Preliminary Study Of Climate Recorded By The"Old Red Sand" Of Keren Profile In Jinjiang Of Fujian Province Since The Late Pleistocene

The distribution area of KR "old red sand" of Jinjiang in Fujian locating in the southeast coast of China is the typical region strongly influenced by the East Asian monsoon which can nicely record the paleoclimate evolutionary process of the East Asian monsoon. Based on the previous age model, this paper analyzed the environmental proxies of sediments of KR section "old red sand", for example grain size, elements, organic and magnetics, and has been preliminary divided the sequence of climatic change of the south coast of Fujian during late pleistocene epoch. After comparing the different regional climate change, the present study yielded the primary conclusions as follows:(1)Significance of climate and environment proxies in "old red sand":Grain Size Parameter reflect that the source material of KR old red sand is relatively single, also,the sedimentary environment is rather stable. The variation of mean grain size demonstrates a cycle changes of winter monsoon intensity, and then indicate the region climatic wet and dry changes. The result of macroelements analysis reflect that, overall, the research area since middle-late late pleistocene is in a warm chemical weathering environment. The microelement content shows KR "old red sand" is a continental sediments, but the sedimentary exist more strong and complex epigenetic change. The result of magnetisability analysis reveals that the surface layer of old red sand profile contains many magnetic minerals, and from the field surface, the magnetic minerals content decreased gradually along with the depth.(2)The paleoclimate evolutionary process of the research area during the middle late Pleistocene epoch can be divided into four stages:about54.0-42.5ka B.P., the climatic pattern was expressed as the combination of warm wet-cold dry-warm wet-cold dry; about42.5-28kaB.P., it showed warm and humid climate; about28-10kaB.P., early climate was very dry and cold, gradually warmer late; the Holocene period (since lOka B.P.), it showed warm and humid climate. The last fifty thousand years, the paleoclimate evolution of the research area has experienced the alternative variation about cold dry-warm wet-cold dry and warm wet.(3)we get environmental sensitive grain size group in KR profile by using grain size-standard deviation method, then, using red noise spectrum analysis with the redfit3.8 show that it exist a obvious precessional and half precession cycle in changes of the sensitive grain size group sequence, That’s probably a reflection of the solar radiation in orbit-scale plays an important role in the process of Asian monsoon change. But, the result have a difference with the previous researchers, in which show a23ka and19ka precession cycle, Maybe, it is the climate change in the study area respond to the low-latitude monsoon circulation in orbit-scale.