PALEOECOLOGY OF STROMATOLITE FACIES IN THE LACUSTRINE EOCENE GREEN RIVER FORMATION, SANPETE COUNTY, CENTRAL UTAH

The Eocene Green River Formation is a lacustrine deposit exposed in southern Wyoming, northwestern Colorado, and northeast and central Utah. In Utah, several intermontane ponded basins developed, including central Utah’s Lake Flagstaff. Localities of interest in Sanpete County include a series of Green River cuestas and slide blocks, spanning approximately 15 miles from Spring City to Manti, Utah; these localities were positioned along the eastern shoreline of Lake Flagstaff. The purpose of this research is to develop an accurate history of carbonate microbial mat communities within the Green River Formation of Lake Flagstaff.

The stratigraphy of the Green River Formation in central Utah exhibits a variety of interbedded siliciclastic and carbonate lithologies in both the lower and upper members: calcareous mudstones, shales, wackestones, packstones, and grainstones. Volcanic tuffs, which interrupt normal lacustrine deposition, can be found in both members and vary in thickness from a few centimeters to over a meter in thickness. Stromatolite facies (boundstones) also are observed in both members, and stromatolite preservation varies stratigraphically and geographically. Many specimens show typical carbonate preservation, but at some localities, the stromatolite laminae (mm) are highly silicified or are preserved with stevensite. Further, localities show diverse size distributions; most range from 1-55 cm in height. Many of the stromatolites exhibit a basal laterally-linked morphology, but are then dominated by domal or closely to widely spaced columnar forms. It is not uncommon for branching to occur within specimens. In addition, other fossils found in the stromatolite facies include fish debris, ostracodes, burrows, and plant impressions.

Lacustrine stromatolites provide information about the lake chemistry and climate of Lake Flagstaff as well as allow a comparison to the other Green River lakes of Utah, such as Lake Uinta. By noting the stratigraphic occurrence of stromatolites and the related fauna and flora, and by analyzing stromatolite morphologies and preservation styles, further insight into the paleoecology of the Eocene Green River Formation of Lake Flagstaff is determined.