Dennis L. Newell
10 September 18
Extensive lacustrine microbialite deposits exposed along the shores of Great Salt Lake (GSL), Utah preserve a rich continental paleoenvironmental record. Newly reported microbialite carbon and oxygen stable isotope ratios in carbonate, nitrogen isotope ratios in organic matter, and preliminary organic matter radiocarbon ages archive paleolake hydrological and biogeochemical changes from the late Pleistocene through the Holocene. Positive correlations between 18O and 13C in ~15 – 7.6 cal ka microbialite carbonate are consistent with a hydrologically closed-basin lake with fluctuations in volume, chemistry, and associated changes in lake primary production. The 15N of microbialite bulk organic matter (5 – 18 ‰ vs. AIR) shows that the balance between nitrogen fixation and assimilation of dissolved inorganic nitrogen has varied
significantly at times in the lake. Inverse ?
18O and 13C correlations are enigmatic, but in combination with high 15N in some deposits may imply periods of higher salinity and stable lake stratification similar to modern GSL conditions. We compare our C and O datasets with Pleistocene Lake Bonneville carbonate stable isotope records and demonstrate progressive development of spatially-isolated hydrological basins during the shift to
warmer and drier conditions in the Holocene.