Download outline of the geology of the perth region

OUTLINE OF THE GEOLOGY OF THE PERTH REGION
Philip Commander
Department of Environment, Perth
ABSTRACT
Perth is located on a coastal plain consisting largely of unconsolidated sediments or dune limestone, with the eastern
suburbs on weathered Precambrian crystalline rocks. The coastal plain is underlain by between 30 m and 70 m of
Quaternary superficial sands, limestone and clay; and below this is some 10 km of sediments of the Perth Basin.
Palaeocene sediments occupy a deep erosional channel below the city, cut into the Mesozoic sediments. The Darling
Fault forms the eastern boundary of the basin with the Precambrian crystalline rocks of the Yilgarn Craton, which
consist of granite, gneiss migmatite with minor schist, cut by dolerite dykes. The Precambrian rocks are deeply
weathered with a lateritic profile. A variety of construction materials are readily available in the Perth Region and their
sources are protected from sterilisation by planning controls.
1
INTRODUCTION
The city of Perth (Key Figure 1) lies on the Swan Coastal Plain, which is developed on the sedimentary rocks of the
Perth Basin. The coastal plain is covered by a relatively thin sequence of alluvial, aeolian and littoral sediments of
Quaternary age (Key Figure 3), bounded inland by the Darling Scarp. The scarp follows the line of the Darling Fault,
separating the Perth Basin from the crystalline rocks of the Yilgarn Craton, which underlie the eastern suburbs in the
Darling Range.
The granitic and gneissic rocks of the Yilgarn Craton are the oldest rocks, having Archaean ages of around 2500 million
years (my). These are intruded by dolerite dykes of Proterozoic age. Proterozoic sediments are preserved on the western
margin of the craton adjacent to the Darling Fault. The Darling Fault is a major structural feature with a displacement of
some 10,000 m and marks the eastern boundary of the Perth Basin, a half graben (a one-sided rift valley).
The Perth Basin contains laterally continuous sediments from Permian (280 my) to Cretaceous age (65 my),
representing the infilling of a rift valley with mainly continental sediments. The western side of the basin split away
during the Early Cretaceous at the time of continental break-up, and is now believed to be under the Himalayas north of
the Indian subcontinent. This major structural event in the Early Cretaceous (Neocomian) resulted in uplift and erosion,
followed by deposition of marine and non-marine sediments, which ceased in the late Cretaceous. The Darling Fault has
essentially not been active since the late Cretaceous. The centre of the Swan Syncline, in gently folded Cretaceous and
Jurassic sediments, was subsequently eroded by a valley cut by a forerunner of the Avon River in the Perth area, and
sediments of Palaeocene age (54-58 my) were deposited under the city centre and western suburbs (Key Figure 4).
Uplift along the Darling Range has occurred during the Tertiary, evidenced by the youthful valleys, and the truncation
of the Avon palaeochannel west of Darkin swamp in the Helena River Catchment, prior to the late Pliocene.
Erosion of the Cretaceous sedimentary rocks during the Late Tertiary (Pliocene) created the planar unconformity
surface on which are deposited the Late Pliocene-Quaternary superficial formations of the coastal plain, formed as a
result of sea level changes throughout the Quaternary (Wyrwoll, this volume). Prior to this there was also erosion and
infilling of a channel probably associated with the Murray River (now filled with Rockingham Sand).
Uplift of the superficial formations cannot be demonstrated, though it has been suggested (Baxter, 1977) that the
progressive increase in elevation of the Yoganup Shoreline northward indicates post Late Pliocene uplift to the north
(consistent with the continental uplift postulated by Beard, 1999). Although the Darling Fault does not seem to have
undergone major displacement since the Cretaceous, lineaments trending in a north-north-west direction, such as along
the Canning River, appear to cross from the Yilgarn Craton, and may have some influence on the trends within the
Quaternary.
The geology of the region, including the definition of formations, is described by Seddon (1972), Quilty (1974),
Playford and others (1976), Allen (1976), Searle (1984) and Davidson (1995) from outcrop, oil drilling, water bore logs
and marine surveys. The region is geologically mapped in detail at a scale of 1:50 000 on the Environmental Geology
Series (e.g. Gozzard, 1982, 1986; Jordan, 1986), and regionally at 1:250 000 (Wilde and Low, 1978, 1980). Key
graphic borehole logs are represented on the 1:50 000 Environmental Geology Series. Geological and geophysical logs
Australian Geomechanics Vol 38 No 3 September 2003 – The Engineering Geology of Perth Part 1
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OUTLINE OF THE GEOLOGY OF THE PERTH REGION
P COMMANDER
from water bores are held by the Department of Environment and Water, and detailed borehole data from geotechnical
investigations are stored in the Pertech database.
