湖南嘉禾大窝岭剖面吴家坪阶-长兴阶界线牙形石生物地层及一次碳同位素负偏
Conodont Biostratigraphy and a Negative Excursion in Carbonate Carbon Isotopes across the Wuchiapingian-Changhsingian Boundary at the Dawoling Section, Hunan Province

吴家坪阶-长兴阶界线位于这两次生物大灭绝事件之间,科学界对该界线附近是否发生重大地质事件仍然知之甚少,有关该时期的环境变化、碳循环的研究也不深入.嘉禾大窝岭剖面牙形石生物地层以及碳同位素变化的研究,为进一步探讨吴家坪期-长兴期附近的生物及环境事件提供基础材料.晚二叠世时以深水盆地相沉积为主的大窝岭剖面位于湖南省嘉禾县袁家镇附近.该剖面大隆组出露较好,岩性主要为硅质岩、硅质灰岩、灰岩以及泥岩.在大隆组中共识别出牙形石1属3种(含一个未定种):Clarkina wangi,C.deflecta,C.sp.,并识别出牙形石C.wangi带和C.changxingensis-C.deflecta组合带.根据C.wangi的首现,将大窝岭剖面的吴家坪阶-长兴阶界线(Wuchiapingian-Changhsingian boundary,简称WCB)置于第11层底部.该剖面全岩无机碳同位素数据显示在13~15层发生了一次快速的负偏,从2.18‰负偏到-1.39‰,负偏值近3.50‰,可与浙江煤山及四川上寺等剖面进行很好的对比,揭示这次碳同位素负偏在华南区域上可具对比性.
The research of conodont biostratigraphy and carbon isotope change at the Dawoling section provides basic materials for the exploration of creatures and environment change in the Wuchiapingian-Changhsigian period. The Dawoling section at Yuanjia Town, Jiahe county, Hunan Province, recorded basinal deposition during the Late Permian. The Talung Formation is well-exposed and displays siliceous rock, siliceous limestone, limestone and claystone. Three conodont taxa (one is undetermined) of genus Clarkina: C. wangi, C. deflecta and C. sp. are identified, and these enable the tentative assignment of a C. wangi Zone overlain by a C. changxingensis C. deflecta assemblage Zone. The Wuchiapingian-Changhsingian boundary (Wuchiapingian-Changhsingian boundary, WCB) is placed at the first occurrence (FO) of C. wangi at the base of bed 11 at this Dawoling section. A rapid negative shift from 2.18‰ to -1.39‰ in carbonate carbon isotope in beds 13-15 correlates well with the Changhsingian GSSP(Global Stratotype Section and Point) section at Meishan in Zhejiang and the Shangsi section of Sichuan. Therefore, this negative excursion could be a regionally correlation horizon in south China