Permo-Triassic sediment provenance and paleodrainage in Central to Western Europe

Relief degradation and drainage evolution in the aftermath of major orogenies have been extensively studied for young mountain belts. For ancient orogenic settings such reconstructions often remain enigmatic with respect to, e.g., exhumation and erosion rates, sediment dispersal paths and sediment budgets as well as associated paleolandscapes and sediment routing systems. Sedimentary provenance analysis provides an essential tool to constrain these complex systems in space and time.

Here we present a multi-method provenance study from the Black Forest, the Palatinate Forest and the Vosges (SW Germany and NE France) that includies heavy mineral assemblage data from 100 sandstone samples as well as detrital zircon U-Pb geochronology and grain-size measurements from 40 selected samples. The samples cover approximately 10 to 15 Myrs from Zechstein to Upper Bundsandstein strata (Wuchiapingian to early Anisian). Additional data comprise detrital tourmaline and garnet geochemistry as well as detrital monazite geochronology.

The heavy mineral assemblages are rather uniform, dominated by the stable phases zircon, tourmaline and rutile (along with other TiO₂-polymorphs) and complemented by variable apatite content as well as minor monazite. Zircon U-Pb ages range from ~0.25 to 3.5 Ga, showing prominent Variscan (30%), Caledonian (23%) and Cadomian (28%) age components, along with older ages (19%). Grain-size data indicate an overall decrease of zircon size with increasing U-Pb age. The zircon age distributions suggest an increase of Cadomian and older ages at the expense of Variscan ages with decreasing stratigraphic age of the samples. This observation is independent of zircon grain size. It is interpreted to reflect a change from more local sources in Late Permian time to a significantly enlarged catchment area in the Early Triassic that includes tapping new source regions. This comes along with a homogenization of sediment composition across the entire drainage and depositional area in the late Olenekian to early Anisian. Our study serves as an example of heavy-mineral based fingerprints for regional-scale drainage basin widening due to relief planation in the aftermath of major orogenic phases.