This chapter gives a basic description of the geology relevant to geotechnical issues and is a framework to crossreference other papers in this volume. The relationship between the various formations and rock units is illustrated
diagrammatically on Key Figure 5. Detailed structure contour maps for each of the Mesozoic formations are given by
Davidson (1995).
2
SUPERFICIAL FORMATIONS OF THE SWAN COASTAL PLAIN
The coastal plain sediments, on which the greater part of Perth is built, consist of a number of formations of Late
Pliocene to Recent age (Table 1), laid down in marine, alluvial and aeolian environments, on a relatively planar
westward-sloping unconformity surface. Most of these sediments are assigned to the Kwinana Group (Playford and
others, 1976). The sediments are generally difficult to date, and current interpretations are likely to change with further
research. The sediments have been defined from outcrop (Playford and others, 1976), and from extensive descriptions
of cuttings from exploratory water bores, principally by A. D. Allen (Allen, 1976) and W. A. Davidson (Davidson,
1995). The sediments are collectively referred to as the superficial formations (Allen, 1976). The sediments are oldest in
the east and young to the west; they are described from oldest to youngest.
Table 1: Perth Basin stratigraphic column.
Age
Quaternary
Holocene
Pleistocene
Tertiary
Pliocene
---------------------
-------- ---------major
Palaeocene
-----------------------Cretaceous
-------- ---------major
Senonian-Maastrichtian
Senonian-Maastrichtian
Senonian
Turonian-Senonian
Albian-Cenomanian
Neocomian-Aptian
Neocomian
--------------------Jurassic- Cretaceous
Jurassic
8
-------- ---------major
Formation
Alluvial, colluvial, estuarine and swamp deposits
Muchea Limestone
Safety Bay Sand
Becher Sand
Tamala Limestone
Bassendean Sand
Gnangara Sand
Guildford Clay
Ascot Formation
Yoganup Formation
unconformity -------------------------------------------Rockingham Sand
Kings Park Formation
Mullaloo Sandstone Member
Como Sandstone Member
unconformity -------------------------------------------Lancelin Formation
Poison Hill Greensand
Gingin Chalk
Molecap Greensand
Osborne Formation
Mirrabooka Member
Henley Sandstone Member
Leederville Formation
Pinjar Member
Wanneroo Member
Mariginiup Member
South Perth Shale
Gage Formation
unconformity -------------------------------------------Parmelia Formation
Yarragadee Formation
Cattamarra Coal Measures
Australian Geomechanics Vol 38 No 3 September 2003 – The Engineering Geology of Perth Part 1
OUTLINE OF THE GEOLOGY OF THE PERTH REGION
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2.1
RIDGE HILL SANDSTONE
The Ridge Hill Sandstone crops out along the base of the Darling Scarp on the Ridge Hill Shelf. It is described as a thin
ferruginous sandstone 10–15 m thick, with a basal conglomerate overlying the Precambrian rocks and capped by laterite
(Playford and others, 1976). It occurs at an elevation of 76-91 m above sea level in small isolated outcrops covering
only a small proportion of the Ridge Hill Shelf physiographic region (Gozzard, 1982, 1986).
2.2
YOGANUP AND ASCOT FORMATIONS
The Yoganup and Ascot Formations occur in the subsurface, although small areas of Yoganup Formation are mapped by
Gozzard (1982, 1986) and Jordan (1986) at the base of the Darling Scarp. They unconformably overlie either Mesozoic
sediments or Precambrian rocks at the foot of the Darling Scarp. The Yoganup Formation consists of up to 10 m of
unconsolidated poorly sorted sand, gravel and pebbles, with minor clay, in a belt up to 5 km from the Darling Scarp
(Davidson, 1995), and is overlain unconformably by the Guildford Formation in the Perth area. It is a littoral sediment
and appears to pass westwards into the Ascot Formation, though the relationship is uncertain.
The Ascot Formation consists of indurated to friable, grey to fawn calcarenite with thinly interbedded sand, commonly
containing shell fragments, glauconite, and phosphatic nodules (Davidson, 1995). In the southern Perth area, the thick
beds of shelly, silty clay with glauconitic clay near the base (Davidson, 1995), formerly known as the Jandakot Beds,
were incorporated into the Ascot Formation by Kendrick and others (1991).
The Ascot Formation has a discontinuous distribution and its top is eroded unevenly. The Yoganup and Ascot
Formations are Late Pliocene to early Pleistocene age (Kendrick and others, 1991). The Yoganup Formation contains
mineral sand deposits in north-south trending orebodies representing former strand lines.
2.3
GUILDFORD FORMATION/GUILDFORD CLAY
The Guildford Formation was defined by Low (1971) in a type section from 0-33 m in the West Guildford artesian bore.
Playford and others (1976) describe it as lenticular interbeds of sand, clay and conglomerate, calcareous in places.
