2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 300-4
Presentation Time: 9:45 AM


AGIĆ, Heda, Department of Earth Sciences, Uppsala University, Villavägen 16, Uppsala, 752 36, Sweden, WARD, Lewis M., Division of Geological and Planetary Sciences, California Institute of Technology, MC 100-23, 1200 E. California Blvd, Pasadena, CA 91125, JUAREZ RIVERA, Marisol, Geology, University of California-Davis, One Shields Avenue, Davis, CA 95616, KERRIGAN, Zak, Graduate School of Oceanography, University of Rhode Island, 215 South Ferry Road, Narragansett, RI RI 02882-119, PETRYSHYN, Victoria A., Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, CORSETTI, Frank A., Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089 and TRIPATI, Aradhna, Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA CA 90095-156

Walker Lake, a terminal sodium bicarbonate lake in Western Nevada (Great Basin, USA) contains numerous carbonate structures, including stromatolites. The lake is a remnant of the larger Pleistocene Lake Lahontan system that has been isolated for the last ~12 ka. Stromatolites of unique macroscale morphology were collected at the ancient Lahontan shoreline during the 2014 International Geobiology Course.

Initial observations of a stromatolite bed revealed a bowl-shaped carbonate framework composed of stacked, weakly laminated, vertical and horizontal petal-like structures with copious pore space. One laterally-oriented petal was taken off of the main structure and studied. Petrographical observations exhibit two types of alternating microfabrics and three transitions in microfabric. Both sparry crystal fans of calcite, and convex layers of fine micrite with occasional trapped crystals and fossils, were observed.

Calibrated 14C ages (IntCal13) for the proximal and the distal end of the stromatolite are 35,540 YBP and 33,580 YBP, respectively. Clumped isotope (D47)-based estimates of temperature steadily increase throughout most of this interval, from the beginning of accretion, to the middle of the structure. By the distal end, values are at their peak, and at the tip temperatures decrease again. D47-temperatures correspond to microfabric, with textural changes associated with evidence for climatic fluctuations.

We suggest the stromatolite formation may have been initiated during warmer intervals, induced by the chemical precipitation of calcite fans which served as a substrate for a biofilm growth. Microbial activity trapped the fine sediment and formed micrite. Colder conditions propagated fan precipitation. Microfabric alternation throughout the stromatolite records environmental change in the span of ca. 2000 years of Lake Lahontan history, likely in response to lake level fluctuations.