Light fractions can also be heavy hitters: Comparison of detrital zircon U–Pb and detrital K‐feldspar Pb–Pb as provenance indicators—A case study from Cretaceous strata of southern Utah, USA

Abstract

AbstractComparison of detrital zircon U–Pb geochronology and detrital K‐feldspar Pb–Pb isotopic data from Upper Cretaceous sandstones of southern Utah reveals important provenance information that is unrecorded by more chemically and physically durable detrital minerals like zircons. To better understand these signals, we also present an updated database of Pb‐isotopic ratios in ores, whole rocks and feldspars, for potential sediment source terranes in North America. Detrital K‐feldspar Pb‐isotopes indicate sediment provenance of the Western Cordillera/Mojave, Yavapai‐Mazatzal and Wyoming terranes, with limited input from recycled Sevier fold‐thrust belt strata. The K‐feldspar data broadly support previous interpretations, largely based on detrital zircon datasets, of a Cretaceous palaeo‐river system transporting sediment from the southwest. However, the light‐fraction data also provide important, complementary and otherwise unrecognized perspectives as compared to detrital zircon datasets. For example, K‐feldspars indicate a stronger apparent influence of Western Cordillera/Mojave and Wyoming terrane sources than previously interpreted. We interpret the K‐feldspar Wyoming terrane signal as the result of south‐directed longshore drift, with preferential loss of zircons due to hydraulic sorting processes. As relatively new detrital K‐feldspar detrital methods continue to be developed, this multi‐proxy approach to provenance could be informative in other sedimentary basins where suitable source terranes can be identified.