{{Short description|Sedimentary basin and region in New South Wales, Australia}} {{Use Australian English|date=August 2019}} {{Use dmy dates|date=October 2019}} {{Infobox Australian place | type = region | name = Sydney Basin | state = nsw | image =Karte_Sydneybecken.png | image_upright = 1.1 | caption = Map of the Sydney Basin | image_map1 = IBRA 6.1 Sydney Basin.png | map_caption1 = The interim Australian bioregions,<br />with the Sydney Basin in red | map_type = nomap | pop = 6300000 | pop_footnotes = <ref name=bioregionalassessment>{{cite web |url=https://www.bioregionalassessments.gov.au/assessments/sydney-basin-bioregion |title=Sydney Basin bioregion |work=Bioregional assessments |publisher=Australian Government |date=28 September 2016 |access-date=25 March 2018 }}</ref> | est = | area = 36295.97 | area_footnotes = <ref name=GA/> | coordinates = {{coord|33|56|53|S|150|45|36|E|region:AU-NSW_type:landmark_source:kolossus-dewiki|display=title,inline}} | lga = | lga2 = | lga3 = | lga4 = | stategov = | fedgov = | logo = | url = | rainfall = 650-1300 | rainfall_footnotes = <ref name=bioregionalassessment/> | near-n = North Coast | near-ne = ''Tasman Sea'' | near-e = ''Tasman Sea'' | near-se = ''Tasman Sea'' | near-s = South Coast | near-sw = Australian Alps | near-w = South Eastern Highlands | near-nw = South Eastern Highlands | near = }}
The '''Sydney Basin''' is an interim Australian bioregion and is both a structural entity and a depositional area, now preserved on the east coast of New South Wales, Australia and with some of its eastern side now subsided beneath the Tasman Sea. The basin is named for the city of Sydney, on which it is centred.
Around {{convert|5000|m}} thick, the Sydney Basin consists of Permian and Triassic sedimentary rocks, which stretches from Newcastle in the north to Batemans Bay in the south, and west to the Great Dividing Range. The basin is also home to the major centres of Newcastle, Gosford, and Wollongong, as well as the state capital of Sydney, and contains economically significant reserves of coal.
Sydney's famous harbour and the sculptured cliffs of the Blue Mountains are signature formations of relatively hard upper strata of sandstone. The basin contains the UNESCO World Heritage-listed Greater Blue Mountains Area.<ref>Herbert, C., 1983. Geology of the Sydney Basin 1: 100 000 sheet 9130. New South Wales Department of Mineral Resources, Sydney.</ref>
==Geography== According to NSW Primary Industries, the basin extends through approximately {{convert|350|km}} of coastline from Newcastle in the north to Durras Lake (near Batemans Bay) in the south. From Durras Lake the western boundary continues in a line through Lithgow to around Ulan (near Mudgee). To the north the boundary extends {{convert|120|km}} along the Liverpool Range to a point {{convert|80|km}} north of Muswellbrook, and then runs {{convert|200|km}} back to the coast at Newcastle. To the east the basin continues to the edge of the continental shelf.<ref name=dpi_sbsd>{{cite web |url=http://www.dpi.nsw.gov.au/__data/assets/image/0007/96847/20758.gif |title=Sydney Basin Structure Diagram |publisher=NSW Primary Industries |access-date=24 March 2008 }}</ref>
The total area of the basin is approximately {{convert|44000|km2}} onshore plus {{convert|5000|km2}} offshore.<ref name=dpi_sbgo>{{cite web |url=http://www.dpi.nsw.gov.au/minerals/geological/overview/regional/sedimentary-basins/sydbasin |title=Development of the Sydney Basin |publisher=NSW Primary Industries |access-date=24 March 2008 }}</ref> The centre of the basin is located around {{convert|30|km}} west of the Sydney central business district at Fairfield, though only the youngest Triassic (middle Triassic) rocks are exposed in the Sydney area.<ref name=am_dotsb>{{cite web |url=http://www.amonline.net.au/geoscience/events/event-sydney-basin.htm |title=Sydney Basin – Geological Overview |publisher=Australian Museum |access-date=24 March 2008 }}</ref>
