Sandstone Cliffs of the Hawkesbury River Valley

April 11, 2016


Photographer: Phil Lachman
Summary Author: Phil Lachman
This picture shows one of the amazing vertical sandstone cliffs of the Hawkesbury River valley at Mooney Mooney, New South Wales, Australia. The Lower Hawkesbury River Estuary is a drowned river valley that cut into Hawkesbury sandstone bedrock during the ice ages when ocean levels were much lower than they are now. It's part of the Sydney Basin, created in the Permian and Triassic periods (200-250 million years ago), consisting almost entirely of horizontally bedded sedimentary rocks.
The interpretation now generally accepted for this sheet sandstone (up to 950 ft or 290 m thick) is that an ancient, large, braided river system is its origin. Hawkesbury Sandstone was uplifted at the end of the Triassic. Following this, the uplifted sandstone bedrock was eroded over millions of years to form deep V-shaped valleys bordered by steep cliffs. These valleys were then drowned during the last sea level rise (about 20,000 to 7,000 years ago) to form the changed valley shape that we see today.

The rugged sandstone country surrounding the lower river is rich with evidence of Aboriginal culture; axe grinding grooves, wells and engravings. In Dharug National Park more than 10,000 engravings have been recorded. Photo taken on March 27, 2016.
Photo Details: Camera Model: Canon EOS 50D; Lens: 18-250mm; Focal Length: 73.0mm; Aperture: ƒ/9.0;
Exposure Time: 0.0010 s (1/1000); ISO equiv: 640.