塔里木盆地东部罗西1井中奥陶统的藻丘

A MICROBIAL MOUND OF THE DARRIWILLIAN (MIDDLE ORDOVICIAN) YIJIANFANG FORMATION FROM WELL LUOXI 1,EASTERN TARIM BASIN,NW CHINA

塔里木盆地东部碳酸盐岩型罗西台地西缘内斜坡带的罗西1井钻遇中奥陶统达瑞威尔阶一间房组—大坪阶鹰山组灰岩。330m厚的一间房组中—下部取芯段见藻丘建造,群落结构以隐藻为主,由隐藻纹层和藻团粒、藻凝块和藻屑纹层交替组成,结晶孔洞构造发育,指示偏深水的低能带沉积,其中的少量动物骨屑如介形类、三叶虫、腕足类和床板珊瑚等可能来自其东边的台地浅水相生屑滩。一间房组近顶部演变为海退型砂屑滩序列。

Well Luoxi 1 is located at the inner slope of the western Luoxi Carbonate Platform,eastern Tarim Basin.Middle Ordovician limestone consists of sequences of the Yingshan Formation（Dapingian）and Yijianfang Formation（about 330m thick,Darriwillian）in ascending order.Microbial mound is yielded from the middle-lower part of the Yijianfang Formation as algal-dominated biotically.Intercalated microfacies of laminated cyanobacteria,thrombolites as well as laminated algal-debris illustrate that rich algal layers occur throughout the unit.Stromatotactis structures are common.Nevertheless,a relative deeper marine and lower-energy setting controlled the mound occurrence.Less metazoanal compositions including ostracoda,trilobite,brachiopod and tabulate coral debris within the micritic limestone sequences are possibly derived from eastward,the shallower shoals of the platform.Near the top of the Yijianfang Formation is succeeded by regressional sandy bank facies.