Salinity stratification in the Permian Phosphoria sea; a proposed paleoceanographic model

The Late Permian Phosphoria Formation of the western United States contains 1.7 x 10(12) t of phosphate and locally as much as 32.9% total organic car bon. The mineral wealth of the Phosphoria Formation is generally attributed to Late Permian upwelling along the western margin of the continent. Unlik e in most modern environments, upwelling in the Late Permian occurred proxi mal to a broad, shallow, evaporative sea rather than an abrupt continental margin. Evaporite deposits that are contemporaneous with the organic and ph osphate-rich strata are present within the Phosphoria and adjacent basins. Elevated concentrations of the biomarker gammacerane are ubiquitous in the organic-rich facies of the Phosphoria Formation, which suggests that the ba sin was salinity stratified, Depositional environments incorporating both u pwelling and salinity stratification are unusual and poorly documented in m odern settings. We infer the presence of salinity stratification in the Pho sphoria basin and propose a paleoceanographic model of the Phosphoria sea d uring the deposition of organic- and phosphate-rich sediment. From the west ern margin of the continent, upwelling water flowed into the evaporative Ph osphoria sea, replacing and overriding hypersaline bottom water that draine d westward. This paleoceanographic model of the Phosphoria sea may help to explain the distribution and preservation of organic- and phosphate-rich st rata in the Phosphoria Formation.