Spatio-temporal pattern of detrital clay-mineral supply to a lake system on the north-eastern Tibetan Plateau, and its relationship to late Quaternary paleoenvironmental changes

Abstract

Clay-mineral fingerprints from modern and fossil lake sediments from Lake Donggi Cona, situated on the north-eastern Tibetan Plateau were studied to determine changes in sediment provenance and environmental development since the late Glacial. To infer the source areas of the lake sediments, characteristic facies units (cover sediments and soils) from the catchment of the lake were studied concerning their clay-mineral compositions and through statistical analyses using the Fuzzy C-Means algorithm.Sediment contributions from the various geological provinces in the catchment of the lake are reflected in a systematic spatial pattern of variable clay-mineral assemblages, which is most pronounced in modern fluvial and lake sediments. Downcore changes in the clay-mineral fingerprints of lake sediments provide information on the spatio-temporal variability of detrital sediment supplies, related to climate-influenced changes in environmental boundary conditions.Since the late Glacial, water-level fluctuations driven by glacier melt appear to have exerted the greatest control over the transport paths of detrital sediments. Probably glacial melt-waters carried mainly illitic rich pre-Cenozoic debris into the lake from the northern and north-western catchment areas. During the Holocene the detrital clay mineral supply was mainly controlled from pre-Cenozoic and Neogene sources. However, because of the increased summer monsoon precipitation the lake level rose dramatically to at least modern levels, resulting in a relative increase in the supply from pedogenic karstic weathering sources mainly from the east, which during the Holocene was possibly flooded more widely than today. During the late Holocene a decreasing input of smectite suggests a relative reduction in the supply of far-traveled aquatic suspensions into the lake. In contrast, during the same interval kaolinite concentrations increased, which suggests a relatively strong sediment supply from the east, possibly triggered by a current flowing from east to west.