Holocene sedimentology of Old Man Lake, south eastern South Australia

Abstract

Old Man Lake lies nestled within an inter-dunal hollow of the Robe Range, 13 km south of Robe. Three lithologically distinct Holocene sequences are observed in cored sections of the lake. A basal-dune sequence which is overlain by an estuarine sequence. Following the estuarine sequence is a lacustrine sequence. The sequence stratigraphy correlates to Holocene sea level change.

The occurrence of C25 highly branched isoprenoids (HBI) are characteristic of marine diatoms. Their observation in Old Man Lake sediments coupled with their appearance in Hamelin Pool (Shark Bay-Western Australia), may imply a restricted marine, rather than a marine, environment. Assuming a restricted marine environment, C25-HBI may be used in the extrapolation of Holocene sea level changes, reflected in core sequence stratigraphy.

Fossil thrombolites characterise the eastern margin of Old Man Lake. The bryozoa, C. aciculata and green luminescing aragonitic gastropods are closely associated with the thrombolites. These three features may collectively imply a greater ground-water inflow operating in the past. Wetter conditions are known to have prevailed 6900 to 5000 years ago (Dodson 1974).