Perth basin
Encyclopedia
The Perth Basin is a thick sedimentary basin
in Western Australia
. It lies beneath the Swan Coastal Plain
west of the Darling Scarp
, representing the western limit of the much older Yilgarn Craton
, and extends further west offshore. Cities and towns including Perth
, Busselton
, Bunbury
, Mandurah
and Geraldton
are built over the Perth Basin.
during the breakup of Gondwana
, as the Australian continental plate began rifting away from the African
and Indian continental plates
.
During the Permian, what is now the Perth Basin was the eastern half of a rift valley
that formed as the continental plates were pulled apart. This pulling apart, which continued until the Jurassic
, led to the central zone subsiding as a graben
allowing the sea to enter with the subsequent deposition of transgressive
marine sediments. The Perth Basin architecture is dominated by listric, extensional faulting
that formed during sedimentation and controlled the distribution of the sediments.
The primary mechanism for sedimentation was originally subsidence creating accommodation (space for sediments to accumulate), followed by fault extension and more recently, sediment loading, i.e. the basin continuing to subside because of the weight of sediments within it.
The eastern boundary of the main Perth Basin is the Darling Fault
, topographically expressed as the Darling Scarp. Small outliers of the Perth Basin, such as the Collie Sub-basin
, lie east of the Darling Fault.
(a source of titanium
) and zircon
, by Iluka Resources
and other companies. Some of these mines are controversial for environmental reasons.
Various formations from Cainozoic to Jurassic age are economically significant freshwater aquifer
s. Younger aquifers are an important suppliant to reservoir water in the city of Perth and elsewhere. The Yarragadee Formation, one of the thickest formations in the basin, is a very good aquifer in the southern part of the basin.
The Perth Basin contains Permian and Jurassic coal
measures, the most important being mined primarily for electricity generation in the Collie Sub-basin
at Collie
in the south-west of the state.
The Perth Basin is also prospective for natural gas
and oil, with recent exploration wells, including Origin Energy
/Arc Energy's Hovea 2, confirming large resources of natural gas, but difficult reservoir
geology and characteristics have prevented the full utilisation of these energy reserves. The oil is sourced from the Kockatea Shale.
Sedimentary basin
The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification...
in Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
. It lies beneath the Swan Coastal Plain
Swan Coastal Plain
The Swan Coastal Plain in Western Australia is the geographic feature which contains the Swan River as it travels west to the Indian Ocean. The coastal plain continues well beyond the boundaries of the Swan River and its tributaries, as a geological and biological zone, one of Western Australia's...
west of the Darling Scarp
Darling Scarp
The Darling Scarp, also referred to as the Darling Range or Darling Ranges, is a low escarpment running north-south to the east of the Swan Coastal Plain and Perth, Western Australia...
, representing the western limit of the much older Yilgarn Craton
Yilgarn craton
The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...
, and extends further west offshore. Cities and towns including Perth
Perth, Western Australia
Perth is the capital and largest city of the Australian state of Western Australia and the fourth most populous city in Australia. The Perth metropolitan area has an estimated population of almost 1,700,000....
, Busselton
Busselton, Western Australia
-Growth and development:According to the Australian Bureau of Statistics the Shire had a permanent resident population of 25,950 in 2004 with the town of Busselton accounting for 67% or 17,400 of the total. The Shire's permanent population is expected to continue to increase significantly to...
, Bunbury
Bunbury, Western Australia
The port city of Bunbury is the third largest city in Western Australia after the State Capital Perth and Mandurah. It is situated south of Perth's central business district...
, Mandurah
Mandurah, Western Australia
Mandurah is the second-largest city in Western Australia and is located approximately south of the state capital, Perth.The city attracts a large number of tourists, including many international visitors...
and Geraldton
Geraldton, Western Australia
Geraldton is a city and port in Western Australia located north of Perth in the Mid West region. Geraldton has an estimated population at June 2010 of 36,958...
are built over the Perth Basin.
Geological setting and evolution
The Perth Basin began forming in the Late PermianPermian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
during the breakup of Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
, as the Australian continental plate began rifting away from the African
African Plate
The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...
and Indian continental plates
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
.
