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Tracing provenance and chemical weathering changes in Ankara Stream sediments, central Turkey: Geochemical and Sr-Nd-Pb-O isotopic evidence

2018    Eker, Cigdem Saydam; Sipahi, Ferkan; Gumus, Mustafa Kemal; Ozkan, Ozay

This study aims to analyze the changes in sediment provenance through the geochemical and Sr-Nd-Pb -O isotopic composition of the Ankara Stream bed and overbank sediments (ASBS and ASOS) and to examine the weathering and sediment transport processes in response to step climate variability. Major, trace, and rare earth elements, as well as Sr-Nd-Pb-O isotopic composition, exhibit generally similar variations for the investigated samples. These sediments have relatively high Nd-epsilon((0)) values and low Sr-87/Sr-86 ratios. Similar Pb isotopic ratios also characterize these sediments but have slightly different delta O-18 isotope values with relatively higher delta O-18 isotope values in the ASBS and lower delta O-18 isotope values in the ASOS samples. Chemical indices indicate low moderate chemical weathering in the step dominated climate. The low average Zr/Sc and Zr/Nb ratios indicate that such geochemical change was dominated by the composition of the source rocks but not sedimentary recycling with zircon enrichment, reflecting first-cycle deposit. Low radiogenic Sr-87/Sr-86 ratios and negative Nd-epsilon((0)) values indicate that the investigated sediments are relatively derived from young magmatic provinces, which are intermediate sources. Finally, the findings show that the geochemical compositions of the ASBS and ASOS were dominated by the composition of the source materials that originate from Galatia province and Late Cretaceous-Early Tertiary volcanic rocks in central Anatolia. Reasonable semiarid to arid climatic conditions are observed in the region. Active tectonism, increased erosion, and the investigated sediments are also transported rapidly to the stream channel without chemical alteration, and the sediments are the first-cycle products. (C) 2017 Elsevier Ltd. All rights reserved.