鄂尔多斯盆地西南缘陕西陇县晚奥陶世背锅山组生物礁

LATE ORDOVICIAN REEFS OF THE BEIGUOSHAN FORMATION IN THE SOUTHWESTERN MARGIN OF THE ORDOS BASIN,NORTHWEST CHINA

鄂尔多斯盆地西南缘的陕西陇县李家坡晚奥陶世背锅山组生物礁为典型的台地边缘礁,包括层孔虫礁、珊瑚礁、钙藻礁等几种类型,主要为层孔虫礁。经过系统古生物学研究,鉴定出层孔虫有5个属,分别为Ecclimadictyon(蜂巢层孔虫)、Clathrodictyon(网格层孔虫)、Tuvaechis(图瓦层孔虫)、Rosenella(罗森层孔虫)、Labechiella(小拉贝希层孔虫)等;珊瑚有6个属,分别为Tetradium(四分珊瑚),Hemiagetolitella(拟半阿盖特珊瑚),Plasmoporella(似网膜珊瑚),Eofletcheria(始弗莱契珊瑚),Catenipora(镣珊瑚),Reuschia(劳氏珊瑚);钙藻以Vermiporella(蠕孔藻)和Solenopora(管孔藻)为主。礁发育早期以层状层孔虫包卷砂屑、单体珊瑚、管状海绵、块状钙藻等形态为主要特征,礁发育中后期以块状和球状的层孔虫以及大型的床板珊瑚形成格架为主要特征。礁体发育过程中居礁生物都很丰富,有三叶虫、腕足类、介形类、大棘皮类和丛状的蓝细菌等。通过与塔中台地以及扬子台地的晚奥陶世台缘礁对比,发现造礁生物的属种和礁岩类型均有相似之处,说明中国晚奥陶世生物礁的分布具有等时性。

The Late Ordovician Beiguoshan Formation organic reefs in Lijiapo, Longxian, Shaanxi, are typical platform margin reefs in the southwestern margin of the Ordos basin, Shaanxi Province, Northwest China, and are com- posed of stromatoporoid reef rocks, tabulate coral reef rocks, calcareous algae reef rocks. Stromatoporoids played the most important role in reef-development. The stromatoporoids include Ecclimadictyon, Clathrodictyon, Tuvaechis, Rosenella and Labechiella. The corals are Tetradium, Hemiagetolitella , Plasmoporella , Eo fletcheria , Cateni pora and Reuschia. The calcareous algae comprise Vermiporella and Solenopora. The early stage of reef development is characterized by the laminated stromatoporoids wrapping debris, singular corals, tabulate sponges and massive calcar- eous algae. In the middle and late stage, massive and spherical stromatoporoids and large massive tabulate corals formed the reef framework. Reef-dwelling organisms include trilobites, brachiopods, ostracods, large echinoderms and fasiculate cyanobacteria, and are abundant through the reef development. Comparison of the composition of reef organisms and types of reef rocks in the Lijiapo reefs with those of the marginal reefs of the Tazhong platform of the Tarim Basin and of the Yangtze platform reveals great similarities, even in their development ages.