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 <i>Vittatina costabilis</i> corresponds to one sample near the base of the Copacabana Formation and the upper <i>Lueckisporites virkkiae</i> 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. <i>Lueckisporites virkkiae</i> 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）及绝对年代学（absolute dating）相关新数据。近期针对阿皮拉潘帕（Apillapampa）地区海相与过渡相岩石的地层学与孢粉学研究成果，进一步精确厘定了南美洲乌拉尔阶孢粉类化石（palynomorphs）的地质年代。本次研究对与5层火山灰互层的12件样品开展处理，经处理后均成功获取有效孢粉样品，共鉴定出94种孢粉类化石，可划分为两个非正式孢粉组合：下部组合以肋饰维塔蒂娜孢（*Vittatina costabilis*）为代表，对应科帕卡巴纳组底部附近的1件样品；上部维尔克氏吕克孢（*Lueckisporites virkkiae*）组合则产于上覆海相及含煤过渡相层位中。研究同时通过对牙形石（conodonts）、筵类（fusulinids）的最新综述，以及含锆石互层凝灰岩的同位素稀释热电离质谱法（Isotope Dilution Thermal Ionization Mass Spectrometry, ID-TIMS）U-Pb放射性同位素测年数据，独立约束了地层年代。上述数据表明，该地点科帕卡巴纳组下部海相段的地质年代为阿瑟尔阶（Asselian）至萨克马尔阶（Sakmarian）。维尔克氏吕克孢（*Lueckisporites virkkiae*）是南美洲乃至全球二叠纪生物地层重建中常用的关键孢粉标准化石。因此，本文以广布性标志性分类单元的首现事件为核心依据，对上述孢粉植物群开展了全面的全球对比与地层区划工作，并与南美洲（巴西、乌拉圭、阿根廷）及其他地区的诸多类似二叠纪孢粉植物群建立了地层对比关系，其中部分对比序列还通过放射性同位素测年数据得到了年代约束。