Geochemistry of the Middle Jurassic sediments in Gumushane, north-eastern Turkey: Implications for weathering and provenance

Abstract

The whole-rock geochemistry and Sr-Nd isotope data of Middle Jurassic sedimentary rocks in the Gumushane area (north-eastern Turkey) were analysed to reconstruct the provenance, chemical weathering, sediment recycling history, and tectonic setting of the source area. Based on trace element ratios and rare earth element (REE) patterns, it was interpreted that the sandstones were derived from a source area with felsic-mafic rocks as dominant contributors. The average chemical index of alteration (CIA) and weathering index (WIP) values are low with respect to Upper Continental Crust (UCC) in the studied sandstones and mudstones, but the index of compositional variability (ICV) values are high, thus revealing weak-moderate weathering conditions. The average Th/U ratios of the sandstones and mudstones indicate a relatively simple cycling history. The positive and low negative Nd-epsilon values support the supposition that the source area did not undergo much sedimentary change. A model mixture composed of 60% granite, 5% granodiorite, and 35% gabbro could be deduced to be the potential source composition of Middle Jurassic sediments; this model was reinforced by the Sr-87/Sr-86 ratios and Nd-epsilon((t)) values of the sediments. The Middle Jurassic siliciclastic sedimentary rocks of the Gumushane region were likely deposited in a tectonic environment with a passive margin.