Penrith Explanatory Notes (1991)

Abstract

These notes accompany the Penrith 1:100 000 geological map sheet. The area described in the map and notes is in western Sydney and is thus important - with conflicting landuse pressures. Appendixes include information on geophysical surveys and boreholes. The geology in the Penrith 1:100 000 map sheet area occupies a roughly central position in the Sydney Basin. Rocks in the eastern part of the map area have relatively flat dips but the western part of the area includes the relatively steep dips associated with the Lapstone Monocline/Nepean Fault and Kurrajong Fault - separating the Cumberland Plain from the Blue Mountains Plateau. Although the Permian (and possibly latest Carboniferous) rocks of the Sydney Basin are present at depth and have coal and gas potential, the Triassic section is the main part preserved in the Penrith area. Rocks of the upper part of the Narrabeen Group, Hawkesbury Sandstone, (Mittagong Formation) and the Wianamatta Group have been mapped in the area - the Wianamatta Group being the most important (near-)surface unit (albeit with relatively poor outcrop characteristics). The rocks are mainly sandstones and shales of lacustrine origin. Younger units are Mesozoic (mainly) intrusions - especially the Prospect Picrite, diatremes and dykes. Cainozoic units include poorly consolidated sediments (some coarse, and some extensive). Resource exploitation has been extensive: coarse aggregate; fine aggregate; clay/shale; etc. Much of that material has either been worked out or is now unavailable. Soils and groundwater are also important resources in the area. Both natural and man-induced engineering factors and environmental considerations form part of the discussion - important in an area of riverine plains and extensive urbanisation.

Reference

Jones, D.C., and Clark, N.R., (eds), 1991. Geology of the Penrith 1:100000 Sheet 9030. 201 pp. New South Wales Geological Survey, Sydney.