Multiproxy palaeoeology reconstruction of the mid-Holocene to present salinity, marine incursions and flow regime of Lake Alexandrina and the Goolwa channel, South Australia.

Skinner, R; Fluin, J; Cann, J; Harrison, JJ

Multiproxy palaeoeology reconstruction of the mid-Holocene to present salinity, marine incursions and flow regime of Lake Alexandrina and the Goolwa channel, South Australia.

Date

2007-07

Authors

Publisher

Elsevier Ltd and the International Union for Quaternary Research (INQUA)

Abstract

Multiproxy palaeoecology techniques are used to reconstruct the mid-Holocene to present salinity, marine incursions and flow regime of Lake Alexandrina and the Goolwa channel, South Australia. Microfossils (foraminiferal, ostracoda and diatoms) are analysed in three sediment cores. Foraminiferal remains are used to reconstruct the frequency, duration, and spatial extent of marine incursions upstream through the Goolwa channel to Lake Alexandrina. Diatom analysis provides a quantitative reconstruction of salinity, while the ostracoda analysis is currently exploratory. Three C-14 AMS radiocarbon dates and eight Pb-210 dates for each of the three cores have been submitted for analysis. To support the flow-regime-reconstruction with quantitative data, grain size analysis is included. Preliminary data from the foraminiferal assemblage of core RS1 (taken from just above the Goolwa barrage) illustrates a substantial change in both grain size and presence of foraminifera at a core depth of 130 cm. This may represent a sedimentation rate of 2 cm/yr, since the placement of the Goolwa barrage in 1939. At depths between 130 cm and 0 cm the sediment is barren of foraminifera. Below 130 cm foraminifera are abundant; inner-shelf marine species, especially Elphidium crispum, are dominant from 130 cm to the bottom of the core (216 cm). Only three increments (140-144 cm; 164-168 cm; 174-182 cm) have very low foraminiferal counts (<100). The sediment at these depths is of a much finer grain size. For a majority of the time, it is likely that pre-river-regulation-flow rates of the Murray River were high enough to maintain an open mouth, allowing the mixing of marine and estuarine waters.

Keywords

South Australia, Salinity, Sediments, Quaternary period, Foraminifera, Diatoms

Citation

Skinner, R., Fluin, J., Cann, J., & Harrison, J. (2007). Multiproxy palaeoeology reconstruction of the mid-Holocene to present salinity, marine incursions and flow regime of Lake Alexandrina and the Goolwa channel, South Australia. Presentation to the International Union for Quaternary Research XVII Congress (INQUA) – “The Tropics: Heat Engine of the Quaternary”, 28th July – 3rd August 2007. Cairns, Australia: Cairns Convention Centre. In Quaternary International, 167-168, 390.