Surat Basin

Basin Details and Geological Overview

The large, mature, intracratonic, Early Jurassic to Albian (Early Cretaceous) Surat Basin occupies 300 000km² of central southern Queensland and central northern New South Wales. It has a maximum sediment thickness of 2500 metres and deposition was relatively continuous and widespread. Deposition in the basin commenced with the onset of a period of passive thermal subsidence of much of eastern Australia. During the Early Jurassic, deposition was mostly fluviolacustrine, while by the Middle Jurassic coal swamp environments predominated over much of the basin, except in the north where fluvial sedimentation continued.

Towards the end of the Middle Jurassic, fluvial deposition again predominated and continued until the earliest Cretaceous. A marine transgression followed, depositing paralic and marine sediments and reaching its peak in the Aptian. The subsequent regression caused a fairly abrupt return to fluvial, lacustrine and paludal environments before sedimentation ceased in the Aptian. About 100 hydrocarbon accumulations have been discovered in the Surat Basin, of which about half are producing fields. Most accumulations are reservoired in Early Jurassic sands, with occasional gas occurrences in the Middle and Late Jurassic, but all are sourced from the Permian nonmarine sediments of the underlying Bowen Basin. Proven plays comprise mostly low amplitude anticlinal closures occasionally associated with thrust faulting and drapes over basement highs. Because the basin is largely flat-lying and sedimentation widespread and relatively uniform, other types of traps are unlikely to be important.

Key References