青海囊谦盆地始新世石膏层沉积环境研究  

The Sedimentary Environment of the Late Eocene Gypsum in Nangqian Basin,Qinghai Province

作　　者：袁秦[1,2,3] 樊启顺 魏海成[1,2] 秦占杰 李庆宽[1,2,3] 都永生 王明祥[1,2] YUAN Qin;FAN Qi-shun;WEI Hai-cheng;QIN Zhan-jie;LI Qing-kuan;DU Yong-sheng;WANG Ming-xiang(Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources,Qinghai Institute of Salt Lakes,Chinese Academy of Sciences,Xining,810008,China;Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes,Xining,810008,China;University of Chinese Academy of Sciences,Beijing,100049)

机构地区：[1]中国科学院青海盐湖研究所,中国科学院盐湖资源综合高效利用重点实验室,青海西宁810008 [2]青海省盐湖地质与环境重点实验室,青海西宁810008 [3]中国科学院大学,北京100049

出　　处：《盐湖研究》2020年第1期69-77,共9页Journal of Salt Lake Research

基　　金：国家青年基金(41602024);中国科学院青海盐湖研究所所引导基金(Y360391053)联合资助。

摘　　要：囊谦盆地出露有晚始新世贡觉组石膏—红色泥岩沉积旋回,对研究古气候演化和沉积环境提供了良好的素材。以往的研究仅限于膏盐地层海陆相判定,而对其形成过程未有报道。采集囊谦盆地的盐泉水、贡觉组第三段的石膏和碎屑沉积物样品,并分析锶同位素比值和孢粉组合特征。结果表明,囊谦盆地盐泉水和石膏87 Sr/86 Sr比值分布在0.70853~0.70898之间,且位于陆源水的比值范围内;红色碎屑层孢粉组合主要以麻黄—白刺—栎粉为主,其中干旱成分占到45%,主要以麻黄粉(30%)和白刺粉(13%)为主,指示了干旱的气候环境;裸子植物杉粉在红色泥岩中的含量有所波动,最高含量达到36%,平均含量为9%,指示气候干湿交替变化。综合Sr同位素分析和孢粉分析认为,在全球中纬度干旱的大背景下,囊谦盆地石膏层形成于相对干旱和相对湿润的气候环境交替变化的陆相环境。The Late Eocene section from Gongjue formation in Nangqian Basin includes a unique multi-cycle deposition of red mudstone and gypsum,which provides a unique opportunity to study the variation of paleoclimate in Late Eocene.The previous study was restricted to differentiate the origin of these strata from marine or nonmarine facies.However,studies about the sedimentary environment of these strata are still rare.In this paper,we collected the samples from Nangqian Basin,Qinghai province,and analyzed the strontium isotope of gypsum and salt springs and the sporo-pollen assemblages of mudstones.Results show that the 87 Sr/86 Sr ratios of gypsum and salt springs vary from 0.70853-0.70898,indicating that the gypsum deposited in nonmarine environment.The palynological assemblages in the red mudstone are dominated by Ephedripites-Nitrariadites-Quercoidites.The xerophytic taxa together contribute nearly 45%,as represented by Ephedripites(30%)and Nitrariadites(13%),indicating a typical arid environment.The pollen produced from gymnospermous trees,such as Taxodiaceae pollenites appears sporadically,and reaches as high as 36%,with an average 9%,which may reflect a humid or swampy habitat.On the basis of 87 Sr/86 Sr ratios of gypsum and salt springs,and the palynological assemblages,we conclude that in Late Eocene when the global drought happened in the mid-latitude region,there is a continental brackish lake in Nangqian Basin experienced relatively dry climate with several humid periods,resulting in the multi-cycle deposition of mudstone and gypsum.

关 键 词：囊谦盆地 石膏 锶同位素 孢粉 沉积环境 

分 类 号：P512.2[天文地球—地质学]