Facies architecture, modal analysis and geochemistry of the Early Ediacaran turbiditic series in the Skoura inlier (Central High Atlas, Morocco): Implications for provenance and geotectonic setting.

Abstract

A multidisciplinary approach based on lithostratigraphy, petrography, modal composition and geochemistry was performed for the first time, to study the Early Ediacaran Skoura Turbidites (EEST) of the Skoura inlier, Central High Atlas. It represents widely distributed turbidite successions up to 8 km in thickness. A total of twelve lithofacies types have been distinguished, spread in four profiles, and grouped in three major depositional environments: shallow delta complex (FA1), submarine channel (FA2), and deep-sea fan (FA3). The paleogeographic distribution of the EEST may indicate basin depth changes related to the onset of convergence.Petrographic and modal analyses of EEST reveal greywacke and lith-arenite lithologies displaying similar clast composition, mainly comprising quartz and lithic fragments. Volcanic, plutonic, and metamorphic rocks have been exposed in the source areas feeding the Skoura basin. On Q-F-L diagram, EEST have characteristics of a recycled orogen, suggesting their derivation from an active arc setting. Geochemical data of EEST samples display similar SiO2 and Al2O3 abundances, with relatively intermediate compositions. Most of the studied samples demonstrate their derivation from a composite of oceanic island and continental arc systems providing felsic and mafic to intermediate detritus to the Skoura basin. Rare-earth element patterns show features similar to those of sandstones in modern active margin zones. The EEST rocks are similar with other Early Ediacaran sediments of the Saghro Group in the Anti-Atlas belt. This architecture suggests deposition of the EEST in an orogenic basin developed in a back-arc setting during the Early Ediacaran time.