柴达木盆地旺尕秀地区上侏罗统-下白垩统风成砂的发现及其意义*

本次研究在柴达木盆地旺尕秀地区上侏罗统红水沟组上覆地层中,首次发现了风成沉积。地层主体为一套棕黄色细-中砂岩,由分选、磨圆好的石英砂组成;扫描电镜下可见风成砂特有的碟形撞击坑和新月形撞击坑等特征;层内普遍发育风成大型高角度板状交错层理,层系厚度巨大,风成沙丘前积层特征明显;发育液化作用产生的牵引褶曲、倒转褶曲等常见的风成沙丘同沉积变形构造。根据岩性和沉积构造特征共在地层中识别出4种沉积亚相: 沙丘亚相、丘间亚相、旱谷亚相和沙漠湖亚相,其中沙丘亚相以风成大型交错层理为显著特征,丘间、旱谷和沙漠湖亚相则以水成沉积为主。风成砂沉积的存在丰富了柴达木盆地中生代的沉积类型,为区域地层对比及西北地区晚中生代古气候和古环境研究提供了新的证据和材料。

Discovery and significance of the Upper Jurassic-Lower Cretaceous eolian sands in Wanggaxiu area,Qaidam Basin

In this study,Upper Jurassic-Lower Cretaceous aeolian deposits have been discovered from the stratigraphic succession overlying the Hongshuigou Formation in Wanggaxiu area,the Qaidam Basin. The typical lines of evidence for eolian deposits can be identified in both rock micro-structures and depositional features: The strata mainly consist of pure brown fine-medium grained sandstones dominated by well sorted and rounded quartz grains. Obvious eolian grain surface textures such as dish-shaped impact crater and crescent-shaped impact scars can be observed under SEM. Well-developed thick,large scale and high dip tabular cross-bedding is characteristic of eolian dune foresets. Synsedimentary deformation structures such as drag folds and overturned folds are common in the eolian strata. According to lithology and sedimentary structural characteristics,four subfacies are recognized in the Wanggaxiu eolian deposits. The dune subfacies is characterized by large-scale cross bedding. Waddy,inter dunes and desert lake are featured as aqueous deposits. The discovery of the Wanggaxiu eolian strata has enriched sedimentary types in the Mesozoic sediments in the Qaidam Basin and is of a certain significance for the study of regional stratigraphic correlation,and Late Mesozoic palaeoclimatic and palaeogeographic evolution of the northwest China.