Davidson (1995) redefined the clay portion to Guildford Clay, and described it as intercalating with the Bassendean
Sand and Gnangara Sand. He describes the clay as pale grey blue, but predominantly as brown, silty and slightly sandy
clay, up to 35 m thick, and includes lenses of poorly sorted, conglomeratic and shelly sand. Davidson (1995) also
includes in the formation clay beneath the Tamala Limestone at Fremantle, and a possible lateral equivalent as black
silty clay in the Ferndale-Lynwood area.
The Guildford Clay underlies the Pinjarra Plain geomorphic unit. Its type area is in the Swan Valley around Guildford,
and it appears to represent an alluvial clay deposit. Its provenance appears to be from streams draining the Darling
Scarp as, to the north of the Perth Region, streams draining the Dandaragan Scarp give rise to sandy deposits in the
same physiographic setting. The formation was not formally included in the Kwinana Group by Playford and others
(1976), which only included coastal beach and shallow marine deposits.
The age of the Guildford Clay is uncertain and it may be a wide ranging unit which will be later subdivided. The
Guildford Clay is used for brick clay in the Swan Valley and its engineering properties are described in more detail by
Hillman and Cocks (this volume)
2.4
BASSENDEAN SAND AND GNANGARA SAND
The Bassendean Sand makes up the Bassendean Dune System, lying to the west of the Pinjarra Plain. The Bassendean
Sand is a pale grey to white quartz sand, white or yellow limonite-coated, as much as 80 m thick (Davidson, 1995).
Fine-grained heavy minerals occur throughout the formation. The lower part of the sequence has been distinguished by
Davidson (1995) as the Gnangara Sand, which consists of pale grey, fine to very coarse grained, very poorly sorted,
sub-rounded to rounded quartz sand and abundant feldspar. The type section is 22.5 m thick and is overlain by 21.5 m
of Bassendean Sand. Kendrick and others (1991) have referred to the Bassendean Sand as the regressive dune facies of
the Ascot Formation, however neither the Bassendean nor the Gnangara Sand can be dated. Bastian (1996) has
distinguished the western margin of the Bassendean Sand as the Gnangara Dune Subsystem, and shown that overlying
soils are more highly weathered (and thus older) than the soils over Tamala Limestone immediately to the west.
The Bassendean Sand provides building sand for mortars, aggregates and fill. It also locally contains mineral sands.
Pure white sand with 99.8% silica at Gnangara could be suitable for glass manufacture.
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2.5
TAMALA LIMESTONE
Previously known as the coastal limestone, the Tamala Limestone was formally defined by Playford and others (1976)
at a type section on the coast 400 km north of Perth. The Tamala Limestone is a creamy white to yellow or light grey,
cemented calcarenite which forms the Spearwood Dune system. Bastian (1996) has further subdivided the dune system
into its component ridges, the Yokine, Balcatta, Gwelup, Karrinyup and Trigg subsystems, progressively younger from
east to west. The lithology is highly variable, ranging from limestone through calcarenite to sand, with minor calcareous
siltstone or marl (Klenowski, 1976; Gordon, next volume). Indurated caprock forms pinnacles in the subsurface
(exposed in cliffs around the Swan River) with loose sand between. Much of the formation is cross-bedded dune
deposits. There is commonly a sand unit below the calcarenite and around Fremantle there is a clay layer at the base.
Glauconite and phosphatic nodules derived from the Molecap Greensand are sometimes present at the base of the
formation (Davidson, 1995).
In the Perth area the Tamala Limestone is up to 110 m thick. A 5 m section of calcarenite with an upper shell bed just
above present sea level has been distinguished as Peppermint Grove Limestone (Playford and others, 1976). The Tamala
Limestone also forms the offshore islands of Rottnest and Garden Island (Playford and Leech, 1977).
The limestone is characterised by cavities. Caves and sink holes are especially well developed in the Yanchep area.
Cavities are commonly developed at the water table and may mark previous water table positions. Infrequent surface
collapses with formation of dry sink holes have been recorded within the urban area. The older, most easterly, ridges are
leached to sand, whereas limestone predominates in the west.
The Tamala Limestone was formerly used extensively for building stone, particularly for footings, and it is also used for
armour blocks. Parts of the formation with a high lime content were also used for cement manufacture.
2.6
SAFETY BAY SAND
The Safety Bay Sand was defined by Playford and others (1976) to include the Holocene littoral sands (beach ridges) of
the Rockingham area and the coastal aeolian sands of the Quindalup Dunes. It consists of shell fragments with variable
amounts of quartz and minor felspar and a calcium carbonate content of over 50%. The sand is weakly lithified below
the dune surface in places.
In the Woodman Point- Rockingham area a unit of sand underlies the beach ridges and unconformably overlies the
Tamala Limestone. Passmore (1970) proposed the name Cooloongup Sand, while Semeniuk and Searle (1985) later
proposed the name Becher Sand. They described it as fine- to medium-grained quartz sand with lenses of silty
calcareous and shelly clay, with a thickness of 20 m in the Rockingham area.
