GSV Report 95 - Port Campbell Embayment 1:100 000 map geological report
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Product description:Download The downloadable version of this report is supplied in PDF format (30.6MB). Abstract The Port Campbell Embayment in southwestern Victoria is part of the Cretaceous-Tertiary Otway Basin which overlies Palaeozoic bedrock. The basin, within the east-west Bassian structural zone extending across southern Victoria, resulted from the separation of Australia and Antarctica. This involved two main tectonic phases - an Early Cretaceous rift phase marked by rapid subsidence,and a Late Cretaceous-Tertiary post-rift or drift phase characterised by slower subsidence. Five groups make up most of the sedimentary fill of the basin; they represent major depositional cycles, and are generally separated by unconformities or disconformities. The Early Cretaceous Otway Group, a thick monotonous sequence of fluviatile sediments derived from andesitic to dacitic volcanic rocks, was deposited during the rift phase. The Late Cretaceous Sherbrook Group and the Tertiary Wangerrip, Nirranda and Heytesbury groups consist of continental, deltaic and shallow marine sediments laid down after the continents had started to drift apart. There was an increase in marine influence during several episodes of transgression and regression, especially after the Middle Eocene when the rate of seafloor spreading increased and the Southern Ocean opened rapidly. Compressive tectonic activity began in the Eocene and culminated in the Pliocene. A series of northeasterly trending folds was formed, the largest of which is the Crowes Anticline along the crest of the Otway Ranges. In the Pliocene much of the area was uplifted above sea-level, and the alluvial outwash plain of the Hanson Plain Sand blanketed a large area. It formed a peneplain which was later lateritised and dissected. The uplift was also responsible for the formation of the three main physiographic divisions. The Otway Ranges is an area of uplifted Otway Group; the coastal plain consists of dissected Tertiary sediments and adjoins the volcanic plain to the north. Extensive outpourings of basalt occurred in the late Tertiary to early Quaternary in the northern part of the area. The sharp southern limit of volcanics is due to monoclinal scarps which hindered the southward flow of basalt. A more recent phase of volcanic activity was of the explosive type with many maar volcanoes and scoria cones forming. Associated with these was the eruption of stony rise basalts from several centres. The Newer Volcanics were erupted onto a relatively flat and poorly drained area which has supported swamps, lakes and shoreline dunes up to the present day. The Otway Basin is currently of interest for oil and gas exploration. A small gas field near Port Campbell supplies Warrnambool with natural gas. Prospects for further discoveries are moderately good. The Late Cretaceous Waarre Formation has been the main target for exploration to date but deeper units such as the Pretty Hill Sandstone remain largely untested. Other important resources include groundwater and construction materials. Bibliographic reference Tickell, S.J., Edwards, J. & Abele, C., 1992. Port Campbell Embayment 1:100 000 map geological report. Geological Survey of Victoria Report 95. Related products:
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