广西恭城奥陶纪含笔石地层

ORDOVICIAN GRAPTOLITE BIOSTRATIGRAPHY OF GONGCHENG, GUANGXI, CHINA

桂北恭城奥陶纪含笔石地层过去因缺乏生物化石证据将其划归于寒武系清溪组。1997年在其中发现笔石后重新将时代确定为奥陶纪,整套地层可划分为8个笔石带.自上而下为:8.Nemagraptus gracilis带;7.Ptero-graptus elegans带;6.Nicholsonograptus fasciculatus带;5.Acrograptus ellesae带;4.Undulograptus austroden-tatus带;3.Exigraptus clavus带;2.Isograptus caduceus cf.imitatus带;1.Didymograptus(Expansograptus)abnormis带。该地层与我国广东、浙江、江西、安徽等地区,以及澳大利亚、北美、英国等的相应层位可以对比。

The present paper deals with two sections of Huang’ai,Shengping and Tianlingkou Formations in Gongcheng,Guangxi Autonomous Region used to be regarded as of Cambrian age due to the lacking of fossils.In 1997 Ordovician graptolites indicating mainly Middle Ordovician were first discovered from the rocks,and briefly reported in 1999.The details of these two sections are presented herein,and biostrati- graphy discussed.The sections,located in the northeast of Gongcheng,Guangxi with considerably abun- dant Ordovician graptolites,include the following 8 graptolite zones(in descending order):8.Nemagrap- tus gracilis,7.Pterograptus elegans,6.Nicholosonograptus fasciculatus,5.Acrograptus ellesae,4.Undu- lograptus austrodentatus,3.Exigraptus clavus,2.Isograptus caduceus of.imitatus,1.Didymograptus (E.)abnomis.The graptolite biozones are comparable with those in SE China,Australia,Canada,North America and Great Britain.The succession is believed to be representative of deep-water‘Isograptus’fa- cies in the Zhujiang Region of South China.