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兰州地区新近纪地层的沉积相与古环境记录

ISSN号：1000-0550
期刊名称：沉积学报
时间：0
页码：611-619
语言：中文
分类：P512.2[天文地球—地质学]
作者机构：[1]兰州大学西部环境教育部重点实验室,兰州730000, [2]甘肃省地质调查院,兰州730000, [3]中国科学院地质与地球物理所,北京100029
相关基金：国家自然科学基金项目（批准号：40625009、40121061）; 兰州大学引进人才基金（批准号：581406）资助
相关项目：青藏高原和中东亚干旱区环境变化与地表过程研究

关键词：兰州地区, 新近纪, 风尘沉积, 古环境, Lanzhou area, Late Tertiary, eolian deposits, paleoenvironment

中文摘要：

兰州地区位于黄土和青藏高原的过渡带,其第三纪地层对研究风尘沉积发育和青藏高原隆升都有着特殊的意义。本研究以0.25 m为间距对厚度210 m的兰州皋兰山剖面的新近纪地层采集样品901个,在实验室对试验样品进行前处理后对其进行了粒度、磁化率和色度测试。用粒度分布函数的方法分离了沉积物的各成因组分,确定了风成组分和水成组分在全剖面沉积物中所占的百分比。结合色度和磁化率的实验结果分析表明,皋兰山剖面地层以风尘沉积为主,其间夹有河流相沉积的约15层砂岩。古环境的恢复表明,兰州地区从至少约7 Ma开始,沉积地层经历了由河湖相向风尘沉积转变,气候干旱化开始,与黄土高原风尘序列堆积底界8～7 Ma基本一致。6～5.2 Ma构造稳定,是比较开阔的平原环境,并且气候条件比较湿热;5.2～3.5 Ma间构造波动比较频繁,形成了间隔性的河流相砂岩沉积,而在气候表现为干冷;自3.5 Ma开始,兰州地区发生相对构造沉陷,五泉砾岩层的发育是对青藏运动A幕的具体响应。

英文摘要：

Lanzhou Area is located on the northwestern margin of the Loess Plateau and the northeastern margin of the Tibetan Plateau,which Tertiary stratum are specially significant for the research of the Tibetan Plateau uplifts and the development of the eolian sediment.With a thickness of 210 m,the Gaolan section belongs to the late Tertiary according to the magnetostratigraphy.901 samples were obtained from the field in a sampling pace of 0.25 m and subsequently the grain-size,magnetic susceptibility and chroma experiments were accomplished in laboratory.The measured particle size data were separated by a mathematical method to gain the components of different origins as well as the ratio of each component.The analytical results of environmental proxies show that Gaolanshan section is eolian deposition with 15 layers of sand accumulated by rivers.The reconstruction results of paleoenvironment imply that the sedimentary stratum of the section had changed from fluvial deposits to eolian deposits at 7 Ma.That means the initial drying of the internal Asia continent begun at least 7 Ma ago,the conclusion of which is consistent with the main Loess Plateau.Lanzhou area was a relatively open plain and structurally stable with a wet and warm climatic condition in 6～5.2 Ma;in 5.2～3.5 Ma,the tectonic activities were frequent thus the septial river sand formed and the climate was dry cold;the lithosphere of Lanzhou area began to become relatively depressed at 3.5 Ma and Wuquan conglomerate is a result of the phase A of Qinghai-Xizang movement.

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