Sydney Basin

Last updated:10 October 2022

Basin Details and Geological Overview

The Permo-Triassic Sydney Basin straddles Australia's central eastern coast in New South Wales. The basin covers 64 000km2, 36 000km2 onshore and 28 000km2 offshore under water depths of up to 4 500 metres. The Sydney Basin is part of a major basin system that extends over 1 500km from the Bowen Basin in Queensland through to the Gunnedah Basin in NSW. Onshore, the basin contains 4 500 metres of Permo-Triassic clastic sediments, while the offshore basin contains 6 000 metres 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. These depocentres filled with pyroclastic and alluvial-paludal 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. Extension and breakup in the Tasman Sea beginning in the Late Cretaceous resulted in the current structural boundaries of the basin's eastern margin.

Over 100 wells have been drilled in the onshore Sydney Basin, although no wells have yet been drilled offshore. The onshore basin contains rich coal deposits with associated natural gas and minor oil shows. The geochemistry of oil shows indicate a terrestrial source from a clay-rich environment, although not associated with the coal facies. The main trap types are anticlinal and overthrust, with some structural reactivation during Tasman Sea rifting.

Basin Summary Table

State(s) New South Wales
Area (km2) Offshore 28 000
Onshore 36 000
Maximum thickness (m) > 6 000
Age Range Permian-Triassic (Jurassic and Cretaceous section believed to have existed but now eroded).
Basin Overlies Palaeozoic granites, volcanics and metasediments.
Underlies -
Subdivisions Informal 'West', 'Central', 'South' and 'North' subdivisions are used onshore.
Other Offshore structure quite different from onshore.
Indicators Knowledge Detailed field scale geophysical and well data onshore; regional geophysical data only offshore.
Basin type Convergent margin foreland thrust loaded basin.
System(s) Gondwanan.
Water Depth (m) 0-4 000
Exploration Status Frontier (offshore).
Wells 0 offshore, 115 onshore petroleum exploration wells.
Seismic line-km Sparse 2D regional coverage offshore.
Discoveries Nil
Shows Widespread oil and gas shows have been encountered throughout the section.
HC evidence Active petroleum system (Maung and others, 1993).
Geology Source(s) Late Permian coal measures and marine shales.
Reservoirs Permian shallow marine to fluvial sands (but often affected by diagenesis); Triassic Narabeen Group has excellent reservoirs.
Seals Numerous Permo-Triassic intra-formational seals.
Trap types 1) Wrench related structures,
2) overthrust traps,
3) mild basin inversion features,
4) extension down to basement fault bound blocks,
5) sub-thrust traps,
6) stratigraphic traps,
7) extensional, combination traps.
Palaeogeographic summary Early Permian: dominantly marine; late Early Permian to Late Permian: dominantly fluvial, with coal measures; Triassic: dominantly fluvial but some marine and volcanics; Jurassic-Cretaceous: eroded.
Timing Oil generation Commenced Middle Jurassic to Early Cretaceous for Late Permian sources depending on location and amount of eroded section, late generation still occurring. A Late Cretaceous peak is probable.
Gas generation Early Cretaceous to present.
Trap formation Types 2, 4 and 5 Early Permian, type 1 Early Permian to Triassic, type 3 Late Permian, type 6 Late Permian to Triassic, type 7 Early Cretaceous.
Other key times Major Late Cretaceous erosion accompanied breakup between Australia and the Lord Howe Rise.
Other important information 1) The offshore basin lies under a while migration path for several months of the year;
2) The onshore basin includes large urban areas.
Geoscience Australia products available 1) Harrington and others, 1989;
2) Maung and others, 1997.
3) Cadman and others, 1998.