During the Permian, what is now the Perth Basin was the eastern half of a rift valley
Rift valley
A rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic rift or fault. This action is manifest as crustal extension, a spreading apart of the surface which is subsequently further deepened by the forces of erosion...
that formed as the continental plates were pulled apart. This pulling apart, which continued until the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
, led to the central zone subsiding as a graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
allowing the sea to enter with the subsequent deposition of transgressive
Transgression (geology)
A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused either by the land sinking or the ocean basins filling with water...
marine sediments. The Perth Basin architecture is dominated by listric, extensional faulting
Extensional fault
An extensional fault is a fault that vertically thins and horizontally extends portions of the Earth's crust and/or lithosphere. In most cases such a fault is also a normal fault, but may be rotated to have a shallower geometry normally associated with a thrust fault...
that formed during sedimentation and controlled the distribution of the sediments.
The primary mechanism for sedimentation was originally subsidence creating accommodation (space for sediments to accumulate), followed by fault extension and more recently, sediment loading, i.e. the basin continuing to subside because of the weight of sediments within it.
The eastern boundary of the main Perth Basin is the Darling Fault
Darling Fault
The Darling Fault is one of the longest and most significant faults in Australia, extending for at least 1500 km in a north–south orientation near the west coast of southern Western Australia. It is a major geological boundary separating the Archaean Yilgarn Craton in the east from the younger...
, topographically expressed as the Darling Scarp. Small outliers of the Perth Basin, such as the Collie Sub-basin
Collie Sub-basin
The Collie Sub-basin is a pocket of Permian sedimentary rocks with an area of 225 km², enclosed within much older Archean rocks of the Yilgarn Craton, near the town of Collie in southwestern Western Australia., Once considered a unique basin, this area, along with the smaller Wilga and Boyup...
, lie east of the Darling Fault.
Stratigraphy
Letters in brackets after the formation name represent shorthand symbols used on geological maps.Quaternary and Recent
The Quaternary and Recent sedimentation of the Perth Basin is represented by thin, impermanent sand dune systems, biogenic limestones, sandstones and some shales deposited during the last ~20 million years and during ice ages.Cretaceous
- Lancelin Formation
Upper Cretaceous glauconiticGlauconiteGlauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...
marl, infrequently developed on top of the Coolyena Group. - Coolyena Group - Upper Cretaceous marine sediments.
- Poison Hill Greensand (Kcp) consists of pale yellow unconsolidated weathered clay, glauconitic sandstone and shale. It conformably overlies the Gingin Chalk and is in turn overlain by unconsolidate Quaternary sands and alluvium.
- Gingin Chalk (Kcg) is a weakly consolidated fossiliferous chalkChalkChalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
composed of coccolithCoccolithCoccoliths are individual plates of calcium carbonate formed by coccolithophores which are arranged around them in a coccosphere.- Formation and composition :...
s, which interfingers and conformably overlies the Molecap Greensand. - Molecap Greensand (Kcm) is a fine to medium grained marine glauconiteGlauconiteGlauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...
sandstone which uncconformably overlies the Osborne Formation. - Osborne Formation (Kco) conformably overlies the Triassic Leederville Formation, and is composed of a marine sandstone, shale and interbedded shale-sandstone sequence from base upwards.
- Warnbro Group - Early Cretaceous marine sediments representing a transgression.
- Parmelia Formation (J-Kp) forms the topmost hydraulic unit of the Yarragadee Aquifer. It is composed of 100-200 m thickness of well sorted fluvial sandstone deposited in the latest Jurassic to early Cretaceous. It includes a basal siltstone of lagoonal to lacustrine environment, the Otowiri Siltstone, which acts as an aquitard.
- Leederville Formation (Kll) sandstone, siltstone, shale and mudstone deposited in deeper marine environments, with finer sediments predominant in the upper part of the unit. The unit attains a maximum thickness in the axis of the Yanchep Syncline is ~700 m, and thins eastward to approximately 500 m. The Leederville Formation interfingers and merges with the underlying Parmelia Formation in the north of the Perth Basin.
- Gage Formation (Kwg) is a shallow lagoonal sandstone and shale deposited in shallow marine beach-dune-lagoonal environments.
