STABLE ISOTOPE AND RADIOCARBON ANALYSIS OF MODERN LACUSTRINE STROMATOLITES IN GREAT SALT LAKE, UTAH

The Great Salt Lake (GSL), a closed hypersaline lake in northern Utah, is host to numerous modern and fossil stromatolites. Because of current low lake levels, many of these stromatolites are now exposed along the northern shorelines of GSL, including Antelope Island. One stromatolite dome from Antelope Island was sampled for stable isotope geochemistry and compared with current lake water chemistry to see if the former records changes in lake water chemistry. A transect from the center to outer layers of carbonate revealed significant variations in δ¹³C_carb and δ¹⁸O_carb (δ¹³C_carb ranges from 0.97 to 6.64 ‰ PDB; δ¹⁸O_carb ranges from -4.33 to -1.19 ‰ PDB) and strong covariance between δ¹³C_carb and δ¹⁸O_carb (r=0.78). These trends are interpreted to be the result of evaporative- and residence-related effects because of the closed nature of the GSL’s hydrologic system. Additionally, organic carbon was segregated from four locations along the transect for δ¹³C_org and radiocarbon analyses. δ¹³C_org shows considerable variability as well (δ¹³C_org ranges from -21.71 to -25.62 ‰ PDB), possibly correlated to δ¹³C_carb. Radiocarbon dates are pending and will provide temporal constraints on stromatolite formation and hydrologic changes in the GSL.