对青藏高原东南部青海玉树地区的39个泥炭和含炭砂土样品进行了AMS ~(14)C年龄测试,这些样品来自于为研究玉树断裂开挖的2个探槽和2个剖面。通过分析泥炭层及其他含炭地层的宏观岩性及其中样品的AMS ~(14)C年龄,将玉树地区的全新世含炭地层的沉积过程划分为4个阶段:阶段Ⅰ:早全新世,10100~6000a BP,非常适宜泥炭的形成;阶段Ⅱ:中晚全新世, 6000~3500a BP,较不适宜泥炭的稳定形成,沉积物中含炭量相对减少,碎屑增加,颜色变浅;阶段Ⅲ:晚全新世阶段,3500~ 1500a BP。该阶段的气候总体变的更加干旱和凉爽,基本上不能形成泥炭,碎屑沉积在持续增加;阶段Ⅳ:1500a BP 以来:自1500~1100a BP,气候可能更加干冷,沉积物中主要为碎屑沉积;1100a BP 以来,受中世纪暖期气候变化影响,在本区许多地貌单元近地表形成一层灰黑色的炭质层。这4个阶段与红原泥炭所反映的全新世气候变化波动趋势能较一致。气候、地貌和构造因素三者共同控制本区域内泥炭和炭质层的发育和形成。
英文摘要:
39 peat and carbonaceous sand samples collected from Yushu of Qinghai Province that is located in southeast Tibetan Plateau were dated using AMS ~(14)C 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 ~(14)C 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.