A reinvestigation of the conodonts from the boundary interval between the Permian Kuhfeng and Chihsia formations at the Zhengpanshan section in Longtan, Nanjing City
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Abstract:
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