The Australian Government Department of Climate Change, Energy, the Environment and Water classifies the basin as an interim Australian bioregion consisting of {{convert|3629597|ha}}.<ref>{{cite web |url=http://www.environment.gov.au/parks/nrs/science/bioregion-framework/ibra/index.html |title=Australia's bioregions (IBRA) |work=Department of Sustainability, Environment, Water, Population and Communities |publisher=Commonwealth of Australia |year=2012 |access-date=13 January 2013}}</ref> Meanwhile, according to Geoscience Australia the basin covers {{convert|64000|km2}}, of which {{convert|36000|km2}} is onshore and {{convert|28000|km2}} is offshore with water depths of up to {{convert|4500|m}}.<ref name=GA>{{cite web |url=http://www.ga.gov.au/scientific-topics/energy/province-sedimentary-basin-geology/petroleum/offshore-eastern-australia/sydney |title=Sydney Basin |work=Geoscience Australia |publisher=Australian Government |date=2018 |access-date=25 March 2018}}</ref> Another Australian Government agency classifies that the basin covers approximately {{convert|25000|km2}}.<ref name=bioregionalassessment/>
==History and formation== [[File:View_from_North_Head_Lookout_-_panoramio.jpg|thumb|left|260px|The majority of Sydney Basin is raised sandstone plateau, with the exception being the Hunter Valley and the low-lying Cumberland Plain.]] {{See also|Geology of New South Wales}} Minor igneous activity took place in the basin during the Early Jurassic (i.e. 210 million years ago), Late Mesozoic (i.e. 100–90 million years ago) and Cenozoic eras (i.e. 65 million years ago). The Early Jurassic activity resulted in the formation of the Prospect dolerite intrusion in Prospect Hill.<ref>Jones, I., and Verdel, C. (2015). Basalt distribution and volume estimates of Cenozoic volcanism in the Bowen Basin region of eastern Australia: Implications for a waning mantle plume. Australian Journal of Earth Sciences, 62(2), 255–263.</ref> Although Jurassic sedimentation is not observed in the Sydney Basin, there are Jurassic volcanic breccia pipes (diatremes).<ref name="Johnson1989">{{cite book|author=Robert Wallace Johnson|title=Intraplate Volcanism: In Eastern Australia and New Zealand|url=https://books.google.com/books?id=4NBOn7ecZeAC&pg=PA4|date=24 November 1989|publisher=Cambridge University Press|isbn=978-0-521-38083-6|pages=4–}}</ref>
The Sydney Basin is part of a major basin system that extends over {{convert|1500|km}} from the Bowen Basin in Queensland through to the {{NSWcity|Gunnedah}} Basin in NSW. Onshore, the basin contains {{convert|4500|m}} of Permo-Triassic clastic sediments, while the offshore basin contains {{convert|6000|m}} of sediments. The basin overlies the Lachlan Fold Belt and Late Carboniferous volcanoclastic sediments. The basin formed during extension in the Early Permian, with half-graben infilled with the Dalwood and Talaterang Groups. Foreland loading followed with the compression of the Currarong Orogen in the Early Permian.<ref>Crawford, E. A., Herbert, C., Taylor, G., Helby, R., Morgan, R. & Ferguson, J., 1980 – 15. Diatremes of the Sydney Basin, p. 295-323., In Herbert, C. & Helby, R. (Editors.) – A Guide to the Sydney Basin. Geological Survey of New South Wales, Bulletin 26.20(1), 25–33.</ref>
Late Permian uplift associated with the New England foreland loading phase resulted in the formation of depocentres with the northeast Sydney Basin with best preserved marine fossils. These depocentres filled with pyroclastic and alluvial-paludual sediments of the Newcastle Coal Measures. In the Triassic, uplift of the offshore basin resulted in reworking of Permian sediments in fluvial environments. The basin underwent a final phase of deformation (thrusting) in the Middle Triassic where it was uplifted to become dry land, with an erosion occurring from this time to the present.
