cretaceous to Miocene sedimentary rocks unconformably overlie basement southeast of Foveaux Strait (Cook et al. 1999). Only thickness contours (isopachs) estimated from seismic data are shown on the map. The Great South Basin sequence includes basal breccia and conglomerate, Late Cretaceous sandy and carbonaceous fluvial rocks and overlying latest Cretaceous coastal and shallow marine rocks. Sedimentary basins were controlled, in part, by a series of northwest and northeasttrending faults, possibly including reactivated extensions of the onshore Freshwater Fault System. In western Foveaux Strait, Turnbull & Uruski (1993) mapped up to 2 km of younger Cenozoic mud-dominated sedimentary rocks lying unconformably on basement. The youngest are Pliocene, the offshore equivalent of the Te Waewae Formation. Thicker sequences further west are as old as Eocene. Sediment distribution was partly controlled by faults linking the Freshwater Fault System to onshore faults west of Te Waewae Bay (Turnbull & Uruski 1993). Central Foveaux Strait is shallow and swept by strong bottom currents, and the surficial sediments are sand- and gravel-dominated especially in the northwest. Rocky sea floor topography extends north from the Ruggedy Islands, and between Ruapuke Island and Waipapa Point east of Bluff (Cullen 1967; Cullen & Gibb 1965). Pliocene lignite and fossiliferous Miocene rocks have been dredged from near Bluff and off Stewart Island respectively (Watters et al. 1968), implying the local presence of a thin cover of Cenozoic sediment. On the sea floor, shellbeds are dominant in places, particularly further offshore in deeper water (Cullen & Gibb 1965). In the Strait itself, some shellbeds are derived from the commercially important Bluff oyster, Ostrea chilensis, which lives only in areas of fine sandy gravel (Cullen 1962). 47 TECTONIC HISTORY Eastern and Western provinces: Gondwana and allochthonous accreted terranes Basement rocks of the Murihiku map area span the boundary between continental Paleozoic crust with Gondwana affinities (Western Province) and late Paleozoic to Mesozoic volcano-sedimentary terranes (Eastern Province) accreted to the margin of Gondwana during the Mesozoic. The boundary between Eastern and Western provinces has been referred to as the Median Tectonic Line or Median Tectonic Zone (e.g. Bradshaw 1993) and is one of the fundamental structures in the pre-Cretaceous basement of New Zealand. Plutonic rocks of the Median Batholith are inferred to span and stitch this boundary (Mortimer et al. 1999b). In the Murihiku map area the boundary between Eastern and Western provinces is largely concealed by Cenozoic sedimentary rocks or lies beneath Foveaux Strait. Cenozoic tectonism has also locally obscured earlier relationships between basement terranes along the Eastern-Western Province boundary. Paleozoic Pegasus Group schists on Stewart Island are the oldest rocks in the Murihiku map area and represent dispersed fragments of Western Province Takaka terrane basement, which formed at or near the Paleozoic Pacific margin of Gondwana. Eastern Province volcanic and sedimentary terranes, characterised by relatively low metamorphic grades, formed in a variety of subductionrelated settings along or distant from the margin of Gondwana. These settings include an intra-oceanic volcanic arc and related sedimentary basins (Brook Street terrane), a 2000 km long arc-flanking basin (Murihiku terrane), and trench and trench slope environments (Caples terrane). The Dun Mountain-Maitai terrane represents a slice of ophiolitic oceanic crust, unconformably overlain by Maitai Group forearc basin sedimentary rocks. Accretion of the Eastern Province terranes to the Western Province is the result of prolonged convergent tectonics along the New Zealand segment of the paleo-Pacific margin of Gondwana. Triassic to Cretaceous I-type dioritoidgranitoid plutonism within the Median Batholith, along and west of the contact between Eastern and Western provinces, is another important consequence of this convergence. In the Longwood Range, Middle Triassic to Early Jurassic plutonic rocks of the Median Batholith intrude older Brook Street terrane plutonic rocks, and accretion of the older parts of the Median Batholith and Brook Street terrane onto Gondwana took place around 230-245 Ma (Mortimer et al. 1999a). Further evidence is provided by the presence of clastic material from both the Brook Street terrane and the Median Batholith in Middle to Late Jurassic conglomerates of both Southland and Nelson (Tulloch et al. 1999). 48 Rocks of the Murihiku terrane were thrust across the eastern margin of the Brook Street terrane (including the Middle Jurassic Barretts Formation), on the Letham Ridge Thrust during the Middle to Late Jurassic (c. 160-140 Ma) (Landis et al. 1999). Accretion of the Murihiku terrane along the Letham Ridge Thrust therefore post-dates accretion of the Brook Street terrane to the Western Province (Gondwana) by c. 70-100 Ma. Ongoing plutonism in the Median Batholith further to the west did not extend eastwards into the Murihiku or eastern Brook Street terranes, even after docking with the Western Province. This may reflect an absence of thicker continental crust beneath the Eastern Province terranes (Mortimer et al. 2002) suitable for generating granitoid plutonic rocks. The Letham Ridge Thrust probably continues southeast beneath beneath the Murihiku Supergroup into eastern Foveaux Strait where Late Permian rocks (Kuriwao Group) may be relatively thick (see Mortimer et al. 2002, and crosssection A-A’). Numerous unconformities adjacent to Kuriwao Group could, however, imply proximity to a more tectonically active margin of the Murihiku sedimentary basin. The steep north-dipping Hillfoot Fault separates the Murihiku and Dun Mountain-Maitai terranes (Bishop & Turnbull 1996; Mortimer et al. 2002). An active trace has been identified along this fault, although the presence of overlying gently dipping Eocene to Miocene rocks indicates only minor movement on this terrane boundary since the early-mid Cenozoic. Juxtaposition of the Murihiku and Dun Mountain-Maitai terranes along the Hillfoot Fault is likely to have been during the Cretaceous. The insertion of the Willsher Group (a suspect terrane) along the boundary between Murihiku and Dun Mountain-Maitai terranes also probably occurred during this phase of movement. Formation of the Southland Syncline also dates from the Cretaceous, although in the north adjacent to Mt Hamilton it has been tightened during Cenozoic folding. The boundary between the Dun Mountain-Maitai and Caples terranes is marked by the steeply north-dipping Livingstone Fault (Coombs et al. 1976; Cawood 1986). Dismemberment of the Dun Mountain-Maitai terrane within the wider Livingstone Fault System - possibly including strike-slip movement of hundreds of kilometres (Cawood 1986, 1987) - reflects transport along this terrane boundary. Cooling ages of c. 135 Ma in the Caples terrane may reflect uplift at the time of accretion onto the Dun MountainMaitai terrane (Little et al. 1999). Formation of the regionally extensive Taieri-Wakatipu synform may also be related to metamorphism and subsequent uplift of the Caples terrane. Late Cretaceous sedimentary rocks overlie the Livingstone Fault near the Otago coast (Bishop & Turnbull 1996) and indicate juxtaposition of the Caples and Dun Mountain-Maitai terranes prior to c. 90 Ma. Cenozoic uplift inferred along the Livingstone Fault to the north (Turnbull 2000) does not appear to have occurred in the Murihiku map area. Mesozoic deformation within the Median Batholith The Median Batholith on Stewart Island is cut by the Gutter Shear Zone, Escarpment Fault, and Freshwater Fault System. Gneissic rocks in the Longwood Range and strongly foliated metasediments near Bluff indicate that Mesozoic deformation also occurred in these parts of the Median Batholith. The 2-5 km wide Gutter Shear Zone affects units older than c. 120 Ma but is cut by plutons younger than c. 116 Ma, constraining the timing of deformation to c. 118 Ma. Western Province Takaka terrane (Pegasus Group) rocks are restricted to the area within and south of the Gutter Shear Zone. Paleozoic granitoids within and south of the Gutter Shear Zone have been affected by multiple phases of ductile deformation, whereas those to the north are undeformed, except along the Freshwater Fault System. The Escarpment Fault in central and northern Stewart Island cuts granitoids older than 120-110 Ma, but is itself cut by rare dikes that were probably emplaced between about 110 and 105 Ma. Rocks to the south of the Escarpment Fault all have Ar-Ar cooling ages of c. 100 Ma whereas those to the north have cooling ages comparable with their emplacement ages. Lineations indicate that rocks south of the Escarpment Fault were thrust across those to the north and east at c. 110-100 Ma (Allibone & Tulloch 1997; Spell et al. 1999). Ductile shearing associated with the Freshwater Fault System affects rocks as young as c. 125 Ma, indicating that deformation occurred after this time. Cataclasis along some Freshwater faults post-dates foliation development (Allibone 1991) and may be Cenozoic. Fault-bounded slices of granitoid rocks and Paterson Group volcanic rocks were imbricated during reverse movement in the Cretaceous and/or Cenozoic. The Early to mid-Cretaceous movement histories on these major structures indicate that deformation within the Median Batholith is not simply an extension of Triassic and Jurassic tectonism associated with accretion of the Brook Street and Murihiku terranes to the Western Province. Late Cretaceous tectonics Following terrane accretion, cessation of Median Batholith plutonism and internal deformation, and a period of uplift and erosion (the Rangitata Orogeny), New Zealand rifted from Antarctica and then from Australia. In the Murihiku map area rifting was accompanied by opening of the Great South and Western Southland sedimentary basins (Turnbull & Uruski 1993; Cook et al. 1999). Cretaceous sedimentary rocks associated with rifting are the oldest preserved in these basins: the Ohai Group in western Southland, and the Hoiho Group in the Great South Basin. Northeast- and northwest-trending faults at Ohai and beneath the Waiau Basin controlled sedimentation in halfgraben (e.g Sykes 1989; Turnbull & Uruski 1993). A major fault which separates plutonic rocks from conglomerates on the southeast coast of Stewart Island, east of Port Pegasus, may mark the northwestern margin of the Great South Basin. Cenozoic tectonics and basin development A period of tectonic quiescence in southwestern New Zealand in the Paleocene was followed by Middle Eocene opening of fault-controlled basins. These basins formed in response to regional extension propagating northward along the Moonlight Fault System (Fig. 15) from the Solander Basin (Norris & Turnbull 1993; Turnbull & Uruski 1993). In contrast, rifting continued in the Great South Basin with deposition of thick clastic Paleocene sedimentary rocks (Cook et al. 1999). Extension, rapid subsidence and sedimentation continued into the Late Oligocene in Western Southland. Initiation of the Alpine Fault in the Early Miocene changed the tectonic setting to convergent strike-slip, resulting in basin eversion in the Waiau and Te Anau basins. Fiordland moved northeast relative to the Longwood and Takitimu ranges in the Middle Miocene, reactivating the Moonlight and northern Livingstone fault systems, the northwest extension of the Freshwater Fault System in Foveaux Strait, and faults surrounding the Takitimu Mountains. In contrast to Western Southland, the area east of the Moonlight Fault System and the Takitimu Mountains remained relatively tectonically stable throughout the early Cenozoic, with formation of the Waipounamu Erosion Surface across southern New Zealand (LeMasurier & Landis 1996), followed by coal measure deposition in shallow basins. Eocene to Oligocene subsidence in the Winton Basin was probably controlled by reactivation of Late Cretaceous faults extending east from Ohai (Cahill 1995). Local more rapid subsidence continued in the Winton Basin into the Late Miocene, and maximum regional subsidence is marked by an Early Miocene marine transgression (Chatton Formation) which reached inland to Waikaia. In the Late Miocene to Pliocene, the Northern Southland ranges were uplifted in response to shortening east of the Alpine Fault. Intermontane basins developed and gravel units (Prospect Formation and Pebbly Hill Gravels) accumulated, with continuing uplift into the Quaternary resulting in the younger Gore Piedmont and Clydevale gravels. Infaulting of middle Cenozoic sedimentary rocks into the already tilted Southland Syncline ranges on northeast-trending faults also dates from the Late Miocene to Pliocene, as does probable southeasterly-directed overthrusting along the Dunsdale Fault System (Hatherton 1979) and its northern extensions (Isaac & Lindqvist 1990). Most of the present-day topography of Murihiku was probably formed by the end of the Pliocene. 