关键词: 微生物岩, 凝块石, 中型构造, 早三叠世, 海平面变化

Abstract: After a detailed description of the earliest Triassic thrombolite at the Dawen section, Guizhou Province, South China, four mesostructural categories were distinguished: spotted, layered, dendritic, and reticular mesostructures of thrombolite. The sedimentary characters and the lithologic statistics of the four types of thrombolites indicated that those thrombolites were formed in a subtidal environment, where the spotted and layered thrombolites usually in a lower-energy, deep-subtidal environment, in contrast with the dendritic and meshed thrombolites in a shallow-subtidal environment. The stacking pattern of eighteen shallowing-upward cycles in the microbialitic succession showed that this area experienced a relative fall in sea-level during the Hindeodus parvus Zone, and its minimum appeared during the Isarcicella staeschei Zone and the earliest period of the I. isacica Zone, then the sea-level began to rise. The fall of sea-level in the latest Permian are found at various sections in the world, and the pattern of sea-level changes during the earliest Triassic (the H. parvus, the I. staeschei, and the I. isacica zones) are correlated with some areas in Palaeo-Tethys. Those fluctuation patterns probably indicated the eustatic sea-level changes to a certain extent.

Key words: microbialite, thrombolite, mesostructure, earliest Triassic, sea-level change