A preliminary study of the climate and environment of Yushu area in Qinghai Province based on the carbon-bearing strata in trenches and profiles

39 peat and carbonaceous sand samples collected from Yushu of Qinghai Province that is located in southeast Tibetan Plateau were dated using AMS 14C technology. The samples were collected in two trenches and two profiles along the Yushu fault zone. The lithology of peat and carbon-bearing strata was analyzed with the AMS 14C ages of samples in the strata. The four phases of deposition process of the Holocene strata were distinguished in this paper. Phase Ⅰ: the early Holocene, 10100~6000a BP. This phase was suitable for formation of peat well. Phase Ⅱ: Mid-later Holocene, 6000～3500a BP. The phase was less suitable for stable sedimentation of peat. Carbon content was less than that of phase Ⅰ, and detrital deposit grew remarkably. The color of the strata became light. Phase Ⅲ: late Holocene, 3500~1500a BP. The climate in this phase started becoming dry and cool. The peat was not formed because of dryness and coldness. The detrital deposit continued to increase. Phase Ⅳ: from 1500a BP to present. The climate in 1500~1100a BP became drier and cooler and the detrital deposit was dominant at this stage. However, a carbonaceous sequence was developed in the Medieval Warm Period （MWP） after 1100a BP. The carbonaceous sequence was observed in lots of geomorphic units. The four phases conformed to the global climate changes reflected by peat from Hongyuan. All of the climate changes, geomorphology and tectonics controlled the growth and deposition of peat and carbon-bearing strata in Yushu area.