ROCK LAYERS OF THE SYDNEY BASIN

Each layer of rock in the Central Coast cliffs tells a story about the landscape at the time when the rock layers were deposited. The Diagram below shows a north-south cross-section of the Sydney Basin from Newcastle to Wollongong The oldest layers are at the bottom, but because the Sydney Basin near Bouddi Peninsula has tilted down to the south-west, the base of each cliff is older as you travel north. Travelling south, you can see successively younger layers on the clifftops. The photographs show the tilting of the rock layers at Bullimah Headland in Bouddi National Park. The earliest shaly layers underlying the Central Coast contain marine fossils. This points to a time when a rising sea level formed a north-south seaway in the Sydney-Bowen Basin. Below you can see specimens of siltstone with fossils from Mulbring, due west of Newcastle. Link to Fossils As the sea level fell the area was transformed into a coastal plain. Deposits of alluvial gravels from the New England area from the north-east alternated with finer-grained sandstone and shale, some of which came from explosive volcanoes.