The effects of weathering and sediment source mixing on whole-rock geochemical provenance studies, Cook Inlet forearc basin, south-central Alaska, USA

The provenance of most basin systems today is interpreted based on radiogenic ages or the geochemical composition of detrital minerals, which has all but replaced the use of whole-rock geochemical approaches that can effectively complement provenance information inferred from detrital approaches. Here, we further investigate previous provenance models developed using detrital zircon U-Pb geochronology by applying whole-rock major and trace element geochemistry of fine-grained clastic rocks from the late Oligocene−middle Miocene Tyonek Formation, late Miocene Beluga Formation, and Pliocene Sterling Formation in the Cook Inlet Basin, Alaska, USA. When taken alone, our new geochemical data suggest solely intermediate igneous sediment sources to the basin. When paired with existing detrital zircon U-Pb data, however, significant mixing of felsic and mafic sediment sources is evident, which indicates that thorough mixing of geochemically distinct source terranes can mask the input from individual sources in whole-rock geochemical studies. Furthermore, we demonstrate that both weathering and provenance influence the major element chemistry of sediment source terranes as well as the resultant basinal strata. Our conclusions indicate that the combination of whole-rock geochemistry with other detrital approaches provides a robust interpretation of sedimentary basin provenance.