Sydney Basin

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 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 and Wollongong, 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.
Geography.
According to NSW Primary Industries, the basin extends through approximately 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 along the Liverpool Range to a point north of Muswellbrook, and then runs back to the coast at Newcastle. To the east the basin continues to the edge of the continental shelf.
The total area of the basin is approximately onshore plus offshore. The centre of the basin is located around west of the Sydney central business district at Fairfield, though only the youngest Triassic (middle Triassic) rocks are exposed in the Sydney area.
The Australian Government Department of the Environment and Energy classifies the basin as an interim Australian bioregion consisting of . Meanwhile, according to Geoscience Australia the basin covers , of which is onshore and is offshore with water depths of up to . Another Australian Government agency classifies that the basin covers approximately .
History and formation.
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. Although Jurassic sedimentation is not observed in the Sydney Basin, there are Jurassic volcanic breccia pipes (diatremes).
The Sydney Basin is part of a major basin system that extends over from the Bowen Basin in Queensland through to the Basin in NSW. Onshore, the basin contains of Permo-Triassic clastic sediments, while the offshore basin contains 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.
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.
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.
References.
Attribution.
 (accessed on 25 March 2018).