49 Quaternary tectonics The western side of the Murihiku map area is currently being deformed, as Fiordland moves northeastward in relation to the area east of the Waiau River in response to oblique compression within the Pacific Plate southeast of the Alpine Fault (see Fig. 3). Much of this motion is presumed to be along the Moonlight Fault System, where strike-slip movement has been inferred from earthquakes (Anderson et al. 1993). Quaternary fault traces occur along this system, including one beneath the Mararoa Weir abutments (R.M. Carter, pers. comm.) on an extension of the Hauroko Fault. Shortening across faults southwest of the Takitimu Mountains, and sinistral strike-slip movement east of the Takitimu Mountains on the Tin Hut Fault (Landis et al. 1999), is probably also related to Fiordland motion. The northeast- and northwest-trending Quaternary fault traces within the Hokonui and Taringatura ranges (including the Hillfoot Fault), and a fault which deforms terraces at Mossburn, may represent adjustment of these areas in response to bending of the Southland Syncline. Late Quaternary fault scarps on the Blue Mountains and Spylaw faults represent the compressive regime covering much of Central Otago, where block faulting along northeast-trending faults is widespread (Jackson et al. 1996). The Clifton Fault and an active fault northeast of Mossburn (Fig. 40) are inferred to be splinters of the Livingstone Fault System (Fig. 15). Figure 40 The trace of an active fault northeast of Mossburn. The trace (arrowed) is downthrown to the east by about 2 metres, and extends from the Acton Stream in the north (top) to the braided Oreti River (bottom). The photograph dates from 1957; although more recent aerial photos exist, they do not show the trace as clearly because of the effects of cultivation. NZ Aerial Mapping vertical air photo 2525/23, survey SN 1020 50 ENGINEERING GEOLOGY This section provides generalised information to assist geotechnical investigations and hazard assessments, but is not a substitute for detailed site investigations. Potential difficulties with some rock types are highlighted. Paleozoic to Mesozoic rocks Plutonic rocks exposed on the coast and on headlands such as Pahia Point are strong, hard and fresh, but inland in the Longwood Range they are typically very weathered. Joints are generally widely spaced (0.5-5 m). Gneissic foliation is normally not a significant pervasive defect. Weathering within the Longwood Range may extend to at least 10 m below the surface and the most weathered rocks are extremely weak, prone to slipping and rilling in fresh exposures. Brook Street terrane volcanics and volcaniclastic sedimentary rocks in the Takitimu Mountains are hard and fresh on steep faces, but on more gentle terrain are prone to frost-shattering which exploits pervasive close jointing. In lower-lying areas such as north of Ohai they tend to weather readily to weak soft clayey soils. Zeolite alteration makes Brook Street terrane rocks vulnerable to disintegration when crushed. On Twinlaw and Woodlaw, Brook Street terrane rocks are deeply weathered although fresh, strong material can be quarried below the weathering zone (see Fig. 21B). Coastal exposures at Riverton are very fresh and hard. Paleozoic rocks in the Greenhills to Bluff area are generally very strong and hard, capable of supporting steep faces and providing large blocks. Deep weathering may be present in old gullies and beneath vegetation cover on flatter slopes. On Stewart Island, the plutonic rocks around Oban are variably weathered and range from extremely weak, to very strong and hard when fresh. Rock strength is influenced by jointing, topography and degree of weathering more than by rock type. Volcanic and plutonic rocks within the Dun Mountain Ophiolite Belt north of Mossburn, in the Lintley Range and around Otama tend to be hard and relatively fresh but are closely jointed. Serpentinite north of Mossburn is a very weak rock, but contains hard “knockers” of gabbro and diorite. Maitai Group sedimentary rocks range from strong to extremely weak, the strength diminishing with decreasing grain size, and increased weathering and cleavage development. Sandstones are generally closely jointed (0.1-0.5 m); although large faces in mudstones of Greville and Waiua formations may stand steeply, surface fretting is common. Caples terrane sandstones are strong, hard, variably jointed rocks. Slopes cut in fresh rock are generally stable, although rock falls may occur on very steep faces. Rock strength decreases with increasing weathering, but closely spaced joints are more significant defects. Bedding is a significant rock defect only in fine-grained lithologies. In t.z. IIA and IIB semischists rock strength decreases with increasing foliation development, and in t.z III schist foliation is a major rock defect. Landslide debris in semischist and schist terrain is predominantly weak with little internal strength, but larger landslides shown on the map face are extremely variable in their engineering properties. They range from large intact blocks separated by shear zones, to internally chaotic masses. The zeolite content of Murihiku Supergroup sedimentary rocks induces rapid weathering and breakdown of clasts and fresh surfaces, even in hard freshly quarried material. Jointing is very close in mudstones. Sandstones are less closely jointed (0.1-0.5 m) and normally these rocks are relatively strong and can support steep batters, although small block falls may be promoted by closer jointing. Conglomerates, often preferentially quarried as they contain hard clasts, are easily fractured around clasts and tend not to perform well in steep batters. Late Cretaceous and Tertiary sedimentary rocks The wide lithological variation in these rocks is reflected by their range of rock strengths and properties. Sandstones are usually hard when fresh; jointing is variably spaced (0.1-2 m). Mudstones of the Waicoe and Winton Hill formations are prone to landsliding and may cause engineering difficulties in road batters. Forest Hill Formation and Clifden Subgroup limestones are hard, generally widely jointed rocks which are strong and can support large cliffs (see Fig. 32B). Sandstones within the Ohai and Nightcaps groups are generally strong and widely jointed, but coals and carbonaceous mudstones (such as the Orauea Mudstone) are more clay-rich and weaker. Slope stability may be a problem in mine batters where carbonaceous mudstone is abundant. Claystone and siltstone in the Mako and Gore coal measures are soft, weak rocks and can be unstable on steeper slopes, especially when wet. The large landslide at Landslip Hill has failed in Gore Lignite Measures beneath a hard, strong silcrete cap. Pebbly Hill Gravels and quartz gravels within East Southland Group are poorly consolidated weak soils. Quaternary sediments Gravel and sand in Quaternary moraines, outwash plains, alluvial terraces and fans are loose, weak sediments. Schistose or non-schistose clasts in Caples-derived gravels are harder and less prone to weathering than clasts in gravels derived from Murihiku or Dun Mountain-Maitai terrane rocks. Gravels of the Waiau catchment are rich in hard, strong Fiordland-derived plutonic rocks, and a minor Fiordland-derived component is also present in the upper Oreti catchment. Aparima gravels have a significant component of relatively hard Brook Street terrane volcanics. Regolith, including extremely weathered rock, loess and loess colluvium, is a weak rock or soil, and is vulnerable to shallow landsliding on steeper slopes. 51 GEOLOGICAL RESOURCES The Murihiku map area contains a wide variety of geological resources, the most economically significant being gold, sub-bituminous coal and lignite, aggregate, limestone, and peat. Mining for alluvial gold was widespread in the late 19th and early 20th centuries, but few hard-rock deposits were found or exploited. Coal mining was initially on a small scale from many scattered pits and developed into a major industry at Ohai in the 1940s to 1960s, but has since declined. Lignite has been mined for many years from Eastern Southland and in the Waikaia and Pomahaka areas. Considerable reserves of lignite were delineated in Eastern Southland following a comprehensive exploration programme in the 1980s (Isaac & Lindqvist 1990). Some alluvial gold mines are still operating, and prospecting for gold and platinum continues. Aggregate and limestone quarrying is ongoing and large reserves are available. The economic geology of the map area has most recently been described by Doole et al. (1989) and Lindqvist et al. (1994), based on Geological Resource Map of New Zealand data; this section summarises and updates those reports. Past production figures are given by Williams (1974), Doole et al. (1989) and Lindqvist et al. (1994); more recent annual production statistics are available from the Ministry of Economic Development. Hall-Jones (1982) gave histories of many of the goldfields. METALLIC RESOURCES Hard-rock gold mineralisation Most known gold lodes within the Murihiku map area are in the Longwood Range. Several lodes were discovered in the 1870s and 1880s adjacent to the contact between Takitimu Subgroup and Median Batholith intrusive rocks. Gold occurs in both altered plutonic and volcanic rocks. Ore crushing batteries were erected on the Arethusa and Printz’s reefs but the mining was short-lived (Hall-Jones 1982) and although only 1.5 kg are recorded as having been produced, output was probably much greater. More recent exploration in the Longwood Range has identified several gold anomalies (Nicholson et al. 1988) in both the Pourakino and Orauea catchments. Traces of gold have been reported from the Dun Mountain Ophiolite Belt near Otama, as well as a gold-bearing quartz lode, but there is no evidence of significant mineralisation (see Lindqvist et al. 1994). On Stewart Island gold has been reported in the northern Ruggedy Range and at North Red Head Point. Brittle faulting, pyritic silicified breccia, and quartz veining with disseminated pyrite southwest of West Ruggedy Beach may be the source of the gold. Gold on Waituna Bay beach (Howard 1940) may be derived from deformed and extensively altered Ruggedy Granite and Paterson Group volcanic rocks that crop out at either end of the bay and along the coast to the north. 