My students and I continued research on lacustrine sedimentary basins, and on the sedimentology and paleoceanography of the western U.S. Permian continental margin.
Last summer Meredith Rhodes and Jeff Pietras initiated fieldwork on the Eocene Green Formation in Wyoming. The goals of this project are to interpret the evolution of lacustrine facies in the context of Laramide basin tectonics and Eocene climatic patterns, through a combination of field and laboratory studies. We have also begun collaborative work with Clark Johnson and Brian Beard on the radiogenic isotopic record of lacustrine carbonate facies, with the objective of elucidating the paleohydrology of Lake Gosiute. Preliminary results show considerable variation in 87Sr/86Sr ratios, related to changes in sedimentary provenance and degree of weathering. Mike Smith has begun work on improved radioisotopic dating of tuffs that are interbedded in the Green River Formation, in collaboration with Brad Singer. We hope to obtain age resolutions of 100 k. y. from sanidine separates, which is an order of magnitude better than previously published work. These dates will allow greatly improved estimates of sediment accumulation rates, direct testing of Milankovitch-scale cyclicity, and synoptic reconstruction of the evolution of Green River Formation lakes in different basins. Marwan Wartes completed his MS thesis on Permian lacustrine and associated nonmarine deposits of the Junggar-Turpan-Hami basins. This study has provided the first definitive evidence that huge Permian lakes in this region originated through Early Permian rifting, probably followed by Late Permian thermal basin subsidence.
Colin Walling began fieldwork in Wyoming and surrounding areas on the Permian Phosphoria Formation, focusing on possible eolian transport of silt. Eolian dust transport has important implications for climate, due to the potential for windborne iron to increase marine productivity and thus reduce atmospheric CO2 (the "Martin hypothesis"). Because arid environments were widespread in Pangea, windblown dust may have contributed significantly to marine carbon burial. The Phosphoria offers an excellent opportunity to test this hypothesis due to the association of silty facies and high organic matter enrichment in a well-preserved marine shelf. To help trace the origin of this dust we will conduct d18O analyses on quartz silt grains in collaboration with John Valley and Mike Spicuzza. A low-temperature origin for the quartz grains would imply that they originated from deflation of the exposed Wyoming shelf during sea level lowstands. An eolian origin has also been proposed for silty facies of the approximately coeval Brushy Canyon Formation in west Texas, which is the subject of an ongoing collaborative research project involving Toni Simo, and Ph.D. candidate Marybeth Wegner, and Exxon. We have used biological marker compounds in organic-rich facies to chart the position of an oxygen-minimum layer, which migrated upward on the Delaware basin slope through time in response to marine transgression.
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