Abstract The upper Stormberg Group (Elliot and Clarens formations) of the main Karoo Basin is well-known for its fossil vertebrate fauna, comprising early branching members of lineages including mammals, dinosaurs, and turtles. Despite 150 years of scientific study, the upper Stormberg Group lacks radioisotopic age constraints and remains coarsely dated via imprecise faunal correlations. Here we synthesise previous litho- and magnetostratigraphic studies, and present a comprehensive biostratigraphic review of the upper Stormberg fauna. We also present the results of the first geochronological assessment of the unit across the basin, using U-Pb dates derived from detrital zircons obtained from tuffaceous sandstones and siltstones, the youngest of which are considered maximum depositional ages. Our results confirm that the Elliot Formation contains the Triassic–Jurassic boundary, making it one of the few fossiliferous continental units that records the effects of the end-Triassic Mass Extinction event. Our work suggests a mid-Norian–Rhaetian age for the lower Elliot Formation and a Hettangian–Sinemurian age for the upper Elliot Formation, although the precise stratigraphic position of the Triassic/Jurassic (Rhaetian/Hettangian) boundary remains somewhat uncertain. A mainly Pliensbachian age is obtained for the Clarens Formation. The new dates allow direct comparison with better-calibrated Triassic-Jurassic faunas of the Western Hemisphere (e.g., Chinle and Los Colorados formations). We show that sauropodomorph, but not ornithischian or theropod, dinosaurs were well-established in the main Karoo Basin ~220 million years ago, and that typical Norian faunas (e.g., aetosaurs, phytosaurs) are either rare or absent in the lower Elliot Formation, which is paucispecific compared to the upper Elliot. While this is unlikely the result of geographic sampling biases, it could be due to historical sampling intensity differences.

中文翻译：

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Stormberg 群上游年代地层框架：对南部非洲三叠纪-侏罗纪边界的影响

摘要 主要 Karoo 盆地的上 Stormberg 群（Elliot 和 Clarens 地层）以其化石脊椎动物群而闻名，包括哺乳动物、恐龙和海龟等谱系的早期分支成员。尽管进行了 150 年的科学研究，但上风暴山群缺乏放射性同位素年龄限制，并且通过不精确的动物群相关性仍然粗略地确定了年代。在这里，我们综合了以前的岩石地层学和磁地层学研究，并对上斯托姆伯格动物群进行了全面的生物地层学回顾。我们还使用了从凝灰质砂岩和粉砂岩中获得的碎屑锆石的 U-Pb 日期，展示了对整个盆地单元的首次地质年代学评估的结果，其中最年轻的被认为是最大沉积年龄。我们的结果证实，艾略特组包含三叠纪-侏罗纪边界，使其成为少数记录三叠纪末大灭绝事件影响的化石大陆单元之一。尽管三叠纪/侏罗纪（Rhaetian/Hettangian）边界的精确地层位置仍然有些不确定，但我们的工作表明，Elliot 组下部为诺里阶-雷蒂阶中期，Elliot 组上部为 Hettangian-Sinemurian 时代。克拉伦斯地层获得了一个主要是 Pliensbachian 时代。新的日期允许与西半球更好校准的三叠纪-侏罗纪动物群（例如 Chinle 和 Los Colorados 地层）进行直接比较。我们展示了蜥脚类恐龙，但不是鸟臀目或兽脚类恐龙，恐龙在大约 2.2 亿年前在主要的卡鲁盆地中已经成熟，典型的诺里安动物群（例如，坚龙类、植龙类）在下埃利奥特组中要么是罕见的，要么是不存在的，与上埃利奥特组相比，后者是稀有的。虽然这不太可能是地理抽样偏差的结果，但可能是由于历史抽样强度差异造成的。