EVIDENCE FOR ACTIVE TECTONICS ALONG THE AUSTRALIAN PASSIVE MARGIN: QUATERNARY MARINE TERRACES OF WARATAH BAY, VICTORIA

Located within the interior of the Australia-Indian plate, the continental margin of Australia is generally described as a classic passive margin. However, along the southeastern coast, historical seismicity and a variety of anomalous geologic and geomorphic features indicate active crustal deformation. At Waratah Bay, Victoria, a prominent flight of at least six uplifted marine terraces wraps around the rocky headland of Cape Liptrap and extends northeastward toward the Yanakie isthmus inland of Wilson’s Promontory. Wave cut platforms developed across Paleozoic marine sedimentary bedrock are covered by Quaternary deposits of silicic beach and dune sands, angular quartz gravels, and estuarine silt and clay horizons. The spatial distribution of the terraces was defined through field mapping, aerial photo analysis, and GPS surveying. A series of topographic profiles surveyed across the terraces show that tread elevations decrease toward the northeast away from Cape Liptrap. Uplift and tilting of these terraces may reflect Quaternary slip along the NE trending Waratah Fault. Active crustal deformation in this region may result from denudation and isostatic flexure, variations in the crust/mantle thermal structure, and/or far-field intraplate stresses.