Geology of New South Wales
Geologically the Australian state of New South Wales consists of seven main regions:
There are a few other sedimentary basins, the Great Artesian Basin can be broken into the Eromanga Basin in the west and the Surat Basin to the east. The Sydney Basin extends north into the Gunnedah Basin, which goes even further north into the Bowen Basin which extends into Queensland, under the Surat Basin. The New England Orogen has a few small Basins included, such as the Lorne Basin, the Myall Syncline, and Gloucester Basin. The Oaklands Basin is in the south of the state under the Murray Basin. The Darling Basin is in the state's west, but mostly covered by the Murray Basin. Gilgandra Sub-Basin and Paka Tank Trough are potential places for coal and gas.[2]
New South Wales is home to some important mining operations including Broken Hill and coal mining and burning in the Hunter and Illawarra.[3]
Delamerian orogeny
Lachlan Fold Belt
Rocks from the Lachlan Fold Belt are exposed through the south east and central parts of NSW, and underlie the
The Australian Capital Territory is embedded in New South Wales in the Lachlan Fold Belt. The Narooma Terrane is another terrane abutted on the southeast corner of New South Wales which can be considered as a component of the Lachlan Fold Belt.
Hunter-Bowen orogeny
The Hunter-Bowen orogeny also known as the New England Orogen contains rocks from Late Paleozoic to early Mesozoic times. It was formed as an arc-forearc zone as the Pacific Plate was subducted to the west.[4]
Darling and Barka Basins
The
The deeper basins included turbidites. Felsic volcanic material was also erupted in the Rast and Mount Hope Troughs. The Florida, Babinda, Majuba and Mineral Hill Volcanics are found on the East side of the Kopyje Shelf. Most of the sediment however is quartz sand.
Subsequently in the early Devonian the basin content was pushed back up, and the Mulga Downs Group was deposited by rivers up until the Carboniferous Period. This formed the Barka Basin. Rock from this group is mostly quartz sandstone, with a small amount of siltstone.[5]
Sydney Basin
The Sydney Basin consists of
The first rocks formed in the Permian were the Dalwood Group and lower Shoalhaven Group. Material for this came from basaltic volcanoes to the north in the Hunter region. The Greta Coal Measures then formed in the north side in an alluvial fan from the mountains of the New England Orogen. The basin sank lower and sea water came much further inland, covering the Permian sediments and the basement further west, and the Maitland Group and upper Shoalhaven Group were deposited. The Muree/Nowra Sandstone formed in the centre of the basin.[7]
In the next stage the Hunter – Bowen Orogeny cause faulting and folding on the north side of the basin. In the Late Permian river and delta deposition formed the Tomago and Whittingham Coal Measures in the north. But deepening seawater formed the Kulnura Marine Tongue and Bulga Formation. In the southern part of the basin a delta formed the lower Illawarra Coal Measures. The Erins Vale Formation interrupts this. Marine transgression formed Dempsey Formation, Denman Formation, Bargo Claystone, and Ball Bone Formation. Beach deposition then formed Waratah/Watts Sandstone and the Darkes Forest Sandstone and Angus Place Sandstone. Over the beach land formed again with the Newcastle and Wollombi Coal Measures in the north, and upper Illawarra Coal Measures in the south. Early in the
The
The basin was later buried under 1 to 4 km of
Great Artesian Basin
Part of the Great Artesian Basin is along the northern border of New South Wales and also extends north into Queensland. This is also known as Surat Basin. It occupies one fifth of the state of New South Wales. The eastern border extends from Bebo to Narrabri to Murrurundi to Dunedoo to Narromine. The basin was formed in the Jurassic and Cretaceous periods.[10]
The oldest Jurassic rocks in the basin are found in the northeast near the Queensland border. They are called Precipice Sandstone,[11] Evergreen Shale and Boxvale Sandstone,[12] Hutton Sandstone from Pliensbachian to Aalenian in age.[13] In the south east of the basin these deposits are known as Purlawaugh Formation which are aged between Pliensbachian to Bathonian.[14] The northern parts are then covered with coal and shale from the Injune Creek Group.[15] In the east they are covered with quartz sand, at the point where run off entered the basin called Blythesdale Group between Tithonian and Barremian[16] or Pillaga Sandstone which is now known as Pilliga Sandstone.[10][17]
In the Cretaceous sea water entered and deposited shale from the Rolling Downs Group[18] which also contains some calcareous sandstone. Continental sediment also occasionally show in the Cretaceous.[10]
Most of the basin is covered by alluvium and lake deposits from the
Because the basin is an important site for
Clarence Moreton Basin
The
The first rocks in the Clarence Moreton Basin of New South Wales are the Chillingham Volcanics. These are from some time in the Triassic period, and for a band north and south of Chillingham. They consist of conglomerate at the base, Rhyolite, lithic rhyolitic tuff, and shale.[21] The Nymboida Coal measures extend from Nymboida to Kangaroo Creek. They consist of lithic sandstones (wackes, minor arenites), siltstone, polymictic conglomerate, coal, rhyolitic tuff, and basalt. The total thickness is over 1000 meters. The outcrop is 90 square kilometers, and it forms a north west trending band 29 km long on the southwest tip of the basin.[22] Fossils reveal a date of middle Triassic. A lower part is called Cloughers Creek Formation.[19][23] The Basin Creek Formation[24] includes the coal mined at Nymboida. The Bardool Conglomerate forming a 180 m thick layer,[25] is also a unit in the coal measures. The conglomerate includes a 15 m thick layer of basalt exposed at Copes Creek.[19]
The Red Cliff Coal Measures are from late Triassic. It forms a belt 2.5 km wide and 19 km long from Buchanans Head trough