2.7
MARINE SEDIMENTS
Holocene sediments unconformably overlie the two prominent dune ridges of the Tamala Limestone offshore, Garden
Island Ridge (which includes Rottnest) and Five Fathom Bank Ridge (Seddon, 1972). The unconformity is developed
on complex topography, including a gorge, presumably a continuation of the Swan River Channel, identified by seismic
survey in the Tamala Limestone on Fairway Bank midway between Fremantle and Rottnest (Searle 1984). The
sedimentation resulted from rapid inundation and erosion of the Tamala Limestone ridges by rising sea levels which
probably reached a maximum of +2 m about 6500 years BP, steadily declining thereafter to the present level.
The Holocene sediments are mostly moderately sorted carbonate sands and minor detrital quartz, derived from Tamala
Limestone, of bank, beach, beachridge and dune facies. The beach, beachridge and dune facies are represented onshore
by the Safety Bay Sand. The nearshore carbonate banks are up to 25 m thick and are aligned with passages through the
submerged Tamala Limestone Ridges (Searle, 1984). They are relatively homogenous, with infrequent thin beds of
coarse shell material. The carbonate sediments overlie the quartz sand of the Cooloongup Sand (Passmore 1970) which
forms a thin veneer less than 5 m thick on the Tamala Limestone. The banks are covered by seagrass meadows,
although these have been declining in extent in the last few decades. Submerged constructional beach rock platforms
are developed on the western shores of the major islands.
The banks partition the Warnbro-Cockburn depression (between Garden Island Ridge and the present coastline) into
marine basins, which are floored by 2-7 m thick unconsolidated carbonate muds, silts and fine sands. From north to
south these basins are Gage Roads, Owen Anchorage, Cockburn Sound, Warnbro Sound and Madora Basin (Seddon,
1972; Searle, 1984).
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Australian Geomechanics Vol 38 No 3 September 2003 – The Engineering Geology of Perth Part 1
OUTLINE OF THE GEOLOGY OF THE PERTH REGION
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2.8
SWAN AND CANNING RIVER ALLUVIUM
The extensive alluvium along the Swan River as far downstream as the Narrows has not been formally named. It has
been mapped by Gozzard (1986), but may be difficult to distinguish from the Guildford Formation. Similar alluvium is
mapped along the Canning and Helena Rivers (Gozzard, 1986; Jordan, 1986).
Andrews (1971) mapped alluvium below the city centre, distinguishing dune sands and alluvial and estuarine
components. He described soft dark grey or black organic clay of marine origin with shells near the causeway to 9 m
thick as estuarine, and coarse sands and occasional gravels to fine to coarse yellow brown and grey sand with clay
lenses as alluvial, although this may be confused with the subsequently named underlying Mullaloo Sandstone.
Andrews also distinguished two sequences of estuarine mud at the Narrows Bridge, an older indurated ‘blue mud’ and a
younger sequence of ‘black mud’. Sediments in the bed of the Swan Estuary are mapped as sand to black silt with
coarse shell fragments (Gozzard, 1986). The engineering properties of the alluvium are described in detail by Stewart
and Goh (this volume).
Clay has been extracted for brick or pipe clay at Queens Gardens, East Perth, and at Ascot.
2.9
COLLUVIUM
Colluvium has been mapped by Gozzard (1986) at the base of the Darling Scarp, lying between 40-100 m above sea
level. He describes the material as sandy silt and gravelly silt, with pebbles of granite, dolerite and laterite.
2.10
SWAMP DEPOSITS
Up to several metres of peat occurs in wetlands, especially those within the swales of the Spearwood Dune System around
Lake Monger and at Balcatta. Extensive removal of peat for housing development around Jones St, Stirling, has caused
oxidation of pyrite and acidic conditions (Appleyard, next volume). The peat has been used in preparation of garden soils.
2.11
COFFEE ROCK
Limonite cemented sand occurs through most of the Bassendean Sand, particularly near the water table (Davidson, 1995).
It is also noted by Andrews (1971) in dune sand in the city centre, and occurs in sandy alluvium. It ranges from lightly
cemented ferruginous sand to a dark red–brown nodular and indurated layer colloquially called coffee rock. As well as
being associated with the zone of water table fluctuation, similar deposits form as nodules around Proteaceae roots.
2.12
MUCHEA LIMESTONE
The Muchea Limestone occurs as isolated patches of soft marly limestone, rarely exceeding 1 m thick (Playford and
others, 1976). Areas mapped by Gozzard (1982) and Jordan (1986) coincide with areas of groundwater discharge on the
western margin of the Pinjarra Plain and along Ellen Brook.