Key References

Author(s) Year Title
Alder, J.D., Hawley, S., Maung, T., Scott, J., Shaw, R.D., Sinelinikov, A. and Kouzmina, G. 1998 Prospectivity of the offshore Sydney Basin: A new prospective. The Australian Petroleum Production and Exploration Association (APPEA) Journal, 38(1), 68-91
Bembrick, C.S., Herbert, C., Scheibner, E. and Stuntz, J. 1973 Structural subdivisions of the New South Wales portion of the Sydney-Bowen Basin. Geological Survey of New South Wales, 116, 105-117
Bowman, H.N. 1981 Brief notes on the offshore coal potential of New South Wales. Geological Survey of New South Wales, Report GS 1981/372
Bradley, G.M., Yoo, E.K., Moloney, J., Beckett, J. and Richardson, S.J. 1985 Petroleum data package, Sydney Basin NSW. NSW Geological Survey Report GS 1985/004, 229
Brakel, A.T. 1986 Global sea level change as a method of correlating the Late Permian coal measures in the Sydney, Gunnedah and Bowen Basins, eastern Australia. BMR Journal of Australian Geology and Geophysics, 10, 79-116
Branagan, D., Herbert, C. and Langford-Smith, T. 1976 An outline of the geology and geomorphology of the Sydney Basin, Science Press, Department of Geology and Geophysics, University of Sydney
Cadman, S. J., Pain, L. and Vuckovic, V. 1998 Bowen and Surat Basins, Clarence Morton Basin, Sydney Basin, Gunnedah Basin and other minor onshore basins, Queensland, NSW and NT. Australian Petroleum Accumulations Report 11, Bureau of Resource Sciences, Canberra
Carey, S.W. 1969 Tectonic framework of the Sydney Basin. Abstracts for the 1st, 2nd, 3rd and 4th Symposia on Advances in the Study of the Sydney Basin. University of Newcastle, NSW, 53-59
Doyle, H.A., Underwood, R. and Polack, E.J. 1966 Seismic velocities from explosions off the central coast of New South Wales. Journal of the Geological Society of Australia, 13, 355-372
Eadington, P.J., Hamilton, P.J. and Bai, G.P. 1991 Fluid History Analysis - A New Concept for Prospect Evaluation. APEA Journal/Sydney Basin, 282-294
Evans P.R. and Migliucci, A. 1991 Evolution of the Sydney Basin during the Permian as a foreland basin to the Currarong and New England Orogen. Newcastle Symposium on the Advances in the Study of the Sydney Basin, University of Newcastle, Department of Geology, v.25, 22-29
Finlayson, D.M. and McCracken, H.M. 1981 Crustal structure under the Sydney Basin and Lachlan Fold Belt, determined from explosion seismic studies. Journal of the Geological Society of Australia, 28, 177-190
Gostin, V.A. and Herbert, C. 1973 Stratigraphy of the Upper Carboniferous and Lower Permian sequence, southern Sydney Basin. Journal of the Geological Society of Australia, 20, 49-70
Grybowski, D.A. 1992 Exploration in Permit NSW/P10 in the offshore Sydney Basin. APPEA Journal, 32, 251-263
Harrington, H.J. 1982 Keynote Address: Tectonics and the Sydney Basin. Abstracts for the 16th Symposium on Advances in the Study of the Sydney Basin, 15-19. University of Newcastle, NSW
Harrington, H.J., Brakel, A.T. and Hunt, J. 1983 Tectonic settings of central and eastern Australian Permian coal basins. 6th Australian Geological Convention, Geological Society of Australia, Abstracts 9, 278
Harrington. H.J., Brakel, A.T., Hunt, J.W., Wells, A.T., Middleton, M.F., O'Brien, P.E., Hamilton, D.S., Beckett, J., Weber, C.R., Radke, S., Totterdell, J.M., Swaine, D.J. and Schmidt, P.W. 1989 Permian coals of Eastern Australia. Bureau of Mineral Resources, Australia, Bulletin 231
Hawley, S.P., Glen, R.A. and Baker, C.Y. 1995 1:100,000 scale Newcastle Coal Field Regional Geology Map. NSW Department of Mineral Resources, Geological Survey of NSW
Herbert, C. 1987 Petroleum Prospectivity in the Sydney Basin. Newcastle Symposium on the Advances in the Study of the Sydney Basin, University of Newcastle, Department of Geology, v.21, 107-113
Maung, T.U., Alder, D., Shaw, R. and Hawley, S. 1997 Offshore Sydney Basin petroleum prospectivity bulletin. Petroleum Resources Branch, Bureau of Resource Sciences
Mayne, S.J., Nicholas, E., Bigg-Wither, A.L., Rasidi, J.S. and Raine, M.J. 1974 Geology of the Sydney Basin - A Review. Australian Bureau of Mineral Resources, v.149, 229
Middleton, M.F. 1989 Coal-Rank Trends of Eastern Australia in Permian Coal Basins. IN: Harrington, H.J. (Editor) 'Permian Coals of Eastern Australia', Bureau of Mineral Resources Bulletin 231, 333-352
Packham, G.H. (editor) 1969 The Geology of New South Wales. Geological Society of New South Wales Incorporated. Journal. Geological Society of Australia, 16(1). 654
Robertson Research (Aust.) Pty Ltd. 1981 Exploration Report, PEL 242,243,244. NSW Department of Mineral Resources Report PGR 1982/02
Shepherd, J. and Huntington, J.F. 1981 Geological fracture mapping in coalfields and the stress fields of the Sydney Basin. Journal of the Geological Society of Australia, 28, 299-309
Smyth, M. 1983 Hydrocarbon Source Rock in the Sydney and Gunnedah Basins. Advances in the Study of the Sydney Basin. Proceedings of the 17th Symposium, University of Newcastle
Tye, S.C, Fielding, C.R. and Jones, B.J. 1996 Stratigraphy and Sedimentology of the Permian Talaterang and Shoalhaven Groups in the southernmost Sydney Basin, NSW. Australian Journal of Earth Sciences (1996), v.43, 57-69