Post-rift vertical movements and horizontal deformations in the eastern margin of the Central Atlantic: Middle Jurassic to Early Cretaceous evolution of Morocco

Abstract

Wide regions of Morocco, from the Meseta to the High Atlas, have experienced km-scale upward vertical movements during Middle Jurassic to Early Cretaceous times following the appearance of oceanic crust in the Central Atlantic. The area experiencing exhumation was flanked to the W by a domain of continuous subsidence, part of which is named the Essaouira-Agadir basin. Comparison with vertical movement curves predicted by lithospheric thinning models shows that only 50-60 % of the subsidence documented in the Essaouira basin can be explained by postrift thermal relaxation and that \30-40 % of the observed exhumation can be explained by processes (in)directly related to the evolution of the Central Atlantic rifted margin. Syn-sedimentary structures in Middle Jurassic to Lower Cretaceous formations of the Eassouira-Agadir basin are common and range from m-scale folds and thrusts to km-scale sedimentary wedges. These structures systematically document coeval shortening generally oriented at high angle to the present margin. As a working hypothesis, it is suggested that regional shortening can explain the structural observations and the enigmatic vertical movements.

The Upper Jurassic-lower Cretaceous Siliciclastic System in the Morocco Offshore - Prevenance, Transport and Deposition

“…Differently from what generally expected for passive continental margins, large parts of Morocco experienced in Late Jurassic to Cretaceous times, that is during the post-rift stage an event of exhumation and erosion which produced large amount of terrigenous deposits (Bertotti and Gouiza, 2012) that were transported through fluvial systems to the W, formed coastal and deltaic systems in the present coastal region and eventually were deposited in the deep offshore. A distal portion of the turbiditic system is exposed in the Canary Islands.…”

“…The kinematics of exhumation in this northern region is fairly well documented by a significant number of low-temperature geochronological studies (Bertotti and Gouiza, 2012;de Lamotte et al, 2009;Ghorbal et al, 2008). Following the Variscan orogeny, the entire region was peneplained and began subsidence possibly in relation with Central Atlantic rifting allowing for the deposition of Triassic to Jurassic clastics and carbonates.…”

“…Here, subsidence has been continuous through Permian to Cretaceous time although an increase in subsidence rates has been observed starting at around 150Ma (Bertotti and Gouiza, 2012). These movements, which have been tentatively associated with E-W shortening (Bertotti and Gouiza, 2012) ended in the middle Cretaceous when the central area was exposed, began subsiding and was covered by Upper Cretaceous shallow water carbonates.…”

“…200km wide stretching from Rabat to the Massif Ancien de Marrakech and, further to the S, to the Siroua Plateau inverted the sense of vertical movements and started moving upward causing erosion The area experiencing exhumation was flanked by subsiding domains in the E and, more importantly, to the W (Essaouira and Agadir basins) (Hafid, 2000). Here, subsidence has been continuous through Permian to Cretaceous time although an increase in subsidence rates has been observed starting at around 150Ma (Bertotti and Gouiza, 2012). These movements, which have been tentatively associated with E-W shortening (Bertotti and Gouiza, 2012) ended in the middle Cretaceous when the central area was exposed, began subsiding and was covered by Upper Cretaceous shallow water carbonates.…”

“…Possibly the only tectonic model proposed to explain these observations suggests that the upward moving domain of the Massif Ancien de Marrakech and the subsiding region of the Essaouira-Agadir basin were linked by internally weakly deformed region gradually titling towards the W (Bertotti and Gouiza, 2012).…”