Extension and breakup in the Tasman Sea beginning in the Late Cretaceous resulted in the current structural boundaries of the basin's eastern margin. In the south and west the Basin finishes in cliff lines formed on sandstones and conglomerates of the primary Permian sediments, with waterfalls being widespread on all escarpments.<ref name=GA/>
===Timeline=== [[File:Prospectdolerite.jpg|thumb|220px|The Prospect dolerite intrusion in Greater Western Sydney]] *'''Permian:''' 299–252 million years ago; The settling and evolution of swamp forest, which would shape tremendous coal measures. To note, Australia's coal is younger than the Carboniferous coal of the Northern Hemisphere. *'''Early Triassic:''' 252–247 million years ago; dark, high-carbon Narrabeen shales can be viewed at Long Reef and Narrabeen. The Australian continent was part of the Gondwana supercontinent and the Sydney basin was situated within a depositional basin. The Ashfield Shale, which overlies the Sydney sandstone, indicates an alteration in river flow direction and its depositional style. That was when southeast-streaming rivers deposited fine grained sands and muds within a river delta which settled on a shallow sea's shore.<ref name = SOP>[https://www.sopa.nsw.gov.au/About-Us/History-and-Heritage/Geological-History Geological History] by Sydney Olympic Park.gov.au</ref> *''' Mid Triassic:''' 247–235 million years ago; A monolithic river with its beginnings to the south-west of Broken Hill, in what was Antarctica at that time,<ref>Jones, I., Verdel, C., Crossingham, T., and Vasconcelos, P. (2017). Animated reconstructions of the Late Cretaceous to Cenozoic northward migration of Australia, and implications for the generation of east Australian mafic magmatism. Geosphere, 13(2), 460–481.</ref> had its delta in what was the Sydney Basin. It is around five times bigger than the Amazon River. There is predominance of silica sand with minor lenses of clay. Plant fossils are scarce, but some fish fossils are found in the clay lenses. *'''Late Triassic:''' 235–201 million years ago; As the river slowed with the erosion of the mountain range, finer shales were laid out. This strata is rich in seed fern fossils. *'''End of Triassic:''' 201 million years ago; Ascension and shifting at the Lapstone fault, with the Blue Mountains rising and the western Sydney plain descending to a flat land and Sydney CBD jousting upward. *'''Jurassic:''' 201–145 million years ago; Erosion, with Ashfield Shales remaining on top. Deep V-shaped valleys in the Hawkesbury sandstone. Fracturing, volcanic intrusions form Prospect Quarry, Mount Tomah, Mount Wilson and Hornsby Quarry.<ref>Wilshire: Wilshire, H.G., The Prospect alkaline diabase-picrite intrusion, New South Wales, Australia in Journal of Petrology, Vol. 8 (1), pp 97–163, 1967.</ref> *'''Cainozoic (Tertiary and Quaternary):''' 66 million years to present; Gondwana broke up around 40 to 60 million years ago. That is when the Australian continent started to form where it drifted and rifted, where Sydney's rocks were elevated, canted and then later eroded by the weather. Sydney's sedimentary rocks were shaped into a landscape that was defined by bedrock valleys exposed into a raised plateau. Sydney's largest rivers, such as the Hawkesbury, Parramatta, Georges and Hacking Rivers eroded the region's deepest valleys. In this period, the Ashfield Shale got weathered to create a flatter landform with low, undulating topography and reasonably fertile soils, which heavily contrasted the plateaus, cliffs and gorges on the sandstone areas in the Sydney Region.<ref name = SOP/> The Botany Bay Basin was also developed at that time, which is infilled with sand. *'''Late Pleistocene:''' 12 000 years ago; Submerging the Sydney river valleys with the post-glacial sea level rise where estuaries and deep harbours were formed.<ref>Branagan, D.F., and Packham, G.H., 2000. Field Geology of New South Wales. 3rd Edition. New South Wales Department of Mineral Resources, Sydney.</ref>
==Hydrology== The hydrology of the basin comprises three main drainage basins as defined by the New South Wales Office of Water that lie entirely or mainly within the geography of the basin; namely the Central Coast catchment, the Hawkesbury-Nepean catchment, and the Sydney Metropolitan catchment.
In addition, some of the rivers of the Hunter-Central Rivers catchment and the Southern Rivers catchment also lie mainly in the basin. In the Hunter-Central Rivers catchment, the Hunter River sub-catchment forms the northern boundary of the basin. In the Southern Rivers catchment, the Illawarra sub-catchment and the Shoalhaven sub-catchment forms the southern boundary.
==See also== {{stack|{{portal|New South Wales|Geography|Geology}}}} * Cumberland Plain * Geography of Sydney * Geology of Australia * Illawarra Coal Measures * Mittagong Formation * Narrabeen group * Sydney sandstone * Wianamatta Shale * Tasman Abyssal Plain
== References == {{Reflist}}
=== Attribution === {{CC-notice|cc=by4|url=http://www.ga.gov.au/scientific-topics/energy/province-sedimentary-basin-geology/petroleum/offshore-eastern-australia/sydney|author=Commonwealth of Australia (Geoscience Australia) 2018.,}} (accessed on 25 March 2018).
== External links == * [http://www.nationalparks.nsw.gov.au/npws.nsf/Content/Sydney+Basin+Bioregion NSW National Parks and Wildlife Service – Sydney Basin Bioregion] * [http://www.dpi.nsw.gov.au/minerals/geological/overview/regional/sedimentary-basins/sydbasin NSW Department of Primary Industries – Sydney Basin – Geological Overview] * [http://www.water.nsw.gov.au/Water-management/catchments/default.aspx NSW Office of Water – Basins and catchments]
{{Interim Biogeographic Regionalisation for Australia (IBRA) |state=autocollapse}} {{Rivers of the Sydney Basin |state=autocollapse}}
Category:Biogeography of New South Wales Category:Eastern Australian temperate forests Category:Geology of New South Wales Category:IBRA regions Category:Sedimentary basins of Australia