Molluscan biogeography and biostratigraphy of the Tertiary of southeastern Australia

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Abstract
A zonation based on Mollusca for the Tertiary of southeastern Australia (Murray, Otway, Bass and Gippsland Basins) is proposed, consisting of a sequence of 18 informal assemblage zones ranging in age from Middle Paleocene to Late Pliocene. The assemblages are defined using the molluscan fauna of a typical locality which gives the name to the assemblage. Factors such as larval dispersal, molluscan distribution, provincial differences, facies variation and the nature of the Tertiary sequence, which affect correlation by means of molluscs, are discussed and have been taken into account when formulating the zones. Composition of the molluscan fauna of the southeastern Australian Province has been analysed under four headings, Australian-New Zealand element, Tethyan Indo-Pacific element, Endemic element, and Cosmopolitan element. The relative proportions of each element fluctuated with time and it is concluded that the Tethyan Indo-Pacific and Endemic elements increased with time at the expense of the Australian-New Zealand and Cosmopolitan elements.