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Northwest Africa’s Ediacaran to early Cambrian fossil record, its oldest metazoans and age constraints for the basal Taroudant Group (Morocco)


Letsch, Dominik; Large, Simon J E; Bernasconi, Stefano M; Klug, Christian; Blattmann, Thomas M; Winkler, Wilfried; von Quadt, Albrecht (2019). Northwest Africa’s Ediacaran to early Cambrian fossil record, its oldest metazoans and age constraints for the basal Taroudant Group (Morocco). Elsevier Oceanography Series, 320:438-453.

Abstract

The Anti-Atlas area in southern Morocco preserves one of the most complete latest Ediacaran to Cambrian shallow-marine carbonate records in the world and serves as a standard for global chemostratigraphic δ13Ccarb curves. Contrary to the excellent chemostratigraphic coverage, neither metazoan fossils (only stromatolites and calcified algae) nor radiometric age constraints were hitherto available for the basal part of this carbonate record, the Tifnout Member of the Adoudou Formation of the Taroudant Group. We report an Ediacara-type fauna from shallow-marine sandstones from the basal Tabia Member and microfossils from dolostones from both the Tabia and the Tifnout members of the Adoudou Formation. The former are discoidal fossils and share many characteristics with the form genus Aspidella and exhibit a peculiar style of preservation, pointing towards an early diagenetic two-stage (carbonate followed by silica) cementation history, leading to good preservation of these supposedly once soft-bodied organisms. The dolostone-hosted microfossils are preserved as sparite-filled molds enclosed by a thin opaque envelope. Despite their small size, they resemble late Ediacaran calcifying metazoans such as Namacalathus and tubular small shelly fossils. Together, these fossils constitute the oldest known direct evidence for presumably metazoan life from Northwest Africa. We also report new time constraints for the Adoudou Formation and fossils enclosed therein based on combined LA-ICP-MS and high-precision CAID- TIMS U-Pb zircon geochronology of detrital and volcanic zircons. Together with new chemostratigraphic (δ13Ccarb) and literature data, these new age constraints suggest a late Ediacaran age (time span between ca. 561 and 542 Ma) for the discoidal Ediacara-type fossils from the basal Tabia Member, and a latest Ediacaran to earliest Cambrian (time span between ca. 544 and 540 Ma) and an early Cambrian age (time span between ca. 528 and 523 Ma) for the two microfossil faunas from the Tifnout Member.

Abstract

The Anti-Atlas area in southern Morocco preserves one of the most complete latest Ediacaran to Cambrian shallow-marine carbonate records in the world and serves as a standard for global chemostratigraphic δ13Ccarb curves. Contrary to the excellent chemostratigraphic coverage, neither metazoan fossils (only stromatolites and calcified algae) nor radiometric age constraints were hitherto available for the basal part of this carbonate record, the Tifnout Member of the Adoudou Formation of the Taroudant Group. We report an Ediacara-type fauna from shallow-marine sandstones from the basal Tabia Member and microfossils from dolostones from both the Tabia and the Tifnout members of the Adoudou Formation. The former are discoidal fossils and share many characteristics with the form genus Aspidella and exhibit a peculiar style of preservation, pointing towards an early diagenetic two-stage (carbonate followed by silica) cementation history, leading to good preservation of these supposedly once soft-bodied organisms. The dolostone-hosted microfossils are preserved as sparite-filled molds enclosed by a thin opaque envelope. Despite their small size, they resemble late Ediacaran calcifying metazoans such as Namacalathus and tubular small shelly fossils. Together, these fossils constitute the oldest known direct evidence for presumably metazoan life from Northwest Africa. We also report new time constraints for the Adoudou Formation and fossils enclosed therein based on combined LA-ICP-MS and high-precision CAID- TIMS U-Pb zircon geochronology of detrital and volcanic zircons. Together with new chemostratigraphic (δ13Ccarb) and literature data, these new age constraints suggest a late Ediacaran age (time span between ca. 561 and 542 Ma) for the discoidal Ediacara-type fossils from the basal Tabia Member, and a latest Ediacaran to earliest Cambrian (time span between ca. 544 and 540 Ma) and an early Cambrian age (time span between ca. 528 and 523 Ma) for the two microfossil faunas from the Tifnout Member.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
Dewey Decimal Classification:560 Fossils & prehistoric life
Uncontrolled Keywords:Geology, Geochemistry and Petrology
Language:English
Date:1 January 2019
Deposited On:11 Dec 2018 15:09
Last Modified:17 Sep 2019 19:46
Publisher:Elsevier
ISSN:0422-9894
OA Status:Closed
Publisher DOI:https://doi.org/10.1016/j.precamres.2018.11.016
Project Information:
  • : FunderSNSF
  • : Grant ID200021_156244
  • : Project TitleNeoproterozoic-Cambrian geodynamic history of the Anti-Atlas (Morocco) and implications for the European Alpine basement

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