Jurassic
- Yarragadee FormationYarragadee AquiferThe Yarragadee Aquifer is a significant freshwater aquifer located in the south west of Western Australia and predominantly beneath the Swan Coastal Plain west of the Darling Scarp. It has a north-south range from about Geraldton to the south coast, but with a split in the formation south of Perth...
(Jy) is one of the thickest units in the Perth Basin and forms a significant freshwater aquiferAquiferAn aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
. It is composed primarily of non-marine fluviatile feldspathic, poorly sorted sandstones which are porous and poorly cemented, hence allowing for considerable groundwater reserves. The Yarragadee Formation grades from a shale-siltstone dominated base to a cleaner sandstone in the upper portions of the formation, probably representing increased subsidence or filling of the basin during the late Jurassic. - Cadda Formation (Jd) conformably underlies the Yarragadee Formation and is composed primarily of shale and siltstone, with occasional beds of very coarse sandstone. The upper portions of the unit are composed of a marlMarlMarl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...
grading into a marine limestoneLimestoneLimestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
, representing stable tectonics at this time. - Cattamarra Coal Measures (Jc) are a sequence of non-marine, probably fluviatile sandstones, shales and silts including bituminous coalBituminous coalBituminous coal or black coal is a relatively soft coal containing a tarlike substance called bitumen. It is of higher quality than lignite coal but of poorer quality than Anthracite...
, and are up to 300 m thick. The Cattamarra Coal Measures conformably overly the Eneabba Formation. - Enneabba Formation (Je) is a lower-Jurassic terrigenous red-bed unit composed of interbedded sandstone with variably coloured limestone. The Enneabba Formation is conformable with the Lesueur Sandstone in the south of the Perth Basin and unconformable with the Kockatea Formation in the north, suggesting it is transgressive.
Economic geology
Cainozoic sand dune systems are locally being mined for mineral sands, mainly rutileRutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...
(a source of titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
) and zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
, by Iluka Resources
Iluka Resources
Iluka Resources is a mining company involved in the mining and processing of titanium based and zircon products. The company mines heavy mineral sands and separates the concentrate into its individual mineral constituents rutile, ilmenite, leucoxene and zircon...
and other companies. Some of these mines are controversial for environmental reasons.
Various formations from Cainozoic to Jurassic age are economically significant freshwater aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
s. Younger aquifers are an important suppliant to reservoir water in the city of Perth and elsewhere. The Yarragadee Formation, one of the thickest formations in the basin, is a very good aquifer in the southern part of the basin.
The Perth Basin contains Permian and Jurassic coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
measures, the most important being mined primarily for electricity generation in the Collie Sub-basin
Collie Sub-basin
The Collie Sub-basin is a pocket of Permian sedimentary rocks with an area of 225 km², enclosed within much older Archean rocks of the Yilgarn Craton, near the town of Collie in southwestern Western Australia., Once considered a unique basin, this area, along with the smaller Wilga and Boyup...
at Collie
Collie, Western Australia
-External links:*...
in the south-west of the state.
The Perth Basin is also prospective for natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
and oil, with recent exploration wells, including Origin Energy
Origin Energy
-History:Origin Energy was formed in February 2000, as a result of a demerger from the Australian conglomerate Boral Limited, in which the energy business was removed from the building and construction materials business to form the new company....
/Arc Energy's Hovea 2, confirming large resources of natural gas, but difficult reservoir
Oil reservoir
A petroleum reservoir, or oil and gas reservoir, is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. The naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability...
geology and characteristics have prevented the full utilisation of these energy reserves. The oil is sourced from the Kockatea Shale.
External links
- Hovea Gas Field Permiting & History, APPEA
- Roc Oil presentation on Cliffhead Oil Well, Perth Basin, WA. (pdf, 350kb)
- Cliff Head Oil Field, Roc Oil
- 3D-GEO Australia: Multiple Regional Studies completed over the last 10 years. Currently we have a full in-house study.
Further reading
- Raine, M. J. and K.G. Smith (1972) Bibliography of the Perth Basin, Western Australia Canberra : Bureau of Mineral Resources, Geology and Geophysics, report ; no. 157. ISBN 0-642-95921-8 Prepared by the Petroleum Exploration Branch of the Bureau of Mineral Resources, with assistance from the Geological Survey of Western Australia.