ORIGIN AND EVOLUTION OF LAKE AINSWORTH, NORTHEASTERN NEW SOUTH WALES, AUSTRALIA: COASTAL FLUCTUATIONS IN THE SOUTHERN HEMISPHERE

Lake Ainsworth is a freshwater coastal dune lake in northeastern New South Wales. In its close proximity to the ocean, some studies have suggested it may have been intermittently open to the sea in the past.

The regional geologic setting includes the alluvial flood plain that Lake Ainsworth is settled on, which is a collection of marine, estuarine, and alluvial deposits of Pleistocene and Holocene age. The Lake Ainsworth site has been subjugated to changing sea levels. Since the last interglacial sea level high stand 120,000 years ago, inner and outer barrier systems have been preserved. During Holocene time, seas peaked again at 1 meter above present sea level, but preserved 4-6 metres above modern sea level, indicating 3-5 metres of uplift.

This study was designed to interpret map and core information to deduce the origin and evolution of the lake. A Vibracore machine was used to gather core data from the area surrounding Lake Ainsworth. The coring information was used to discover amounts of past marine influence, while looking at the stratigraphy to give insight to possible origins of the lake. GIS mapping and the use of ArcView 8 were used to compile information into maps and diagrams.

The core data showed the first 16-20 cm was peat, and the remaining meter of the cores was alternating clay and fine-grained sand. There was no evidence of shells or marine deposits. Based on these cores, Ainsworth was not likely formed by ocean interaction, and has no evidence of a marine environment based on this study's findings. Ainsworth was possibly formed while changing sea levels rose to their present day heights. The groundwater potentially rose with the sea levels, leading to the formation of the lake in a depression.