Disentangle the hydrodynamic sorting and lithology effects on sediment weathering signals

Abstract

River sediment can be used to quantitatively investigate the silicate weathering intensity only if the weathering signal preservation and propagation are well understood, and especially the effects of hydrodynamic sorting and provenance lithology can be disentangled properly. Rivers entering the East China Sea have different climatic and geological settings and sediment source-to-sink transport patterns, which allow us to quantify the link between the chemical composition of river sediments and controlling factors of silicate weathering, hydrodynamic sorting, source rock natures and sedimentary recycling. We examine the geochemical evolution of sediments from these fluvial networks in weathering diagrams of A-CN-K [Al2O3-(CaO⁎ + Na2O)-K2O, Nesbitt and Young, 1984] and MFW [Mafic-Felsic-Weathering, Ohta and Arai, 2007]. The seeming “weathering trends” in these weathering diagrams are greatly influenced by mineral sorting given that the river sediment transport, deposition and resuspension are mainly subject to hydrodynamic conditions. The MFW diagram can better distinguish the influence of felsic and mafic source rocks, on condition that the weathering contribution from recycled sedimentary and metamorphic rocks in the catchment is minor. Nevertheless, both the A-CN-K and MFW diagrams are insensitive to sedimentary recycling induced quartz addition. Here, we propose a diagram of A-CNK-Si to disentangle the major factors controlling the river sediment geochemistry like chemical weathering, hydrodynamic sorting and provenance inheritance. This novel approach can decode the silicate weathering signals preserved in sedimentary records after removing the mineral sorting and quartz dilution effects, which will allow us to better reconstruct the geochemical evolution of Earth's surface.