Cambrian Reefs in the Western North China Platform, Wuhai, Inner Mongolia
Mid to late Cambrian thrombolites and maze like maceriate reefs from the western North China Platform, Wuhai, Inner Mongolia, northwestern China, occur in the middle of a succession dominated by thin bedded lime mudstone shale/marlstone alternations, and are laterally surrounded by limestone conglomerate and/or grainstone. Thrombolite, characterized by meter scale lenticular mounds composed of millimeter to centimeter scale mesoclots and wackestone matrix, occurs in the lower middle part of the sequence. Thrombolite mesoclots are composed of microstromatolites with alternating dark gray and light gray micritic laminae. The maze like maceriate reefs occur in the middle to the upper part of the sequence, commonly forming lenticular mounds up to 1 m thick. They are characterized by centimeter to decimeter scale branched maze like structures, whose biogenic portions (maceria) are selectively dolomitized. The maceriae are composed of poorly preserved microstromatolites and siliceous sponges. Inter macerial sediments consist of lime mud and scattered bioclasts. These Wuhai reefs are generally similar to but older than various other Cambrian reefs previously reported from the Shandong region, northeastern China.