柴达木盆地中新世叠层石沉积特征及其环境和构造意义

SEDIMENTARY FEATURES AND TECTONO-ENVIRONMENTAL SIGNIFICANCE OF THE MIOCENE STROMATOLITES IN WESTERN QAIDAM BASIN

柴达木盆地西部地区发育了大量的各种类型的湖相叠层石,主要集中在中新世早中期下油砂山组的地层中。根据野外考察并参考国内外的叠层石研究,柴西地区叠层石主要包括丘状、指状、柱状和多边形叠层石4种类型,每一种叠层石的宏观形态、内部成份和构造都具有独特的特征,且形成于不同的沉积环境中。据地球化学元素、孢粉和生物化石等分析可以确定,叠层石形成于气候温暖、水体盐度较高和陆源碎屑流入较少的环境中。与现代叠层石的对比进一步明确了新生代柴达木盆地湖相叠层石的沉积特点和属性特征。结合柴达木盆地中新世的沉积特征、湖相叠层石的属性以及柴达木盆地与青藏高原的关系,进一步讨论了中新世期间青藏高原和柴达木盆地的构造情况以及隆起程度。

The distribution and development with sedimentary characteristics of Miocene stromatolites in western Qaidam Basin were discussed in this paper. The stromatolites were mainly occurred in the Xiayoushashan Formation in an age of Early and Middle Miocene. According to the field survey and laboratory study, the stromatolites in the Qaidam Basin could be classified into four types, namely, dome-shaped, finger-shaped, column-shaped, and polygonal ones, which were characterized by their own special morphology, internal composition and textures, therefore, the stromatolitic kinds could be acted as an indicator of varied depositional environments. Based on the evidence from geochemistry, spore and fossils, it was presented that the stromatolites developed in a warm and salty lacustrine environment, with less terrigenous input. Compared with the modern stromatolites, the Neogene stromatolites in the Qaidam Basin was further elucidated in sedimentation and features. Combined with the Miocene sedimentary features and lacustrine stromatolites property, a close relation between the Qaidam Basin and the QinghaiTibet Plateau was further discussed, which thought the basin＇s elevation during Early-Middle Miocene being less than 1 500 m.