--> Characterization of Microbialites from Antelope Island's Bridger Bay and Promontory Point, Great Salt Lake, Utah

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Characterization of Microbialites from Antelope Island's Bridger Bay and Promontory Point, Great Salt Lake, Utah

Abstract

The shallow waters of hypersaline Great Salt Lake support extensive microbial carbonate formation, especially in Bridger Bay on the northwestern tip of Antelope Island and along the southwestern tip of Promontory Point. Lake levels in the fall of 2014 and 2015 were near 60-year lows (as low as 1278.1 m [4193.3 ft] AMSL, compared to the near-term historical average of about 1280 m [4200 ft]), giving unprecedented access to the microbial structures. Characterizing the microbialites of Bridger Bay and Promontory Point, including facies delineation and areal extent, can inform interpretations of similar deposits in the ancient rock record (e.g., lacustrine Eocene Green River Formation), including potential petroleum reservoirs. The goals of this project were to 1) characterize, in detail, the different types of microbial carbonates found in these two areas, including thin, low-profile, mostly featureless, circular, domical microbialites; ring structures resulting from exposed collapsed domes; carbonate grains such as ooids and eroded pustular microbial growths; and large, thickly layered stromatolites; 2) delineate facies transitions from onshore to offshore, including exposed carbonate mud flats, remnants of older microbialite communities, ooid shoals, and offshore organic-rich mud; 3) document the differences in the microbial communities from the sheltered waters of Bridger Bay (smaller, flat, superficial domal structures) and the windward side of the bay's northern spit (much larger [up to 3-4 m in diameter and up to 4 m tall], albeit eroded, thickly layered stromatolites, possibly remnants of some of the largest stromatolites found in Great Salt Lake); and 4) document the unusual polygonal growth pattern of microbial domes near Promontory Point. The aforementioned characteristics where documented through routine field observations, petrographic analyses, and aerial photography using a quadcopter mounted with a high-resolution video camera.