The basin was next uplifted and eroded and then deepened considerably and Bundamba group rocks form a complete V shape on both sides of the basin. In the northern parts the rock is mostly friable sandstone, but in the south it is divided into conglomerate below and siltstone above. The Laytons Range Conglomerate
The Marburg subgroup
The next layer of rocks in the basin forming a nested U shape in its exposure is the Kangaroo Creek Sandstone.[32] This sandstone has saccharoidal texture, and glistens white and cream. This is not due to angular sand grains, but results from silica crystallization. It is up to 150 m thick.[19]
The Grafton Formation
During the Cainozoic, rifting along the east coast of Australia commenced and uplifted the eastern side of the Clarence Moreton Basin.[20] This resulted in the splitting off of the Lord Howe Rise and the opening of the ocean floor.[34]
Murray basin
After Australia separated from Antarctica the Murray basin was formed. The basin floor only subsided slowly over time.[5] The basin became filled with up to 600 m of sediments during the Cenozoic.[35]
From Paleocene to Eocene the western side was flooded with sea water and deposited the Warina sand.[36] The sea withdrew and later in the Eocene silt and clay of the Olney Formation[37] were deposited. One minor sea incursion resulted in late Eocene resulted in the Buccleuch Formation[38] in South Australia. This group of deposits is termed the Renmark Group and was earlier known as Knight Group.[39]
The sea level rose again in Late
During
The
The Pooraka Formation[52] formed in the north west due to increased erosion resulting in colluvium depositing. The colluvium forms fans, cones and scree slopes, and often contains clay and breccia. In the flat areas the Shepparton Formation[53] also resulted from river deposits of floodplain clay.[5]
Most of the existing surface dates from Quaternary period. The river deposits from the east have been progressively overlaying the marine deposits further west, as the shore line receded. Within the Pleistocene deposits are three layers of sand that are aquifers, deposited during higher rainfall periods of the interglacials. The floodplain deposits from the current rivers are the Coonambidgal Formation, however this term is used informally for the older Pleistocene flood deposits as well.[54] During the dryer glacial periods the area was arid.[55]
Oaklands basin
The Oaklands Basin covers approximately 3 800 square kilometres in the Riverina district of southern New South Wales, between the towns of Mulwala, Jerilderie, Griffith, Coleambly, Oaklands and Albury. This Permo-Triassic basin trends north-northwest-south-southeast and is concealed beneath the south-eastern portion of the Murray Basin. The basin overlies the Ovens Graben (Ovens Valley Graben in Victoria) which extends from the Murrumbidgee River west of Darlington Point in New South Wales to Wangaratta in Victoria. It is approximately 25 km wide at Oaklands and approximately 15 km wide at its northern extent. The Oaklands Basin hosts to more than 1000 m thick sediments. The basin was first discovered in 1916 when water drillers discovered coal near Coorabin. Coal has been the main focus for exploration within the basin since this time. Extensive coal exploration drilling has been undertaken, mostly in the Coorabin area. In addition two coal drilling programs by the NSW Department of Industry, designed to help define the limits of the basin, have resulted in wide-spaced drilling coverage over most of the basin. Petroleum exploration within the basin has been minimal, consisting of a small number of geophysical surveys and two stratigraphic wells. In 2009 four new lines of high quality 2D seismic have been acquired by DTIRIS (formerly the NSW Department of Industry and Investment). This survey has further delineated the boundaries of the basin, established the thickness of the sediment fill and imaged the structures of the Ovens Valley Graben along the margin and central portion of the basin.[56]
Volcanic rocks
New South Wales has 26,000 km2 of volcanic rocks from
Geological history
In the Cambrian and earlier period only the far west of New South Wales existed in its present form. It was joined to what is now Western North America in the Rodinia supercontinent. North America was detached opening up the Pacific Ocean. In the Ordovician period, sediment deposited on the newly formed sea floor, and in the Silurian a back arc basin behind a chain of volcanoes was formed and then accreted back onto the east coast of Australia to form the Lachlan Fold Belt. The main structure in this is north-south, and this is reflected nowadays with the orientation of rivers and mountain ranges.
Fossils
Collecting fossils is legal in New South Wales under the New South Wales Mining Act with ownership applying to the land owner.[57] Opalised fossils about 100 Mya occur at
At Canowindra is the most important fish fossil site in the world. It dates from 360 Mya in the Devonian and includes Groenlandaspis, Canowindra grossi, Remigolepis walkeri and Bothriolepis yeungae. A museum is there called Age of Fishes Museum. At Cuddie Springs is a fossil site containing Diprotodon and the Thunder Bird.
The Griman Creek Formation contains Cretaceous dinosaur fossils.[60]
Economic geology
Mining
A variety of mines occur in New South Wales, including
Disasters
The oldest
The
History
Study
Government
The Department of Mines commenced in late 1874, and the Geological Survey of New South Wales was brought into existence on 1 January 1875. Charles Smith Wilkinson was its first supervisor. In the 1950s to 1970s the administering body for mines was the New South Wales Department of Mines or New South Wales Department of Mines and Agriculture. Before 2004 New South Wales Department of Mineral Resource After 2004 until July 2009 mining in New South Wales was administered by the
References
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- ^ "Hutton Sandstone". Australian Stratigraphic Names Database. Geoscience Australia. 20 August 2009.
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- ^ "Rolling Downs Group". Australian Stratigraphic Names Database. Geoscience Australia. 22 December 2008.
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