PP12A-06
Paleoenvironmental reconstruction of ~40ka stromatolites from the ancient Lake Lahontan, Nevada, USA
Monday, 14 December 2015: 11:35
2012 (Moscone West)
Lennart van Maldegem, Max Planck Institute for Biogeochemistry, Jena, Germany; MARUM - University of Bremen, Bremen, Germany, Luoth Chou, University of Illinois at Chicago, Department of Earth and Environmental Sciences, Chicago, IL, United States, Joy Buongiorno, University of Tennessee, Knoxville, TN, United States, Laura A Zinke, University of Southern California, Los Angeles, CA, United States, Victoria A Petryshyn, University of California Los Angeles, Department of Earth, Planetary, and Space Sciences, Los Angeles, CA, United States, Russell Scott Shapiro, California State University Chico, Chico, CA, United States, Olivia Piazza, University of Southern California, Earth Sciences, Los Angeles, CA, United States, Sean J Loyd, California State University Fullerton, Fullerton, CA, United States, Aradhna Tripati, University of California Los Angeles, Planetary and Space Sciences, Department of Atmospheric and Oceanic Sciences, Institute of the Environment and Sustainability, Los Angeles, CA, United States, John R Spear, Colorado School of Mines, Golden, CO, United States, Frank A Corsetti, University of Southern California, Department of Earth Sciences, Los Angeles, CA, United States and International Geobiology Course 2015
Abstract:
During the Late Pleistocene, present day Walker Lake, Nevada was part of Lake Lahontan, an extensive lake covering large portions of northwestern Nevada, USA. The water level of Lake Lahontan has fluctuated significantly over time, reaching maximum high stands during the last glacial maxima (MIS stages 2 and 4). Fossil stromatolites are found sixty meters above the present day shoreline of Walker Lake. Like other lacustrine sedimentary features, stromatolites are laminated and may preserve a geochemical record of their environment of formation. As accretionary growth structures, stromatolites also have the potential to preserve in situ lake conditions that constrain water depth. Preliminary petrographic analysis of Walker Lake stromatolites suggests that they have undergone minimal diagenesis and appear to contain predominantly abiogenic features. Using radiocarbon dating, we found a formation age from ~41,460 to ~35,680 (calibrated YBP, IntCal13) over 14 cm, placing the age of formation within late MIS 3--a time noted for severe climatic shifts including Dansgaard-Oeschger (DO) events. Clumped isotope (Δ₄₇) analysis revealed large temperature fluctuation of the surrounding water column during formation of the stromatolites. Using geochemical data of conservative trace metals we modeled the fluctuation of volume of Walker Lake to be almost 50% over the course of the ~5780 years of stromatolite accretion. The Walker Lake stromatolites formed under dynamic temperature and lake level conditions. Based on both the fine laminations and overall complexity of macrostructure, the Walker Lake stromatolites show more similarities to stromatolites formed in the Proterozoic then to modern day stromatolites. Therefore, the Walker Lake stromatolites offer an interesting and unique analog for studying stromatolite formation, climate dynamics and water chemistry in the Proterozoic.