52 Alluvial gold There are many alluvial gold occurrences in the Murihiku map sheet, including beaches from the Waiau River to the Catlins coast, and placer deposits in the sediments of the Mataura and Clutha rivers and their tributaries (Fig. 41) Gold at the Tunnel Claim west of the Waiau River (Fig. 37; Wood 1969), and at Orepuki and Round Hill (Macpherson 1938) was recovered from beach deposits on raised marine benches and from streams reworking them. At Round Hill, gold was mined from Early Quaternary sediments and weathered alluvium, with a total production of 2488 kg from the Round Hill Gold Company alone (Lindqvist et al. 1994). The Arethusa (Longwood) Nugget reputedly weighed 36 ounces (1.02 kg). The source for this gold may have been mineralisation in Takitimu Group rocks of the adjacent Longwood Range. Some gold is also present in the Waiau River, where a dredge once operated south of Blackmount (Hall-Jones 1982). Dredging and sluicing of numerous beach placer deposits further east, from Fortrose to Haldane, produced some very fine-grained gold (Lindqvist et al. 1994). Although prospected in the 1990s (MacDonell 1992) there is no current mining. Sluicing and dredging operations recovered gold along the Waikaia and Waikaka rivers from their headwaters downstream to the Mataura River, and on the Waimumu and Charlton alluvial goldfields near Gore. The gold was derived from lodes in the Otago schists, reworked into Miocene and younger quartzose gravels, and then into Late Quaternary alluvium. Mining began in the late 1800s, but records are incomplete and regional assessments do not give total production, although it was probably several thousands of kilograms. The Waimumu field alone produced 570 kg (Mutch & Baker 1989). The King Solomon Mine east of Waikaia produced 605 kg of gold from underground workings in infaulted fluvial and fan gravels. Some of the gold in the older alluvial deposits is quite coarse, and intergrown with quartz (Falconer 1987; Clough & Craw 1989; Craw 1992). Prospecting continues, with several small alluvial mines operating (Fig. 42). Alluvial gold was panned and sluiced from creeks that drain both the eastern and western sides of the Tin Range on Stewart Island (McKay 1890; Williams 1934a; Howard 1940). Minor amounts of alluvial gold were obtained from the Kopeka River and tributaries in southeastern Stewart Island (Williams & Mackie 1959). Traces of gold have also been recorded on Waituna, West Ruggedy, Smoky, Newton and Port William beaches in the north of the island (Howard 1940). Silicon and ferrosilicon Quartz gravel from the Cenozoic sedimentary rocks of eastern Southland has been prospected as a potential feedstock for production of silicon and ferrosilicon, partly Ohai Pomahaka Mako Orepuki Alluvial goldfields N Eastern Southland coalfields (Miocene) Orepuki, Mako and Pomahaka coalfields (Eocene) Ohai Coalfield (Cretaceous) 50 km Rivers Roads Figure 41 Coalfields and estimate areas for the Eastern Southland, Mako, Pomahaka, Orepuki and Ohai coalfields. The main alluvial gold workings in the Murihiku map area are also shown. influenced by the proximity of coal and hydroelectric power supplies. Sufficient quantities of quartz gravel are available in the Pebbly Hill Gravels, and in Q5 marine terraces at Awarua, but the percentage of impurities inhibits their utilisation (Turnbull & Ker 1970; Hope et al. 1971). Modern and more cost-effective treatment methods may result in a renewal of interest in this resource. Other metallic minerals Platinum was recovered as a by-product of alluvial gold mining from many claims around the Longwood Range, west of the Waiau River and as far east as the Catlins (Williams 1974). The platinum ranges from very fine grains up to nuggets of several ounces, and is probably derived from the margins of the Waiau Basin (Mitchell 1995). Numerous prospecting programmes, and recent drilling of the Hekeia Gabbro in the southern Longwood Range, have recorded some platinum values (e.g. Rossiter 1989; Cowden et al. 1990; Ford 1999). Traces of platinum occur in the Greenhills Ultramafic Complex (Spandler et al. 2000). Copper occurs in mineralised breccia and shear zones as chalcopyrite, associated with pyrite and pyrrhotite, within granophyre and diorite of the Dun Mountain Ophiolite Belt near Otama. Extensive prospecting in the 1970s failed to locate any economic deposits (McPherson 1973; Lindqvist et al. 1994). Traces of copper are reported from the Longwood Range, the Takitimu Mountains and on Stewart Island (McKay 1890; Lindqvist et al. 1994). The intrusive contact between Codfish Granite and Paterson Group andesitic rocks south of Richards Point coincides with a zone of altered rocks that contain common pyrite and traces of chalcopyrite (Allibone 1986) and which may be the source of copper mineralisation noted by McKay (1890) (cf. Rolston 1972). 53 Figure 42 Waikaka gold dredge working Late Miocene to Pliocene and Early Quaternary quartz gravel, south of Waikaka township (October 2002). This operation has now closed. Photo CN43866/17: D.L. Homer Manganese as psilomelane with up to 59% Mn occurs with barite in a lode in the southeastern Longwoods (Beck 1962) but has never been mined. Molybdenum is found in a small quartz lode in the northwestern Longwood Range (Willett 1943). Mercury as cinnabar was reported from Caples terrane rocks in the Waikaka area by Henderson (1923), with up to 12% Hg (Lindqvist et al. 1994). Tin as cassiterite was worked on a small scale from streams around the North Arm of Port Pegasus and on the southern Tin Range on Stewart Island. A single short adit driven along a wolframite- and cassiterite-bearing quartz vein a few centimetres wide within a narrow greisen zone near the summit of the Tin Range had no significant recorded production (McKay 1890; Williams 1934a, 1974). NON-METALLIC RESOURCES Coal The Murihiku area has extensive deposits of coal, both Tertiary lignite and the higher rank Cretaceous subbituminous coals of the Ohai field (Fig. 41). Nearly all known occurrences of coal have been worked to some extent since the late 1800s, and several pits are still in operation. The Ohai Coalfield was extensively mapped and 54 surveyed in the 1950s and 1980s (Bowen 1964; Bowman et al. 1987; Sykes 1988). A detailed survey was made of the Eastern Southland Coalfield, utilising drilling, down-hole logging, geological mapping and paleoenvironmental analysis during the 1970s and early 1980s (Isaac & Lindqvist 1990). Other smaller fields are covered in the regional resource assessment by Lindqvist et al. (1994). The Ohai Coalfield lies in a east-trending structural depression north of Twinlaw (see Fig. 28). Faulting is widespread, and the coal-bearing rocks are folded into numerous anticlines and synclines (Bowen 1964; Bowman et al. 1987). The coal contains 0.3-0.6% sulphur and 1-8% ash. Seams up to 23 m thick lie within the Morley Coal Measures of the Ohai Group. Seams are lenticular and often split or are washed out by fluvial sand channels, and syndepositional faulting and folding are indicated (Sykes 1988). Most of the open-cast and underground mines were north of Ohai, although several pits were located nearby at Nightcaps. 100-150 million tonnes (Mt) of reserves are estimated to remain, down to depths of 500 m (Lindqvist et al. 1994). Although some coal has been mined from the unconformably overlying Eocene Beaumont Coal Measures (Bowen 1964), the seams are thin (2-3 m), with high ash, and of lesser economic interest. Eastern Southland Coalfield lies between Gore, Invercargill and the Mataura River. The structure is simple with low dips, except near the Bushy Park and Hedgehope faults. Lignites within the Gore Lignite Measures are mainly in the “middle measures”; individual seams are laterally persistent and typically 1-8 m thick, but locally as thick as 19 m (Croydon and Ashers Siding) (Isaac & Lindqvist 1990). Seams are low in ash (less than 10%) and sulphur (0.140.65%). Coal rank is highest in the northwest and lowest in the south, reflecting variation in the original depth of burial. The thickest seam at Waimumu has 42% bed moisture, suggesting former burial of 810 m, whereas Makarewa lignite with 64% bed moisture has never been buried deeper than 145 m. Drilling programmes between 1975 and 1984 outlined significant resources in nine areas (Isaac & Lindqvist 1990) (Fig. 41). The total resource at less than 200 m of cover has been estimated to be 6760 million tonnes Indicated and 1570 million tonnes Inferred coal-in-ground. Studies confirmed large scale open pit mining was technically feasible and the Ashers-Waituna (Kapuka) deposit was identified by the Liquid Fuels Trust Board as the best site to provide feedstock for a coal to liquid fuel conversion plant. To date the project has been judged uneconomic. Mining for electricity generation is being considered. Other smaller areas of lignite are present elsewhere, for example, south of Tapanui in the Pomahaka valley, in the Maitland area, and in the Wendon valley. Eocene coal was mined from Beaumont Coal Measures in the Orepuki Coalfield (Willett 1946a). It is of subbituminous B rank (Wood 1969), due to significant burial beneath Waiau Group sedimentary rocks. The coalfield is structurally complex but has not been fully investigated; inferred reserves of 1 Mt may exist. Scattered small deposits of Beaumont Coal Measures have been mined around the flanks of the Takitimu Mountains (summarised by Turnbull & Uruski 1993). A small mine exploited the Eocene Mako Coal Measures north of Hedgehope (Rout 1947), and although one drillhole intersected the seam during Eastern Southland Coalfield exploration, the extent of reserves is unknown (Isaac & Lindqvist 1990). Eocene lignite has also been worked from seams 2 to 5 m thick in several small pits in the Pomahaka Coalfield, west of Clydevale. Drilling in the 1970s resulted in estimated coal-in-ground reserves of 5.4 Mt (Liggett 1979). Peat Peat deposits cover significant areas of the Southland Plains, and several are currently being exploited (Fig. 39). Large deposits occur southeast of Invercargill, east of Otautau, and south of Mossburn. The deposits are up to 15 m thick. These deposits range from fine-grained Sphagnum peats to accumulations of branches, logs and stumps. Very large reserves exist east of Invercargill, although partly protected as botanical reserves. Hydrocarbons The Cretaceous and Tertiary sedimentary sequences within the Murihiku map area have been investigated by several exploration programmes and wells. The onshore hydrocarbon potential is discussed by Turnbull & Uruski (1993), Lindqvist et al. (1994) and Cahill (1995), and the offshore by Turnbull & Uruski (1993) and Cook et al. (1999). The Winton Basin has been tested by three wells, and a seismic survey in the 1980s, summarised by Cahill (1995). Although the basin is up to 2800 m deep, with Eocene coal measures as potential souce rocks at the base, only the J T Benny-1 well, drilled in the 1960s, had hydrocarbon shows. The Waiau Basin sequence, up to 5 km thick in the map area, has potential source rocks (Ohai and Nightcaps groups) at depth, with potential reservoir rocks and structural and stratigraphic traps in several places (Turnbull & Uruski 1993). One well west of the map area produced no evidence of hydrocarbons. Oil was produced from shale within the Nightcaps Group at Orepuki between 1899 and 1903 (Willett & Wellman 1940) but further extraction would be uneconomic. This oil shale is of interest as a potential source rock in the Waiau Basin west of Orepuki (Turnbull & Uruski 1993). Oil shale within Gore Lignite Measures, south of Waikaia, was used as a fuel for gold dredges in the early 1900s. Production of methane from Ohai Group coals has been tested near Ohai, and the underground gasification of these higher ranking coals has some potential (Cave & Boyer 1990). Oil seeping from plutonic rocks on Stewart Island may have travelled along faults from the hydrocarbon-bearing sedimentary rocks of the Great South Basin to the southeast. The hydrocarbon potential of the Great South Basin, tested by several wells beyond the map area, was summarised by Cook et al. (1999). Aggregate The Murihiku map area is relatively well endowed with aggregate sources, except for the Catlins and Stewart Island. Most aggregate is extracted from Quaternary and Recent alluvium in river beds, or from modern or Q5 beach gravels along the south coast. The composition of alluvium varies across the map area, depending on the predominant rock type in the catchment. The Pebbly Hill quartz gravel deposits and quartz gravels near Waikaka are worked as an aggregate source and for decorative purposes. All of these deposits have very large reserves which, in the case of pits working modern river beds, are replenished during floods. Aggregate is quarried from Caples t.z. I sandstone in the Blue Mountains. Caples semischists make poorer aggregate as they break down more rapidly; nevertheless, semischist is frequently quarried for base course metal for roading. Where Murihiku Supergroup sedimentary rocks predominate, good aggregate is scarce because of pervasive 55 zeolitisation, and conglomerate horizons are often worked preferentially as the clasts are commonly hard. Some Maitai Group sedimentary rocks - mainly Little Ben Sandstone have been quarried for roading aggregate. “Rotten rock” from small quarries in weathered outcrops of most basement units is widely used throughout Southland as base course for farm roading. Bluff Intrusives and Greenhills Group metasediments (especially tuffs) are also worked for aggregate. The basic tuffs within the Greenhills Group are more suitable than the veined mafic intrusive rocks (Lindqvist et al. 1994). Aggregate on Stewart Island is in very short supply, and it has sometimes been shipped across from the mainland. The existing quarry in variably weathered diorite cannot provide aggregate of a suitable standard and exploration is under way for a better source. Limestone The Murihiku area has large reserves of Cenozoic limestone suitable for agricultural use. Thin limestones within Permian Maitai and Kuriwao groups have been also worked, but largely as a source of aggregate. Most quarries are in Forest Hill Formation (Fig. 30) although limestonerich facies of the Chatton Formation have been worked at Waimumu (McKellar 1968) and Balfour (Isaac & Lindqvist 1990). Forest Hill Formation limestone is variably hard and may require blasting. Silica sand Quartz sand within the Gore Lignite Measures north of Invercargill, and on Landslip Hill, has been worked for plastering sand and as an abrasive, respectively (Lindqvist et al. 1994). Serpentinite Serpentinite, used as a magnesium source in fertiliser, was formerly quarried at Black Ridge northeast of Mossburn. Serpentinite and dunite are now quarried from ultramafic rocks at Greenhills. Reserves have not been calculated but within the Greenhills Ultramafic Complex are likely to be many millions of tonnes. Clay Several sources of kaolinitic clay within the map area have been worked in the past. Clay minerals are abundant in deeply weathered granitic rocks on Stewart Island, but have not been exploited. The Ohai Group includes clays as “seat earths” beneath coal seams, and these have potential for ceramic use (Bowen 1964), but mining is likely to be difficult and the extent of the clays is unknown. Nightcaps Group clay at Waimeamea has been used for brick-making (Wood 1969). Clay was mined from the Pomahaka Coalfield and from Mako Coal Measures west of Hedgehope. Thin beds of kaolinitic clay within the Gore 56 Lignite Measures are unlikely to have economic potential. Although montmorillonite and illite occur within Waicoe and Winton Hill formation mudstones, these have never been worked and the mudstones are unsuitable for ceramic manufacture (Wood 1969). Loess, suitable for brick and tile manufacture, is extremely widespread within the map area, although the only current operation is for making field tiles, at Pukerau. Loess resources within the map area are very large. Building stone and riprap Riprap for river protection work is intermittently quarried from Maitai and Murihiku rocks near Mossburn, and from Dun Mountain Ophiolite Belt rocks near Otama. Large blocks of Forest Hill Formation limestone are suitable for river protection work. Norite was quarried for reclamation at Bluff (Watters et al. 1968) and, together with norite from Ruapuke Island, has also been used as a building stone (Hayward 1987). Hayward also records Triassic sandstone as having been used in buildings at localities across the Murihiku sheet, including Waikawa in the Catlins. However the zeolitic cement in these sandstones is a drawback as it renders them vulnerable to weathering. Groundwater Groundwater is a valuable resource within the Murihiku map area, especially with increasing demand for water from the dairy industry. Lindqvist et al. (1994) summarised actual and potential aquifers and their properties; a regional map and discussion of aquifers is given by Hughes (2001). The greatest yields are from aquifers within loose sandy gravels close to rivers, and from modern and raised beach gravels. These aquifers are unconfined and vulnerable to pollution. Groundwater is also obtained from older terrace gravels, but these aquifers are limited by a high clay content (Hughes 2001). Groundwater in deeper gravels is typically contained within coarser, less clay-bound gravel in lenticular buried channels with no connection to nearby channels, and adjacent wells may not be tapping the same aquifer. Cenozoic sedimentary rocks can also produce groundwater. Some quartz sands and gravels in the Eastern Southland Coalfield produce strongly artesian flows from depths as great as 200 m. Some of this groundwater is of high quality, but in other wells it is unacceptably acidic through interaction with coal-bearing strata (Hughes 2001; Rosen 2001). The Chatton Formation, interbedded with lignite measures, hosts an aquifer system near the Toetoes Bay coastline (Lindqvist et al. 1994). Groundwater is also extracted from fracture systems within Forest Hill Formation (Hughes 2001), and may also be present in older, harder rocks, within joints and fractures rather than in pore spaces as it is in the younger rocks. Yields from such fracture systems are generally low. GEOLOGICAL HAZARDS Numerous geological hazards exist within the Murihiku map area. They include landsliding, earthquake shaking and liquefaction, erosion, tsunami, and groundwater contamination. Many of these hazards are influenced by geological factors such as rock properties and distribution, and the presence and activity of faults. The hazards are summarised here, but this map and text should not be used for detailed natural hazard zonation or assessment of specific sites. Recording of site-specific natural hazard information is the responsibility of local authorities, and an awareness of the presence of major hazards, and their potential for recurrence, is essential for regional and district planning purposes. Regional hazard assessments are given by Van Dissen et al. (1993) and Glassey (2002). Earthquakes (by G. L. Downes) Since organised European settlement began in New Zealand, no large earthquakes and very few moderate or small earthquakes are known to have occurred within the Murihiku map area. Seismicity has been low in recent times (Fig. 43). However, moderate to strong shaking with some damage has been caused by large earthquakes originating outside the map area, such as the 1979 M7.3 Puysegur Bank earthquake and the 1988 M6.7 Te Anau earthquake. Magnitude and Modified Mercalli intensity are frequently used earthquake terms. Magnitude is a means of ranking the size of earthquakes. It is calculated using instrumental records of earthquake shaking. There are various ways of doing this, which result in magnitudes of different types, e.g., local magnitude (ML), surface wave magnitude (MS), and moment magnitude (MW). These may differ by small amounts. MW is the most reliable, but is only available for large earthquakes. In this publication, the generic term magnitude may be assumed to be ML for small and moderate earthquakes, and MW or MS for large earthquakes that have occurred since instrumental measures have been available. The Modified Mercalli intensity scale (MM scale; see text box) is a 12-level descriptive scale used to rank the strength or intensity of shaking produced by an earthquake at a location. The MM intensity level is determined by noting the effects of shaking on people, fittings, structures and the environment at the place of interest and comparing them with descriptors in the scale. MM 10 is the highest MM intensity level so far reliably observed in New Zealand. Earthquake occurrence in the southern South Island (Fig. 43) is predominantly within a zone of seismicity along the Pacific - Australian plate boundary, part of which is formed by the Alpine Fault. Deformation caused by intraplate collision is responsible for many earthquakes, most occurring at depths down to about 160 km. The largest of these earthquakes, although not originating within the Murihiku map area, can cause moderate to strong shaking within it. For example, the 1988 M6.7 Te Anau earthquake, 57 km beneath Fiordland, caused shaking intensities of MM5 or MM6 in the map area, with intensities up to MM8 closer to the epicentre. The earthquake caused a temporary interruption of power supplies to Invercargill. The Modified Mercalli Intensity scale (MM) (in part; summarised from Downes 1995) MM 2: Felt by persons at rest, on upper floors or favourably placed. MM 3: Felt indoors; hanging objects may swing, vibration similar to passing of light trucks. MM 4: Generally noticed indoors but not outside. Light sleepers may be awakened. Vibration may be likened to passing of heavy traffic. Doors and windows rattle. Walls and frames of buildings may be heard to creak. MM 5: Generally felt outside, and by almost everyone indoors. Most sleepers awakened. A few people alarmed. Some glassware and crockery may be broken. Open doors may swing. MM 6: Felt by all. People and animals alarmed. Many run outside. Objects fall from shelves. Glassware and crockery broken. Unstable furniture overturned. Slight damage to some types of buildings. A few cases of chimney damage. Loose material may be dislodged from sloping ground. MM 7: General alarm. Furniture moves on smooth floors. Unreinforced stone and brick walls crack. Some preearthquake code buildings damaged. Roof tiles may be dislodged. Many domestic chimneys broken. Small slides such as falls of sand and gravel banks. Some fine cracks appear in sloping ground. A few instances of liquefaction. MM 8: Alarm may approach panic. Steering of cars greatly affected. Some serious damage to pre-earthquake code masonry buildings. Most unreinforced domestic chimneys damaged, many brought down. Monuments and elevated tanks twisted or brought down. Some post-1980 brick veneer dwellings damaged. Houses not secured to foundations may move. Cracks appear on steep slopes and in wet ground. Slides in roadside cuttings and unsupported excavations. Small earthquake fountains and other instances of liquefaction. MM 9: Very poor quality unreinforced masonry destroyed. Pre-earthquake code masonry buildings heavily damaged, some collapsing. Damage or distortion to some post-1980 buildings and bridges. Houses not secured to foundations shifted off. Brick veneers fall and expose framing. Conspicuous cracking of flat and sloping ground. General landsliding on steep slopes. Liquefaction effects intensified, with large earthquake fountains and sand craters. MM 10: Most unreinforced masonry structure destroyed. Many pre-earthquake code buildings destroyed. Many pre-1980 buildings and bridges seriously damaged. Many post-1980 buildings and bridges moderately damaged or permanently distorted. Widespread cracking of flat and sloping ground. Widespread and severe landsliding on sloping ground. Widespread and severe liquefaction effects. 