VARIED AND UNUSUAL SEDIMENTS AND DIAGENETIC FEATURES IN SHALLOW CORES FROM MODERN ACID SALINE LAKES IN WESTERN AUSTRALIA AND VICTORIA

Twenty-five shallow cores from seven acid and two neutral saline lakes in southern Western Australia and Victoria show a variety of clastic, chemical, and biogenic sediments, highly-altered Archean rock regolith, and diagenetic features. PVC pipes were used to manually sample vertical sections of lake and adjacent sandflat facies to depths of ~ 0.5 meter. Cores include laminated and massive gray and red mud, tan, red, grey, and white sand laminations and thin beds, lignite thin beds, and bedded halite and gypsum. Abundant diagenetic features overprint much of these sediments with an unusual mineral suite composed of halite, gypsum, hematite, goethite, jarosite, alunite, and kaolinite. Many of these minerals precipitate directly from shallow acid lake waters as well, suggesting a near continuum from surface to shallow subsurface chemical precipitation. Diagenetic features include displacive crystals, grain coatings, cements, concretions, and dissolution pipes and dissolution surfaces. Variations in shallow groundwater pH, salinity, and major and minor ions at various spatial scales favor different combinations of these minerals. In some places, diagenetic features are highly-localized, such as at Twin Lake West, where three cores taken within a 6 m area on a sandflat (groundwater pH ranges from 2.6 – 3.2) show distinctly different colors, textures, and minerals. In addition, some cores show soft sediments composed of diagenetic minerals aligned in patterns similar to metamorphic foliations, suggesting intense alteration of Archean host rock. This acid lake deposition, early diagenetic overprinting, and host rock alteration results in multi-colored rocks with appearances dissimilar to those from typical lakes. Supplemental studies suggest diverse palynological and microbiological remains in these cores. This work may lead to better interpretations of ancient terrestrial and extraterrestrial red beds and evaporite sequences and the physical, chemical, and biological processes by which they formed.