Late Quaternary carbonate microbialite complex on the west shore of Great Salt Lake, Utah, USA

A Late Pleistocene carbonate microbialite complex at Death Point on the western shore of Great Salt Lake, UT, USA, coats Paleozoic bedrock over an area 70 x 40 m. The complex largely formed while Lake Bonneville flooded the basin. Three distinct stratigraphic units separated by minor unconformities have been identified. The oldest unit (Unit 1) occurs over the entire outcrop area and ranges from 10 cm to 2.5 m in thickness. It precipitated as aragonite in the wave-agitated shoreline environment during the early transgressive phase of Lake Bonneville and was subsequently pervasively dolomitized. Some near-vertical faces of Unit 1 are overlain by an 8-cm-thick calcite microbialite (Unit 2) precipitated in deeper water of the regressive phase of Lake Bonneville. The youngest microbialite unit (Unit 3) overlies the calcite layer and precipitated as aragonite when the lake had dropped to levels similar to those of modern Great Salt Lake. The elevation, stratigraphy, distinct mineralogical layers, diagenetic history and long depositional span distinguish the Death Point microbialite complex from other microbialites in the Lake Bonneville/Great Salt Lake lacustrine system. The geochronology of Death Point microbialite will lead to modifications of the Lake Bonneville hydrograph, showing significantly lower lake levels in the early-transgression stage.