浙西冷坞二叠系生物礁的基本特征

冷坞生物礁是由海绵动物组成的园丘礁。它是目前在下扬子地区碳酸盐岩地层中首次发现的生物礁。礁核岩性为海绵骨架灰岩及泥晶生物屑灰岩。造架生物主要为海绵动物,附礁生物门类众多。前礁发育滑塌岩;后礁发育叠层石,白云化作用明显。园丘礁处于中等动荡的水动力条件,其兴衰明显地受陆源碎屑物的控制。冷坞生物礁各相带标志明显,反映了园丘礁呈线状礁带组合的可能性,可望在浙西找到隐伏的生物礁。生物礁各相带在平面上的相对位置,表明茅口期华夏古陆是存在的,礁附近的海岸线呈北东走向。

PRINCIPAL FEATURES OF PERMIAN REEF IN LENGWU AREA,ZHEJIANG PROVINCE

The knoll reef in Lengwu Area composes of sponges and belongs to Lengwu Formation,Maokou Stage of Lower Permian.Up to the present,it is the only one reef discovered in the carbonate strata of Lower Yangtze River Area.The thickness of the crop-out reef is over 60 m with the area less than 1 Km2.The reef core lithology is sponge frame-stone and biomicrite.The main frame-building organisms are of sponges and there are diverse attaching organisms.Slip block developed at fore reef while stromatolites developed at back-reef with obviously dolomitization.Both the base and the cap of the reef are attributed to terrigenous elas-tics and most of the facies of strata equivalent to Lengwu Formation in Lower Yangtze River Area changed into terrigenous elastics.The occurrence of the reef is mainly controlled by terrgenous clastics.The various facies belts of the reefs in Lengwu Area are distinct and reflect the possibilities of linear assemblage of the knoll reefs.Therefore,it is hopeful to discover some buried facies reefs in Western Zhejiang.The corresponding locations of the various facies belts for the reefs show the plane configuration of the distribution for land and sea during the period of Early Permian,Maokou stage.It is proved that the Cathaysia did exsit in Maokou Stage and the adjacent seashore line trends northeast.