Orogen-scale erosional patterns from sediment fingerprinting and unmixing modeling of Alpine river sediments

Clastic sediments and sedimentary rocks are almost always complex mixtures of detritus supplied by several different source rocks. Modern sedimentary provenance analysis should aim not only to identify these source rocks, but also to quantify the (relative) contribution of the different sources through space and time. This is often challenging because of limited and incomplete databases, overlapping or unknown source fingerprints, and a general lack of awareness of the proper statistical tools and procedures.  

In this contribution, we highlight the use and advantages of statistically robust fingerprinting (i.e., establishing endmember compositional signals of source rocks) and (un)mixing modeling (i.e., quantitatively reconstructing relative source contributions in a mixed sediment) on a large orogenic scale, the European Alps. Multiple provenance proxies (sediment petrography, heavy mineral analysis, bulk geochemistry, zircon fission track dating, and zircon U-Pb dating) are used to define compositional endmembers of the main Alpine source rocks and regions. Unmixing modeling is used to identify and quantify the contribution of the endmember sources to mixed sediment carried by the main large Alpine rivers (the Adige, Dora Baltea, Drau, Enns, Inn, Mur, Rhine, Rhone, and Salzach rivers). In a second step, the same methodology is applied to Oligocene and Miocene fluvial and shallow marine sedimentary rocks from the Alpine foreland basin. The data is interpreted in the context of changing fluvial network architecture and erosional patterns in response to climatic and tectonic changes in the orogen, but also in terms of compositional bias, such as contrasting mineral fertility and diagenesis.