Structural style and evolution of a Late Triassic rift basin in the Central High Atlas, Morocco: controls on sediment deposition

Abstract

Late Triassic continental sediments deposited in an active-rift setting are exposed in the Oukaimeden-Ourika Valley, located in the Central High Atlas Basin of Morocco. The Oukaimeden Sandstone Formation is dominated by ephemeral and perennial braided fluvial facies, and is an outcrop analogue for Triassic sandstone hydrocarbon reservoirs found in Atlantic margin and North African basins. This paper documents detailed analysis of the outcrop data to investigate the influence of tectonics on deposition and the interplay with climatic controls. The geodynamic evolution of the basin is interpreted to be influenced by Atlantic rifting to the west and the formation of the Tethys Sea to the north, which led to the development of ENE and NNE striking normal faults. The present-day fault and outcrop geometry reflects later inversion due to the Alpine compression that led to uplift of the High Atlas and subsequent erosion.The ENE trending rift-basin is bound by normal faults, which are probably in part reactivated older Hercynian structures. The facies distribution was controlled by a complex interplay of tectonic and climatic controls. Evidence for syn-sedimentary movement of both fault sets is observed, with stratigraphic thickening and associated progressive change in bedding dip. These faults controlled the basin dimension, geometry of the half-graben and created the accommodation for sediment deposition. The presence of breccia deposits close to the main ENE bounding faults indicates footwall erosion and deposition of basin margin fans. The location and orientation of the main fluvial system was controlled by these structures, and the main channel belts ran parallel and proximal to the controlling faults, whereas away from the main syn-depositional faults overbank deposits dominate. Smaller contemporaneous NNE oriented faults are generally shorter with less throw, and had only a limited influence on gross sedimentation patterns. These faults are interpreted to be syn-sedimentary, displaying characteristics that suggest basal detachment within the Triassic, and as such provide evidence for the extension direction during late Triassic time. A periodic change from ephemeral to perennial systems, with associated changes in architectural style, is potentially attributed to climatic control, although a structural influence cannot be dismissed.

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

“…5) (e.g., Medina 1995;Baudon et al 2009). Upper Permian to Liassic sediments pinch-out between Upper Cretaceous and basement rocks to the W of Imi-n-Tanout (Figs.…”

Las sucesiones terrígenas del Triásico superior y la base del Jurásico del Alto Muluya (Marruecos): estratigrafía y contexto geodinámico

“…Se caracterizó (Fig. 7) por un contexto geodinámico extensional relacionado con el rifting del Atlántico central (Manspeizer, 1988;Laville, 1988;Laville & Piqué, 1991;Piqué & Laville, 1993Laville et al, 2004;Oujidi et al, 1997;Mahmoudi & Bertrand, 2007;Baudon et al, 2009;Quarbous et al, 2009) cuyos efectos llegaron plenamente al Atlas, reactivándose muchas de las fallas que ya habían afectado al basamento herciniano. Esta removilización fue la que individualizó las cuencas del Alto Muluya, cuyo relleno fue a la vez contemporáneo con los procesos extensionales que, a lo largo del Jurásico, determinarían la apertura del Tethys occidental.…”

“…Este relleno, netamente sintectónico (synrift: Laville & Piqué, 1991;Laville et al, 1995Laville et al, , 2004Bouatmani et al, 2004;Baudon et al, 2009), se producía en un medio continental con descargas detríticas sucesivas que, desde los abanicos aluviales situados al borde de los macizos montañosos, pasaban a formar sistemas aluviales trenzados con las llanuras de inundación cada vez más extensas. Las importantes variaciones de espesor y los notables cambios de facies atestiguan la reactivación de los relieves, lo que se producía por la continuación del proceso del rifting (Fig.…”

The subsurface structure and stratigraphic architecture of rift-related units in the Lishu Depression of the Songliao Basin, China

“…Bosworth, 1985;Cohen,1990;Bois, 1993;Nøttvedt et al, 1995;Cloetingh et al, 1997;Gawthorpe & Leeder, 2000;Martins-Neto, 2000;Arabi et al, 2003;Alves et al, 2003;Garcia et al, 2008;Baudon et al, 2009). A single model is typically used to describe the unique tectonic and sedimentary conditions operating during a given stage, even though each stage may consist of several phases of activity.…”