3
TERTIARY SEDIMENTS
Tertiary sediments occupy restricted valleys cut into the underlying Mesozoic bedrock (Key Figures 4, 5) and are
eroded and truncated by the unconformity on which the superficial formations are deposited. The valleys relate to
former drainage systems (now the Avon and Murray Rivers), which have been subsequently modified.
3.1
ROCKINGHAM SAND
The Rockingham Sand, defined by Passmore (1970), occupies a concealed valley cut into the underlying Leederville
Formation and extends from Rockingham south south east to Mandurah. It consists of brown to pale grey somewhat
silty, slightly feldspathic, medium to coarse grained sub-angular sand (Davidson, 1995) and reaches a maximum
thickness of 110m. Its age is suggested to be Pliocene, but the sands cannot be dated, and it is likely to have been
formed by a proto Murray River.
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3.2
MULLALOO SANDSTONE MEMBER
Sands in the top of the Kings Park Formation from the city centre through to City Beach are distinguished as the
Mullaloo Sandstone Member of the Kings Park Formation by Quilty (1974) from Claremont, and from the offshore oil
exploration well Quinns Rock 1. Davidson (1995) gives an onshore thickness of 200 m in the western suburbs. He
suggests that the sandstone is incised into the siltstones and shales of the Kings Park Formation, though an
unconformable relationship cannot be demonstrated, and the Mullaloo Sandstone occupies the centre of the Kings Park
Formation subcrop.
Davidson (1995) describes the Mullaloo Sandstone as a poorly sorted, fine to very coarse grained, pale brownish green,
slightly glauconitic and clayey sand. Sands assigned by Davidson to the undated Mirrabooka Member along the upper
Swan River may also actually be correlatives of the Mullaloo Sandstone.
3.3
KINGS PARK FORMATION
The Kings Park Formation occupies a deep infilled valley cut through the Cretaceous sequence to the top of the
Yarragadee Formation, coinciding broadly with the current position of the Swan River, and in the subsurface coinciding
partly with the axis of the Swan Syncline. Its type section is in the Kings Park No 2 Bore where it is 469 m thick. The
formation consists of grey calcareous, glauconitic siltstone and shale.
A basal member, the Como Sandstone, is defined by Davidson (1995) from water bore AM 40 in Como. The nature of
the basal contact is uncertain, and this may represent a sandy facies at the unconformity. Davidson (1995) raises the
question as to whether sediments currently assigned to the Poison Hill Greensand are actually Como Sandstone.
4
MESOZOIC SEDIMENTS OF THE PERTH BASIN
The Mesozoic sedimentary rocks represent the infilling of the Perth Basin rift valley and are widespread throughout the
basin. The Jurassic to Early Cretaceous sediments are mainly continental, whereas the uppermost Late Cretaceous
sediments are predominantly marine. Mesozoic sedimentary rocks outcrop only north of Bullsbrook along the Gingin
and Darling Scarps and are elsewhere concealed by Cainozoic sediments.
A major structural event in the Neocomian (Early Cretaceous), dominated by north south faulting, resulted in uplift and
erosion of the Jurassic and Earliest Cretaceous sediments. In the Perth Region, the Pinjar Anticline was formed with
complimentary synclines, the Yanchep and Swan Synclines to the west and east respectively. The Early Cretaceous
Warnbro Group was deposited on this unconformity, with the basal Gage Sandstone and South Perth Shale deposited on
flanks (but not the crest) of the Pinjar Anticline. The overlying Leederville Formation deposition was widespread. The
uppermost Cretaceous sediments are now preserved only in the synclines and had been eroded prior to the deposition of
the Kings Park Shale.
The formations are defined from outcrop or borehole intersections, and are correlated and mapped through the
Metropolitan region by Davidson (1995) using geophysical logs and palynology mainly from the seventy Artesian
Monitoring bores. Uncertainties with mapping and identification lie particularly with the Late Cretaceous greensands
(Mirrabooka Member and Poison Hill Greensand).
The sediments are described from young to old. Sediments older than Early Jurassic have not been intersected in the
Perth Region, but are known to occur at depth (Playford and others, 1976). The sediments are weakly consolidated, and
individual sand grains are recovered during rotary drilling. The pre-Neocomian strata have been subject to a greater
depth of burial than the Warnbro and Coolyena Groups and are faulted, whereas faults cannot be demonstrated to cut
post-Neocomian strata.
4.1
LANCELIN FORMATION/POISON HILL GREENSAND/GINGIN CHALK/MOLECAP GREENSAND
The youngest Mesozoic strata are preserved in the centre of the Swan Syncline north of Perth (Key Figure 4). They
consist of Late Cretaceous marine shale, chalk, marl and greensands. The greensands and chalk close to the Darling
Scarp appear to pass westwards into marl in the Yanchep Syncline and offshore (Lancelin Formation).
