MICROBIALITE DEVELOPMENT DURING THE PROTRACTED INHIBITION OF SKELETAL-DOMINATED REEFS IN THE ZHANGXIA FORMATION (CAMBRIAN SERIES 3) IN SHANDONG PROVINCE, NORTH CHINA

Abstract: Coralomorph-lithistid demosponge-microbial reefs are developed in deep subtidal settings of the lower part of the Zhangxia Formation (Crepicephalina Zone: Drumian of Cambrian Series 3) in the Jiulongshan section of the Laiwu area of Shandong Province, North China. These reefs are several tens of centimeters thick and formed upon stabilized substrates of microbial origin. The coralomorph-bearing reefs are clearly distinguishable from demosponge-calcimicrobial reefs and Epiphyton bioherms by the development of dendritic thrombolites and the immediately overlying columnar-layered stromatolites. The microbial degradation of sponges facilitated the precipitation of micritic, peloidal, and clotted carbonates, leading to the formation of coralomorph-bearing thrombolitic cores. In contrast, Epiphyton preferentially grew upward, and the accumulation of Epiphyton clumps formed the dendritic thrombolites and the overlying columnar frameworks of the stromatolites. Marked changes in the microbialite texture ...