Main content area

Geochemical characterization of the middle and late Pleistocene alluvial fan-dominated infill of the northern part of the Weihe Basin, Central China

Rits, Daniël S., Beets, Christiaan J., Prins, Maarten A., van Balen, Ronald T., Troelstra, Simon R., Luo, Chao, Wang, Bin, Li, Xiaoqiang, Zhou, Jie, Zheng, Hongbo
Palaeogeography, palaeoclimatology, palaeoecology 2017 v.482 pp. 57-69
basins, calcium, carbonates, clay, climate, dolomite, evaporation, hinterland, iron, loess, manganese, monsoon season, runoff, salinity, strontium, summer, tectonics, China
Major reorganizations in climate and tectonic regime occurred in East Asia during the Pleistocene, resulting in large-scale environmental changes. In this paper a detailed geochemical and mineralogical record of these changes is presented from a distal alluvial fan sedimentary sequence in the northern Weihe Basin. We established that, in addition to glacial-interglacial variation, there are three distinctly different units deposited over the past 1m.y. These units are the result of variations in the overall tectonic regime in the northern Weihe Basin.Fine-grained detrital minerals were predominantly delivered during colder climatic periods, whereas evaporative minerals were dominantly deposited during the warmer, interglacial periods, probably as a result of strong seasonal contrast. This compositional variation demonstrates the importance of climate control on hinterland erosion, surface runoff, chemical weathering and evaporation.Al-normalized ratios of indicative major elements relative to average loess composition, indicate important variations in sedimentary processes, mostly related to sediment flux. Si-enrichment is an index for past flooding events, while Fe enrichment, just like K and Ti, reflects influx of clays. In contrast, Ca and Mn are strongly enriched throughout the core, associated with the authigenic precipitation of carbonates, especially during interglacial periods.The lower (~1000–690ka) and upper (~330–0ka) units of the core are characterized by relative intense and frequent flooding, which coincided with extensive ponding in the study area. In the middle unit (~690–330ka) increased salinity levels caused by evaporation, as reflected in the high Sr/Ca ratio and dolomite abundance, led to increased carbonate precipitation. Simultaneously, the increased influx of fine sediments indicates increased clay production in the source area as a result of a more intense summer monsoon strength after 600ka.