Syn-depositional Mesozoic siliciclastic pathways on the Moroccan Atlantic margin linked to evaporite mobilisation

Rémi Charton,Christian Kluge,David Fernández-Blanco,Aude Duval-Arnould,Orrin Bryers,Jonathan Redfern,Giovanni Bertotti

doi:10.1016/j.marpetgeo.2021.105018

Abstract

Evaporite mobilisation in evaporite-cored anticlines leads to topographic growth that can alter sedimentary routing in shallow marine environments. This paper analyses two evaporite-cored anticlines perpendicular to the NW Africa coast to understand how their tectonic evolution influenced sediment pathways during the Early to Middle Jurassic and Early Cretaceous exhumation of the Mesozoic margin hinterland. The Essaouira-Agadir Basin in Morocco underwent evaporite deposition during the Atlasic and Atlantic rifting. Subsequent loading and tectonics resulted in re-mobilisation and generation of a variety of evaporite structures. Structural data obtained from analysis of Google Earth images processed using Move 2D allowed derivation of the thickness of sedimentary units on both flanks of the structures. Integrated with sedimentary logs from nine locations around evaporite-cored structures and two onshore wells, this data constrains the depositional record and allow an assessment of siliciclastic flux in the Essaouira-Agadir Basin. The results show the importance of syn-sedimentary evaporite tectonics on basin morphology, which influences the distribution of clastics delivered by fluvial systems and deepwater processes into the basin. This paper constrains the evolution of the Amsittène and Imouzzer anticlines in the Early to Middle Jurassic and support that their growth is associated with halokinesis. Mesozoic syn-sedimentary fold growth would have provided an important control on sediment discharge pathways and on the location of sediment entry points on the shelf margin, that ultimately fed deep water fan systems. This knowledge is key to predict the reservoir presence on the eastern margin of the Central Atlantic Ocean and to some extent, its conjugate margin in Nova Scotia.

Highlights

In the absence of tectonic forces, the mobility of weak evaporites could lead to surface topography influences potential sediment path ways (e.g., Venus et al, 2015)
An outstanding example is the influence of Triassic evaporites of the Eastern Diapiric Province in the post-rift sedimentary architecture of Agadir-Essaouira Basin (EAB) in the Western High Atlas
Mesozoic evaporite mobility is interpreted to have been instrumental in the formation of both anticlines from the Early and into the Middle Jurassic (Fig. 10)

Summary

Introduction

In the absence of tectonic forces, the mobility of weak evaporites could lead to surface topography influences potential sediment path ways (e.g., Venus et al, 2015). Extensive fieldwork and high-resolution 3D seismic surveys document this relationship between halokinesis and sediment channelling in fluvial and shallow-marine environments (e.g., Venus et al, 2015; Rojo and Escalona, 2018). This relationship is poorly documented in remote onshore areas and/or in areas with scarce field data. An outstanding example is the influence of Triassic evaporites of the Eastern Diapiric Province in the post-rift sedimentary architecture of Agadir-Essaouira Basin (EAB) in the Western High Atlas The present-day onshore segment of the EAB is the only Atlantic coastal basin in NW Africa bearing Triassic evaporites (Hafid et al, 2008). Thickest evaporitic bodies in the EAB platform domain, as well as their Jurassic cover, are located atop of half-grabens (Tari and Jabour, 2013)

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Discussion

Conclusion