The climatic-environmental evolution since the interstadial epoch of the last glaciation along the Jiufangtai profile of the Salawusu River Valley

Abstract: The Salawusu River Valley, located in the transition zone between the loess plateau and the Mu Us desert, has kept sensitive records of paleoclimate since the last interglacial period. The profile which contains the aeolian sand with some interbeddings of sandy soil and limnetic paleosol facies in the downstream part of the valley was recently termed Jiufangtai Stratigraphic Section. In this paper, the authors focused the study on the top section since the interstadial epoch of the last glaciation and employed a series of geological methods, such as the AMS-14C, OSL dating method, grain size, magnetic susceptibility, Rb, Sr elements and their ratios. Based on the data obtained and the climatic-stratatigraphic comparison with the relative marine isotope stage, the authors further divided the strata into the following sequences: (1) the MIS 1 sequence (0~11 ka B.P.), which was a mainly dry period at the beginning of the Holocene, consistent with records from the arid-semiarid transition zones in other places. And the 1.5~1.8 cal ka B.P. was a wet phase when the modern Salawusu River formed; (2) MIS 2 sequence (11~28 ka B.P.), which was a lasting and stable dry and cold period; (3) MIS 3 sequence (28~52 ka B.P.), which mainly contained 2 warm and humid periods (MIS 3a and MIS 3c), and a cold period (MIS 3b), similar to things of MIS 1. The lacustrine facies in MIS3 sequence was similar to the particular warm and wet stage in the Tibetan Plateau and its adjacent areas, which recorded the strong summer monsoon event during 30~40 ka B.P.. It is concluded that the paleoclimatic records had a comparable sedimentary response to the global and regional climate events. Thus, the valley is an ideal zone for studying climate changes in China. In addition, some comprehensive analysis should be conducted in the reconstruction of the valley paleoenviroment history, because there are varying degrees of limitations in different assumptions.