Publication Date:
2008-05-29
Description:
An interval of episodic carbonate productivity, lithostratigraphically recognized as the Calcaires inferieurs' (upper member of the Adoudou Formation), took place across the Neoproterozoic-Cambrian transition onlapping the western Saghro inlier, Morocco. Sedimentation of the Calcaires inferieurs' 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 inferieurs' 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.
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