中国西南部地区卡尼期危机及其成因探讨

Carnian Crisis Occurring in SW China and Its Ideational Origin

卡尼期是全球古气候变化显著、特提斯域沉积发生突然转折的时期。欧洲学者基于阿尔卑斯地区(奥地利、意大利)卡尼阶岩性从碳酸盐岩到黑色页岩、碎屑岩的等时性变化,以及相应的碳酸盐台地古生物的死亡,提出了卡尼期危机、碳酸盐生产力危机、卡尼期多雨事件、Reingraben转换,以及黑色页岩事件等概念;这些现象在喜马拉雅Spiti盆地、伊朗、印度尼西亚等地亦有显示。在东特提斯(中国西南部)地区的卡尼阶中也表现为岩性和古生物的变化,但尚未引起国内研究者的重视。与古特提斯西部、印度喜马拉雅等地卡尼阶相似,中国西南部特提斯域所见的卡尼期碳酸盐岩沉积(如海绵礁灰岩)被灰黑色、深灰色页岩(或深色板岩)或中酸性火山岩覆盖,显示该时期碳酸盐生产的突然中止、生物礁的突然死亡和岩性的急剧变化。我们认为晚三叠世巨型季风和古特提斯周缘地区(尤其是中国南方地区)的造山运动及火山作用、变质作用,使大气CO2浓度增加、泛大洋东部海域(古太平洋)向特提斯海水汽输入增强,特提斯海沿岸地区相对干旱的气候向相对潮湿的气候变化,更潮湿的古气候与相对高浓度的大气CO2共同作用使大陆风化速率增高,陆源硅质碎屑输入增多,造成了卡尼期危机。

The global climate and tethysic sedimentary rocks varied sharply during the late Triassic Carnian period.According to the noticeable lithologic change of from carbonate to black shale,and the sudden creatures＇ death at carbonate platform in Alps Region（e.g.Austria,Italy）,several concepts were proposed by European geologists as Carnian Crisis,Carbonate Productivity Crisis,Carnian-Pluvial Event,Reingraben Turnover,Black Shale Event.The similar geological phenomena were seen in the Spiti Basin of Indian Himalaya,Iran,Indonesia,and SW China.Carnian Carbonate rocks（e.g.sponge reef limestone） were covered by grayish-black,dark gray shale,slate or neutral-acidic volcanics,which indicated the similar lithologic change and death of carbonate platform in Tethys area of SW China.It was deduced that the Carnian Crisis was triggered by the megamonsoon and the orogeny occurred in the south China.The CO2 releasing caused by volcanism and metamorphism,more wet climate influenced by megamonsoon would be in charge of more remarkable continental weathering,which caused more clay and siliciclastic material inputting into Tethys Ocean and reacted on Carnian Crisis.