Provenance from the whole-rock geochemical composition of terrestrial clastic deposits

How can inorganic geochemical data from terrestrial deposits be used as a provenance tool? We demonstrate a new approach that deviate from earlier studies focussing on marine deposits. Our study is based on the intracontinental Permo-Triassic Rotliegend and Buntsandstein groups and equivalents in central Europe (mainly Germany and Denmark), both being deposited under arid conditions, and mainly having felsic sources. The results are from both published and unpublished data of >1500 sedimentary samples, mostly sandstone. The K2O/Na2O ratio is in line with regional variations in feldspar compositions and indicates local catchments. Thus, limited weathering has preserved the feldspar. The mafic-felsic trace-element ratios La/Sc, Th/Sc, Y/Co, and Ti/Nb seem most promising for provenance discrimination, in combination with La/Lu, and Zr/Sc and V/Zr as heavy-mineral tracers. V/Zr and Zr/Sc mostly correlate with Y/Co, indicating different zircon affinity rather than sorting. More dominance of felsic compositions and higher Zr/Sc ratios for Triassic than Permian strata are in line with more sedimentary recycling during the Triassic than Permian. We confirm that both K2O/Na2O and immobile trace-element ratios are suitable provenance indicators to reveal source-rock differences for terrestrial deposits from arid climates. We furthermore stress that previously developed discrimination schemes for marine depositional facies, specific grain size and texture for identification of tectonic settings are unsuitable for terrestrial deposits. Different terrestrial tectonic situations will influence the detrital composition such that rift, foreland, and sag basins likely have different chemical compositions. For robust provenance interpretations, we recommend focussing on immobile elements that are little affected by grain-size variations, to combine several element ratios, and to complement geochemical investigations with data from other methods.