The Sedimentary Response to Gondwana Glaciation in Hirnantian (Ordovician) of the Eastern Chongqing and the Northern Guizhou Region, South China

Key words: 
• Kuanyinchiao Formation /
• glaciation /
• sedimentary response /
• eastern Chongqing and northern Guizhou region /

Abstract: The global glaciation happened in Hirnantian of the Late Ordovician, the lithofacies, biologic facies and sedimentary environment of Hirnantian Kuanyinchiao Formation in the eastern Chongqing and northern Guizhou region, were the response to the glacial event. There were 3 types of lithofacies as a whole. The first type was composed of grainstone with coral. could be subdivided into bioclast limestone, calcarenite, oolitic sparite limestone and spararenite. Which formed in the shoal with medium to high energy. The major components of the second one were the silty limestone and silty argillaceous limestone that formed in tidal flat, where the plentiful brachiopoda and a few trilobites lived. These two types of lithofacies were both the inshore carbonate sediments resulted from sea level drop. The associations of marlstone and calcareous shale, argillaceous siltstone and silty mudstone, and the carbonous marlstone, constituted the last type. And its mixed biofacies containing brachiopoda, trilobites, graptolite, especially the bloomed Hirnantia fauna, indicated the cold water environment and temperature drop of seawater in Principal Glacial Age (Hirnantian). The tidal flat distributed near the Qianzhong(Central Guizhou)Uplift, and the shoal also occupied local area upon the tidal flat, and shallow shelf distributed far away from uplift. As a whole, the sedimentary environment of Kuanyinqiao Formation was shallower than the black shales of Wufeng Formation and Longmaxi Formation formed in anoxic deep-water shelf, the sea-level and seawater temperature was much lower in Hirnantian. All of which were the results influenced by the glacier events in Hirnantian.