湘西北奥陶纪层序地层研究

MIGRATE OF CARBONATE PLATFORM MARGIN AND SEA LEVEL CHANGES OF ORDOVICIAN IN THE NORTHWESTERN HUNAN

有关奥陶纪层序地层研究，在湘西北地区尚属首次．通过对１１个剖面详细的野外露头层序界面的辨认、追索以及对亚层序（ｓｕｂｓｅｑｕｅｎｃｅ）的划分和堆叠形式的识别，将奥陶系初步划分为两个中层序（ｍｅｓｏｓｅｑｕｅｎｃｅ）或二级层序，１１个正层序（ｏｒｔｈｏｓｅｑｕｅｎｃｅ）或三级层序．根据层序所确定的海平面升降曲线，可与北美、澳大利亚、华北等地进行对比．

The middle-northwestern Hunan of Ordovician was an important area for the gradual alternation from stable platform and platform margin to slope and basin through the outer continental shelf. The deep-shallow change of the sea is determined according to the synthetical study of petrology sedimentary structure, organic paleoecology type, migration of carbonate platform margin and alteration of the slope site. Then the change curve was worked out for the relative sea level in Ordovician. There were three times of rising and falling of the sea level, which became relatively higher in the Lianghekou, Guniu and Baota Stages than Miaopo and Wufen Stages. The relative sea level change of the study area identified here has a comparatively good coincidence in rising and falling tendency in correlation with the eustasy curve of Ross(1988).