Pleistocene Loess Deposits Reveal Paleoenvironment Of The Hominins Lived In The South Luo River Region

The South Luo River is located in the geography boundary belt between northern and southern China, where the climate is dominated by wax and wane of the Asian monsoon circulation; this region is also regarded as an important corridor of the Paleolithic cultural exchange between northern and southern China during Pleistocene. In the Quaternary, loess was accumulated in the South Luo River in intermountain basins and on river terraces, with a thickness of several tens of meters, recorded the paleoenvironment changes of this catchment. Tens of thousands of Paleolithic artifacts buried in these loess-paleosol deposits, which were left by the hominins lived in this region since the middle Pleistocene, were discovered in the past two decades. Therefore, it is significant to investigate the environmental changes during Pleistocene in order to fully understanding the Paleolithic cultural development and the human evolution.In this thesis, the elemental geochemical and Sr/Nd isotopic analyses were carried out to identify the loess origin and its provenance; To reconstruct the paleoclimate and paleovegetation changes by analyses of loess grain-size, magnetic susceptibility and organic matter carbon isotope; Elemental carbon and charcoal analysis were used to reveal wildfire and fire used by the hominins. Compare the environmental changes with phases of human activity to reveal the relationship among hominin activities, climate changes and wildfires.Origin and provenance analysis of the loess is basis for reconstructing environment changes used these loess deposits. The grain-size and chemical analyses show that the loess in the South Lou River region has similar particle size distribution and chemical composition with that of Chinese Loess Plateau (CLP) indicating they have an eolian origin. Sr/Nd isotope analysis showed that the South Luo River loess has a relatively high87Sr/86Sr ratio and very low εNd (0) value, indicating that the studied loess has multiple sources. Combined the loess distribution, sedimentary characteristics and modern dust storms monitoring data, we conclude that the South Lou River region loess deposition may mainly supplied by two sources, one is the local sources in our study region and the other one is dust from the remote northern and northwestern China.Grain size of the loess in the South Luo River region show that, the grain size is finer and has little variation since the middle Pleistocene, revealing that the cold air from the north has been blocked by the Qinling mountains and significantly weakened; The uniform chemical elements content, higher Chemical Index of Alteration (CIA) indicating that compared with Chinese Loess Plateau, the summer monsoon was enhanced in the South Luo River region and the climate was warmer and more humid. In the context of gradually drying and colding in the northern China during the Quaternary, a stable and relatively warm and humid climate in the South Luo River region may provide a niche for the hominin lived in.Organic matter carbon isotopic composition of bulk loess samples (δ13Corg) are obviously linked with the magnetic susceptibility of the loess, reveals the vegetation changes in this region was mainly forced by the climate variations. Before0.4Ma, the loess δ13Corg value is stable, mainly around-24‰, it revealed a pure C3plants dominated vegetation; after0.4Ma, the δ1Corg value increased and changed with the fluctuations of glacial-interglacial changes, the δ13Corg have a wide distribution. The vegetation is C3dominated and C3-C4mixed vegetation, C4vegetation increased in the interglacial. Integrate δ13Corg, palynologicla and paleontological data we conclude that the hominins lived in the South Luo River region in the Pleistocene was under a mixture of woodland and grassland vegetation context.Total charcoal content in the loess was correlated with the magnetic susceptibility and δl3Corg changes show that occurrences of the wildfire were mainly controlled by the climate and vegetation changes in the Pleistocene. Phases of hominin used fire which were record in the Longya Cave deposits were corresponding to the high charcoal content period record in the loess deposit, indicating that frequently wildfire occurrence may have provided advantage for fire-using of the hominins. Elemental carbon content of loess represents a high-temperature fully burnt or combustion of fossil fuels. The Element Carbon content was in a relatively low value below the surface loess samples may indicate that the hominins have not known to initiatively select the efficient fuel in the Paleolithic ages.