羌北双壳类祁阳蚌组合的发现及其地层学意义

藏北羌塘盆地独雪山地区,在原先认为不整合于早侏罗世火山岩系之上的“中侏罗统雀莫错组”中, 新近发现了一套早侏罗世淡水双壳类祁阳蚌(Qiyangia)组合,表明羌北盆地存在早侏罗世沉积地层,其为一套海陆交互相沉积的粗碎屑岩→灰岩→细碎屑岩夹灰岩,下侏罗统与中侏罗统为连续沉积。据此资料,该区侏罗系目前采用的岩石地层单位系统及地层的对比认识存有问题,文章对此套早侏罗世沉积的岩石地层划分方案进行了讨论, 指出雁石坪地区的侏罗系岩石地层系统作为等时的地层单位运用于羌北盆地北西部并不适宜,羌北盆地已有的地层系统格架有必要重新认识。

Discovery of the Bivalvia Qiyangia Assemblage in Northern Qiangtang Area and Its Stratigraphic Significances

A set of Early Jurassic fresh water Bivalvia assemblage, Qiyangia assemblage, was discovered recently from the "Qoima Co Formation" in Duxue Mountain area, Qiangtang basin, north Xizang (Tibet). The "Qoima Co Formation" overlies unconformably ly on the the Early Jurassic volcanics, was considered Middle Jurassic before, is composed of a set of marine-continental interbedded sediments, from coarse debric rocks, limestone to fine debric rocks, is continuous with overlying Middle Jurassic. Based on these new data, the lithostratigraphic division program of this Early Jurassic sediments was discussed. It is pointed out that considering the Jurassic lithostratigraphic units in the Yanshiping area as contemporary units in northwestern Qiangtang basin is inappropriate. It is necessary to recognize the stratigraphic frame in northern Qiangtang basin.