Global biostratigraphic comparison and correlation of an early Cisuralian palynoflora from Bolivia

This paper presents new data about Early Permian (Cisuralian) strata, palynostratigraphy and absolute dating from the Copacabana Formation in central Bolivia. Recent stratigraphic and palynologic data from marine and transitional rocks at Apillapampa refine the age of Cisuralian palynomorphs in South America. Twelve samples interbedded with five volcanic ashes (processed and productive) yielded 94 palynomorph species arranged in two informal palynoassemblages: the lower assemblage Vittatina costabilis corresponds to one sample near the base of the Copacabana Formation and the upper Lueckisporites virkkiae assemblage occurs in overlying marine and coal-bearing transitional intervals. Ages were also independently refined by a modern review of conodonts, fusulinids, along with those U–Pb radiometric ages (Isotope Dilution Thermal Ionization Mass Spectrometry [ID-TIMS] of zircon-bearing interbedded tuffs). These data suggest that the lower marine member of the Copacabana Formation at this location is Asselian and Sakmarian. Lueckisporites virkkiae is a key species of palynomorph utilised in South American and global Permian biostratigraphic reconstructions. Hence, a thorough global comparison of these palynofloras and correlations is addressed in this contribution, considering first appearances of mainly cosmopolitan diagnostic taxa. Correlations are established with many similar Permian palynofloras, some also constrained with radiometric data, in South America (Brazil, Uruguay and Argentina) and elsewhere.

本论文报道了玻利维亚中部科帕卡巴纳组（Copacabana Formation）早二叠世（乌拉尔统，Cisuralian）的地层、孢粉地层学（palynostratigraphy）及绝对年代测定（absolute dating）相关新数据。阿皮拉潘帕（Apillapampa）地区海相与过渡相岩石的最新地层学及孢粉学研究，厘定了南美地区乌拉尔统孢粉型化石的时代。12件与5层经处理可产出孢粉的火山灰互层的样品，共产出94种孢粉型化石，可划分为两个非正式孢粉组合：下组合以Vittatina costabilis为代表，对应科帕卡巴纳组底部附近的1件样品；上组合Lueckisporites virkkiae则见于其上覆的海相及含煤过渡相地层中。地层年代还通过牙形类（conodonts）、纺锤有孔虫（fusulinids）的最新综述，以及含锆石夹层凝灰岩的同位素稀释热电离质谱（Isotope Dilution Thermal Ionization Mass Spectrometry，ID-TIMS）U-Pb同位素测年结果得到独立厘定。数据表明，该地点科帕卡巴纳组下部海相段的时代为阿谢尔阶（Asselian）与萨克马尔阶（Sakmarian）。Lueckisporites virkkiae是南美及全球二叠纪生物地层重建中应用广泛的关键孢粉型化石。因此，本文基于主要广布性指示分类群的首现特征，对本次研究的孢粉植物群开展了全面的全球对比与地层关联分析。本次研究与南美（巴西、乌拉圭、阿根廷）及其他地区诸多相似的二叠纪孢粉植物群建立了地层对比关系，其中部分类群的时代也通过同位素测年得到约束。