Climate Variations During 7900 A B.P.-2600 A B.P. In The Regions Along The Middle Reaches Of Yi River

Holocene begins at 11.5 ka B.P., a geological period which is the most closely related tohuman activity although it is very short. Both the origin of human society and lay of the naturalenvironment occur in this period, so the climate change of this period has becoming focus of thecurrent international research on the past climate changes.The regions along the middle reaches of Yi River in Shandong is the center of the cultureareas of Haidai Region, where the Neolithic period culture was very advanced and prehistorichuman activity. But the research of Holocene climate change in this area is not enough. So thestudy can fill the blank of Holocene environment evolution in this area and provide the basis ofthe research of the development of the ancient culture.Through a lot of field works, a profile in Linyi Hedong district near the airport has beenselected which is continuous and complete. Analyze the samples climate substitution indexessuch as grain size, geochemical element, discuss the climate change between 7900 a B.P.-2600 aB.P. in this area. The conclusions are as follows:（1） 7900 a B.P.-6200 a B.P.: the period of climate change.The curves of Al₂O₃、Fe₂O₃and TiO₂contents start to increasing in the research profile. Theweathering eluvial indexes and the ratios of CaO/MgO、SiO₂/Al₂O₃and SiO₂/（Al₂O₃+Fe₂O₃） arebecoming smaller; The content of Sr quickly become smaller from maximum in the entire studyregional, the content of V gradually began to increase from minimum and the loss on ignition（LOI） is increasing until the maximum in the whole profile, the content of sand in size ofcomponents starts reducing, fine sand and clay contents are bigger and the average particle sizeis larger. All of these indicate that the chemical weathering enhance, climate change to be humid.At the same time rainfall gradually increases.（2） 6200 a B.P.-4400 a B.P.: the most warm and wet period in Holocene.The value of Al₂O₃、Fe₂O₃and TiO₂still stay at a higher state. The change of the weatheringeluvial indexes and the ratios of CaO/MgO、SiO₂/Al₂O₃and SiO₂/（Al₂O₃+Fe₂O₃） are consistent and stable increasing, but the increasing range is not big. Content of Sr is stable, and hasremained very low state, Rb/Sr presents stable gentle trend of increasing, the average content ofV is the biggest within the study period. All of these show chemical weathering is strong, and theclimate is rainfall, most warm and wet in this period.6200 a B.P.-4700 a B.P.: LOI has been reducing in this stage, the variation is small, but thevalue is still high for the whole study profile. The content of clay is the maximum of the wholeresearch profile, the content of fine sand change to increasing. In the 5200a B.P., average particlesize suddenly appeared a surge, suggested that a large paleoflood happened in that period, so thewater drive coarse particle in this deposit, the particle size particles suddenly get big.4700 a B.P.-4400 a B.P.: climate was not stable. Values of Al₂O₃、Fe₂O₃obviously decrease,the weathering eluvial indexes and the ratios of CaO/MgO、SiO₂/Al₂O₃and SiO₂/（Al₂O₃+Fe₂O₃）gradually become bigger, The curve of Sr increase more stable compare with the previous stage,Rb/Sr reducing stable, instruct that the change of climate happened volatility. And thecomposition of grain size curve changes more twists and turns, due to the influence of paleofloodin Holocene, which lead to the change of particle size not stable.（3） 4400 a B.P.-3986 a B.P.: climate change to colder and drierThe value of Fe₂O₃、Al₂O₃is smaller, the weathering eluvial indexes and the ratios ofCaO/MgO、SiO₂/Al₂O₃and SiO₂/（Al₂O₃+Fe₂O₃） gradually become bigger, the content of Srincreases steadily and the content of V starts reducing. The value of LOI evidently decreasedcompared with the previous period and has been in reduced overall; the content of powder sandis increasing, shows that the small surface runoff, handling capacity reduction and the particlesize is fine. All the indexes comprehensive reflects the reduce rainfall, chemical weatheringabate, the climate change to cold and dry.（4） 3986a B.P.-2600a B.P.: climate is not stable and flexible.The values of Fe₂O₃、Al₂O₃、TiO₂are all low; the curves of CaO/MgO、SiO₂/（Al₂O₃+Fe₂O₃）in this period are twists and turns. Compare with the previous stage, the content of Sr increasesgradually but Rb/Sr decreased. In this period, the value of LOI is the minimum in the wholestudy section. The grain composition mainly is silt, and coarse sand generally increases. In thisperiod climate continue to deteriorate at a chilly and fluctuation state. Overall, Yi River midstream area is warm and wet during 7900 a B.P. -2600 a B.P.,including climate many times fluctuation change, such as in 4400 a B.P. appear an apparentlycooling phenomenon.