陕西渭北二叠纪-三叠纪之交叶肢介化石及其地层对比

Conchostracans from the Permian-Triassic Transition in Weibei Area of Shaanxi Province and Its Biostratigraphic

陆相二叠纪-三叠纪地层划分与对比对全面认识该时期全球性重大生物与环境突变事件具有重要意义,也是当前国际古生物学与地层学研究的重点和难点.选择陕西渭北为重点研究区域,通过对该地区石川河剖面和后周公庙剖面的叶肢介化石进行系统的分类学研究,恢复了叶肢介化石的面貌和组合特征,从而利用叶肢介化石组合来进行该地区二叠纪-三叠纪之交的生物地层划分和对比.其中,石川河剖面共产出叶肢介化石4属8种,后周公庙剖面共产出叶肢介化石2属3种.据此,该地区二叠纪-三叠纪之交的叶肢介化石由老到新可划分为3个组合,分别是晚二叠世晚期的Pseudestheria minutaPseudestheria xinjiangensis组合,二叠纪-三叠纪过渡期的Euestheria gutta-Palaeolimnadiopsis vilujensis组合和早三叠世早期的Magniestheria subcircularis-Cornia germari组合,并且通过这些叶肢介化石组合可以大致建立不同沉积区之间的生物地层对比关系.另外,两条剖面上都存在叶肢介化石与海相化石同层产出的现象,认为通过研究陕西渭北地区由于多期次海泛事件所导致的海、陆混合生物群,有望建立二叠纪-三叠纪之交该地区与海相地层的生物地层对比关系.

As global challenging key issues of paleontology and stratigraphy, the terrestrial Permian Triassic （P-Tr） stratigraphic subdivision and correlation have great significance for a comprehensive understanding of the nature of the global biotic and environmental event. Here, we try to establish the biostratigraphic correlation framework of the terrestrial depositions, and further explore the correlation between the marine and terrestrial P-Tr depositions, based on the P Tr transitional mixed ma- rine-terrestrial biota in Weibei area of Shaanxi Province. The present study focuses on the taxonomy, evolutionary lineage and stratigraphy of P-Tr transitional conchostracans （clam shrimps, spinicaudatans） in the terrestrial and terrestrial marine silici- clastic facies, which are regarded as an intermediate link for biostratigraphic correlation between terrestrial and marine se quences. A total of eight species in four genus and three species in two genus conchostracans were identified in the Shichuanhe Section and Houzhougong miao Section, respectively. Accordingly, in the study it proposes that the conchostracans fauna may be subdivided into three assemblages including the latest Permian Pseudestheria minuta-Pseudestheria xinjiangensis assemblage, the P-Tr transitional Euestheria gutta-Palaeolimnadiopsis vilujensis assemblage and the earliest Triassic Magniestheria subcircularis-Cornia gerrnari assemblage. Especially, the Euestheria gutta-Palaeolimnadiopsis vilujensis assemblage is proposed as marker of the P-Tr transitional beds of the terrestrial strata among various regions.