Sediment production in the Crati River drainage basin (Calabria, Southern Italy)

The composition of modern stream sands derived from different source rocks outcropping in the Crati River basin was analyzed in order to evaluate the contribution of each type of bedrock to the sandy bedload. To asses the contribution of specific source rock types to the fluvial sand, the concept of Sand Generation Index (SGI), expressing the capacity of a given lithology to produce sand-sized sediments relative to another, was applied. The Crati river basin is an active tectonic area where mechanical erosion prevails over chemical alteration and where the high uplift rates of the structural domains favour a high rate of clastic sedimentation that flows into the valley system. It is composed mainly of sedimentary rocks, exposed in 67,74 percent of its areal extent, and subordinately of metamorphic (26,07 percent) and plutonic (6,19 percent) lithotypes. Petrographic analyses show that the modern sands of the main channel are litho-feldspar-quartzose and receive input from tributaries draining different lithologies from the Sila Massif, the Catena Costiera and the Pollino Massif. The sand generation indices, calculated for the Crati drainage indicate an SGI of 5,5 for the Sila Massif plutonites and of 2,4 for the Sila and Catena Costiera metamorphites. The results indicate that the Sila Massif, which occupies only 6,19% of the catchment area, has by far the highest production capacity of sandy bedload, owing to its granitoid lithotypes. Thus, this actualistic study demonstrate that fluvial sand composition can be strongly influenced by source rocks that occupy only a minor portion of the drainage area and it may be helpful in the analysis and reconstruction of source terrains in ancient siliciclastic deposits.