Capricorn Basin

Location Map

Map of Eastern Australia showing the Capricorn Basin in relation to Australia

Map of Eastern Australia showing the Capricorn Basin in relation to Australia
© Geoscience Australia

Basin Details and Geological Overview

The Cretaceous to Cainozoic age Capricorn Basin is a northwest to southeast elongate basin located off the southeast coast of Queensland. Water depths range from 3500 metres in the southeast where sediments are up to 4000 metres thick, to 100 metres at the northern basin margin. The basin is poorly explored, with only three wells drilled (all dry) and no significant exploration activity since 1968.

There are two possible models for the tectonic evolution of the Capricorn Basin. One model is that the Capricorn Basin formed during the Late Jurassic-Early Cretaceous from the same extensional event that formed the Townsville and Queensland Basins farther north. An alternative model is that the Capricorn Basin formed in the Late Cretaceous as a failed rift arm at the northern end of the Tasman rift system. This second model divides the basin fill into five basin phases: Late Cretaceous to Early Palaeocene rift phase; Late Palaeocene to Early Eocene late rift phase; Early to Middle Eocene early thermal sag phase; Middle to Late Eocene post-tectonic structural reactivation phase; and a Late Oligocene to Recent late sag/rapid regional subsidence phase. The stratigraphy of the Capricorn Basin consists of continental rift-phase conglomerates and red beds of Late Cretaceous to Early Palaeocene age.

These are overlain by Eocene age mixed marine and continental quartzose sandstones and lignites, in turn overlain by a thick marine sequence of Late Oligocene to Recent age limestone and marl. Although potential reservoirs and traps appear to be present, the petroleum prospectivity is considered low due to a lack of evidence for burial and thermal maturity of potential source rock intervals and by the absence of a proven regional seal.

In addition, most of the Capricorn Basin is located beneath the Great Barrier Reef Marine Park in which petroleum exploration is prohibited.

Summary Table

CAPRICORN BASIN

State(s)

Queensland

Area (km2)

Offshore

45,000

 

Onshore

0

Maximum thickness (m)

5700

Age Range

Early Cretaceous to Cainozoic.

Basin

Overlies

Palaeozoic metasediments of the Tasman Fold Belt

 

Underlies

-

 

Subdivisions

 

 

Other

Separated from the Maryborough Basin to the south-west by a basement high, the bunker ridge.

Indicators

Knowledge

Regional geophysical and some well data.

 

Basin type

Divergent margin failed rift

 

System(s)

Capricorn

 

Water Depth (m)

100 - 3500

Exploration

Status

Frontier

 

Wells

2 petroleum exploration.

 

Seismic line-km

Not determined.

 

Discoveries

Nil

 

Shows

Nil

 

HC evidence

-

Geology

Source(s)

Cretaceous rift-fill shales and coals; Paleogene sources are possible in the deepest parts of the basin.

 

Reservoirs

Cretaceous to Paleogene sandstones.

 

Seals

Intraformational shales.

 

Trap types

Structural; stratigraphic pinchout also possible.

 

Palaeogeographic summary

Cretaceous: continental alluvial and fluvial rift-fill;
Paleogene: various fluvial, deltaic, coastal and shelf environments, depending upon age and location; Neogene: inner shelf to slope carbonates.

Timing

Oil generation

Neogene if generation has occurred.

 

Gas generation

Neogene if generation has occurred.

 

Trap formation

Eocene (structural reactivation)

 

Other key times

Rapid subsidence has occurred since the Pliocene.

Other important information

Most of the Capricorn Basin lies within the Great Barrier Reef Marine Park, in which petroleum exploration activity is prohibited.

Geoscience Australia products available

Hill, 1994. Record 1994/1.

Stratigraphy

Capricorn Basin Stratigraphy

Stratigraphic correlation chart
© Geoscience Australia

Regional Cross-sections

Capricorn Basin Regional Cross Section

Capricorn Basin Regional Cross Section (Hill 1994)
© Geoscience Australia

Key References

Author Year Title
Benbow, D.D. 1980 The petroleum prospects of the Great Barrier Reef region. The Australian Petroleum Exploration Association (APEA) Journal, 20(1), 159-175
Bureau of Resource Sciences 1996 Oil and Gas Resources of Australia, 1995
Chaproniere, G.C.H., Pigram, C.J., Symonds, P.A. and Davies, P.J. 1990 The northeast Australian margin and adjacent areas – a biostratigraphic review and geohistory analysis. Bureau of Mineral Resources, Australia, Record 1990/7
Ericson, E.K. 1976 Capricorn Basin. Economic geology of Australia and Papua New Guinea. Australasian Institute of Mining and Metallurgy, 464-476
Gray, A. R. G. 1990 A summary of the petroleum potential of the offshore Queensland continental margin. Queensland Government Mining Journal, v.91, 489-494
Hill, P.J. 1992 Capricorn and northern Tasman Basins; structure and depositional systems. Exploration Geophysics, Vol. 23, pp. 153-161.
Hill, P.J. 1994 Geology and geophysics of the offshore Maryborough, Capricorn and northern Tasman Basins: results of AGSO Survey 91. Canberra, Australian Geological Survey Organisation, Record 1994/1
Palmieri, V. 1971 Tertiary subsurface biostratigraphy of the Capricorn Basin. Geological Survey of Queensland, Australia, Report 52
Palmieri, V. 1974 Correlation and environmental trends of the subsurface Tertiary Capricorn Basin. Geological Survey of Queensland, Australia, Report 86