According to NSW Primary Industries, the basin extends through approximately of coastline from Newcastle in the north to Durras Lake in the south. From Durras Lake the western boundary continues in a line through Lithgow to around Ulan. 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 rocks are exposed in the Sydney area. The Australian GovernmentDepartment 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.
Formation
Minor igneous activity took place in the basin during the Early Jurassic, Late Mesozoic and Cenozoic eras. 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. 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 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.
Timeline
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.
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, 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 Glossopterisfern 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.
Cainozoic : 66 million years to present; Development of the Botany Bay Basin, which is infilled with sand.
Late Pleistocene: 12 000 years ago; Submerging the Sydney river valleys with the post-glacial sea level rise.
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.