57 1976 M6.5 Milford Sound 1988 M6.7 Te Anau 1993 M6.8 Secretary o S o o 1979 M 7.3 Puysegur Bank Depth < 40 km Intensity Depth > 40 km 4 - 4.9 5 - 6.4 6.5 + o o E o o o o Figure 43 Locations of earthquakes in southwestern New Zealand with magnitudes >3.5, for the period 1964 June 2002. Some significant earthquakes are highlighted. Murihiku map area is shaded. Large shallow earthquakes may rupture to the ground surface along faults. Major faults west of the Murihiku area include the Hollyford, Dusky and Moonlight Fault systems, and the Alpine Fault. Of these, the Alpine Fault is the most active, and considered capable of producing up to magnitude M8 earthquakes. Large earthquakes producing surface fault ruptures on the onshore part of the Alpine Fault probably occur every few hundred years (Rhoades & Van Dissen 2000; Norris et al. 2001), the last known being in 1717. The probability of fault rupture of the southwest onshore segment of the Alpine Fault in a M8 earthquake within the next 20 years is 6-14% 58 (Rhoades & Van Dissen 2000; Norris et al. 2001). Such an event is expected to generate felt intensities of MM6 at Invercargill (Glassey 2002), causing widespread contents damage to houses and some minor structural damage. While most of the deformation associated with the plate boundary occurs near the boundary, some is being transferred east of Fiordland. Large active faults within the Murihiku map area (Fig. 44) include the Hauroko Fault (part of the larger Moonlight Fault System), the Tin Hut Fault System (Fig. 45), the Blue Mountain No 1 Fault (Beanland & Berryman 1986), and the Hillfoot Fault. Smaller traces are mapped within the Hokonui Hills, in the Catlins (Settlement Fault of Speden 1971; Bishop & Turnbull 1996), near Clinton (Clifton Fault) and on the Spylaw Fault (Beanland & Berryman 1986). More detail on some of these faults is given by Van Dissen et al. (1993), Stirling et al. (1998) and Glassey (2002). Recurrence intervals (i.e. the average time interval between large earthquakes, Table 1) range from about 600 years to 3000 years or more (Stirling et al. 2000). Other possibly active faults have been identified, but rupture histories are known for few of these and it has not been possible to determine whether the criteria have been met for declaring a fault to be active, that is, evidence of movement within the last 125 000 years or repeated movement within the last 500 000 years. Earthquakes ranging up to magnitude M7.3 can be expected on surface rupturing faults within the Murihiku area. Earthquakes of magnitude M7 and above often generate long duration shaking, possibly in excess of one minute. Surface rupture with vertical or horizontal offsets of perhaps several metres, may occur on or near mapped fault traces, along strike from those traces, or as new ruptures Hauroko Fault on other parts of the faults. Physical offset on active faults will affect objects and the landscape on or within a few hundred metres of the faults. Shaking will be more intense toward faults, possibly MM9 along ruptures, and will also be stronger in deep soft soils. The degree of damage to be expected from various intensities is summarised in the text box. Liquefaction, the phenomenon whereby saturated soils and unconsolidated sediments change from a solid to a liquid state, is often caused by strong earthquake ground-shaking. Liquefaction occurs at intensities of MM7 and higher, and may occur at distances of 100-150 km from earthquakes of magnitude M7-7.9. Ground shaking and acceleration during large earthquakes are amplified in weak, unconsolidated sediments greater than 20 m in depth, such as near estuaries, river flats and swamps. This amplification can increase shaking intensity locally by one or two MM intensity levels over that experienced on nearby firm ground (Van Dissen et al. 1993). The fine-grained, watersaturated artificial fill at Bluff Harbour is particularly prone to this type of settlement (Glassey 2002). Spylaw Fault Tin Hut Fault System Hillfoot Fault Blue Mountain No. 1 Fault Clifton Fault Invercargill N Settlement Fault Landslides Active Faults Rivers 20 km Roads Figure 44 Known active fault traces and large landslides within the mainland Murihiku map area. 59 Table 1 Estimated return periods for earthquakes within the Murihiku map area, calculated by W. Smith from the seismicity model of Stirling et al. (2000). Intensity Mean return period (years) Invercargill Gore Te An MM6 40 50 10 MM7 350 300 45 MM8 5000 2600 320 MM9 78000 36000 4700 In the future, the Murihiku map area can expect moderate to strong shaking from relatively frequent large to very large earthquakes outside the area, and from infrequent moderate to large earthquakes within its boundaries. Probabilistic hazard analysis suggests that maximum peak ground acceleration (PGA) during a 475 year period in Invercargill is 10-30% g (“g” = acceleration due to gravity; Stirling et al. 2000). The maximum PGA increases to the west, and PGA of 1.0 g can be expected near the Alpine Fault. Active faults within the Murihiku area with longer return periods of up to 1000 years will also produce high PGA values, particularly on soft ground. In terms of shaking intensity, the mean return periods for average ground for some locations within the Murihiku area are given in Table 1. Tsunami (by G. L. Downes) Coastal flooding and damage due to tsunami are possible along the entire coastline of the Murihiku map area, including Stewart Island, and for several kilometres up estuaries such as Jacobs River, New River and Bluff Harbour. Tsunami are generated by large sudden movements of the sea floor caused by local or distant earthquakes, volcanoes, or by local submarine or coastal landslides, possibly initiated by strong earthquake shaking. They can also be generated by meteorite impact. An uprising of the sea in the 1820s caused the deaths of many Maori on the beach near Orepuki and affected much of the coast (Bradley 2002). The event was almost certainly a tsunami with a local origin, suggesting that waves generated by large offshore earthquakes or submarine slumping could significantly affect much of the Murihiku coastline. In contrast, distant source tsunami have had less impact in the Murihiku area. The largest tsunami known were those caused by very large earthquakes on the west coast of South America in 1868, 1877, and 1960. These produced strong water level oscillations over several days along the 60 entire eastern seaboard of New Zealand, with damage in many places. In 1877, water levels in Bluff Harbour varied by up to 1.2 m, moving buoys and creating strong currents. In 1960, the effects at Bluff were minor, with a rise and fall of only 15 cm, but at Colac Bay “debris and seaweed was festooned along the waterfront and water reached right up to baches on the high ground” (Southland Times 25 May 1960). Tsunami generated by distant events take many hours to reach New Zealand, sufficient time for Civil Defence to take appropriate action. Locally generated tsunami are of more concern as wave heights may be large enough to be damaging and life-threatening, possibly catastrophic, and travel times may be too short for Civil Defence to issue warnings. Very strong shaking is warning enough to leave coastal locations and move inland. Local tsunami may persist for up to twelve hours, and distant source tsunami for as much as three days. The first waves of any tsunami are often not the largest. Wave heights are difficult to predict in advance, and may vary greatly within a short distance due to local bathymetry or topography. Landslides Landslides within the Murihiku area are most common in the semischist terrain in the north, and in Mesozoic and Cenozoic mudstones (Fig. 44). Semischist landslides are slow-moving and complex failures, and a number are active, at least in part. Damage from further movement will generally be restricted to local farm infrastructure. Landslides within Murihiku Supergroup rocks in the upper Wairaki River and in the Catlins are dip-slope failures along mudstone beds. Small landslides (up to 1 km2) in Cenozoic sediments (Fig. 44) are mainly in Waicoe or Winton Hill Formation mudstones; these pose only a local risk. A spectacular landslide in Gore Lignite Measures on Landslip Hill (Fig. 46) records repeated movements and parts of it remain active. Figure 45 The upper Wairaki River area, looking south over a prominent Holocene trace in the Tin Hut Fault System (centre) (Landis et al. 1999). Hills immediately to the left (east) of the fault are underlain by Caravan Formation, Takitimu Subgroup. Ohai township is in the far distance. Photo CN43884/22: D.L. Homer 61 Volcanic hazard Solander and Little Solander islands in western Foveaux Strait, beyond the map area, are the eroded remnants of an andesitic volcano associated with subduction of the Australian Plate beneath the Pacific Plate at the Puysegur Trench. There is seismic evidence for several other volcanoes nearby (Turnbull & Uruski 1993). Solander volcano is of Pleistocene age (Bishop 1986) and the others are as old as Miocene. No ash deposits associated with these volcanoes have been identified in Southland, and Solander volcano is quiescent, but there remains a possibility of renewed volcanic activity in the vicinity of Solander Island. Any resumption of activity would be signalled by swarms of low-magnitude earthquakes preceding any eruption by weeks, months, or even years. Subsidence due to mining The hazard posed by ground collapse following underground mining is largely restricted to the Ohai district, although small areas above old underground lignite mines within the Eastern Southland Coalfield or in peripheral mining areas such as Waikaka and Maitland may be at risk. The hazard has not been quantified; that would require detailed examination of old mine plans together with an assessment of rock strengths above old workings. Groundwater contamination Groundwater contamination is potentially a serious hazard. This hazard is increasing with changes in land use, for example from sheep farming to intensive dairying. There is evidence that agriculture, horticulture and factories are already affecting groundwater chemistry in Southland, especially in shallow aquifers, where high nitrate levels and faecal coliform indicator bacteria have been found in bores (Hughes 2001). Localised groundwater contamination is mainly found close to such sources as septic tanks and offal pits, and where wellhead protection is inadequate. The Edendale Aquifer, the only Southland aquifer that has been systematically studied, has been showing elevated nitrate levels since the mid-1980s, and pesticide residues have also been found (Hughes 2001). Figure 46 Active landsliding in Gore Lignite Measures on Landslip Hill, north of Waipahi. Older landslides with smoother topography and degraded headscarps are visible on either side of the active landslide. The scarp is supported by silcrete within the Gore Lignite Measures (Lindqvist 1990). Photo CN44012/7: D.L. Homer 62 AVAILABILITY OF QMAP DATA ACKNOWLEDGMENTS The geological map accompanying this booklet is based on information stored in the QMAP Geographic Information System maintained by the Institute of Geological & Nuclear Sciences. The data on the map are a subset of available information. Other