末次冰期以来乌兰布和沙漠北缘的环境变迁  

ENVIRONMENTAL EVOLUTION OF THE NORTHERN BORDER OF ULAN BUH DESERT SINCE LAST GLACIATION

作　　者：赵杰[1] 李德文[1] 孙昌斌[1] 赵俊香[1] 

机构地区：[1]中国地震局地壳应力研究所,地壳动力学重点实验室,北京100085

出　　处：《第四纪研究》2017年第2期380-392,共13页Quaternary Sciences

基　　金：国家自然科学基金项目（41471002、41171001和40971013）和地震行业专项项目（批准号：201408023）共同资助致谢U、Th和K元素含量在核工业北京地质研究院完成,14C样品前处理、AMS测量、同位素测定、年龄计算和校正由北京大学科技考古实验室完成;编辑部和评审专家为本文提供了深入细致的修改意见.

摘　　要：乌兰布和沙漠北部边缘是人类活动与环境变化相互作用较为典型的区域，对其形成和演化历史的恢复重建有助于认识和理解区域人地关系。本文基于遥感解译、野外调查和室内分析，对乌兰布和沙漠北缘（磴口以西地区）十多个湖相地层出露点（包括3个典型剖面）进行了较为详细的地貌、沉积和年代学研究，获得了研究区湖泊退却最后阶段的地层记录。测年结果表明研究区大部分在9．315—7．375kaB．P．（10．64～8．06eal．kaB．P．）的时限内退出湖泊环境，局部（可能为河汊或湖湾）湖相沉积可延续至全新世中晚期。沉积研究表明，所观察到的湖相地层大体形成于42cal．kaB．P．以来的河口环境，但河流过程和湖泊过程的相对强弱存在明显的时空分异。剖面下部（约42cal．kaB．P．以来）沉积物相对较粗，推移质占主导，斜层理局部可见，反映波浪作用对沉积物的搬运沉积具有主导作用，湖水相对较深，有利于动力较强的波浪的形成；剖面上部（大约在全新世以来）沉积物普遍变细，以悬移质沉积为主，最后阶段均沉积具水平层理的“红胶泥”，软体动物大量繁衍，指示晚期湖泊近岸区域水动力条件弱、湖水浅、坡降小，沉积过程以静水堆积为主导。空间分异特征反映了河口环境河流冲积过程与湖泊滨岸过程在不同位置的作用程度不同，主要与三角洲平原上分流河道的规模和持续时间，以及堆积区水下地形特征及其与河口的相对距离有关。基于地层记录和沉积环境分析，结合前人资料，本文认为研究区湖泊由深变浅直至消亡的过程主要与晋陕峡谷溯源侵蚀引起的河套古湖出口下切有关。Ulan Buh Desert is typified by the interaction between human activities and climate change, and the reconstruction of history of formation and evolution will help to understand in the human-earth relationship. Combined on analysis of remote sensing and previous data, in this paper, more than ten exposing sites （including 5 profiles） of lacustrine deposit in the northern border of Ulan Buh Desert （to west of Dengkou County） are investigated in details by geomorphic, stratigraphic and chronological means, and a latest records before the lake retreating are obtained. The results show that the lake retreating began around 9. 315-7. 375ka B.P. （ 10.64 ～ 8.06 cal.ka B.P.）in most of the study area, but locally may continue to Middle- or Late-Holocene, perhaps, for some bays. Field and laboratory data indicates that the lacustrine strata was generally deposits formed at estuary environment since about 42cal.ka B.P., but the intensity of fluvial and lake processes was obviously various in both time and space. Temporally, before the Holocene, deposits are relatively coarser ones with oblique bedding, somewhere; reflecting relatively deep water of lake and dominant wave role in transportation and deposition of sediments, the relatively deep lake was advantageous to the formation of strong wave. Since the Holocene, sediments were becoming finer, and the setting of the suspended load predominates in deposits, all of which were covered by the red clay with horizontal bedding. It shows that the most shore were in still water environment. Spatial differentiation of sediments has mainly reflected the mutual growth and decline between the processes of rivers and lakes, and can be regard as response to scale of distributary channels on the delta plain, and to the relative distance of setting site from mouth of distributary channels. Based on stratigraphic records and analysis of sedimentary environments, combined with previous data in the study and its adjacent areas, we believe that the shallowing and retreating of t

关 键 词：乌兰布和沙漠北缘 末次冰期 河口环境 三角洲 粒度分析 河套平原 

分 类 号：P532[天文地球—古生物学与地层学] P941.73[天文地球—地质学]