The figure shown above is an extract from the geological map of the Sydney area area (SI 56-05) around Gosford. This area is part of the Sydney Basin, which extends from Newcastle in the north, beyond Woolongong in the south and to Katoomba in the west. The basin is the green area surrounding Sydney as shown on the image below. The darker blue on the above image (TRng) is the Gosford Formation which is at the top of the Narrabeen Group. The lighter blue Hawkesbury Sandstone (TRh) sits on top of that. These have been classified as Triassic. Small red areas (Tv) are basaltic volcanic remnants, likely eroded volcanic plugs. Yellow areas (Qa) are recent, localized sediment deposits.The Triassic sediments were deposited rapidly during Noah’s Flood as the floodwaters were rising. They display lots of evidence of the the huge water flows that were involved in their deposition at that time.
For example, the deep cuts through the sandstone along the freeway between Sydney and Newcastle show sandstone strata, multiple metres thick, with much evidence of fast-flowing water, such as cross bedds and rip-up clasts. Dr Patrick Conaghan, Senior Lecturer at the School of Earth Sciences at Macquarie University at the time, interpreted the conditions under which the sand was deposited for some of these sediments, describing a wall of water up to 20 m (65 feet) high and 250 km (150 miles) wide coming down from the north at enormous speed.
The rocks of the Gosford area are part of a larger area of geological relationships. They were deposited as part of a series of geological processes that occurred during the biblical Flood, processes that built the eastern side of continental Australia. For details of these processes see The Geological History of the Sydney area, Australia, from a Biblical Flood Perspective.