Research On Pedogenetic Properties And Paleo-environmental Implication Of Loess In Dry Valley Of The Minjiang River

Soil are traditionally regarded as good records of paleo-climatic changes, provided insights into past long-term climatic changes, as a result, soil are widely used to indicate paleo-clmatic conditions and paleo-environmental evolution. With the development of paleo-climate and paleo-environment to higher resolution, research of soil provides important evidences for the global climatic evolution . abrupt oscillations and climatic change regularities. A better understanding of soil process is invaluable in predicting the future impacts of global environmental change on terrestrial ecosystems.Loess sections located in dry valley of the Minjiang River. These section are of ideal for the study on the climatic change in past 21ka of Minjiang River area. In order to reveal comprehensively the paleo-climate evolution of Minjiang River area, high precision sampling was done in Jiaochang section. Samples of stable carbon isotope were tested and a synthesis analysis was made combined to ¹⁴C dating , magnetic susceptibility(MS), carbonate(CaCO₃), Fet, Fed/Fet and grain size.The pedogenetic properties of loess were used to rebuild the paleo-climate in dry valley of the Minjiang River. The main results andconclusion are as follow:1. CaCCh and pH change irregularly in profile. The content of organic carbon of epicedian is higher than 20g/kg and organic carbon in profile decompose very slowly.2. These sections had good consistency compared to ice core records and deep-sea oxygen records, at the same time, they had been an important part of global climate changes. In addition, it is possible that the Jiaochang loess also recorded several typical climatic changes, including Yonger Dryas event> two Heinrich Events and so on, which can be compared with those of other sections.3. The research shows that the climate of this region during the period of the last glacial maximum (LGM) in research areas was mainly warm and dry. At the same time, it also responded the trend of the global climate change. During early Holocene, the climate was warmed and humid, experiencing a decline in temperature; During the early period of Middle Holocene, the climate was very warm and humid with small climatic fluctuations; While during the late period, the climate has relatively intense fluctuation; During late Holocene the climate came to dry and cold. In general, the climatic evolutional process was from warm-dry climate to cold-dry one.4. Based on the territorial vegetation evolution history inferred from the organic stable isotope variations, the territorial climatic changes since the last 21ka had experienced a series of stages. After 4.45ka, climate of Minjiang River area behaved unstably and cyclically, the temperature decrease step by step from middle Holocene to now and at present, aridity is still continuing.