Foraminiferal response to Holocene environmental changes of a tidal estuary in Victoria, southeastern Australia

The Holocene strata in the Anderson Inlet area in Victoria can be stratigra phically divided into four units, Unit I, Unit II, Unit III, and Unit IV. U nit I and Unit IV lack fossils and were deposited in non-marine, probably f luvial environments. Unit II and Unit III contain abundant foraminifera wit h molluscs, ostracods and bryozoans. Foraminiferal analysis suggests that U nit III was formed in a partially sheltered marine environment, while the h igh plankton content and relatively high diversity of benthic species in Un it II indicate that this unit was deposited in an open bay at water depths possibly less than 5 m. The foraminiferal data are integrated with radiocar bon dates to arrive at the following Holocene palaeoenvironmental history i n this area: (1) low alluvial plain stage (10,000-7000 yr B.P.); (2) open b ay environment stage (7000-5500 yr B.P.); (3) partially sheltered marine en vironment stage (5500-4500 yr B.P.); (4) alluvial plain and coastal lagoon environment stage (since about 4500 yr B.P.). The foraminiferal fauna show a clear response to these palaeoenvironmental changes. Globigerina bulloide s can be used as an indicator for cold water marine environments. The high concentration of this species in these middle Holocene sediments shows a st rong cold water influence on the coastal environments which reduced the eff ect of regional warm currents during this period. The Holocene palaeoenviro nmental changes in the area were controlled by the Holocene sea-level fluct uations associated with the deglaciation history during this period. Simila r integrated studies of shallow to marginal marine strata in southern Afric a, America and New Zealand will lead to a better understanding of Holocene relative sea-level change and the interplay between Holocene cold and warm water regimes in the Southern Hemisphere. (C) 2000 Elsevier Science B.V. Al l rights reserved.