Abstract

Ooids of Great Salt Lake, Utah (GSL) have been studied periodically by geologists since the 1960's. These studies have documented the locations of ooid deposits, bulk composition, mineralogy, and internal structural variations of GSL ooids. Ooids have also been identified in sediment cores from lakes predating the Great Salt Lake, but similar descriptions have not been made for these ooids. Samples of ooids from cores in Pilot Valley, UT/NV and Knolls, UT have been obtained, along with samples from the Great Salt Lake at Bridger Bay and Rozel Point. The cortical fabrics and crystal morphologies of these ooids were studied in thin section and under scanning electron microscopy. Examples of cortex morphologies previously documented in GSL ooids were observed, to some degree, in ooids from Pilot Valley and Knolls. Knolls ooids had unique cortical layers that were resistive to acid and appeared to be dominantly comprised of clays. Bulk dissolution ages were obtained for ooids from each location. Ooids form both Pilot Valley and Knolls had average ages that pre-date Lake Bonneville, whereas GSL ooids from Bridger Bay had an average age of roughly 3,500 years before present (yr BP) and Rozel Point ooids had an average age of 500 yr BP. Along with a bulk age, ooids from Bridger Bay at the Great Salt Lake were subjected to serial dissolutions during which a split of gas was taken from each stage and an age was obtained. Ages spanned 7,000 years with the final dissolution stage delivering an average age of 9,000 yr BP. Based on this data it is likely that GSL ooids at Bridger Bay have been forming since the cessation of Lake Bonneville and that many of the nuclei in Bridger Bay ooids are remnant peloids from the Gilbert level of Lake Bonneville.

Degree

College and Department

Physical and Mathematical Sciences; Geological Sciences

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