Constraining Mesozoic early post-rift depositional systems evolution along the eastern Central Atlantic margin

Extensive Mesozoic outcrops exposed in the Aaiun-Tarfaya Basin, in the Atlantic margin of Morocco, have been overlooked for decades. Original subdivisions and dating of rocks, performed more than five decades ago, have survived until today virtually without any update. In the north eastern margin of the basin, key Mesozoic sections have been revisited. Its coastal position next to the Variscan Anti-Atlas Orogen allows insight into the interplay between local tectonics and eustasy during deposition of sedimentary sequences on passive margins. High-resolution stratigraphy and sedimentology have allowed for an improved understanding of the depositional systems and evolution during the early opening of the Atlantic and provided a valuable control point recording the syn- and early post-rift evolution of the basin. Three formations are described: (i) a basal continental red bed unit unconformably overlying the Palaezoic Variscan basement of the Ifni Inlier; (ii) a unit dominated by intertidal elastics and microbial carbonates, and (iii) a shallow marine unit comprising mixed siliciclastic-carbonates. Despite the sedimentological affinity of these outcrops to Triassic or Lower Jurassic deposits elsewhere in Morocco, these units had previously been assigned an Early Cretaceous age, based on limited non-conclusive fossil fauna and basin-scale lithostratigraphic correlation. New collections of macrofauna have yielded a Bathonian age for the upper part of the succession and a possible Triassic/Early Jurassic for the lower part. The whole succession displays an overall transgressive trend not consistent with the eustatic Bathonian sea-level fall. Local post-rift tectonic pulses exhuming the Western Anti-Atlas coupled with eustasy are responsible for increased sediment supply at this time. Enhanced tectonic subsidence, overcoming sea-level fall, is interpreted to be the main driver for creation of accommodation and preservation of this sequence. Resumed sedimentation on structural heights offshore suggests exhumation of the Western Anti-Atlas ceased by the early Callovian, reducing clastic input to the region and allowing the development of a carbonate platform. Variable regional exhumation and local tectonics along the Moroccan margin during the early post-rift stage influenced the highly variable nature of clastic vs carbonate deposition, thickness distribution and depositional environments at this time. (C) 2019 Elsevier B.V. All rights reserved.