The greensands occur in the Wanneroo area and from West Swan along Ellen Brook to Gingin. The Molecap Greensand is
difficult to distinguish from underlying Mirrabooka Member, and the Poison Hill from the Como Sandstone.
The Molecap and Poison Hill Greensands are similar, being fine to medium or coarse grained, yellowish brown to greenish
grey or dark grey, glauconitic, silty and locally clayey. Phosphatic nodules are common in the upper part of the Molecap
Greensand. The intervening Gingin Chalk is difficult to distinguish in borehole samples in the northern Perth area.
12
Australian Geomechanics Vol 38 No 3 September 2003 – The Engineering Geology of Perth Part 1
OUTLINE OF THE GEOLOGY OF THE PERTH REGION
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4.2
OSBORNE FORMATION
The Osborne Formation is preserved in the centre of the Swan Syncline, underlying the superficial formations between
Kwinana and Bullsbrook and extending north eastwards to Gingin. The formation, as redefined by Davidson (1995),
consists of a basal sand (Henley Sand Member), middle shale (Kardinya Shale Member) and upper greensand
(Mirrabooka Member).
Davidson (1995) gives the formation thickness as a maximum of 180 m, with maximum thicknesses for the Henley
Sand of 100 m, Kardinya Shale 140 m, and Mirrabooka Member 160 m. The Mirrabooka Member is difficult to
distinguish from the overlying Molecap Greensand and its distribution and relationships are ambiguous.
Clay quarried at Bullsbrook on the Gingin Scarp is most likely Kardinya Shale, rather than Leederville Formation as
mapped by Gozzard (1982).
4.3
LEEDERVILLE FORMATION
The Leederville Formation underlies almost the entire region west of the Darling Fault, except where it has been eroded
and replaced by the Kings Park Formation. Davidson (1995) subdivided the formation into three members, the basal
Mariginiup, middle Wanneroo, and upper Pinjar Member. The Mariginiup Member represents a transition from the
underlying South Perth Shale, whereas the Wanneroo Member is an interbedded sandstone and shale. The Pinjar
Member is predominantly shaley. The maximum thickness of the formation is 450 m in the Swan Syncline, and it thins
onto the Pinjar Anticline.
The Wanneroo Member of the Leederville Formation is a major confined aquifer used for public water supply, watering
of public open space and for irrigation of vineyards in the Swan Valley (Davidson, 1995).
4.4
SOUTH PERTH SHALE
The South Perth Shale is thinly interbedded grey to black siltstone and shale, with minor thin sandy beds and local thin
calcareous beds (Davidson, 1995), and has a maximum thickness of about 300 m. It occurs in the subsurface below the
western part of the coastal plain, extending to the Darling Fault between Maddington and Bullsbrook.
4.5
GAGE FORMATION
The Gage Formation is the basal unit of the Warnbro Group, unconformably overlying the Yarragadee Formation and
occurring beneath the western part of the coastal plain. As a basal deposit of the Warnbro Group, it is likely it was
formed by reworking of Jurassic sediments. It is thickest in the Swan Syncline north of Perth, suggesting fault
controlled deposition.
4.6
PARMELIA FORMATION
The Parmelia Formation underlies the north eastern part of the Perth Region between Muchea and Gingin, where it is
unconformably overlain by the Leederville Formation. The lithology is not well known in this area, but is likely to
consist of interbedded sand and siltstone/shale with the basal Otorowiri Siltstone Member conformably overlying the
Yarragadee Formation.
4.7
YARRAGADEE FORMATION
The Yarragadee Formation extends throughout the Perth Basin at depth, except along the Darling Fault south of
Armadale. The formation consists mainly of sandstone with minor interbedded siltstone or shale. The formation is
believed to be around 2000 m thick in the Perth area.
Groundwater from the Yarragadee Formation is used for public water supply and for geothermal heating (Davidson,
1995; Commander, this volume).
4.8
CATTAMARRA COAL MEASURES
The Cattamarra Coal Measures (formerly the Cattamarra Coal Measures Member of the Cockleshell Gully Formation)
underlies the Yarragadee Formation at depth, and directly underlies the Leederville Formation and superficial
formations south of Armadale, just west of the Darling Fault (Key Figures 4, 5). The formation in this area consists of
thickly interbedded sandstone and shale. Coal measures have not been recorded in the Perth Region. It is in faulted
contact with the Yarragadee Formation to the west.
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OUTLINE OF THE GEOLOGY OF THE PERTH REGION
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The formation is a local aquifer used only in south Keysbrook and Pinjarra. The Cattamarra Coal Measures has also
been used for deep well waste disposal at Kwinana.
