Isotope hydrology of early paleogene Lake Flagstaff, central Utah: Implications for Cordilleran evolution

Abstract

Lacustrine sediments from Paleogene foreland basins of the North American Cordillera serve as powerful integrators of information on climatic and tectonic conditions, but episodes of hydrologic connection between basins may confound straightforward interpretations. We use stable isotope ratios of carbon and oxygen in authigenic carbonates of the Flagstaff Formation in central Utah to investigate the history of the lake system which produced these sediments. Flagstaff limestone and dolostone exhibit isotopic compositions consistent with having formed from the same fluid at surface conditions, indicating high evaporative concentration was unnecessary to drive dolomite precipitation. Isotopic data are consistent with the Flagstaff Formation having been produced by a large lake which occupied its basin from the late Paleocene into the early Eocene. Lake Flagstaff was hydrologically distinct from Lake Uinta to the north, but may have been connected to Lake Claron in the south. Paleoaltimetry estimates suggest that the mean elevation of Lake Flagstaff's catchment in the Sevier Highlands did not exceed 1.5 km. The growing evidence from stable isotope data that Cordilleran elevations were relatively low in the early Paleogene is in stark contrast to structural and sedimentological evidence for a high Nevadaplano and a topographically rugged Sevier thrust belt.