川西北地区晚三叠世卡尼期洪水事件沉积的碳、氧同位素记录*

川西北地区绵竹和安县等地发育的下卡尼阶岩性以灰色鲕粒灰岩、海绵礁丘粘结及障积成因的凝块石灰岩为主，上卡尼阶岩性突变为灰黑色页岩、粉砂岩，这与西特提斯地区卡尼阶在岩性和颜色上有很大的相似性。本次研究用激光微区碳、氧同位素测试方法分析了川西北地区卡尼阶中有孔虫、双壳类及腕足类化石壳体和植物叶片化石的碳、氧同位素，结果显示上卡尼阶化石中氧同位素值较下卡尼阶略有变小，上卡尼阶泥质粉砂岩中化石的碳同位素较下卡尼阶灰岩明显变小，可能反映了淡水输入的影响。结合研究区卡尼阶的沉积学特征，笔者认为川西北地区同样受到卡尼期洪水事件的强烈影响，潮湿气候条件下的淡水输入是造成川西北地区海绵礁（丘）大量周期性死亡及最后消失的影响因素之一。

Oxygen and carbon isotopic records of the Late Triassic Carnian pluvial event deposits in northwestern Sichuan Province

Distinct lithological mutations from grey ooides,sponge reef limestone to grayish black shale,and then argillaceous siltstone are distinguished from the Upper Triassic Carnian marine sediments in the Mianzhu and Anxian counties in northwestern Sichuan Province,which is very similar to the sediments representing the Carnian pluvial event in western Tethys area.The stable oxygen and carbon isotopic compositions of the Carnian fossils of foraminifer,bivalve and brachiopodous shells and plant leaves are analyzed using laser micro-sampling technique.The analysis results indicate the slightly lowerδ18O values and remarkable lower δ13C values of the Upper Carnian than those of the Lower Carnian.It’s believed that the isotopic compositions reflect that fresh water input into the Paleotethys ocean.We suggest that the Carnian pluvial event severely affected the deposits in the eastern Tethys area.The freshwater input in the humid conditions is one of the causes that triggered the periodic deaths and finally disappearing of the sponge reefs in the study area.