广西乐业地区吴家坪期牙形石的发现及其意义

Discovery and Significance of Wuchiapingian Conodonts from Leye of Guangxi

吴家坪期作为二叠纪晚期两次灭绝事件(瓜德鲁普世末灭绝事件和二叠纪末灭绝事件)之间的一次快速的生态复苏时期,是地质历史时期一个重要的阶段.该时期扬子台地中部及滇黔桂地区碳酸盐岩台地仍有广泛分布;其中乐业碳酸盐台地是南盘江盆地内一个典型的孤立碳酸盐岩台地,在瓜德鲁普统茅口组顶部不整合面之上发育连续的吴家坪期海相碳酸盐岩沉积.此前该地二叠纪地层划分对比仍依据传统的化石生物地层分带,与牙形石生物地层相比,精细程度尚不足.对乐业台地内部的刷把村剖面和六为剖面合山组底部牙形石进行了研究,在这两个剖面共鉴定出牙形石2属8种(含一个新种),包括Clarkina asymmetrica、C.aff.asymmetrica、C.daxianensis、C.dukouensis、C.leveni、Hindeodus julfensis、H.typicalis和Hindeodus praechangxingensis sp.nov..其中在刷把村剖面识别出C.asymmetrica和C.leveni两个牙形石带,六为剖面识别出C.asymmetrica一个牙形石带.根据牙形石关键分子的首现,乐业台地在经历了瓜德鲁普世-乐平世之交全球大海退后,至少到C.asymmetrica带才开始海侵并重新开始碳酸盐岩沉积,可为该区碳酸盐岩台地-盆地演化和区域地层对比研究提供重要依据.

Wuchiapingian is a key interval as a fast ecosystem recovery period between two mass extinctions,the End-Guadalupian crisis and the End-Permian mass extinction.Carbonate platforms were widely distributed in the middle of Yangtze platform and the Dian-Qian-Gui area during this interval.Among them,the Leye carbonate platform is one of the typically isolated carbonate platforms within the Nanpanjiang basin.The continuous Wuchiapingian marine carbonate(Heshan Formation)was deposited above the disconformity surface on the top of Guadalupian Maokou Formation.The traditional Middle-Late Permian stratigraphic frame scale in this area mainly relies on the fusulinids biozones,while only a few Wuchiapingian conodonts have been reported.Here,conodonts from the base of Heshan Formation at the Shuabacun Section and the Liuwei Section in the Leye platform have been obtained and studied.Eight conodont species(including one new species)belonging to two genera in total were identified,and they are Clarkina asymmetrica,C.aff.asymmetrica,C.daxianensis,C.dukouensis,C.leveni,Hindeodus julfensis,H.typicalis and Hindeodus praechangxingensis sp.nov..In ascending order,two conodont zones,the C.asymmetrica Zone and the C.leveni Zone can be identified at the Shuabacun Section.And one conodont zone,the C.asymmetrica Zone is also identified at the Liuwei Section.Based on this,we surmise that the beginning of the early Wuchiapingian carbonate deposition occurs in the C.asymmetrica Zone at Leye carbonate platform,after the global end-Guadalupian regression.It can provide important data for studying the local carbonate platform and basin evolution and also regional stratigraphic correlation.