青海囊谦古近纪盆地沉积特征及沉积环境分析

Sedimentary Characteristics and Environment of the Paleogene Nangqian Basin in Qinghai Province

囊谦盆地是在藏东北段沿金沙江-红河构造带分布着一系列呈NNW向展布的中小型古近纪盆地的典型代表。通过野外地质调查、分析测试和室内综合研究,在盆地演化的格架内,系统分析了囊谦盆地贡觉组古气候、沉积相标志、物源以及沉积环境等方面的特征,认为贡觉组可划分为三段式结构,沉积环境为冲积扇-河流-湖泊-三角洲环境;砾石成分较复杂,分选、磨圆差,填隙物为次棱角状的不等粒砂泥质和方解石或铁质胶结物,指示盆地沉积环境为近源、快速堆积环境,且古流方向多变;沉积时期自下而上属温暖潮湿-干旱气候环境,且蒸发强烈。

Nangqian basin is a typical representative of the medium-mini-type Paleogene basins controlled by the local north-northwest-trending faults and distributing along the Jinsha-Red River belt in the northeastern margin of Qinghai-Tibet.Combined with the results of field geological investigation,and analysis and determination of samples,as well as the indoor comprehensive study,the paleoclimate characteristics,indications of sedimentary facies,the provenance,as well as depositional environment of Gonjo Formation in the Nangqian basin were systematically analyzed in the framework of basin evolution.It is concluded that the Gonjo Formation can be divided into a three-stage structure,and the depositional environment is an alluvial fan-river-lake-delta environment;the complex conglomerate gravel composition,the poorly sorted and rounded sandstone,and the fillings being the sub-angular shaped inequigranular grit,the calcite cement or the ferruginous cement indicate that the sedimentary environment is proximal and quickly accumulated,and the paleocurrent direction is versatile;the depositional environments belong to warm and moist-dry climate with strong evaporation.