SEDIMENTARY ROCKS AND FOSSILS
Corals and coralline algae extract calcium carbonate from seawater, which they use to produce hard skeletons for protection. As these marine organisms die and crumble their fragments are ground up by the pounding action of waves and are wind-blown against the Island, forming beaches and dunes.
Over time, rainwater seeping through the sand has cemented the grains into a type of sandstone known as calcarenite. Around 25 percent of the Island, over much of what is the settlement area today, is in fact covered by this calcium carbonate-based sandstone.
Carbon dating of fossils in a number of the dune deposits suggests an age of 20,000 to 40,000 years, but it is believed that the calcarenite beach deposits behind Ned's Beach were formed in the last interglacial period around 130,000 years ago when sea levels were roughly the same as they are at present.
While these ancient beaches were forming, the now extinct horned turtle, Meiolania platyceps, was roaming Lord Howe Island. Its bones have been found as fossils in the soft calcarenite rock. Meiolania platyceps is one of a group of bizarre fossil turtles of prehistoric appearance, having horns on the skull, and a long tail with bony rings and a heavy terminal club. The meiolaniid group of turtles is known only from Southern Hemisphere locations - Lord Howe Island, New Caledonia, mainland Australia and Argentina.