NUTRIENT CYCLING IN THE PHOSPHORIA SEA

The Phosphoria Formation was deposited in an epicontinental basin on the western margin of North America during the mid-Permian. Oceanographic constraints have suggested that the Phosphoria Sea was situated adjacent to a coastal upwelling system, where nutrients delivered from the deep ocean could have enabled extremely high rates of primary productivity. This inference is supported by an abundance of organic- and phosphate-rich shales and cherts in the Phosphoria Formation. Despite the considerable economic interest in these deposits, little attention has been paid to the unique nutrient dynamics that characterized this depositional environment. Using a range of geochemical tools, we aim to answer two important questions about nutrient cycling in the Phosphoria Sea: 1) what were the diagenetic conditions in sediments where phosphate mineral formation was extensive? and 2) what role did nitrogen bioavailability play in enabling widespread phosphogenesis? Answering these questions will not only elucidate the mechanisms behind phosphogenesis in the Phosphoria Sea, but also will shed light on the controls on macronutrient cycling in the ocean on geological timescales. Here we present preliminary carbon and nitrogen isotopic data from the Retort phosphatic shale member of the Phosphoria Formation, and consider possible scenarios for the status of major nutrient cycles in the Phosphoria Sea.