Paleoclimate Change In The Middle And Late Pleistocene Revealed By The Core CH0310 In The Qiadam Basin

Paleoclimate and paleoenvironment can be reconstructed by lake sediments. In the Qiadam Basin, a huge intermountain basin, there are continuous,integrated and thick sediments in the Quaternary which is significant for recognizing the uplifting of the Qinghai-Tibet Plateau and understanding the paleoclimatic and paleoenvironmental change within the region. A 520-meter-long sediment core (labeled CH0310) was retrieved from Qarhan paleolake to analyze the regional climate change in the middle and late Pleistocene.On the basis of the points derived by matching the observed magnetostratigrphy to the geomagnetic polarity timescale, an orbital tuned timescaale for core CH0310 was developed, which assigns an age of 440 kyr for the base of the core. By analyzing climate proxies of calcium carbonate,magnetic susceptibility and total organic matter(TOC), the experimental results show that it is positively correlated between magnetic susceptibility and coarse sand content level and anti-correlated between the clay content level and magnetic susceptibility; the inverse correlation between magnetic susceptibility and TOC was presented in the fine-grain sediments and the positive correlation in the corse-grain sediments, which indicates that the different climate response patterns of magnetic susceptibility are different among the different sediment layers in CH0310 and the complex factors of lake magnetic susceptibility, so special care is vital if using magnetic susceptibility as a single indicator to reflect the paleoclimatic and paleoenvironmental changes.Furthermore, the calcium carbonate analytical result denotes that the origin of its ingredients is uncertain and the content in is relatively stable (more than 60% of the samples concentrates between 9%～13%).For the core CH0310, TOC can serve as a good proxy indicator of climate and the high data indicates that the paleoclimate is warm and moist, whereas it is cold and dry, the warm(cold) and the moist(dry) have been synchronous.The features of climate change in the middle and late Pleistocene can be revealed by TOC, according to the TOC, there are periodic cycles of climate change in the middle and late Mid-Pleistocene in Qiadam Basin since 440～21kyr, which can be divided 10 phrases. In the 2(～29.2kyr),4(68.3～87 kyr),6(126～214 kyr),8(257～306 kyr),10(349～381kyr)phases, the low TOC relatively indicates that the paleoclimate is cold and dry. while in the 3(29.2～68.3kyr),5(87～126kyr).7(214～257kyr),9(306～349kyr),11(381～433kyr)phases, the paleoclimate is warm and moist. What's more, it is revealed that the climate has changed to drier. Compared with the adjacent core named CK6 in Qiadam Basin andδ18O record in the Ocean, the climate change in the middle and late pleistocene revealed by the core CH0310 and that of the core CK6 can be well comparable, there are periodic cycles of climate change bewteen warm-moist and cold-dry, and the sychronization is consistent. There are periodic cycles of climate change in the middle and late Pleistocene in Qiadam Basin, which can be well corresponded to A18O record in the Ocean from MIS3 to MIS11.Not only the climate change in Qiadam Basin have the global features, but also the regional characteristics of climate is obvious because of the differences in MIS7 and MIS9.