A sedimentological model for the continental Upper Triassic Tadrart Ouadou Sandstone Member: recording an interplay of climate and tectonics (Argana Valley; South‐west Morocco)

Abstract

The continental Upper Triassic Tadrart Ouadou Sandstone Member was deposited in an extensional setting on the Pangaean continent, strongly influenced by a low‐latitude climatic regime (10° to 20° north). Complex interaction of basin subsidence and climatically driven processes led to high facies variability and a lack of correlatable units across the Argana Valley exposures. A process‐orientated approach integrating detailed facies with architectural element analysis was undertaken, which resulted in a multistage depositional model for the Tadrart Ouadou Sandstone Member. The basin‐scale model shows that basal alluvial fan and braided river systems are confined to the centre of the Argana Valley exposures. Aeolian deposits occur throughout the sequence, but dominate in the north. After a phase of playa deposition, prominent basin‐wide fluvial incision of up to 8 m marks the onset of perennial fluvial flow. These well‐sorted, internally complex and locally highly amalgamated fluvial sandstones are widespread throughout the basin and are focused in a north to south (south‐west) flowing channel system. After a final stage of aeolian sedimentation, sandstone deposition of the Tadrart Ouadou Sandstone Member in the Argana Valley is terminated rapidly by the onlap of lacustrine mudstones of the Sidi Mansour Member. The study revealed that, except for one pronounced period of perennial conditions, sedimentation is controlled largely by ephemeral fluvial flow, alternating ground water tables, deflation processes and periods with limited periodic local run‐off. The study highlights that facies architecture in the basin is the result of complex interaction of local syn‐sedimentary tectonics and the climatic regime within the basin, but also the climate of the catchment area to the east. The data suggest a proximal to mid‐distal basin setting in the rain‐shadow to the west of a mountain range (Massif Ancien), which exerted a strong control on the depositional environments of Triassic deposits exposed in this part of South‐west Morocco.

Morphodynamics of rivers strongly affected by monsoon precipitation: Review of depositional style and forcing factors

“…Another common feature in modern and ancient seasonal river deposits is the presence of in-channel mud drapes and layers (e.g., Williams, 1971;Soleilhavoup, 1975;Tunbridge, 1981;Sneh, 1983;Stear, 1985;Abdullatif, 1989;Olsen, 1989;Singh and Bhardwaj, 1991;Singh et al, 1993;North and Taylor, 1996;Shukla et al, 2001;Billi, 2007;Nichols and Fisher, 2007;Fisher et al, 2008;Fielding et al, 2009;Allen et al, 2011;Mader and Redfern, 2011;Plink-Björklund and Birgenheier, 2013;Plink-Björklund et al, 2014a) (Fig. 9).…”

“…16f, 17a), (g) cross strata to mud drapes (Fig. 18a), and (h) climbing ripples to mud drapes (e.g., Tunbridge, 1981;Sneh, 1983;Turner, 1986;Abdullatif, 1989;Deluca and Eriksson, 1989;Nichols and Hirst, 1998;Shukla et al, 2001;Hinds et al, 2004;Hampton and Horton, 2007;Mader and Redfern, 2011;Donselaar et al, 2013;Plink-Björklund and Birgenheier, 2013;Plink-Björklund et al, 2014a). Any of these depositional unit types may or may not be capped by a mud drape.…”

“…In systems with conglomeratic sediments, these depositional units are 0.5 m to multi-meter thick, and fine upwards from conglomerates to sandstones (e.g., Turner, 1986;Rhee and Chough, 1993;Nichols and Hirst, 1998;Hinds et al, 2004;Uba et al, 2005;Mader and Redfern, 2011) (Fig. 16a-e).…”

“…In many cases, the mud layers show desiccation cracks (e.g., Tunbridge, 1981;Stear, 1985;Abdullatif, 1989;Olsen, 1989;Nichols and Fisher, 2007;Allen et al, 2011;Mader and Redfern, 2011) (Fig. 9c), pedogenic modification (e.g., Nakayama and Ulak, 1999;Shukla et al, 2001;Fielding et al, 2009;Allen et al, 2011;Mader and Redfern, 2011;Plink-Björklund and Birgenheier, 2013) (Fig. 9a) or root traces (e.g., Abdullatif, 1989;Shukla et al, 2001).…”

Architecture and evolution of a tectonically-induced Middle Eocene clastic wedge on the southern Tethyan carbonate shelf, North Eastern Desert, Egypt

“…This facies association reflects the deposition from stream flows similar to those suggested by Mader and Redfern (2011). The presence of cut-and-fill structures with erosional bases and dominant stratification indicate that these deposits were formed by flooding with high discharge (cf.…”