Geochemical differences between the Harşit Stream channel and terrace sediments (NE Turkey): Implications for mixed source rocks, weathering and mass transfer

Abstract

There are minor geochemical differences between Harşit Stream bed and terrace sediments, and these can be owing to the impacts of climatic differences and chemical weathering rather than source rock composition. The bed sediments have lower average SiO2, Al2O3, Fe2O3, K2O, TiO2 and MnO concentrations than terrace sediments, but higher concentrations of MgO, CaO and Na2O. The rare earth element (REE) distributions, Eu/Eu*, (Gd/Yb)N, La/Th and (La/Yb)N ratios of the bed and terrace sediments indicate that they derived from a mixture of 3% granodiorite + 50% gabbro + 47% felsic tuff and 5 % granodiorite + 37% gabbro + 58% felsic tuff, respectively. The CIA, PIA, WIP values and ICV, Rb/Sr ratios indicate that the bed sediments are lowly weathered and terrace sediments are lowly to moderately weathered. The distribution of C-values and Sr/Cu ratios indicate an arid to semiarid climatic conditions for the bed sediments and an arid to semi-moist climatic conditions for terrace sediments. During weathering of the mixed source rocks, Na indicates the greatest loss for the bed and the terrace sediments, and P shows the lowest loss for both of sediments. The average of Si, Al, Na, K and Mn exhibits more loss in bed sediments than terrace sediments, the Fe, Mg, Ca and P exhibits less loss in bed sediments than terrace sediments.