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地质学,西宁盆地晚始新世泥岩地层粒度特征及其古环境指示意义

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西宁盆地晚始新世泥岩地层粒度特征及其古环境指示意义

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职称论文发表期刊摘要: 西宁盆地较为完整地保存着一套新生代(约55~17Ma)地层,盆地内的水湾村附近出露的晚始新世石膏-红色泥岩旋回沉积序列,是研究晚始新世气候演变的理想地质记录。关于这套地层的沉积环境存在不同的观点,尤其是关于其中泥岩地层成因的争论颇多,主要有洪积扇远端沉积、咸水深湖沉积和风积成因三种观点,差别甚大,至今没有统一的认识。沉积物的粒度可以用来反演其形成时的沉积动力及沉积环境,为了明确该段地层中泥岩的沉积环境,本文选取水湾剖面代表性泥岩样品进行了系统的粒度测量及分析,结果表明西宁盆地晚始新世泥岩沉积与黄土高原典型黄土-古土壤粒度特征类似,应为风积地层,而不是洪积扇远端或咸水深湖沉积。西宁盆地晚始新世风积地层的发现为盆地区域构造和古气候演化研究提供新的研究视角。

关键词: 古地理学;西宁盆地;晚始新世;泥岩-石膏旋回;粒度特征;风积地层

HOU Jili1,, LIU Xiuming2,*, MA Mingming1,, ZHANG Yuyin2,, WU Haibin3,
(  1、School of Geographical Sciences,Fujian Normal University,Fuzhou 350007;       2、 Key Laboratory of Humid Subtropical Eco-geographical Process (Fujian Normal University),Ministry of Education, Fuzhou 350007;       3、Department of Environmental and Sciences,Macquarie University,Sydney NSW 2109,Australia;  )
Abstract: A continuous sequence of Cenozoic sediments (about 55~17Ma) is preserved in Xining Basin.In this basin,the Shuiwan section which is characterized by multi-cycle of mudstone and gypsum deposits that formed during late Eocene (about 40~33.3Ma) is an ideal site for the study of the paleoclimate evolution.Three different opinions were raised for the origin of mudstone:a distal alluvial fan environment,a deep saline lake environment,and even aeolian deposits.Granularity of sediments can be used to reveal their deposit dynamics and conditions.So in order to reveal the depositional environment of the mudstone-depositions,some pilot samples were collected from Shuiwan section,and systematic and detailed grain size measurements were conducted.The results show that the grain size properties of mudstone are similar with those of typical loess-palaeosol of Chinese Loess Plateau (CLP),so the mudstones should be aeolian deposits,but not distal alluvial fan or deep saline lake sediments.This view provides a new sight for regional tectonic and paleoclimate evolution studies in Xining Basin during late-Eocene.
Keywords: Paleogeography; Xining Basin; late-Eocene; Mudstone-Gypsum cycles; grain size; Aeolian deposits

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