Fig. 4: Conceptual representation of the pre-MPT and modern eastern Australia coastline.

a, Pre-MPT period when Fraser Island was not present or, more likely, notably reduced in size. Longshore drift of sediment under dominant southeast winds was largely unimpeded. North of Fraser Island, quartz-rich sands would have invaded the inner shelf and prevented widespread coral reef formation. b, Modern southeastern Queensland coastline with Fraser Island blocking and re-directing quartz sands off the continental shelf edge14. Quartz-rich sands are reduced and carbonate-rich sediments dominate north of Fraser Island, which allowed coral reef formation. The white star represents the location of Lady Elliot Island, the southernmost emergent coral reef. Data from ref. 56 (bathymetry data), Esri, DigitalGlobe, GeoEye, i-cubed, USDA FSA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo and the GIS User Community.