Spatial uniformity in the mineralogical and geochemical compositions of surface sediments in Lake Qinghai and their controlling factors

Abstract

To advance the understanding of the spatial variability of sediment composition and its controlling factors in a large hydrologically closed lake, the spatial distributions in the mineralogy and geochemistry of 18 surface sediment samples along three transects across the deepest part of Lake Qinghai on the northeastern Tibetan Plateau were investigated. The data show (1) that the surface lake sediments are almost the same in the XRD patterns, (2) that the sediments do not have considerable changes in geochemical compositions along three transects and (3) that the standard deviations of the lake sediments are low in grain size, elemental abundances, δ13C and δ18O values of carbonates, and total organic carbon and nitrogen, with the exception of one sample (QH-11) from the westernmost part of the northern sub-basin. These characteristics indicate that the spatial variability of the surface sediment across Lake Qinghai is very low in geochemical and silicate mineralogical compositions, with limited differences in the chemical composition of carbonates associated with river water dilution. Sample QH-11 has anomalously high levels of MgO, a high carbonate content, and positive δ13C and δ18O values in bulk and fine-grained carbonates, probably because of the effect of calcareous tufa. Spatial uniformity in the mineralogical and geochemical compositions of surface sediments in Lake Qinghai can be attributed to the flat topography of the lakebed and stable sediment provenances, the latter dominated by dust deposition and authigenic carbonates. The spatial uniformity and dominance of dust and authigenic aragonite of surface sediments across Lake Qinghai provide a potential record of the hydroclimate in the past, which is associated with changes in the Westerlies and the summer monsoons.