西藏申扎地区二叠系下拉组地层划分及其沉积(微)相

The Stratigraphic Division of Xiala Formation from Xainza Area,Tibet and Its Facies(Microfacies)

重新测制并研究了西藏申扎地区扎扛-木纠错剖面的下拉组。根据岩石地层及生物地层的研究,将下拉组划分为3个岩性段:第一段为灰白或紫红色中层状生屑灰岩段,时代为早二叠世空谷晚期至中二叠世罗德期;第二段为浅灰色至深灰色含珊瑚格架灰岩的生物碎屑灰岩段,时代为中二叠世沃德期至卡匹敦期;第三段为灰黑—深灰色中层或厚层状含燧石结核或条带的泥晶灰岩段,时代为晚二叠世吴家坪期。利用微相的方法,在下拉组的3个岩性段中识别出7种微相类型,并根据微相组合划分出台地边缘生屑滩、台地边缘生物礁、陆棚、局限台地等沉积(微)相。通过以上研究,认为下拉组从早二叠世空谷晚期至晚二叠世吴家坪期内连续沉积,沉积环境由开阔的碳酸盐台地环境过渡到较为封闭的局限环境,中、晚二叠世间不存在明显的地层及相的缺失。

The Xiala Formation can be divided into 3 parts which are grey and purple mid-bedded bioclast limestone（first part）,grayish to dark grey bioelast and bioconstructed limestone（second part）, dark grey mid-or thick-bedded cherty micrite （third part） and their ages are Late Kungurian to Roadian,Wordian to Capitanian, Wuchiapingian respectively, according to lithostratigraphy and biostratigrphy based on reworking Zakang-Mujiucuo Section of Xainza area, Tibet. Seven types of Microfacies and four types of facies -- platform edge bioelast beach facies, platform edge bioherm, continental shelf, restricted platform -- can been recognized from Xiala Formation using microfacies teehonology. It is considered that the age of Xiala Formation is from Late Kungruian to Wuchiapingian successively and the sedimentary environments evolve from open carbonate platform to restricted platform. Thus, there is not exist stratigrahic gap and facies loss between Guadalupian and Lopingian in Xainza area.