Diapiric growth within an Early Jurassic rift basin: The Tazoult salt wall (central High Atlas, Morocco)

Abstract

The central High Atlas (Morocco) constitutes a diapiric province that hosts a complex array of elongated diapirs and minibasins that formed during the Lower Jurassic rift of the Atlas Basin. This paper aims to study the structure and growth evolution of the Tazoult diapiric wall, located in the central High Atlas, by means of structural and sedimentological fieldwork integrated with remote sensing mapping. The Tazoult salt wall is a 20 km long × 3 km wide NE‐SW trending ridge that exposes Upper Triassic red beds and basalts along its core. The succession flanking the salt wall ranges from Hettangian to Bajocian ages displaying spectacular sedimentary wedges in the SE and NW flanks. The Hettangian‐early Sinemurian carbonates mainly crop out as blocks embedded in the core rocks. The ~1 km thick Pliensbachian platform carbonates display large subvertical flap structures along the flanks of the Tazoult salt wall with unconformities bounding tapered composite halokinetic sequences. In contrast, the ~2.5 km thick late Pliensbachian‐Aalenian mixed deposits form tabular composite halokinetic sequences displaying small‐scale hook halokinetic sequences. Passive diapirism resulted in the lateral extrusion of the evaporite‐bearing rocks to form an allochthonous salt sheet toward the adjacent SE Amezraï minibasin. The Bajocian platform carbonates partially fossilized the Tazoult salt wall and thus constitute a key horizon to constrain the timing of diapir growth and discriminate diapirism from Alpine shortening. The Pliensbachian carbonate platform evolved as a long flap structure during the early growth of the Tazoult salt wall, well before the onset of the Alpine shortening.

Diagenetic evolution of lower Jurassic platform carbonates flanking the Tazoult salt wall (Central High Atlas, Morocco)

“…The core of the anticlines are composed of Triassic evaporite‐bearing shales and sandstones intruded by Middle to Late Jurassic magmatic bodies (Frizon de Lamotte et al, ; Hailwood & Mitchell, ; Jossen & Couvreur, ; Laville & Harmand, ). These anticlines were recently interpreted as diapirs that started forming and were active during, at least, Early and Middle Jurassic times (Bouchouata, ; Bouchouata et al, ; Ettaki et al, ; Martín‐Martín et al, ; Michard et al, ; Moragas et al, ; Saura et al, ; Teixell et al, ; Vergés et al, ).…”

“…The study of the geometry and evolution of diapiric structures that were active from Early to Middle Jurassic times in the central High Atlas, and their interaction with the flanking rocks, has been addressed in later years (Bouchouata, Canerot, Souhel, & Almeras, ; Ettaki, Ibouh, Chellaï, & Milhi, ; Martín‐Martín et al, ; Michard, Ibouh, & Charrière, ; Moragas et al, ; Saura et al, ; Teixell, Barnolas, Rosales, & Arboleya, ; Vergés et al, ). The presented study of diagenesis in the Tazoult salt wall is part of a prolonged work of our group in the Central High Atlas, detailed below, in which extensive field work and remote sensing mapping was carried out.…”

“…Integrated analysis of both structural geology (Saura et al, ; Vergés et al, ) and sedimentology of the lower–middle Jurassic mixed carbonate‐clastic system (Joussiaume, ; Malaval, ) allowed the discovery of well‐preserved and unequivocal halokinetic depositional sequences and to highlight the role of salt tectonics as an additional control on the evolution of the Central High Atlas rift basin during Early and Middle Jurassic times. Concerning the Tazoult salt wall, the study of stacks of halokinetic sequences with both carbonate and mixed carbonate/clastic deposits along the structure indicated its evolution as a 20‐km long, NE‐SW trending salt wall forming a structural and sedimentary high for at least 20 Myr from Pliensbachian to Bajocian times (Martín‐Martín et al, ). This first study was complemented through subsidence and thermal analysis evaluated using vitrinite data (Moragas et al, ) and analogue models (Moragas et al, ).…”

Lateral terminations of salt walls and megaflaps: An example from Gypsum Valley Diapir, Paradox Basin, Colorado, USA

“…Similarly, Martín‐Martín et al. () determined the 3D geometry of the Tazoult salt wall in Morocco (including megaflaps), showing along‐strike variations of flanking stratal geometries. In both cases the variations in stratal geometries were explained as being caused, in part by changes in the style and/or amount of shortening along the lengths of the walls.…”

“…Rowan, Lawton, and Giles (2012) showed along-strike variations in minibasin-scale folding, local halokinetic drape folding, and small-scale deformation of a welded salt wall in La Popa Basin. Similarly, Martín-Martín et al (2016) determined the 3D geometry of the Tazoult salt wall in Morocco (including megaflaps), showing alongstrike variations of flanking stratal geometries. In both cases the variations in stratal geometries were explained as being caused, in part by changes in the style and/or amount of shortening along the lengths of the walls.…”