5
PRECAMBRIAN SEDIMENTARY ROCKS ALONG THE DARLING SCARP
Proterozoic sedimentary rocks of the Cardup Group crop out in a zone 1 km wide at the base of the Darling Scarp south
of the Canning River, and probably extend in the subsurface westwards to the Darling Fault. A basal sandstone and
conglomerate, the Whitby Formation, unconformably overlies the granitic rocks and is overlain by interbedded
sandstone and shale (Neerigen Formation) and shale (Armadale Shale). The sediments are weakly metamorphosed and
dip steeply or moderately westwards. There is pronounced slatey cleavage sub-parallel to the bedding. The sedimentary
rocks are thought to have formed between 750 – 600 thousand years (Ma), and they are cut by dolerite dykes of the
Boyagin Swarm (Myers, 1990).
Quartz veins are numerous in the Cardup Group, locally following the contact with the underlying Archaean rocks. The
shale has been extracted for brick clay and, because of the low permeability, disused quarries have been used for waste
disposal.
6
ARCHAEAN CRYSTALLINE ROCKS OF THE DARLING RANGE (YILGARN
CRATON)
The Archaean crystalline rocks in the Western Gneiss Terrane of the Yilgarn Craton, which occur in the Darling Range,
consist of granite, migmatite and gneiss, with metamorphic rocks north of Bullsbrook.
Gneissic rocks lie within 10 km of the Darling Fault (Wilde and Low, 1980) and occur around Roleystone and between
Mundijong and North Dandalup. Mafic gneisses around Roleystone include amphibolite, biotite amphibolite,
amphibolite bearing schists with minor felsic units and pods of ultramafic tremolite or talc (Wilde and Low 1980). The
gneisses between Mundijong and North Dandalup contain shear zones, and intensive shearing has resulted in the
formation of blastomylonite. Shear zones in granitic rock follow zones of sericite schist (Whincup, 1969). Migmatite is
extensive along the Darling Scarp, surrounding the mafic rich rocks at Roleystone. North of Bullsbrook, thin bands of
quartz mica schist are intercalated in the gneisses. These become more common northwards into the Chittering
Metamorphic Belt (Wilde and Low, 1978).
Dolerite dykes intrude all the Precambrian rocks. The dykes average about 10 m thick, but range from a few centimetres
to 200 m. Most dykes are sheared or altered (the margins commonly to amphibolite) and fresh dykes are rare. Dykes
near the Darling Scarp have a general northerly trend which is emphasised by shearing.
The Archaean rocks are deeply weathered with lateritic duricrust over saprolite of kaolinised granite (commonly up to
30 m thick) or of dolerite, overlying saprock (Anand and Butt, next volume). The laterite ranges from massive to
nodular and pisolitic ironstone. Lateritic gravel is extracted for roadbase.
7
CONSTRUCTION MATERIALS
The Perth Region contains a variety of rock and sedimentary material suitable for supplying sand, limestone, clay and
hard rock for building materials and construction purposes. In comparison with the Eastern States capitals, Perth is in a
position of significant advantage in terms of location, quality and price of its basic raw materials (Landvision, 1996).
Priority resource areas have been identified within the framework of the State Planning Commission Policy on Basic
Raw Materials, 1992, which is to protect and facilitate the extraction of valuable deposits of raw materials required to
serve the future needs of Perth. Location and geology of basic raw materials are summarised in Table 2. Detailed
locality maps of sources are given by Landvision (1996).
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Australian Geomechanics Vol 38 No 3 September 2003 – The Engineering Geology of Perth Part 1
OUTLINE OF THE GEOLOGY OF THE PERTH REGION
P COMMANDER
Table 2: Extractive industry in the Perth Region.
Material
Aggregate, roadstone
Roadbase
Roadbase
Armour blocks
Fireclay
Brick clay
Brick clay
Armour blocks
Building stone
Lime
Brick, pipe clay
Sand
Peat
Roadbase
Shellsand (for cement)
Geology
Granite, migmatite, dolerite
Pisolitic laterite
Tamala Limestone
Granite
Weathered granite and schist
Armadale Shale
Osborne Formation
Tamala Limestone
Tamala Limestone
Tamala Limestone
Guildford Clay
Bassendean Sand
Swamp deposits
Calcareous lake deposits
Marine deposits
8
Locality
Darling Range
Darling Range
Coast
Darling Range
Darling Range
Darling Scarp
Gingin Scarp
Coast
Coast
Coast
Swan Valley, Serpentine
Gnangara, Jandakot
Balcatta
Lake Walyungup
Cockburn Sound
REFERENCES
Allen A. D. (1976) Outline of the hydrogeology of the superficial formations of the Swan Coastal Plain. Western
Australia, Geological Survey Annual Report for 1975, 31-42.
Anand R.R. and Butt C.R.M. (in press) Distribution and evolution of ‘laterites’ and lateritic weathering profiles, Darling
Range, Western Australia. Australian Geomechanics, The Engineering Geology of Perth Part 2.
