Tectonic and Climate Changes Expressed as Sedimentary Cycles and Stratigraphic Sequences of the Paleogene Lake Uinta System, Central Rocky Mountains, Utah and Colorado

Abstract

Lake Uinta strata record both long- and short-term changes in climate and tectonic regime. Late Paleocene to late Eocene deposits are characterized by evaporite units (including halite and bicarbonate salts) and organically derived carbonate with extreme positive {delta}{sup 13}C and slightly negative {delta}{sup 18}O values that serve as evidence the lake was the center of a closed hydrologic system. Large reconfigurations of the lake system were tectonically induced and gave rise to relatively thick, lithologically distinct stratigraphic sequences. Simultaneous climate changes initiated very rapid lake level expansions and contractions as well as shifts in lake-water alkalinity and salinity (or chemistry) which resulted in the development of small- to large-scale sedimentary and stratigraphic cycles. Maastrichtian to earliest Eocene phases formed in local depressions (piggy back basins) on the thrust sheets, and in the incipient Uinta basin. Lake system reached its greatest aerial and volumetric extent in the middle and late Eocene and was centered in the foreland formed in front of high-angle reverse faults that bounded the rising Laramide structural blocks. At this time chemical precipitates, including basin centered carbonate and evaporite facies, formed during episodes of tectonically induced subsidence at the center of the clastic sediment-starved basin. Some fault-bounded marginsmore » of the Uinta basin are marked by synorogenic coarse debris that extends from the mountain front to the clastic sediment-starved lake. Tectonically induced stratigraphic sequences of the Lake Uinta system express environments for several million years whereas climatic cycles reflect much shorter episodes and very rapidly changing conditions.« less