湖北黄石二门二叠系/三叠系界线剖面长兴阶牙形刺分带及有机碳同位素的变化

THE CHANGHSINGIAN CONODONT ZONATION AND VARIATION OF ORGANIC CARBON ISOTOPE OF HUANGSHI ERMEN SECTION,HUBEI PROVINCE

湖北黄石二门二叠系/三叠系界线剖面出露完好,原始沉积连续,由乐平统龙潭组保安段灰黑色硅质岩、大隆组黑色硅质岩—硅质泥岩和下三叠统大冶组黑灰色泥岩以及泥岩夹灰岩组成,为介于典型浅水碳酸盐岩型与深海硅质岩型二叠系/三叠系界线剖面之间的半深海剖面。长兴阶可划分为Clarkinasubcarinata—Clarkinawangi及Clarkinachangxingensis两个牙形刺带。后者又可划分为3个亚带,自下而上依次为Clarkinachangxingensischangxingensis—Clarkinadeflecta亚带、Clarkinameishanensis亚带及Waning—Clarkina亚带,完全可以与二叠系/三叠系界线的全球层型剖面与点进行对比。另外,二叠纪末牙形刺的生态演化呈阶段性绝灭模式;有机碳同位素值在二叠纪/三叠系界线处出现明显的负偏移,指示了二叠纪/三叠纪之交生物绝灭后海水表层水原始产率的降低以及大气和海水中CO2含量的增加。

The well exposed Huangshi Ermen section of Hubei is continuously deposited during the Late Permian and Early Triassic,composed of gray black chert of Baoan Member of Longtan Group, black chert to siliceous mudstone of Dalong Group and gray black mudstone and mudstone with limestone intercalations of Daye Group of Lower Triassic.It's the transitionary semi-pelagic Permian-Triassic boundary (PTB) section between the typical shallow water carbonate section and the typical pelagic chert section.Two conodont zonations is recognized in the Changhsingian,namely _Clarkina subcarinata-Clarkina wangi_ zone and _Clarkina changxingensis_ zone.The latter can be divided into _Clarkina changxingensis changxingensis-Clarkina deflecta_ subzone,_Clarkina meishanensis_ subzone and Waning-_Clarkina_ subzone in ascending order,corresponding to the Global Stratotype Section and Point (GSSP) of PTB well.Moreover,stepwise extinction progress of conodont is conspicuous during the late Permian.The negative excursion of organic carbon isotope is obvious at the PTB,indicating the reductive primary production of the surface marine water after the mass extinction event, and the increase of CO2 in the atmosphere and ocean.