QUATERNARY DEPOSITIONAL ENVIRONMENTS AND PALEOCLIMATE INTERPRETATIONS FROM LACUSTRINE EVAPORITE MINERALS

Closed basin lacustrine evaporites and associated sediments in drill cores have been used for Quaternary paleoenvironmental reconstructions. These deposits have been dated by radiocarbon measurements and by 230Th/234U disequilibrium methods to 200,000 years. They preserve detailed information on paleoenvironments, paleolake temperatures, chemical compositions of paleoinflow and paleolake waters, and ancient life. The suite of sedimentary structures, petrographic textures, and fossils (i.e., ostracodes, diatoms, pollen) allow interpretations of paleodepositional environments ranging from deep lakes, stratified and non-stratified saline lakes, saline pans, and mudflats and other subaerially exposed settings. Records of ancient lake temperatures have been obtained from the homogenization temperatures of brine inclusions in halite. Stratigraphic variations in evaporite mineralogy (i.e., calcite, gypsum and glauberite), are related to fluctuations in ancient inflow water sources and climate, and different mixing ratios of inflow waters between relatively wet and dry periods. Fossils add extra information on ancient lake depths, chemistries, and inflow water compositions. Finally, brine inclusions in salt crystals are excellent repositories for ancient microbes because their low oxygen and high salinity environments are ideal for long-term preservation of organic compounds. The reported isolation of a 100,000 year-old haloarchaeal species from a Death Valley drill core indicates lacustrine evaporites will be the focus of future studies on ancient organisms trapped in crystals.