single or multi-factor maps can be generated from the GIS as required, for example maps showing single rock types, or mineral localities in relation to host rocks. Other digital data sets which may be integrated with the basic geology include gravity and magnetic surveys, active faults, earthquakes, landslides, mineral resources and localities, fossil localities, and petrological samples. Data can be presented for userdefined areas or within specified distances from roads or coastlines. Maps can be produced at varying scales, bearing in mind the scale of data capture and the generalisation involved in digitising; maps produced at greater than 1:50 000 scale will not show accurate, detailed geological information unless they are based on point data (e.g. structural information). The Murihiku geological map was compiled by I.M. Turnbull (NZMS 260 sheets D43, D44, D45, E44, E45, F45, F47, G44, G46, G47) and A.H. Allibone (C50, D48, D49, D50, E48, E49) with help from N. Mortimer (F44, F46 and part D46), D. Thomas (E47 and part E46), P.J. Glassey, A.J. Tulloch, M.S. Rattenbury, S. Wilson and F.J. Brook. Unpublished geological maps of the Blackmount, western Ohai, and Taringatura Hills areas were provided by R.M Carter and R.J. Norris, C.J. Patchell, and the late J.D. Campbell respectively. C.R. Anderson, Y. Cook, E. Ladley, B. Morrison, C.J. Paterson, C. Reid, R.J. Smillie, P. Stenhouse, S. Wilson, C.J. Adams, P.J. Forsyth, M. Falconer, J.G. Begg and H.J. Campbell helped with the fieldwork; Campbell and Begg also helped with the paleontology. Tulloch provided radiometric and geochemical data and assisted with the interpretation of the Stewart Island rocks. Raster image files of QMAP sheets, with digital versions of accompanying booklet texts, are available on CD-ROM. Image files can also be downloaded from the GNS web site http://www.gns.cri.nz. If required, QMAP series map data can also be made available in vector GIS format. The data record maps on which the digital geology is based are filed in GNS offices at Dunedin and Gracefield (Lower Hutt) and, although unpublished, are available for consultation. The map units and geological legends used on the detailed maps are based on a lithostratigraphic mapping philosophy, and may differ from those shown on this published QMAP sheet. The QMAP database will be maintained, and updated where new geologic mapping improves existing information. For new or additional geological information, for prints of this map at other scales, for selected data or combinations of data sets, or for derivative or single-factor maps based on QMAP data, please contact: The QMAP Programme Leader Institute of Geological and Nuclear Sciences Ltd P O Box 30368 Lower Hutt. Contributions from staff of the Geology Department, University of Otago (including D.S. Coombs and C.A. Landis) are acknowledged with thanks. A.F. Cooper gave permission to use information from theses. Helicopter support was provided by South West Helicopters (C. Brown, D. Sutherland, W. Pratt, and the late T. Green), and fixed wing support by Wanaka Flightseeing (A. Woods). K. Geeson (Seaview Water Taxi), R. Tindal (N.Z. Forest Service), and A. Gray and P. Lowen (Department of Conservation) helped with seaborne access to Stewart Island. Coastal geology was supported by R. Russ and the crew of R/V Huia. D.J.A. Barrell (Quaternary geology), P.J. Glassey and G.L. Downes (Hazards) contributed to the map text; digitising was done by J. Arnst, B. Smith Lyttle, D. Thomas and C. Thurlow. N.D. Perrin and R. Thomson helped with landslide mapping and interpretation of Quaternary geology; bathymetric data were supplied by the National Institute of Water and Atmospheric Research and manipulated by P.G. Scadden. The map and legend were prepared for publication by D.W. Heron, B. Smith Lyttle, C. Thurlow and M. Coomer; the base map was obtained from Land Information New Zealand. Discussion and comment on all or part of the map and text from D.J.A. Barrell, H.J. Campbell, P.J. Forsyth, N. Mortimer, D.D. Ritchie and A.J. Tulloch are gratefully acknowledged. The map and text were reviewed by J.G. Begg, M.J. Isaac and M.R. Johnston. Funding was provided by the Foundation for Research, Science and Technology, under contracts CO5809, CO5X0003 and CO5X0206. 63 REFERENCES This list includes references cited in the text (+), and used in map compilation (*) Adams, C.J.; Campbell, H.J.; Belousava, E.; Griffin, W.L.; Pearson, N. 2001: Laser ablation ICPMS U-Pb dating and Hf isotopic compositions of detrital zircons: an application to provenance comparisons of Late Triassic sandstones in the Eastern Province of New Zealand (Abstract). 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New Zealand Journal of Geology and Geophysics 40: 151-155.+ Anderson, H.; Webb, T.H. 1994: New Zealand seismicity: patterns revealed by the upgraded National Seismograph Network. New Zealand Journal of Geology and Geophysics 37: 477-493. + Anderson, H.; Webb, T.; Jackson, J. 1993: Focal mechanisms of large earthquakes in the South Island of New Zealand: implications for the accommodation of Pacific-Australia plate motion. Geophysical Journal International 115: 1032-1054.+ Arafin, M.S. 1982: Tertiary geology of the Birchwood area. BSc (Hons) thesis, University of Otago, Dunedin.+* Ballance, P.F.; Campbell, J.D. 1993: The Murihiku arc-related Basin of New Zealand (Triassic-Jurassic). In Ballance, P. F. ed. South Pacific Sedimentary Basins. Sedimentary Basins of the World 2. Amsterdam, Elsevier Science Publishers B.V. Pp. 21-33.+ Banks, M.J. 1977: Geology of the northeast Longwood Range, Southland. 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New Zealand Journal of Geology and Geophysics 37: 169-180.+* Bishop, D.G.; Reay, A.; Koons, P.O.; Turnbull, I.M. 1992: Composition and regional significance of Mid Bay and Mason Bay reefs, Foveaux Strait, New Zealand. New Zealand Journal of Geology and Geophysics 35: 109-112.+ Bishop, D.G.; Turnbull, I.M. (compilers) 1996: Geology of the Dunedin area. Institute of Geological & Nuclear Sciences 1:250 000 geological map 21. Lower Hutt, Institute of Geological & Nuclear Sciences. 1 sheet + 52 p. + Bluck, R.G. 1998: Annual report, period to 24th May 1998: ANZEX Resources Ltd. New Zealand unpublished openfile mining company report M3602, Ministry of Economic Development, Wellington.* Boles, J.R. 1971: Stratigraphy, petrology, mineralogy, and metamorphism of mainly Triassic rocks, Hokonui Hills, Southland, New Zealand. PhD thesis, University of Otago, Dunedin. * Boles, J.R. 1974: Structure, stratigraphy and petrology of mainly Triassic rocks, Hokonui Hills, Southland, New Zealand. New Zealand Journal of Geology and Geophysics 17: 337-374.+* Bosel, C.A. 1981: The Geology of Bluff Hill. BSc (Hons) thesis, University of Otago, Dunedin.+* Bosel, C.A.; Coombs, D.S. 1984: Foveaux Formation: a warmwater, strandline deposit of Landon-Pareora age at Bluff Hill, Southland, New Zealand. New Zealand Journal of Geology and Geophysics 27: 221-223.+ Bowen, F.E. 1964: Geology of Ohai Coalfield. New Zealand Geological Survey Bulletin 51. 203 p. +* Bowman, R.G.; Brodie, C.G.; Garlick, P.R. 1987: Coal resources assessment, Eastern Ohai Coalfield area. Resource Management and Mining, Ministry of Energy, Wellington.+ Bradley, D. 2002: Tsunami. In Invercargill City Council Lifelines Project Hazards Report. Invercargill, Invercargill City Council. Section 5. Pp. 1-13.+ Bradshaw, J.D. 1993: A review of the Median Tectonic Zone: terrane boundaries and terrane amalgamation near the Median Tectonic Line. 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Journal of the Royal Society of New Zealand 33: 85-95.+ Campbell, H.J.; Owen, S.R. 2003: The Nelsonian Stage: a new Early Triassic local stage for New Zealand. Journal of the Royal Society of New Zealand 33: 97-108.+ Campbell, J.D. 1959: The Warepan Stage (Triassic): Definition and correlation. New Zealand Journal of Geology and Geophysics 2: 198-207.+ Campbell, J.D.; Coombs, D.S. 1966: Murihiku Supergroup (Triassic - Jurassic) of Southland and South Otago. New Zealand Journal of Geology and Geophysics 9: 393-398.+ Campbell, J.D.; Coombs, D.S.; Grebneff, A. 2003: Willsher Group and geology of the Triassic Kaka Point coastal section, south-east Otago, New Zealand. Journal of the Royal Society of New Zealand 33: 7-38.+ Campbell, J.D.; Force, E.R. 1973: Kaihikuan Stage (Middle Triassic): Definition and type locality. New Zealand Journal of Geology and Geophysics 16: 209-220. * Carter, R.M. 1979: Trench-slope channels from the New Zealand Jurassic: the Otekura Formation, Sandy Bay, South Otago. Sedimentology 26: 475-496.+ Carter, R.M.; Hicks, M.D.; Norris, R.J.; Turnbull, I.M. 1978: Sedimentation patterns in an Ancient Arc-Trench-Ocean Basin Complex: Carboniferous to Jurassic Rangitata Orogen, New Zealand. In Stanley, D. J.; Kelling, G. ed. Sedimentation in submarine canyons, fans and trenches. Stroudsburg, Pennsylvania, Dowden, Hutchison and Ross Inc. Pp. 340361 + Carter, R.M.; Lindqvist, J.K.; Norris, R.J. 1982: Oligocene unconformities and nodular phosphate: hardground horizons in western Southland and northern West Coast. Journal of the Royal Society of New Zealand 12: 11-46.+ Carter, R.M.; Norris, R.J. 1977a: Blackmount, Waiau Basin (tour guide). Geological Society of New Zealand Miscellaneous Series 38C. 31 pp.+ Carter, R.M.; Norris, R.J. 1977b: Redeposited conglomerates in a Miocene flysch sequence at Blackmount, western Southland, New Zealand. Sedimentary Geology 18: 289-319.+ Carter, R.M.; Norris, R.J. 1980: Geology of the Blackmount area. Unpublished MS map and notes, Geology Department, University of Otago, Dunedin.+* Cave, M.P.; Boyer, C.M. 1990: Natural gas from coal; Southgas investigations at Ohai, New Zealand. Proceedings of the New Zealand Petroleum Exploration Conference, Queenstown: 357-364. Ministry of Commerce.+ Cawood, P.A. 1986: Stratigraphic and structural relations of the southern Dun Mountain Ophiolite Belt and enclosing strata, northwestern Southland, New Zealand. New Zealand Journal of Geology and Geophysics 29: 179-204.+* Cawood, P.A. 1987: Stratigraphic and structural relations of strata enclosing the Dun Mountain Ophiolite Belt in the Arthurton-Clinton region, Southland, New Zealand. 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E. 1963: Some aspects of the geology of the Mossburn district, Southland, New Zealand. BSc (Hons) thesis, University of Otago, Dunedin.* Mildenhall, D.C. 1970: Discovery of a New Zealand member of the Permian Glossopteris flora. Australian Journal of Science 32: 474-475.+ Mildenhall, D.C. 2003: Analysis of Pleistocene pollen samples from Stewart Island, New Zealand. Unpublished technical file report DCM 328/03, Institute of Geological & Nuclear Sciences, Lower Hutt.+ Mitchell, M.J. 1995: Alluvial platinum-group minerals in southern New Zealand. Pp 377-382 in Mauk, J.L.; St George, J.D. (Eds). Proceedings of the PACRIM Congress 1995, Auckland, New Zealand. Australasian Institute of Mining & Metallurgy, Carlton, Victoria. Mortimer, N. 1993a: Geology of the Otago Schist and adjacent rocks. Scale 1:500 000. Institute of Geological & Nuclear Sciences geological map 7. Lower Hutt, Institute of Geological & Nuclear Sciences. 1 sheet. +* Mortimer, N. 1993b: Jurassic tectonic history of the Otago Schist. Tectonics 12: 237-244.+ Mortimer, N. 2004: New Zealand’s geological foundations. Gondwana Research 7: 261-272.+ Mortimer, N.; Davey, F.J.; Melhuish, A.; Yu, J.; Godfrey, N.J. 2002: Geological interpretation of a deep seismic reflection profile across the Eastern Province and Median Batholith: crustal architecture of an extended Phanerozoic convergent orogen. New Zealand Journal of Geology and Geophysics 45: 349-363.