Preliminary Study of Carbonate Mud-mounds, Middle-Late Ordovician,Tazhong Area

Key words: 
• carbonate /
• mud-mound /
• mud-mound-building /
• organisms /
• mud-mound

Abstract: Carbonate mud-mounds of Middle-Late Ordovician age in Tazhong area grew and developed on an old carbonate platform when it was progressively sinking b elow the sea level.Those laterally climbed up the slope toward high position of the platform,and vertically are the multiple superimposed mud-mound.The main mu d-mound-building organisms are bacterium and algae,such as ortonella and its k ind genus.The secondary organisms are Tabulati,Btyozoa,stromatoproids,spongea,an d so on .It is considered that the rock types of the mud-mounds are dominantly micrite-thromoblites framestone,micrite-thrombolites baffle-framestone,algal micrite-thrombolites bindstone. Mud-mound facies may be divided into three sub facies such as mud-mound centre,mud-mound talus and intermud mound-deposit. Th e evolution of mud-mound was controlled by the relationship between the rate of transgressive and the rate of mud-mounds growth,and by the change of water dep th and turbidity.