Download Geology of the Murihiku Area

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
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do
175° E
35° S
Kaitaia
a
Ba
00
Whangarei
m
0m
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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
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Fa
ne
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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
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Greymouth
45° S
o
Tr
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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
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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
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Waipounamu Erosion Surface (WES)
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OO
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AU
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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
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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