REDUCING BIASES IN DETRITAL PROVENANCE U-(TH)-PB GEOCHRONOLOGY ANALYSES

Mineralogy and U-Pb geochronology can be used to determine provenance of sediment, provenance changes through time, and timing of crustal exhumation. Preparation of datable detrital minerals (zircon and rutile) for provenance research using U-Pb geochronology has been an ongoing subject of debate. A bias that concerns geochronologists is a degree of preferentially including or excluding datable detrital grains during mineral separation and data processing techniques. These biases can lead to under representation of source areas for a given sedimentary unit and affectively remove pieces of the geologic history. The purpose of this paper is to provide insight into biases introduced by quantifying modal abundance of minerals present after each separation step using a Quantitative Evaluation of Minerals by SCANning electron microscopy (QEMSCAN). A reliable technique for sample preparation and processing techniques is formulated based on these results. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometer (LA-ICP-MS) measures U-Pb isotopes at a high throughput. This allows >100 zircon U-Pb dates to be measured per sample to detect a change in provenance signal. The Upper Cretaceous sediments of the Mesaverde Groups, Lewis Shale and Fox Hills Sandstone are being investigated to test these new techniques (Greater Green River Basin, Rawlins, Wyoming). These sedimentary units are being targeted because the age of the source areas are well known and the sequence stratigraphy, sedimentology, and tectonic activity of the area is well characterized.