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.

本论文报道了采自玻利维亚中部科帕卡巴纳组（Copacabana Formation）的早二叠世乌拉尔统（Cisuralian）地层、孢粉地层学（palynostratigraphy）及绝对年代测定相关的全新数据。近期针对阿皮拉潘帕（Apillapampa）地区海相与过渡相岩石开展的地层学及孢粉学研究，细化了南美地区乌拉尔统孢粉形态类群（palynomorphs）的年代界定。本次研究对与5层火山灰层（volcanic ashes）互层的12件样品进行处理（经处理后均产出有效孢粉）后，共获得94种孢粉形态类群，可划分为两个非正式孢粉组合（palynoassemblages）：下部组合肋纹维塔塔孢（Vittatina costabilis）仅见于科帕卡巴纳组底部附近的1件样品，上部维尔基吕克孢（Lueckisporites virkkiae）组合则赋存于其上覆的海相及含煤过渡相地层中。年代学方面，通过牙形石（conodonts）、纺锤虫（fusulinids）的最新研究成果，以及针对含锆石层凝灰岩的同位素稀释热电离质谱法（Isotope Dilution Thermal Ionization Mass Spectrometry [ID-TIMS]）铀-铅（U-Pb）放射性年代测定，进一步独立限定了地层时代。上述数据表明，该地点科帕卡巴纳组下部海相成员的时代为阿瑟尔期（Asselian）与萨克马尔期（Sakmarian）。维尔基吕克孢（Lueckisporites virkkiae）是南美乃至全球二叠纪生物地层重建（biostratigraphic reconstructions）中关键的孢粉指示类群。因此，本文针对主要广布性指示类群的首现层位，对这些孢粉植物群开展了全面的全球对比与地层关联研究。本次研究还与南美（巴西、乌拉圭与阿根廷）及全球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亦通过放射性年代数据得到限定。