| Understanding the process and characteristics of paleoclimatic evolution and predicting the future trend of climate change is the goal of studying the evolution of the Quaternary climate. The loess-paleosol depositional sequence of the Loess Plateau records the climatic and environmental evolution information of the multi-cycle in the Loess Plateau since the Quaternary period, it's a good carrier to study the environmental changes at different scales. The southern margin of the Loess Plateau as the research area of this paper, is a semi-humid to semi-arid transition climate sensitive area, Study on the evolution and characteristics of climate evolution and the climate stability during the transition from the last interglacial to the last glacial period, it's a supplement to the study of climate change in the transitional period and forecast the trend of future climate change, And it has scientific significance to the ecological construction of the Loess Plateau during the transitional period.This paper based on the detailed field investigation, taking the upper part of the upper part of the Paleo-soil layer Si and the lower part of the loess layer Li in the middle late Pleistocene of Caijiapo of Baoji and Yangling in the southern margin of the Loess Plateau as the research object, mass magnetic , calcium carbonate, grain size, and sporopollen fossils were test on the high density collected soil samples, and analyze the change of the index data over time. Explore the climate transition from warm to cold during the middle late Pleistocene, Climate Change Process and Characteristics in Southern Margin of the Loess Plateau, and whether there is a short time scale climate change or unstable climate events, also discuss the consistency and sensitivity of the climate change with other areas of the Loess Plateau, northern China and ice core records, Obtained the following understanding:(1) According to the former established the Loess Plateau time scale, obtain the time boundary for the bottom and top of S1 and L1, combined with the sections thickness of Si and Li, time resolution and relative age of the samples were calculated,at the same time, the boundary between the last interglacial stage and the last glacial period is determined, Yangling section is deep at 9.24m, Caijiapo section is deep at 8.9m.(2) At the end of the last interglacial period, the southern part of the Loess Plateau was affected by the summer monsoon, which was relatively warm and humid,Magnetic susceptibility, clay content appears high value, Strong weathering and the vegetation is dominated by grassland, However, there are also have subtropical species, deciduous broad-leaved species and aquatic plant spore pollen,indicates that local or near source climate warmly and humidity. In the early stage of the last glacial period, was influenced by the winter monsoon, the sediment accumulation accelerated and the grain size became coarse,this is also evidenced by the emergence of dry plants and the increase of coniferous trees; However, in the later stage of this stage,the magnetic susceptibility values become higher, and CaC03 (%) becomes lower,The results showed that the climate changed from warm to cold, the latter has a slight warming trend. The data of each index changed continuously and didn't appear large fluctuation, which indicated that the climate gradually changed and no detection of abrupt climate change events.(3) Compared with the data of the two sections of the southern margin of the Loess Plateau, found that Caijiapo slightly moist than Yangling, and each of the index data amplitude is less than Yangling, it's indicated that the slope direction has some influence on the sensitivity of climate response in the small area.(4) Comparison with other regions of the Loess Plateau, northern China and ice cores record, southern margin of the Loess Plateau is consistent with other regions in response to global climate change,but in response to the sensitivity level, lower than the high latitude and high altitude areas. |
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