塔里木板块塔中区上奥陶统良里塔格组的生物礁类型

REEF TYPES OF THE UPPER ORDOVICIAN LIANGLITAG FORMATION IN THE CENTRAL HIGH,TARIM BLOCK,NW CHINA

塔里木板块塔中Ⅰ号坡折带附近上奥陶统良里塔格组取芯井段中可识别多种生物礁灰岩类型,包括珊瑚骨架/障积岩、海绵骨架/绑结岩、苔藓虫绑结岩、钙藻障积岩、钙质菌藻障积/绑结岩等礁灰岩类,藉此可归纳出珊瑚礁、珊瑚-钙藻礁、层孔虫礁、层孔虫-钙藻礁、珊瑚-层孔虫-钙藻礁、苔藓虫礁丘、钙藻礁丘、灰泥丘和微生物礁等生物建造单元。这些礁体的时空分布模式与古环境分异相关联,纵向上具有灰泥丘向珊瑚-层孔虫-钙藻礁至苔藓虫礁丘和钙藻礁的群落结构更替趋势;空间分布则向台地北缘,即I号坡折带延伸显示由低能带灰泥丘向高能带珊瑚-层孔虫-钙藻礁的相变,而且高能带珊瑚-层孔虫-钙藻主体礁和环其周缘相对低能带的钙藻礁丘、灰泥丘等在一定范围内构成造礁群落结构分异。

The microfacies from drilling cores near the Tazhong Slope Break I, Central High of the Tarim Block show variety of reef limestones. They are respectively recognized as coral framestones/bafflestones, spongia framestones/ bindstones, bryozoanal bindstones, calcareous algal bafflestones, calcified microbial bafflestones/bindstones. Based on the lithological character, nine ecological types are identified including coral reef, coral-algal reef, stromatoporoid reef, stromatoporoid-algal reef, coral-stromatoporoid-algal reef, bryozoanal reef mound, calcareous algal reef, car- bonate mud mound and microbial reef. Occurrences of reef types are shown as vertically alternated of carbonate mud mound, coral-stromatoporoid-algal reef, bryozoanal reef mound and calcareous algal reef in ascending order. Their spatial distributions imply that the lower energy carbonate mud mounds are more favorably concentrated in interior settings of the platform; in contrast, coral-stromatoporoid-algal reefs are of the high energy indicators along the plat- form margin of the Slope Break I. Furthermore, differentiations of reef-building assemblages are also existed from well-limited blocks. Coral-stromatoporoid-algal reefs are of the major units of the high energy belts; they are surroun ded by the coeval calcareous algal reef mounds as well as carbonate mud mounds of the low energy belts.