The Styx Basin is a small Early Cretaceous intracratonic sag basin straddling the central Queensland coast near the town of St Lawrence. The basin covers an area of approximately 300 km2 onshore and 500 km2 offshore, under water depths of up to 100 metres. The maximum known thickness of sediments is 387 metres from a coal exploration bore, but magnetic data suggest a thickening offshore.
The Styx Basin probably developed by subsidence of the Strathmuir Synclinorium, an older feature containing Permian Bowen Basin strata. Styx Basin sediments lap onto Permian strata in the west, but are faulted against them in the east. The basin plunges gently to the north under the waters of Broad Sound but the general dip of the Styx Coal Measures sequence is to the east. In the southern part of the basin, it is bounded to the east by a post-depositional high-angle reverse fault. Adjacent to this fault, the Cretaceous sediments are folded and faulted. The known strata of the basin are referred to as the Styx Coal Measures and consist of quartzose, calcareous, lithic and pebbly sandstones, pebbly conglomerate, siltstone, carbonaceous shale and coal. The environment of deposition was freshwater, deltaic to paludal with occasional marine incursions.
The coals at the base of the Styx Coal Measures lie within the oil window and could potentially generate petroleum, however, there is no known evidence that generation of oil or gas has occurred from this succession. The offshore Styx Basin lies entirely within the Great Barrier Reef Marine Park, in which petroleum exploration activity is prohibited. Coal was mined in the first half of the 20th century with a total production of 1.76 million tonnes, but reserves are currently not of economic importance.