EFFECTS OF ACID LAKE DYNAMICS ON PALYNOLOGICAL RECORDS IN TWO CORES FROM LAKE AERODROME, SOUTHERN WESTERN AUSTRALIA

In order to understand the evolution and the different processes that affect the naturally acidic saline lakes in southern Western Australia, a series of multi-proxy analyses that integrate sedimentology, δ¹³C, total organic carbon percentage, AMS ¹⁴C dating, palynology, geochemistry and petrology are being conducted on sediments retrieved from 10 cores. These include one 21-meter (LA1-09) and one 60-meter (LA2-09) long core drilled about 40 meters apart in Lake Aerodrome, near Norseman, southern Western Australia. The pollen record in both cores shows that the first few centimeters below the surface reflect the modern flora. Palynofloral recovery becomes very poor down hole up to 37 meters and contains arid and/or salt-tolerant elements (Chenopodiaceae, Poaceae, Asteraceae, Myrtaceae) that have been widely distributed in southern western Australia since the late Miocene. Palynofacies analysis indicates that the most abundant particulate organic matter components are degraded and comminuted phytoclasts. AMS ¹⁴C dates were obtained only from the top 3 meters because organic matter is very scarce below this depth, probably as a result of diagenesis or degradation by the acidic groundwaters. Data δ¹³C from LA1-09 show a decrease in values from -22.06 at the top to -25.50 at the bottom. LA2-09 data show a greater variation, with positive excursions at around 30 meters reaching values of -8.52 and -9.07, and at 55 meters with a value of -21.64. Total organic carbon percentages are low in both cores, except at 30 meters and below 45 meters in LA2-09. These results appear to be affected by several factors in the lake, including its unusual geochemistry that allows the precipitation of certain acidity-related minerals, and the lake’s ephemeral nature that permits a highly dynamic sedimentation controlled by four major processes of flooding, evapoconcentration, desiccation, and wind erosion and deposition. This cycle is not necessarily seasonal, as even a single day of rain can make the whole process start over again, thereby creating an unpredictable and very complex environment. Prevailing processes at different locations within the lake have influenced the low degree of correlation in the pollen and palynofacies records in both cores.