CONODONT BIOSTRATIGRAPHY AND SEDIMENTOLOGY OF THE MIDDLE AND UPPER ORDOVICIAN IN BACHU, XINJIANG
CONODONT BIOSTRATIGRAPHY AND SEDIMENTOLOGY OF THE MIDDLE AND UPPER ORDOVICIAN IN BACHU, XINJIANG
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发表时间：
2009
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通讯作者：
L. Yue
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作者：
L. Yue
巴楚县良里塔格山一带沿着出露中、上奥陶统灰岩。该出露区属于塔里木地块中央隆起的西北部。根据牙形石生物地层学确定了这些层序的年代学。中奥陶统上统一间房组顶部的大坪阶和达里维利阶又细分为Periodus flabellum层和Pygodus serra层。上奥陶统下统图木休克组包括Pygodus anserinus层至Baltoniodus alobatus带。只有B。confluens动物群被识别为开田阶（中-上奥陶统）良里塔格组。在一间房组底部的古岩溶和砾岩层中推断出一个间断。这一间断标志着从达里维期开始海侵带的底部。一间房组下部发育两期微藻土丘，早期的Calathium礁丘由中部开始发育3-4层较粗的生物礁滩。在地层的上部，不断加深的层序继续向上，并可能达到波底制度以下的深度。图木休克组中的凝析红色灰岩代表了沙变期海平面高位的顶点，沉积于陆棚外环境。良里塔格组是早卡田期浅海带发育的一个海退带，具有浅滩和三期微藻土丘。
Mid-Upper Ordovician limestone sequences outcrop along the Lianglitag Hills of the Bachu County. This outcrop region belongs to the northwestern part of the Central High of the Tarim Block. Geochronology of these sequences is determined based on conodont biostratigraphy. The top Dapingian and Darriwilian Stage (upper Middle Ordovician)Yijianfang Formation is subdivided into the Periodus flabellum Bed and Pygodus serra Bed. The Sandbian Stage (lower Upper Ordovician)Tumuxiuke Formation includes the Pygodus anserinus Bed to the Baltoniodus alobatus Zone. Only the B. confluens Fauna is recognized from the Kaitian Stage (mid Upper Ordovician) Lianglitag Formation. A hiatus is inferred from a palaeokarst and conglomerate bed at the base of the Yijianfang Formation. This hiatus marks the base of the transgression tract from the Darriwilian onwards. Two phases of microbial-algal mounds occur within the lower part of the Yijianfang Formation, and the early phase of Calathium reef-mound contains 3—4 layers of coarser bioclastic shoals from the middle part. Deepening successions continued upward in the upper part of the formation and probably reached the depth below the wave-base regime. The condensed red limestone in the Tumuxiuke Formation represents the acme of the sea-level high-stand during the Sandbian interval, and it was deposited in a out-shelf setting. The Lianglitag Formation represents a regression tract with shallow shoals and three phases of microbial-algal mounds occurring in the shallow marine belt during the early Katian time interval.