The Ediacaran-Cambrian transition represents a pivotal geological marker, denoting the decline of the Ediacaran biota and the emergence of most modern phyla in an interval marked by perturbations to the carbon cycle (as evidence by carbonate carbon isotopes, δ13Ccarb), biotic turnover, dynamic paleoredox regimes, and magnetic field instability. Following initial international expeditions to the Anti-Atlas belt in Morocco, numerous attempts have sought to pinpoint the exact stratigraphic level of the Ediacaran-Cambrian boundary (E-C) in this important succession, where ca. 3 km of continuous carbonate rocks provide one of the most complete successions for the establishment of a global δ13Ccarb chemostratigraphic reference curve. Subsequently, a growing number of publications have explored the stratigraphy, paleontology, and geochronology of the Ediacaran-Cambrian transition in the Anti-Atlas. Despite extensive efforts, the precise position of the E-C boundary in the Anti-Atlas remains ambiguous, with multiple proposed positions ranging from within the Ouarzazate Group to the lower part of the Tifnout Member (Adoudou Formation, Taroudant Group). Here, we conduct a comprehensive review of the available chemostratigraphic, paleontological, and geochronological data associated with the late Ediacaran-Cambrian Ouarzazate Group and Adoudou Formation within the Anti-Atlas belt. The objective is to refine our understanding of the regional expression of the E-C boundary and offer clarity on the inconsistencies observed among biostratigraphy, chemostratigraphy, and geochronology. This review underscores that the currently proposed boundary relies primarily on the δ13Ccarb excursion, lacking corroboration from other independent markers such as geochronology and globally significant ichnofossil assemblage constituents. Additionally, through the integration of newly available data and enhanced global chemostratigraphy, biostratigraphy, and geochronology, our findings suggest that the E-C boundary within the Western Anti-Atlas may be positioned as low as within the upper unit of the Tabia Member. However, this interpretation relies heavily on a Fortunian age for the ichnotaxa Monomorphichnus, in the absence of co-occurring specimens of the boundary-defining ichnospecies Treptichnus pedum. Moreover, a revised assessment of chemostratigraphic correlation and geochronological markers indicates that the Tabia and Tifnout members in the Central and Eastern Anti-Atlas do not correlate with the same named members in the Western Anti-Atlas. Both the Tabia and Tifnout members of the Central-Eastern Anti-Atlas may instead correlate with the middle part of Tifnout Member in the Western Anti-Atlas. This implies a late Ediacaran to early Cambrian ca. 10 m.y stratigraphic gap in the Central-Eastern Anti-Atlas and hence the E-C boundary in the Central-Eastern Anti-Atlas is likely situated within the unconformity between the Ouarzazate and Taroudant Groups. Lastly, we present unresolved questions regarding the biogenicity and affinities of some described discoidal structures and calcified microfossils from the Tabia Member, with the aim of further stimulating active engagement of the global scientific community in the establishment of robust paleontological and chronostratigraphic constraints for the E-C boundary within the Anti-Atlas belt.

中文翻译：

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反阿特拉斯带（摩洛哥）的埃迪卡拉纪-寒武纪边界：生物地层学、化学地层学和地质年代学综述


埃迪卡拉纪-寒武纪过渡代表了一个关键的地质标志，表示埃迪卡拉纪生物群的衰落和大多数现代门的出现，其特征是碳循环的扰动（碳酸盐碳同位素，δ13Ccarb 证明），生物周转，动态古氧化还原状态和磁场不稳定性。在对摩洛哥的反阿特拉斯带进行初步的国际考察之后，人们进行了多次尝试，试图在这个重要的演替中确定埃迪卡拉纪-寒武纪边界 （E-C） 的确切地层水平，其中约 3 公里的连续碳酸盐岩为建立全球 δ13Ccarb 化学地层参考曲线提供了最完整的演替之一。随后，越来越多的出版物在反阿特拉斯中探讨了埃迪卡拉纪-寒武纪过渡的地层学、古生物学和地质年代学。尽管付出了巨大的努力，但 E-C 边界在反阿特拉斯岩中的确切位置仍然模棱两可，从 Ouarzazate 组内部到 Tifnout 岩层的下部（Adoudou 组，Taroudant 组）有多个拟议的位置。在这里，我们对与反阿特拉斯带内晚期 Ediacaran-Cambrian Ouarzazate Group 和 Adoudou 组相关的可用化学地层学、古生物学和地质年代学数据进行了全面回顾。目的是完善我们对 E-C 边界的区域表达的理解，并阐明在生物地层学、化学地层学和地质年代学之间观察到的不一致。 这篇综述强调，目前提出的边界主要依赖于 δ13Ccarb 偏移，缺乏其他独立标记的佐证，例如地质年代学和全球重要的 ichnofossil 组合成分。此外，通过整合新可用的数据和增强的全球化学地层学、生物地层学和地质年代学，我们的研究结果表明，西部反阿特拉斯内的 E-C 边界可能位于塔比亚段的上部单元内。然而，这种解释在很大程度上依赖于 ichnotaxa Monomorphichnus 的 Fortunian 时代，因为没有边界定义的 ichnospecies Treptichnus pedum 的共同出现标本。此外，对化学地层相关性和地质年代学标记的修订评估表明，中部和东部反阿特拉斯的 Tabia 和 Tifnout 成员与西部反阿特拉斯中的相同命名成员不相关。相反，中东部反阿特拉斯的 Tabia 和 Tifnout 成员可能与西部反阿特拉斯的 Tifnout 成员的中间部分相关。这意味着中东部反阿特拉斯中埃迪卡拉纪晚期至寒武纪早期约 10 m.y 的地层间隙，因此中东部反阿特拉斯的 E-C 边界可能位于 Ouarzazate 和 Taroudant 组之间的不整合范围内。最后，我们提出了有关来自 Tabia 成员的一些已描述的盘状结构和钙化微化石的生物成因和亲和力的未解决的问题，目的是进一步刺激全球科学界的积极参与，为反阿特拉斯带内的 E-C 边界建立强大的古生物学和年代地层学限制。