【作者】 王国庆；

【导师】 夏文臣；

【作者基本信息】 中国地质大学 ， 矿物学、岩石学、矿床学， 2004， 博士

【摘要】 二叠纪晚期爆发的生物灭绝事件是生物演化史上规模最大、影响最深远的事件,一直以来都是地学界的重大研究课题。前人运用多学科交叉的手段,在世界各地的二叠纪地层中对这一事件的性质、规模、阶段性及驱动机制进行了探讨。华南分布有世界范围内最连续、最广布的二叠纪/三叠纪海相地层,为研究二叠纪晚期的生物灭绝事件提供了良好的条件。围绕着二叠系/三叠系界线全球层型剖面与点(GSSP)的建立工作,前人在扬子区内对这一生物灭绝事件进行了大量细致的研究工作,尤以下扬子地区的研究程度最高,中上扬子区二叠纪晚期生物灭绝事件的研究则显得相对薄弱些。本文所选取的中扬子北缘,二叠系乐平统碳酸盐台地相、斜坡相及盆地相分布广泛、界线清楚。对此区域内二叠纪晚期生物灭绝事件的研究,有助于更全面的把握二叠纪末期生物灭绝事件在扬子区内的表现。本文以两个界面(Gudalupian/Lopingian界面和Permian/Triassic界面)的高分辨率牙形石地层研究和晚二叠世牙形石分带研究为基础,在建立起中扬子北缘晚二叠世牙形石地层对比格架的基础上,进一步通过碳酸盐岩微相、碳酸盐岩相序研究以及层序界面和最大海泛面的识别,划分三级层序,恢复海平面变化曲线。在此基础上综合研究海平面变化与生物演替及灭绝过程的耦合关系,探讨二叠纪/三叠纪之交生物灭绝事件及其前奏事件的原因。本文所述及的中扬子区位于扬子板块中部,其北以襄广断裂带与秦岭造山带相邻,南依江南造山带,西至齐岳山,向东以郯庐断裂为限,与下扬子相接,收敛于湖北黄石以东。在此区域的北缘,本文有代表性的选取了碳酸盐台地边缘相的宜昌兴山峡口剖面、利川见天坝剖面,台地边缘斜坡相的恩施天桥剖面、猫耳山剖面,盆地相的恩施苦桃溪、黄石二门剖面进行二叠纪晚期海平面变化及生物灭绝事件的研究。峡口剖面吴家坪阶为巨厚层碳酸盐岩沉积,长兴阶底部为海绵障积灰岩,中上部为钙质泥岩夹薄层灰岩。见天坝剖面发育有长兴阶巨厚层台地边缘礁相沉积。天桥剖面吴家坪阶底部为生屑灰岩,中上部厚层硅质岩、硅质泥岩;长兴阶底部为硅质岩,中上部为厚层灰泥岩。猫耳山剖面吴家坪阶为厚层灰泥岩、泥粒灰岩,中上部亦发育有较厚的硅质岩、硅质泥岩沉积。苦桃溪剖面吴家坪阶底部为生屑灰岩,中上部为硅质岩、硅质泥岩;长兴阶为灰泥岩沉积。黄石剖面吴家坪阶为硅质泥岩夹泥岩,长兴阶由下部的泥粒灰岩夹泥岩向上过渡过硅质泥岩、钙质泥岩。从总体上来看,研究区西部的鄂西地区在二叠纪晚期为一北东东向盆地,海水由西向北东逐渐加深,西部利川地区为碳酸盐台地边缘、至恩施天桥地区为台缘斜坡、再向北东至恩施苦桃溪及建始地区为深水盆地相、向北至峡口地区为北部的碳酸盐台地边缘。研究区中部至东南部黄石地区,在二叠纪晚期基本维持深水盆地<WP=7>相沉积。研究海平面变化必然要以层序地层学分析为基础。而层序的级别、界面的时代、每个层序的时限,以及不同地区、不同露头上层序的划分和对比,都离不开高精度的生物地层研究。从某种意义上来说,层序地层研究成果的可靠度和精度,在很大程度上取决于生物地层学的研究精度。因此,本文的首要目标是建立起研究区内的高精度生物地层格架。牙形石是一种高精度生物地层对比的标准化石,牙形石生物地层具有精度高、可对比性强的特点。研究区内广泛发育的二叠纪晚期碳酸盐岩给牙形石生物地层的研究提供前题条件,因此本文采用牙形石来进行研究区内生物地层的划分与对比。通过细致而艰苦的工作,本文在研究区内建立起完整的二叠纪晚期乐平统牙形石生物地层格架。吴家坪阶牙形石地层在研究区内分为两种类型:恩施地区自下而上发育有Clarkina postbitteri hongshuiensis带,C. postbitteri postbitteri带,C. dukouensis带,C. asymmetrica带,C. guangyuanensis - C. transcaucasica带和C. orientalis带,与前人据宣汉渡口剖面和广西来宾蓬莱滩剖面所建立起来的吴家坪阶牙形石带相当吻合(梅仕龙等, 1994; Mei et al., 1994, 1998a);峡口地区吴家坪阶仅可识别C. liangshanensis和C. orientalis两个带,与浙江长兴煤山D剖面及四川广元上寺剖面相似(王成源和王志浩, 1981; 杨遵仪等, 1987; 李子舜等, 1989)。长兴阶牙形石生物地层以峡口剖面发育最为完全,自下而上为Clarkina wangi - C. subcarinata带,C. changxingensis changxingensis - C. deflecta带及C. meishanensis - H. latidentatus带,与煤山D剖面的长兴阶牙形石带能完好的对应起来(王成源和王志浩, 1981; 张克信等, 1995)。二门剖面及天桥剖面虽只部分出露长兴阶上部的牙形石带,但横向上具有良好的对比性。牙形石生物地层的工作一方面为层序地层学的研究提供了高精度的时间地层格架,另一方面也有助于精确拟定研究区内的二叠系/三叠系及瓜德鲁普统/乐平统界线,探讨二叠纪末期生物灭绝事件发生的时限。在峡口剖面上,二叠纪晚期的牙形石带C. meishanensis - Hindodus latidentatus带及三叠纪早期的H. parvus带和Isarcicella isarcica带均发育完整,同时界线附近的岩石地层、年代地层及碳同位素地层的特征与煤山D剖面均有很好的对应性,可以精确的确定二叠系/三叠系界线于ZSJI263层之底。而黄更多还原

