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通过对恩施地区二叠系-三叠系界线附近含凝灰质黏土岩的野外地质学特征调查,采用锆石U-Pb同位素测试分析,取得其206Pb/238 U加权平均年龄为251.6±1.2Ma,该年龄值为二叠系-三叠系界线附近的火山喷发事件的年龄。结合碳和氧同位素分析,二叠系-三叠系界线附近黏土层之上碳同位素明显负偏,这与该时期生物绝灭事件关系密切。通过区域对比,发现该套黏土岩在区域上可进行连续追踪,不同地区界线附近岩石组合差异性明显,二叠系顶部自西向东总体表现为碳酸盐岩比例逐渐减少、碳硅质岩逐渐增加的特征。
Based on the investigation of the geochemical characteristics of tuffaceous clay rocks near the Permian-Triassic boundary in Enshi area, the 206Pb / 238 U weighted average zircon age of 251.6 ± 1.2Ma was obtained from zircon U-Pb isotope analysis. This age value is the age of the volcanic eruption near the Permian-Triassic boundary. In combination with carbon and oxygen isotope analyzes, the carbon isotope above the clay layer near the Permian-Triassic boundary was obviously negatively biased, which is closely related to the bio-extinction event in this period. Through the regional comparison, it is found that the set of clay rocks can be traced continuously in the area. The differences of rock assemblages near the boundary in different areas are obvious. The top of the Permian is characterized by a decrease in the proportion of carbonate rocks from the west to the east and the gradual decrease of the carbon-silicalites Added features.