Andrews DC (1971) Soils of the Perth Area – the city centre. Aus CSIRO, Div Appld Geomechanics, Technical Report 13
Appleyard S.J. (in press) Groundwater quality in the Perth Region. Australian Geomechanics, 2003, The Engineering
Geology of Perth Part 2.
Bastian L. V. (1996) Residual soil mineralogy and dune subdivision, Swan Coastal Plain, Western Australia. Aust. Jour.
Earth Sciences 43, 31-44.
Baxter J.L. (1977) Heavy mineral sand deposits of Western Australia. Western Australia, Geological Survey, Mineral
Resources Bulletin 10.
Baxter J. L. and Hamilton R. (1981) The Yoganup Formation and Ascot beds as possible facies equivalents. Western
Australia, Geological Survey, Annual Report 1980, 94-95.
Beard J. S. (1999) Evolution of the river systems of the South West Drainage Division, Western Australia. Jour. Roy.
Soc . W.A. 82, 147-164.
Australian Geomechanics Vol 38 No 3 September 2003 – The Engineering Geology of Perth Part 1
15
OUTLINE OF THE GEOLOGY OF THE PERTH REGION
P COMMANDER
Davidson W. A. (1995) Hydrogeology and groundwater resources of the Perth Region Western Australia. Western
Australia, Geological Survey, Bulletin 142.
Geological Survey of Western Australia (1991) The geology and mineral resources of Western Australia, Memoir 3.
Gordon F.R. (in press) Coastal limestones. Australian Geomechanics, 2003, The Engineering Geology of Perth Part 2.
Gozzard J. R. (1982) Muchea Sheet 2031 I and part 2134 IV Perth Metropolitan Region Environmental Geology Series.
Western Australia, Geological Survey.
Gozzard J. R. (1986) Perth, Sheet 2034 II and part 2034 III and 2134 III. Perth Metropolitan Region Environmental
Geology Series. Western Australia, Geological Survey.
Hillman M and Cocks G. (in press) Guildford Formation alluvium. Australian Geomechanics, 2003, The Engineering
Geology of Perth Part 2.
Jordan J. E. (1986) Armadale part sheets 2033 I and 2133 IV Perth Metropolitan Region Environmental Geology Series.
Western Australia, Geological Survey.
Kendrick G. W., Wyrwoll K-H. and Szabo, B. J. (1991) Pliocene - Pleistocene coastal events and history along the
western margin of Australia. Quaternary Science Reviews, v. 10, 419-439.
Klenowski G. (1976) Geotechnical properties of the coastal limestone in the Perth Metropolitan Area. Western
Australia, Geological Survey Annual Report 1975, 42-46.
Landvision (1996) Managing the basic raw materials of Perth and the outer Metropolitan Region. Report for Chamber
of Commerce and Industry Western Australia, April 1996, 166p.
Low G. H. (1971) Definition of two new Quaternary formations in the Perth Basin. Western Australia, Geological
Survey, Annual Report 1970, 33-34.
Myers J. S. (1990) Pinjarra Orogen in Geology and Mineral Resources of Western Australia. Western Australia,
Geological Survey. Memoir 3, 273-274.
Passmore J. R. (1970) Shallow coastal aquifers in the in the Rockingham District, Western Australia, Water Research
Foundation of Australia, Bulletin 18.
Playford P. E., Cockbain A. E. and Low G.H. (1976) Geology of the Perth Basin Western Australia. Western Australia,
Geological Survey, Bulletin 124.
Playford P. E. and Leech R. E. J. (1977) Geology and hydrology of Rottnest Island Western Australia. Western
Australia, Geological Survey, Report 6, 98p.
Quilty P. G. (1974) Cainozoic stratigraphy of the Perth area. Royal Soc of Western Australia Journal 57, 16-31.
Searle D. J. (1984) Sediment transport system, Perth Sector, Rottnest Shelf, Western Australia. University of Western
Australia, Geology Department, PhD Thesis.
Seddon G. (1972) A Sense of Place. University of Western Australia Press, Nedlands.
Semeniuk V. and Searle D. J. (1985) The Becher Sand, a new stratigraphic unit for the Holocene of the Perth Basin.
Royal Soc. of Western Australia Journal 67, 109-115.
Whincup P. (1969) Sequence of development of some structures in the granite of the Lower Helena Valley. Western
Australia, Geological Survey Annual Report 1969, p. 55.
Wilde S. A. and Low G. H. (1978) Perth WA. Western Australia, Geological Survey, 1:250 000 Geological Series.
Wilde S. A. and Low G. H. (1980) Pinjarra WA. Western Australia, Geological Survey, 1:250 000 Geological Series.
Wyrwoll K-H. (2003) The geomorphology of the Perth region, Western Australia. Australian Geomechanics Vol 38 No
3 The Engineering Geology of Perth Part 1
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