全球二叠系瓜德鲁普统(中二叠统)底界以牙形类Jinogondolella nankingensis的首现为标志, “金钉子”层型被定义在美国得克萨斯州瓜德鲁普山国家公园的Stratotype Canyon剖面。然而, J. nankingensis的模式标本和标准产地以及国际年代地层表中瓜德鲁普统底界的高精度绝对年龄均来自南京龙潭正盘山剖面孤峰组的底部。因此, 正盘山剖面实际上已经成为全球瓜德鲁普统底界的对比标准, 然而该剖面孤峰组和栖霞组上部的牙形类化石序列至今没有系统研究。本文基于新获得的牙形类化石和前人已经描述的标本, 在该剖面栖霞组顶部至孤峰组中部共识别出5属9种, 并将此段地层划分为了3个牙形类化石带, 由下至上依次为: 栖霞组顶部的Sweetognathus subsymmetricus–Pseudosweetognathus costatus组合带, 孤峰组中下部的Jinogondolella nankingensis带和J. cf. aserrata带。新的牙形类生物地层研究结果表明正盘山剖面瓜德鲁普统罗德阶底界应位于孤峰组底部, 孤峰组下部属于罗德阶, 中部属于沃德阶, 罗德阶与沃德阶的界线位置由于硅质岩中较难处理出牙形类化石而不清楚, 推测沃德阶底界可能比当前识别出的J. cf. aserrata带底界更低。临近层位产出的放射虫、菊石和腕足类可以和牙形类化石带进行对比, 并提供辅助对比依据。

The base of the Guadalupian Series (Middle Permian) has been defined by the first appearance datum (FAD) of the conodont Jinogondolella nankingensis at the Stratotype Canyon section in the Guadalupe Mountains National Park in Texas, USA. However, both the holotype of the conodont J. nankingensis and the geochronologic age of the Cisuralian-Guadalupian boundary (CGB) in the official International Chronostratigraphic Chart were obtained from the base part of the Kuhfeng Formation at the Zhengpanshan section in Longtan in the suburb of Nanjing City, southeast China. Therefore, the Zhengpanshan section has actually become one of the international standard sections for the correlation around the CGB. However, conodont succession from the section has not been studied in detail so far. In this paper, we review previously reported data and report our newly recovered conodont specimens from the Zhengpanshan section. In total, nine species of five genera have been identified here from the topmost part of the Chihsia Formation to the middle part of the Kuhfeng Formation at the section, and they are Hindeodus minutus, H. typicalis, H. sp., Jinogondolella nankingensis, J. cf. aserrata, J. sp., Pseudohindeodus ramovsi, Pseudosweetognathus costatus and Sweetognathus subsymmetricus. Three conodont zones, the S. subsymmetricus–Pseudosweetognathus costatus Assemblage Zone in the topmost part of the Chihsia Formation and the Jinogondolella nankingensis and J. cf. aserrata zones in the lower-middle part of the Kuhfeng Formation, have been recognized at this section. The updated conodont biostratigraphy shows that the CGB should be placed at the base of the Kuhfeng Formation at the Zhengpanshan section, and the lower part of the Kuhfeng Formation belongs to the Roadian Stage. The middle part of the Kuhfeng Formation has yielded the conodont J. cf. aserrata, which probably indicates a Wordian age. The precise Roadian-Wordian boundary (RWB) is not well identified, because a nearly 2 m interval between the last occurrence (LO) of J. nankingensis and the first occurrence (FO) of J. cf. aserrata is barren of conodonts. The radiolarian, ammonoid and brachiopod horizons, including Altudoceras, Neoplicatifera huangi, Pseudoalbaillella scalprata-P. longtanensis and Hegleria mammilla in ascending order, reported from the Zhengpanshan section are well correlated with the updated conodont zones

国家自然科学基金(42072013, 41830323, 41702007)和中国科学院战略性先导专项(B 类) (XDB26000000)联合资助