SEA LEVEL CHANGES IN THE NEOGENE OF SOUTHERN VICTORIA

Abstract

The distribution and lithology of marine sediments in southern Victoria are related to climatic events and the associated sea level changes. The most extensive transgression on the northern (onshore) margin of the southern Victorian Tertiary basins occurred late in the Early Miocene, with widespread deposition of calcareous muds and localised calcarenites with Lepidocvclina. Shallowing at approximately 14 m.y. affected all southern Victoria, initiating lithological changes in the Otway and Port Phillip Basins, and coinciding with erosion in the Gippsland Basin. Throughout the Late Miocene the grain size of sediments tended to increase and cross-bedded calcarenites became more common, consistent with shallowing deposition and sea withdrawal. By approximately 6 m.y., near the end of the Late Miocene, the sea had completely withdrawn from the onshore areas of southern Victoria.

Pliocene and Pleistocene outcrops are scattered and thin, and marine beds are exclusively of nearshore and shallow deposition. For much of this period sea level was lower than at present. High levels in the Pliocene are indicated at approximately 5 m.y. and 3.5 m.y. High sea levels, associated with the rapid alternation of glacial and interglacial periods which typify the Pleistocene Epoch, were initiated late in the Pliocene, close to 2 m.y.

Changes to the planktonic foraminiferal faunas parallel the sedimentological responses to sea level change. These suggest that palaeoclimatic events were the main controlling factor in Neogene sea level changes in southern Victoria, and allow differentiation of the eustatic and tectonic controls on sedimentation.