Characteristics and controlling factors of development of Paleozoic reef-banks in the Sichuan basin

Abstract：Paleozoic reefs are mainly distributed in Early Cambrian, Early Silurian and Late Permian strata in the Sichuan basin. Geographically, they occur in the Daba and Micang mountains on the northern and northeastern margins of the Sichuan basin (Early Cambrian reefs), on the northern and southern margins of the Sichuan basin (Early Silurian reefs) and western Hubei, eastern Chongqing and northeastern Sichuan (Late Permian reefs). The Early Cambrian reef-bank association includes patch reefs, lime-mud mounds and oolitic shoals. Reef-building organisms are archaeocyatha and cyanobacteria and organisms attached to reefs are trilobites, brachipods, crinoids and sponges. Controlled by sea-level fluctuation, reefs have cycliciy and from west to east the horizons are raised gradually.Early Silurian reefs include patch reefs, lime-mud mounds and biostromes. Reef-building organisms are mostly corals, stromatoporoids, polyzoa and cyanobateria. Their distribution are controlled by terrigenous clastic-carbonate gentle slope affected by oldland and also related to sea-level fluctuations. Late Permian reefs are inner platform patch reefs and platform marginal reefs. Reef-building organisms are primarily sponges. Reef growth and distribution have a close relation with the paleogeomorphological framework and sea level fluctuations.