Wollemi National Park - Geology

Geology

This park is located on the western edge of the Sydney Basin. It sits on four strata of sedimentary rock; the Narrabeen and Hawkesbury sandstone and shale, the Illawarra and Singleton Permian coal measures and the Wianamatta shales. The strata at this area of the Sydney Basin have an upwards tilt to the north-west. Throughout most of the park the Hawkesbury and Wianamatta series have been eroded away exposing the Narrabeen group. The landscape of the park is dominated by deep valleys, canyons, cliffs and waterfalls, formed by the weathering of the sandstone and claystone the Narrabeen group consists of. The parts of the park that lie on the Narrabeen and Hawkesbury sandstones generally have shallow soil with low nutrient levels while areas that lie on the Wianamatta shale usually have deeper and more nutrient rich soils allowing for a greater diversity of plant life. The coal measures are visible beneath cliff lines along river valleys. This layer is generally rich in nutrients and weathers to form deep clay loams. Tertiary basalt is common in the north west of the park. Basaltic peaks include Mount Coriaday, Mount Monundilla and Mount Coricudgy, the highest peak in the northern Blue Mountains. In some location the basalt in the core of extinct volcanoes has eroded faster than the surrounding sandstone.

The Wollemi National Park is key in maintaining the quality of many tributary rivers to the Hawkesbury River and Goulburn-Hunter River catchments. The national park incorporates rivers such as the Wolgan River, Colo River and Capertee River which arise from outside the park. The Colo River is regarded as the last unpolluted river in New South Wales because the majority of it flows through the Wollemi National Park.