芙蓉统和排碧阶底界全球层型剖面的牙形刺生物地层

寒武系芙蓉统和排碧阶全球层型剖面——湖南花垣排碧剖面底界界线层的牙形刺生物地层,由下至上划分为Westergaardodina tetragonia带、Westergaardodina matsushitai带和Westergaardodina bicuspidate 3个牙形刺带,可与该界线层的三叶虫带进行很好对比;同时讨论了芙蓉统和排碧阶底界划在牙形刺Westergaardodina mat-sushitai带和Westergaardodina bicuspidata带之间的合理性;此外,还将该牙形刺分带与华北和东北地区寒武系牙形刺带进行了对比。

CONODONT BIOSTRATIGRAPHY OF THE GSSP OF THE BASE OF THE FURONGIAN SERIES AND PAIBIAN STAGE

Cambrian slope deposits are well exposed in western Hunan.The worldwide known sediments mainly consist of limestones bearing rich trilobite and conodont faunas.The trilobite biostratigraphy of the area is well studied,and now the first GSSP inside the Cambrian System has been ratified by IUGS and will be erected in this region.The Paibi section,Huayuan County,northwestern Hunan Province has been accepted for the GSSP of the base of the Furongian Series and Paibian Stage(Peng Shan-chi et al., 2004a). However,the conodont biostratigraphy of the boundary interval of the base of Furongian Series and Paibian Stage was relatively less investigated,because most of the existing papers on Cambrian conodont of this region focused on the traditional Middle-Upper Cambrian boundary interval,corresponding to the FAD of Linguagnostus reconditus(Dong Xi-ping,1990,1993,1999;Dong Xi-ping&Bergstrom.2001), whereas now the FAD of Glyptagnostus reticulatus has been selected for the GSP of the base of Furongian Series(which is the uppermost Series in Cambrian)and Paibian Stage.Thus,more attention should be paid on the conodont biostratigraphy in the boundary interval bearing Glyptagnostus reticulatus.In October 2001,the present authors and the others carried out a systematic and continuous sampling in the boundary beds of the base of Furongian Series and Paibian Stage of the Paibi section.Nearly 1 000 kg of limestone, representing 196 conodont sampler from the boundary beds of the section were processed,and relatively abundant paraconodont and protoconodont specimens were found and carefully studied in this paper. Based on the stratigraphical ranges of conodont species of the genus Westergaardodina the boundary interval of the base of Furongian Series and Paibian stage in the Paibi section can be subdivided into three conodont biozones(Fig.1 and Table 1),which are in descending order: 3.Westergaardodina bicuspidata Zone 2.Westergaardodina matsushitai Zone 1.Westergaardodina tetragonia Zone The elements of Westergaardodina experienced three different evolutionary periods,as clearly seen from Fig.1.The specific diversity of the genus Wester gaaardodina was very low in the Westergaardodina tetragonia Zone,and became relatively high In the Westergaardodina matsushitai Zone,where many impor- taut species of Westergaardodina including W.matsushitai,W.grandidens,W.elegans,W.moessebergen- sis,W.bisulcata,W.quadrata,W.cf.matsushitai,W.cf.muelleri etc.(Dong Xi-ping,1999;Dong Xi- ping&Bergstr?m,2001)appeared,but decreased sharply in the Westergaardodina bicuspidata Zone. Therefore,based on conodont biostratigraphy,the Perfect level for the base of the Furongian Series and Paibian Stage should be between the Westergaardodina matsushitai Zone and the Westergaardodina bicuspi- data Zone,which closely approximates the FAD of Glyptagnostus reticulatus. The conodont blozones proposed here are well correlated with those erected by Dong Xi-ping(1993 and 1999),and those of North and Northeast China(An Tai-xiang,1982),and are directly correlated with the trilobite biozones of the same section. This study has special interest for Cambrian biostratigraphy because the Paibi section is the GSSP of the base of Furongian Series and Paibian Stage,which is the first GSSP inside the Cambrian System.The conodont succession of the boundary interval is useful for local and regional correlations.