Sedimentology, weathering, age and geomorphological significance of Tertiary sediments on the far south coast of New South Wales

Abstract

The age of the NSW coastal lowland from Tuross to the Victorian border can now be shown to be at least mid‐Tertiary. By this time the coastal plain had twice been partially blanketed by terrestrial sediments. Palaeomagnetic determinations on the more recent of these sedimentary accumulations, the Long Beach Formation, reveal a minimum depositional age of Early Miocene. Eustatic influences may be responsible for the aggradation of the Long Beach Formation and as a consequence the diversion of the lower Bega River from its former Tertiary valley. Marked differences in the pattern of weathering between the older sediments, the Quondolo Formation, and the inset Long Beach Formation are evident, with the former largely silicified and the latter ferruginized. Similarities to the Quondolo and Long Beach Formations in terms of their stratigraphic relationships, chronology and weathering styles are evident within other Tertiary sedimentary formations north along the coastal plain to Ulladulla.