Lyell Collection
Geological Society, London, Special Publications
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Álvaro, J. J.
Right arrow Articles by Ader, M.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Geological Society, London, Special Publications; 2008; v. 297; p. 285-302;
DOI: 10.1144/SP297.14
© 2008 Geological Society of London

The late Neoproterozoic-early Palaeozoic extension along the West African craton and the Peri-Gondwanan terranes

Late Neoproterozoic carbonate productivity in a rifting context: the Adoudou Formation and its associated bimodal volcanism onlapping the western Saghro inlier, Morocco

J. Javier Álvaro1,2, Mélina Macouin3, Hassan Ezzouhairi4, A. Charif4, N. Ait Ayad4, M. Luisa Ribeiro5 & Magali Ader6

1 Departamento Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain
2 Current present address: UMR 8014-LP3, USTL, 59655 Villeneuve d'Ascq, France (e-mail: Jose-Javier.Alvaro{at}univ-lille1.fr)
3 UMR 5563-LMTG, 14 Av. Edouard Belin, Université Paul Sabatier, 31400 Toulouse, France
4 Département de Géologie, Université Chouaib Doukkali, 24000 El Jadida, Morocco
5 INETI—Area de Geociências, Estrada da Portela, Zambujal, 2721-866 Alfragide, Portugal
6 UMR 7047, Institut de Physique du Globe de Paris, 4 place Jussieu, 75005 Paris, France

An interval of episodic carbonate productivity, lithostratigraphically recognized as the ‘Calcaires inférieurs’ (upper member of the Adoudou Formation), took place across the Neoproterozoic–Cambrian transition onlapping the western Saghro inlier, Morocco. Sedimentation of the ‘Calcaires inférieurs’ was highly variable: in relatively stable substrates, a peritidal-dominated mixed platform is recorded where deposition was primarily controlled by autocyclic processes and accommodation space availability, whereas, in unstable substrates, the tectonic activity associated with the inherited block-faulting basement led to deposition of complex slide sheets composed of penecontemporaneous isoclinal folds and disrupted strata. The uppermost part of the ‘Calcaires inférieurs’ displays a negative {delta}13C shift reaching values of –6.5{per thousand}. This shift may represent the {delta}13C excursion to –6{per thousand} that marks the Neoproterozoic–Cambrian boundary in the western Anti-Atlas. Two volcanic episodes bracketed the carbonate productivity. They consist of lower basaltic flows and an upper rhyolitic ignimbrite, with a SiO2 gap between 52 and 74 wt%. The basic rocks resemble those of tholeiitic magmas in continental rifts. The felsic rocks show high light to heavy rare earth element abundances and negative Nb, Ta, P and Ti anomalies, and were probably generated as a result of either fractional crystallization coupled with relative crustal contamination, or from a different magmatic source. The lower basic flows of tholeiitic affinity predated and geochemically differ from the alkaline magmatism of the Alougoum volcanic complex (Boho jbel) that surrounds the neighbouring Bou-Azzer inlier.