SUMMARYRecent compilations of the Illawarra Reversals show remarkable differences in the onset age (265 Ma versus 269 Ma) and the magnetic polarity pattern, hampering the establishment of a reference geomagnetic timescale for the Middle–Late Permian. The Parana Basin hosts a 7-km-thick, discontinuous sedimentary succession spanning the Palaeozoic to the Mesozoic, including the Gondwana 1 supersequence which extends from Late Carboniferous to the Triassic or Jurassic. We provide the magnetostratigraphy of the middle and upper Permian part of this sequence of a ca. 300-m-long core, pertaining to the Passa Dois Group and the Piramboia Formation. Sample demagnetization of NRM revealed two magnetic overprints ascribed to the Brunhes chron and to the emplacement of Parana Large Igneous Province in the Early Cretaceous, respectively. Stable, dual polarity characteristic components (ChRM) were isolated at temperatures higher than 450 °C and interpreted as a primary detrital magnetic remanence (DRM), acquired during or soon after sediment deposition. Available U-Pb dating on volcanic zircons from the literature provided independent chronologic constraints for our magnetostratigraphy. A total of 8 reverse polarity intervals were identified, the lowermost of which (up to 110 m thick) correlates to the Kiaman Superchron. The overlying Illawarra is dominated by a reverse polarity magnetization with thin (4–5 m thick) normal polarity intervals. This pattern agrees with the Illawarra sequence from the Karoo Basin and other proposed timescales for the Permian. The onset of the Illawarra reversals is interpolated to ca. 270 Ma, close to the age of 269 Ma from the Karoo Basin. Combined magnetostratigraphy and geochronology yielded sediment accumulation rates of ca. 8 m Myr–1 for the Passa Dois Group in the northeastern (marginal) sector of the Parana Basin, indicating that Serra Alta and Teresina Formations span 279–274 Ma and 274–254 Ma, respectively.

中文翻译：

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中-晚二叠世磁地层学和南美洲巴拉那盆地东北部伊拉瓦拉反转的开始

摘要最近对伊拉瓦拉反转的汇编显示，在开始年龄（265 Ma 与 269 Ma）和磁极模式方面存在显着差异，这阻碍了中二叠纪中晚期地磁时间尺度的建立。巴拉那盆地拥有一个 7 公里厚的不连续沉积层序，跨越古生代到中生代，包括从晚石炭世延伸到三叠纪或侏罗纪的冈瓦纳 1 超层序。我们提供了该序列的二叠纪中上二叠纪部分的磁地层学。300 米长的岩心，属于 Passa Dois 组和 Piramboia 组。NRM 的样品退磁揭示了两个磁性叠印，分别归因于早白垩世的 Brunhes chron 和 Parana 大火成岩省的就位。稳定的，双极性特征成分 (ChRM) 在高于 450 °C 的温度下被分离出来，并被解释为在沉积物沉积期间或之后不久获得的初级碎屑剩磁 (DRM)。文献中可用的火山锆石 U-Pb 测年为我们的磁地层学提供了独立的年代学约束。总共确定了 8 个反极性间隔，其中最低的（最大 110 m 厚）与 Kiaman Superchron 相关。上覆的 Illawarra 以具有薄（4-5 m 厚）正极性间隔的反极性磁化为主。这种模式与来自 Karoo 盆地的 Illawarra 序列和其他提出的二叠纪时间尺度一致。伊拉瓦拉反转的开始被插值到 ca。270 Ma，接近卡鲁盆地的 269 Ma 年龄。结合磁地层学和地质年代学得出的沉积物积累速率约为。Parana 盆地东北（边缘）区段 Passa Dois 组的 8 m Myr-1，表明 Serra Alta 组和 Teresina 组分别跨越 279-274 Ma 和 274-254 Ma。