【Abstract】 The biotic extinction events in late Permian, which have been an important issue in the geologic community for the past decades, are the most severe and sweeping events in the history of biotic evolution. People have applied different methods to investigate their characteristics, extent, phases and mechanism from different perspective.The most successive and widespread Permian-Triassic strata in south China, facilities the research on late Permian biotic extinction events. Aiming at erecting the Global Stratotype Section and Point of Permian-Triassic boundary, people have carried on detailed research on these events in Yangtze platform. Actually, the lower Yangtze platform was the most thoroughly studied area, while the upper and middle Yangtze platform were not studied as well as it. The north part of central Yangtze platform yields widespread carbonate sediment, carbonate platform slope sediment and basin sediment of Lopingian. Studying late Permian biotic events in this area will further the understanding of those events.This paper was based on high precision biostratigraphy of late Permian, especially near the Guadalupian/Lopingian and Permian/Triassic boundary. Be the method of carbonate microfacies analysis and sequence stratigraphy, this paper tried to recognize third-order sequences and eustatic fluctuation in the studied area, and then took integrated analysis of the relationship between eustatic fluctuation and biotic extinction events.The central Yangtze platform is located south to Qingling orogenic belt, north to Jiangnan orogenic belt, east to Qiyu mountain, and west to Tannu fault. For studying the late Permian sea level change and its influence on the biotic extinction events in this area, the author selected Xiakou section of Yichang city, Jiantianba section of Lichuan city, Tianqiao, Maoershan and Kutaoxi section of Enshi city, and Ermen section of Huangshi city. Xiakou section and Jiantianba section was deposited in edge of carbonate platform. Tianqiao section was deposited in slope of carbonate platform. Kutaoxi and Ermen section were formed in basin environment.Xiakou section concentrated block carbonate sediments in Wuchiapingian, sponge bafflestone in early Changhsingian and calcareous argillite with thin limestone interbeds in middle and late Changhsingian. Jiantianba section yields block reef sediments of Changhsingian. Tianqiao section has bioclastic limestone of late Wuchiapingian, chert and argillaceous chert of <WP=11>middle and upper Wuchiapingian, and thick mudstone of Changhsingian. Maoershan section concentrated coal-bearing series, and thick mudstone and wackstone in lower Wuchiapingian, and thick chert and argillaceous chert in middle and upper Wuchiapingian. Kutaoxi section yields bioclastic limestone from bottom of Wuchiapingian, and chert and argillaceous chert from middle and upper Wuchiapingian. In Changhsingian, it concentrated thick mudstone. Huangshi section yields siliceous argillite with limestone interbeds in Wuchiapingian. Its Changhsingian lithology changes from wackstone with argillite beds to siliceous and calcareous argillite. In conclusion, the west part of the studied area was a northeast oriented basin during late Permian. The sea become deeper from west to north east in this area. The Lichuan area was an edge of carbonate platform. The Tianqiao area was a slope of carbonate platform. Kutaoxi and Jianshi area were deep sea basin. And Xiakou area was the edge of north carbonate platform. The middle and southeast part of the studied area maintained deep sea basin in late Permian.Sequence stratigraphy is an effective method to analyze the eustatic fluctuation. The determination of sequence order, age of sequence boundary and duration of each sequence are based on high precision biostratigraphy. And biostratigraphy is also vital for comparing different section in different area. The precision of sequence stratigraphy depends on the precision of biostratigraphy much. Only in the isochronous frame of biostratigraphy, could the sequence stratigraphy and eusta更多还原