贵州遵义地区早—中三叠世双壳类生物地层研究

Triassic Bivalve Biostratigraphic Sequence in Zunyi,Guizhou Province

遵义地区位于扬子板块上扬子台地中部,下、中三叠统发育良好,夜郎组、茅草铺组、松子坎组及狮子山组地层出露齐全。其中遵义巷口剖面是扬子台地区的经典下-中三叠统地层剖面之一,其产双壳类化石尤为丰富,是该沉积相区生物地层和生态系演化研究的关键剖面。迄今已发现双壳类15属55种(亚种)(本次研究鉴定出12属35种),多数属为世界性的分布类型,由下向上可划分出6个双壳类化石带:Pteriaussurica varibilis-Eumorphotis venetiana组合带,Claraiaconcentrica-Claraia wangi组合带,Eumorphotis multiformis顶峰带,Entolium discites microtis顶峰带,Myophoria(Costatoria)goldfussi mansuyi-Asoellaillyrica组合带和Plagiostoma radiata-Palaeoli ma subcostata组合带。其双壳类生态类群的演变与华南其他地区具有一致性。

The marine Triassic succession is well exposed in the Zunyi area,Guizhou Province,which was located on the Upper Yangtze platform.The Lower-Middle Triassic is divided into Yelang,Maocaopu,Songzikan and Shizishan formations in an ascending order.The Xiangkou section,one of the typical Lower-Middle Triassic sections on the Yangtze platform,contains abundant bivalve fossils,thus it is important for the study of biostratigraphy and marine benthic ecosystems.Total 55 bivalve species in 15 genera have been identified（35 species in 12 genera are examined in this study）,most of which had a world-wide distribution.These bivalves are grouped into six bivalve assemblage zones： Pteria ussurica varibilis-Eumorphotis venetiana assemblage zone,Claraia concentrica-C.wangi assemblage zone,Eumorphotis multiformis acme zone,Entolium discites microtis acme zone,Myophoria（Costatoria） goldfussi mansuyi-Asoella illyrica assemblage zone and Plagiostoma radiata-Palaeolima subcostata assemblage zone in an ascending order,and the age of them are respectively assigned to the earliest Griesbachian,Griesbachian to Early Dienerian,Late Dienerian to Early Smithian,Late Smithian to Spathian,Anisian and Ladinian.The bivalve faunas show an evolution trend similar to those in the other areas of South China.