+ Mortimer, N.; Gans, P.; Calvert, A.; Walker, N. 1999a: Geology and thermochronology of the east edge of the Median Batholith (Median Tectonic Zone): a new perspective on Permian to Cretaceous crustal growth of New Zealand. The Island Arc 8: 404-425.+* Mortimer, N.; Johnston, M.R. 1990: Discovery of a new Rangitata structure offset by the Alpine Fault: enigmatic 350 km-long synform within the Caples-Pelorus terrane. Geological Society of New Zealand Miscellaneous Publication 50A: 99.+ Mortimer, N.; Tulloch, A.J.; Spark, R.N.; Walker, N.W.; Ladley, E.; Allibone, A.; Kimbrough, D.L. 1999b: Overview of the Median Batholith, New Zealand: a new interpretation of the geology of the Median Tectonic Zone and adjacent rocks. Journal of African Earth Sciences 29: 257-268.+ Morton, J. G. 1979: Otamita Stream. BSc (Hons) thesis, University of Otago, Dunedin.* Mossman, D. 1970: Geology of the Greenhills Ultramafic Complex, Bluff Peninsula, South Island. PhD thesis, University of Otago, Dunedin.+* Mossman, D.J. 1973: Geology of the Greenhills Ultramafic Complex, Bluff Peninsula, Southland, New Zealand. Geological Society of America Bulletin 84: 39-62.+ Mossman, D.J.; Force, L.M. 1969: Permian Fossils from the Greenhills Group, Bluff, Southland, New Zealand. New Zealand Journal of Geology and Geophysics 12: 659-673.+* Muir, R.J.; Ireland, T.R.; Weaver, S.D.; Bradshaw, J.D.; Evans, J.A.; Eby, G.N.; Shelley, D. 1998: Geochronology and geochemistry of a Mesozoic magmatic arc system, Fiordland, New Zealand. Journal of the Geological Society of London 155: 1037-1052.+ Mutch, A.R. 1960: S168 - The Nightcaps. Unpublished map, file number VF528, Institute of Geological & Nuclear Sciences, Dunedin.* Mutch, A.R. 1964: Sheet S159 Morley. Geological Map of New Zealand 1:63 360. Wellington, New Zealand, Department of Scientific and Industrial Research. 1 sheet. +* Mutch, A.R. 1967: Riverton. Unpublished map, file number VF351, Institute of Geological & Nuclear Sciences, Dunedin.* Mutch, A.R. 1972: Geology of Morley Subdivision. New Zealand Geological Survey Bulletin 78. 104 p. + Mutch, A.R. 1975: Eastern Southland Coalfield. New Zealand Geological Survey Report M44. 25 p. +* Mutch, A.R. 1975: Eastern Southland Coalfield. Unpublished map, file number VF696, Institute of Geological & Nuclear Sciences, Dunedin.* Mutch, A.R. 1976: N.Z. Forest Products Ltd Groundwater Investigation, Riverton District, Southland. Unpublished technical file report E46/410, Institute of Geological & Nuclear Sciences, Dunedin.* Mutch, A.R. 1977: Drill holes and silicified quartz conglomerate horizons Landslip Hill - S170. Unpublished technical file report G45/334, Institute of Geological & Nuclear Sciences, Dunedin.* Mutch, A.R.; Baker, L.A. 1989: Recent exploration and evaluation of detrital gold in Otago and Southland. In Kear, D. ed. Mineral Deposits of New Zealand. Monograph 13. Australasian Institute of Mining and Metallurgy, Parkville, Victoria, Australia. Pp. 189-196. + Nathan, S. 1993: Revising the 1:250 000 Geological Map of New Zealand - a discussion paper. Institute of Geological & Nuclear Sciences Science Report 93/26. 28 p. Nathan, S.; Rattenbury, M.S.; Suggate, R.P. (compilers) 2002: Geology of the Greymouth area. Institute of Geological & Nuclear Sciences 1:250 000 geological map 12. Lower Hutt, New Zealand. Institute of Geological & Nuclear Sciences. 1 sheet + 58 p.+ Nebel, O. 2003: Geology of the southern Takitimu Mountains. MSc thesis, University of Muenster, Muenster.+* Nicholson, P.; Inger, M.; Cowden, A. 1988: Geological and geochemical report Longwood Range project, Invercargill District. New Zealand unpublished open-file mining company report MR1154 for Sigma Resources, Ministry of Economic Development, Wellington. + Noda, A.; Takeuchi, M.; Adachi, N. 2002: Fan deltaic-to-fluvial sedimentation of the Middle Jurassic Murihiku Terrane, Southland, New Zealand. New Zealand Journal of Geology and Geophysics 45: 297-312.+* Norris, R.J.; Cooper, A.F.; Wright, T.; Berryman, K. 2001: Dating of past Alpine Fault rupture in South Westland. 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Economic Geology 29: 411-434.+ Williams, G.J. 1934b: A granite-schist contact in Stewart Island, New Zealand. Quarterly Journal of the Geological Society of London 90: 322-350.+ Williams, G.J. 1974: Economic geology of New Zealand. AUSIMM Monograph Series 4, 2 nd edition. Parkville, Australasian Institute of Mining and Metallurgy. 384 p.+ Williams, G.J.; Mackie, J.B. 1959: Economic minerals in Stewart Island. Proceedings of a mineral conference, School of Mines and Metallurgy, University of Otago, vol. 6, paper 125.+ Willsman, A. 1990: Stratigraphy, tectonics, and provenance of rocks in the Wether Hill area, western Southland. BSc (Hons) thesis, University of Otago, Dunedin.+* Wood, B.L. 1956: The Geology of the Gore Subdivision. New Zealand Geological Survey Bulletin 53. 128 p. +* Wood, B.L. 1958: Submarine geology of Bluff Harbour. New Zealand Journal of Geology and Geophysics 1: 461-9. Wood, B. L. 1965a: Heriot. Unpublished map, file number VF297, Institute of Geological & Nuclear Sciences, Dunedin.* Wood, B. L. 1965b: Sheet S177 Invercargill. Unpublished map, file number VF1349, Institute of Geological & Nuclear Sciences, Dunedin.* Wood, B.L. 1966: Sheet 24 - Invercargill. Geological map of New Zealand 1:250 000. Wellington, New Zealand, Department of Scientific and Industrial Research. 1 sheet. +* Wood, B.L. 1969: Geology of Tuatapere Subdivision, Western Southland. New Zealand Geological Survey Bulletin 69. 161 p. +* Wood, B.L. 1978: Southland and Western Central Otago. In Suggate, R. P.; Stevens, G. R.; Te Punga, M. T. ed. The Geology of New Zealand. Wellington, Government Printer. Pp. 521-529 + Wood, B. L.; Hitt, G. J. 1964a: Invercargill air photo interpretation. Unpublished map, file number VF1203, Institute of Geological & Nuclear Sciences, Dunedin.* Wood, B. L.; Hitt, G. J. 1964a: Woodend air photo interpretation. Unpublished map, file number VF1204, Institute of Geological & Nuclear Sciences, Dunedin.* Woodward, D.J.; Hatherton, T. 1975: Magnetic anomalies over southern New Zealand. New Zealand Journal of Geology and Geophysics 18: 62-82.+ Youngson, J.H.; Landis, C.A. 1997: The Te Wai Pounamu Erosion Surface (field trip guide). Geological Society of New Zealand Miscellaneous Publication 91B: FT2-1 - FT2-9.+ 71 APPENDIX 1 NOMENCLATURE OF UNITS MAPPED ON STEWART ISLAND biotite muscovite (garnet) granite with subordinate granodiorite Age: Middle to Late Carboniferous Many of the names applied in this map to the intrusive rocks of Stewart Island have not previously been published, although some have appeared in theses. Several manuscripts giving detailed descriptions of the plutonic rocks are either in preparation or in review. A brief description of the new and previously mapped units is given here, sufficient to formalise the nomenclature (new names are underlined). The definitions generally follow lithostratigraphic nomenclatural procedures as outlined by Salvador (1994), modified for plutonic rocks following arguments presented by Cox & Allibone (1995). Intrusive rocks are generally mapped as plutons, which may comprise a variety of rocks with different compositions and textures. However all rocks within a single pluton have field relationships that suggest they are derived from a single or several closely related batches of magma. For this reason, only the most homogeneous plutons have been given names that include a specific composition (such as Ruggedy Granite). The nomination of type areas rather than single outcrops for the plutonic units also reflects their variable internal character. For some units, there are no useful or appropriate geographic names, and the plutons are named from their general type area rather than a discrete place – e.g. Freshwater Northeast, Upper Kopeka. Freds Camp Pluton Previous usage or definition: introduced by Allibone & Tulloch (1997) Name: from Freds Camp, on the south side of Paterson Inlet Type area: coastal outcrops near Freds Camp Content: fine- to medium-grained quartz monzonite, granite and alkali feldspar granite Age: Middle Carboniferous to Early Permian Ridge Orthogneiss Previous usage or definition: introduced by Allibone & Tulloch (1997) Name: from informal usage, after the summit ridge of Mt Allen and Table Hill Type area: open tops of Table Hill and Mt Allen Content: K-feldspar megacrystic and coarse-grained equigranular biotite granodiorite orthogneiss Age: Early Carboniferous Ruggedy Granite Previous usage or definition: introduced by Allibone (1991) Name: from the Ruggedy Mountains Type area: Ruggedy Mountains Content: coarse-grained leucogranitoid ranging in composition from granite to granodiorite Age: Early Carboniferous Table Hill Orthogneiss Previous usage or definition: introduced by Allibone & Tulloch (1997) Name: from Table Hill, north end of the Tin Range Type area: summit and north side of Table Hill Content: fine- to medium-grained homogeneous leucocratic biotite (muscovite) granite, leucogranite and granodiorite orthogneiss Age: Early Carboniferous Neck Granodiorite Previous usage or definition: mapped by Cook (1984) but not previously named Name: from The Neck, outer Paterson Inlet Type area: southernmost part of The Neck Content: massive medium- to coarse-grained biotite granodiorite Age: Early Carboniferous Knob Pluton Previous usage or definition: introduced by Allibone & Tulloch (1997) Name: from Granite Knob and Lees Knob Type area: the south faces of Lees Knob and Granite Knob Content: medium- to coarse-grained and locally megacrystic 72 Big Glory Pluton Previous usage or definition: not previously named Name: from Big Glory Bay, on the south side of Paterson Inlet Type area: western shoreline of Big Glory Bay Content: leucocratic fine-grained biotite muscovite granite Age: undated but inferred to be similar to Freds Camp Pluton Forked Pluton Previous usage or definition: not previously named Name: from Forked Creek, on the south side of the Freshwater Valley Type area: tributaries of Forked Creek around Grid Ref D48/ 2115000/5357000 Content: a plug of alkali feldspar granite and quartz syenite Age: undated but inferred to be similar to Freds Camp Pluton Rakeahua Pluton Previous usage or definition: the name Rakeahua Granite was introduced by Watters et al. (1968); Allibone (1991) recognised several discrete plutons within the original unit and suggested the original Rakeahua Granite be renamed the Rakeahua Batholith. Further mapping has enabled individual plutons to be recognised throughout and the Rakeahua Pluton is now applied to the original type locality, but with a different definition. The term Rakeahua Batholith has been abandoned Name: from Mt Rakeahua Type area: Mt Rakeahua including the summit region and the bush-clad lower slopes Content: heterogeneous coarse-grained gabbro, diorite and anorthosite (Allibone & Tulloch 1997), fine-grained diorite, gabbro, biotite quartz monzodiorite and tonalite Age: Middle Jurassic South West Arm Pluton Previous usage or definition: introduced by Allibone & Tulloch (1997) Name: from South West Arm of Paterson Inlet Type area: shoreline of South West Arm Content: homogeneous medium- to coarse-grained, locally megacrystic biotite granite and granodiorite Age: Middle Jurassic Euchre Pluton Previous usage or definition: not previously named Name: from Euchre Creek on the south side of Paterson Inlet Type area: outcrops in Euchre Creek Content: fine-grained massive homogeneous biotite granodiorite and granite Age: undated but inferred to be similar to South West Arm Pluton Codfish Granite Previous usage or definition: introduced by Allibone (1991) and Allibone & Allibone (1991) Name: from Codfish Island Type area: western Codfish Island Content: