| Description |
viii, 71 leaves : illustrations (some color) ; 29 cm |
| Summary |
"The Yilgarn Craton in Western Australia hosts hundreds of shallow ephemeral hypersaline lakes, the majority of which have acid to neutral pH values. As part of a multidisciplinary study of the evolution of hypersalinity and acidity in the region, three drill cores were studied for their palynofacies and palynomorph contents in order to characterize palynofloral response to environmental changes. Drill cores from two acid lakes, Prado Lake (PL1-09 and PL2-09) and Twin Lake West (TLW1-09), and the neutral-alkaline Gastropod Lake (GLE1-09) south of Norseman recovered Miocene to Holocene sediments of the Revenge and Polar Bear formations. Transmitted light microscopy was used to identify the dispersed organic matter (DOM) as well as palynomorphs. Statistical analyses were performed only for palynofacies since the palynomorph abundances were low. The palynofacies study revealed that the comminuted phytoclasts are the dominant components in the four drill cores; however; there are subtle differences in DOM distributions, even in drill cores from the same lake due to the dynamic nature of the environment. Lake dynamics appear to be controlled by flooding, evapoconcentration, desiccation, and reworking and eolian erosion. Modern observations indicate the possibility of a lake undergoing more than one process at the same time, resulting in different depositional mechanisms. Palynomorph analysis revealed that: 1) an open woodland vegetation with shrubs and herbs (Chenopodiaceae and Myrtaceae) had succeeded the much wetter climate of the Paleogene; 2) reworking has been a part of lake history as evidenced by the recovery of late Eocene palynomorphs (Nothofagidites and Aglaoreidia cyclops) at almost all depths; 3) the first record of a salt tolerant alga, Dunaliella, in the drill cores is likely be an indicator of the onset of salinity in the region; and 4) the apparent absence of Dunaliella in the most recent sediments in the neutral-alkaline Gastropod Lake may be related to either predation by the gastropod Coxiella or the possibility that this Dunaliella species is acidophilic. Both probabilities suggest that Gastropod Lake has become more neutral-alkaline with time"--Abstract, leaf iii. |
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