| Lakes are excellent repositories of fossils and sedimentary features that provide clues to past climatic and geologic events. Sediments from four cores drilled in Lake Aerodrome (LA1-09, LA2-09) and Lake Brown (LB1-09, LB2-09), two of the hundreds of ephemeral lakes in southern Western Australia, were analyzed for their palynological contents to understand the geologic and climatic evolution of the depositional basin. Palynofacies assemblages defined by statistical analyses of dispersed organic matter suggested differences in the depositional conditions and probable correlations between Lake Aerodrome cores. Detailed identifications and quantification of organic-walled microfossils yielded two palynomorph assemblages that reflect a climatic turnover: (1) a wet hinterland (rainforest), freshwater and swampy assemblage found in situ in the basal lignites of LA2-09 (44.58-59.63 meters); and (2) a sclerophyllic and halophilic assemblage in all younger sediments. The first and last appearances of key palynomorphs in the lignites, which contain Aglaoreidia cyclops (documented for the first time in Australia and the Southern Hemisphere), correlate the assemblage with the Middle Nothofagidites asperus Zone of the Werillup Formation. While Myrtaceidites lipsis constrains the age of the sediments from 23.38 meters depth to the top of LA2-09 as Pliocene to Recent, the sequence between 23.38 and 44.58 meters has long-ranging palynomorphs and is likely not older than the Miocene. Above the lignites, the salt-tolerant alga Dunaliella is used as a proxy for saline conditions. Reworking has been established in post-Eocene sediments because well-preserved Eocene freshwater and marine palynomorphs co-occur with sclerophyllic and halophilic palynomorphs. |