homogeneous massive medium-grained biotite granite Age: Late Jurassic Content: diorite forming a small pluton Age: undated but probably Early Cretaceous Deceit Pluton Previous usage or definition: not previously named Name: from Deceit Peaks, south of Doughboy Bay Type area: Deceit Peaks Content: medium- to coarse-grained biotite (muscovite) granite, with subordinate leucogranite and granodiorite Age: latest Jurassic Richards Point Porphyry Previous usage or definition: introduced by Allibone (1991) Name: from Richards Point on the northwest coast Type area: coastal outcrops on the southern side of Richards Point Content: a plug of plagioclase-quartz-biotite-magnetiteporphyritic dacite and granodiorite Age: Early Cretaceous Saddle Pluton Previous usage or definition: not previously introduced, although Frewin (1987) described a “Saddle Suite”. Name: after Saddle Point, on the north coast of Stewart Island west of Oban Type locality: northeast coast of Stewart Island Content: medium- to coarse-grained gabbro, and anorthositic gabbro with norite and troctolite Age: undated, but probably similar to Bungaree Intrusives, Late Jurassic or earliest Cretaceous Bungaree Intrusives Previous usage or definition: not previously named, although Frewin (1987) described a “Bungaree Suite” Name: from Bungaree on the northeast coast of Stewart Island Type area: coastal section from Port William to Murray Beach including the Bungaree area Content: heterogeneous and locally foliated intrusions of diorite, quartz diorite, and quartz monzodiorite with subordinate gabbro, granodiorite and granite Age: earliest Cretaceous Cow & Calf Gabbro Previous usage or definition: named by Watters (1962); not shown on this map. Probably a correlative of the Saddle Pluton and other small gabbro plugs within the Bungaree Intrusives Name: from Cow and Calf Point southwest from Oban Type area: Cow and Calf Point coastal outcrops Content: hornblende pyroxene gabbro and hornblendite Age: undated but probably Early Cretaceous East Ruggedy Intrusives Previous usage or definition: not previously named Name: from East Ruggedy beach Type area: coastal outcrops from East Ruggedy to a boulder beach 2km west of Long Harry Bay Content: numerous minor plugs, plutons and dikes of variably deformed fine- to medium-grained gabbro, diorite, quartz monzodiorite, granodiorite and granite, with gneiss and amphibolite Age: undated, but probably earliest Cretaceous by analogy with Bungaree Intrusives North Arm Pluton Previous usage or definition: not previously named Name: from North Arm of Paterson Inlet Type area: shoreline outcrops around the head of North Arm Content: medium-grained, variably foliated quartz monzodiorite, with subordinate diorite, and granodiorite Age: Early Cretaceous Rollers Pluton Previous usage or definition: named by Frewin (1987) and here formalised Name: from Rollers Point on the northeast coast Type area: Rollers Point Tarpaulin Pluton Previous usage or definition: previously named Tarpaulin Metagranite by Cook (1987), here redefined to include similar rocks on the northern coast of Paterson Inlet and Thomson Ridge Name: from Tarpaulin Beach at The Neck Type area: Tarpaulin Beach, eastern Paterson Inlet Content: generally foliated leucocratic biotite (muscovite) granite and granodiorite Age: Early Cretaceous Smoky Pluton Previous usage or definition: not previously introduced, although Frewin (1987) named a “Smoky granite” Name: from Smoky Beach on the north coast Type area: coastal outcrops between Smoky Beach and Long Harry Bay Content: medium- to coarse-grained massive biotite muscovite (garnet) granite with minor leucogranite, aplite and pegmatite Age: Late Jurassic to Early Cretaceous Freshwater Northeast Pluton Previous usage or definition: not previously named Name: from the northern catchment of the Freshwater River Type area: creeks draining SSW of Mt Anglem and low hills in the centre of the Freshwater Valley 5-6 km east of Benson Peak Content: fine- to medium-grained massive biotite granodiorite and granite with accessory muscovite in more leucocratic parts Age: probably Early Cretaceous Walkers Pluton Previous usage or definition: not previously defined, although Peden (1988) mapped Walkers Hill diorite and Ernest Islands diorite Name: from Walkers Hill southeast of Mason Bay Type area: streams draining the western and southern faces of Walkers Hill Content: a large locally foliated heterogeneous pluton of quartz monzodiorite, with subordinate diorite and granodiorite Age: Early Cretaceous Escarpment Pluton Previous usage or definition: introduced by Allibone & Tulloch (1997) Name: from the escarpment that forms the southern face of the Rakeahua valley Type area: creek exposures east and west of the track up the escarpment to Table Hill Content: variably foliated, medium-grained heterogeneous biotite ± hornblende granodiorite and quartz monzodiorite often rich in gabbroid and dioritoid xenoliths and mafic enclaves Age: Early Cretaceous Easy Pluton Previous usage or definition: not previously named Name: from Easy Harbour, southwestern coast of Stewart Island 73 Type area: coastal outcrops around Easy Harbour Content: medium-grained biotite ± hornblende granodiorite and quartz monzodiorite grading to fine-grained biotite granite around Port Pegasus Age: Early Cretaceous Tikotatahi Pluton Previous usage or definition: not previously named Name: from Tikotatahi Bay south of Port Adventure on the east coast Type area: coastal outcrops around Tikotatahi Bay and the southern side of Port Adventure Content: medium-grained biotite ± hornblende granodiorite and quartz monzodiorite, foliated near its northern margin Age: Early Cretaceous Doughboy Pluton Previous usage or definition: not previously defined, although Doughboy Bay granodiorite mapped by Peden (1988) around Doughboy Bay is included in the Doughboy Pluton Name: from Doughboy Bay and Doughboy Creek Type area: outcrops along Doughboy Creek and Doughboy Bay Content: massive to weakly foliated medium-grained biotite ± hornblende granodiorite and quartz monzodiorite Age: Early Cretaceous Blaikies Pluton Previous usage or definition: introduced by Allibone & Tulloch (1997) Name: from Blaikies Creek southeast of the Tin Range Type area: upper reaches of Blaikies Creek and adjacent open tops southeast of Blaikies Hill Content: variably foliated medium- to coarse-grained biotite ± muscovite ± garnet granite, subordinate granodiorite and minor tonalite Age: Early Cretaceous Upper Kopeka Pluton Previous usage or definition: not previously named Name: from the upper Kopeka River catchment Type locality: the upper Kopeka River 2 km above the Blaikies Creek confluence Content: generally unfoliated medium to coarse biotite ± muscovite ± garnet granite, subordinate granodiorite and minor tonalite Age: undated but probably Early Cretaceous by analogy with the Blaikies Pluton Mason Bay Pluton Previous usage or definition: introduced by Allibone (1991) Name: after Mason Bay Type area: outcrops in sand dunes around the northern half of Mason Bay and adjacent streams Content: variably foliated heterogeneous quartz monzodiorite, granodiorite and granite often containing amphibolite xenoliths and rafts Age: Early Cretaceous Kanihinihi Pluton Previous usage or definition: not previously named Name: from Kanihinihi Point, at the southwest side of Broad Bay 74 Type area: coastal outcrops around Broad Bay and tops south of Smiths Lookout Content: weakly foliated to massive biotite quartz monzodiorite, tonalite and granodiorite Age: undated, probably Early Cretaceous Gog Pluton Previous usage or definition: not previously named Name: from the prominent peak Gog, west of Port Pegasus Type area: outcrops at Fraser Peaks west of Port Pegasus Content: fine- to medium-grained massive granodiorite, granite and leucogranite, with K-feldspar megacrysts in places Age: latest Early Cretaceous Lords Pluton Previous usage or definition: not previously named Name: from the Lords River Type area: middle reaches of the Lords River Content: fine- to medium-grained massive quartz monzodiorite, granodiorite, granite and leucogranite Age: undated, but probably Early Cretaceous by comparison with Gog Pluton Campsite Pluton Previous usage or definition: introduced by Allibone & Tulloch (1997) Name: from an un-named campsite beside a stream 1500m northeast of Mt Allen, in the centre of the pluton Type area: headwaters of the Kopeka River immediately east of Mt Allen Content: fine- to medium-grained massive quartz monzodiorite, granodiorite, granite and leucogranite Age: undated, but probably Early Cretaceous by comparison with Gog Pluton Upper Rakeahua Pluton Previous usage or definition: not previously named Name: from the upper reaches of the Rakeahua River Type area: upper reaches of the southwest branch of the Rakeahua River Content: fine- to medium-grained massive granite, leucogranite, aplite and pegmatite Age: Early Cretaceous Adventure South Orthogneiss Previous usage or definition: not previously named Name: from the area south of Adventure Hill Type area: creeks south of Adventure Hill Content: strongly foliated fine-grained biotite granodiorite and granite gneiss Age: undated; constrained from field relationships as post-Early Carboniferous and pre-Early Cretaceous Kopeka South Pluton Previous usage or definition: not previously named Name: from the south side of the Kopeka River Type area: outcrops in the hills south of the upper Kopeka River Content: foliated fine- to medium-grained biotite garnet granite and granodiorite Age: undated, Paleozoic to Cretaceous This map and text illustrate the geology of the Murihiku area, extending from the lower Clutha River across Southland to the Waiau basin on the fringes of southern Fiordland, and south to Stewart Island (Rakiura). Onshore geology is mapped at a scale of 1:250 000; offshore bathymetry and major structural elements are also shown. Geological information has been obtained from published and unpublished mapping by Institute geologists, from work by University of Otago and mining company geologists, and from various computer data bases. All data are held in a Geographic Information System and are available in digital format on request. The accompanying text summarises the regional geology and tectonic development, as well as the economic and engineering geology of the area. The map area is mostly underlain by Paleozoic and Mesozoic sedimentary rocks of the Murihiku Supergroup, exemplified in the Southland Syncline. Permian igneous rocks, including volcanics and plutonics, form the Takitimu and Longwood ranges on the western margin of the sheet, and Paleozoic to Cretaceous granitic to gabbroic rocks dominate Stewart Island. Cenozoic marine and nonmarine sediments underlie the Te Anau and Waiau basins, and also form extensive coal measures beneath the Southland and Waimea Plains. Quaternary sediments are dominated by the wide gravel plains of the Aparima, Oreti, and Mataura catchments, and, on Stewart Island, the dune fields of the Freshwater Depression. The Murihiku area, especially the western side, includes several major active fault systems. Earthquakes and tsunami are the major geological hazards. The Ruggedy Mountains in northwestern Stewart Island. The Carboniferous Ruggedy Granite forms the conspicuous outcrops; infaulted slivers of Paterson Group lie within the granite at West Ruggedy Beach (left foreground) and in Waituna Bay (centre right). The Freshwater valley (left) is underlain by laminated sand, reworked from dunes blown up from the Ruggedy and Waituna beaches, and from Mason Bay (upper right). The gently sloping surface in the far distance is probably an exhumed Cretaceous peneplain. Photo CN43963/10: D.L. Homer ISBN 0-478-09800-6