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
投稿时间:2018-03-08  修订日期:2018-11-02
DOI:
中文关键词:  囊谦盆地  石膏  锶同位素  孢粉  沉积环境
英文关键词:Nangqian Basin  Gypsum  Strontium isotope  Palynological  Sedimentary environment
基金项目:
作者单位邮编
袁秦 中国科学院青海盐湖研究所 810008
樊启顺 中国科学院青海盐湖研究所 
魏海成 中国科学院青海盐湖研究所 810008
秦占杰 中国科学院青海盐湖研究所 
李庆宽 中国科学院青海盐湖研究所 
都永生 中国科学院青海盐湖研究所 
王明祥 中国科学院青海盐湖研究所 
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中文摘要:
      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。本文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87Sr/86Sr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,其中干旱分子占到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我们认为: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。
英文摘要:
      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 only 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 87Sr/86Sr ratios form gypsum and salt springs vary from 0.70853-0.70898,indicating that the gypsum deposits 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 Taxodiaceaepollenites appears sporadically, and reaches as high as 36% in abundance at some levels, but the average is 9%, which may reflect a humid or swampy habitat. On the basis of 87Sr/86Sr ratios form gypsum and salt springs combine with 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 brief humid periods, which is the reason for the multi-cycle depositions of mudstone and gypsum.
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