GEOCHEMICAL PROVENANCE ANALYSIS OF CONGLOMERATE CLASTS IN THE CRETACEOUS BEAVERHEAD GROUP OF SOUTHWESTERN MONTANA

Both the age and provenance of the Late Cretaceous-Early Cenozoic Beaverhead Group are vital components in analyzing the nature and timing of flat-slab subduction during the Laramide orogeny. Previous provenance analysis has consisted of comparing the lithology and fossil content of conglomerate clasts in the Beaverhead Group to that of various Paleozoic-Early Mesozoic source rocks. In order to perform a more quantitative and accurate provenance analysis, this study focuses on using standard geochemical techniques for the comparison of clasts to source material. By using XRF spectrometry and LA-ICP-MS to obtain major element and trace element abundances, respectively, we hope to quantify the provenance relations between the clasts and their source material. Since the clasts in the Beaverhead Group are mainly carbonate lithologies, we focus our initial investigation on carbonate sources. Source and clast samples were analyzed by making a fused glass disc and mounting any leftover glass bits in epoxy, and then analyzing them on the XRF and LA-ICP-MS machines, respectively. Once all of the initial 27 source samples and 18 clast samples are fully processed, a qualitative analysis of their geochemical signatures will begin. If this analysis shows both a promising amount of distinction between source samples and a sufficient relationship between clasts and their sources, more samples will be collected and analyzed. Once a large dataset of ~100 samples is analyzed, standard machine learning algorithms will be utilized to gain quantifiable provenance relations between the Beaverhead Group and its sources.