Souss Basin Research Articles

Pliocene–Quaternary fluvial and aeolian records in the Souss Basin, southwest Morocco: A geomorphological model

The Souss Basin in SW Morocco is filled by Pliocene–Quaternary fluvial, fluvio-lacustrine and aeolian sediments, representing an excellent archive of palaeohydrology, palaeoclimate and the effects of crustal deformation. In general these sediments indicate stream-dominated alluvial systems, influenced by fluctuations in climate (humidity/aridity). Lakes developed within the basin around the Pliocene–Pleistocene transition and persisted into the Early Pleistocene. During this early period, relatively humid conditions are indicated by the dominance of coarse-grained sedimentation in the upper reaches of fluvial systems, the existence of large lakes and the considerable sediment thicknesses in the centre of the basin. Uplift of the surrounding mountain ranges contributed to piedmont formation by providing large amounts of coarse-grained material that accumulated at the lowland margin. Climatic deterioration in the Middle Pleistocene was accompanied by progressively more irregular and disrupted fluvial regimes. These trends were evident in the Late Pleistocene and became clearer after the mid-Holocene, with aeolian activity becoming the dominant sedimentary agent. Differences between upstream and downstream depositional regimes became marked: while coarse-grained sedimentation has characterized the upper reaches of wadi catchments, fine-grained sedimentation has prevailed downstream. Hiatuses in sedimentation throughout the Pliocene and Quaternary are marked by palaeosol horizons interbedded within the sedimentary sequences, indicating alternate vegetated (stable) and unvegetated (unstable/active) phases (biostasy and ‘rhexistasy’).

Tectonic styles in the Marrakesh High Atlas (Morocco): The role of heritage and mechanical stratigraphy

The Moroccan High Atlas is an intra-continental orogen formed during the Cenozoic in response to crustal shortening and thermal processes. In this study, we focus on the Marrakesh High Atlas (MHA), characterized by the abundance of Paleozoic or older rocks and giving an opportunity for a direct observation of the deep geometry of the chain. We propose an overview of the tectonic style and discuss the role of the heritage on the mechanical stratigraphy. Important variations in the sedimentary pile explain the wide variety of structures related to the activation of various décollement levels. In the southern part of the study area, the main detachment level is situated in the Cambrian series triggering the development of a wide triangle zone. Westward, in the Souss Basin, the Senonian silts and evaporites favour the development of secondary folds. Such structures can also be observed in the north-western part of the MHA, in the western Haouz Basin, where the Cambrian series form the core of the main anticlines. In the south-eastern part of the MHA, the Senonian silts and evaporites become the main detachment. Northeast of the MHA, the Upper Triassic salt acted as a major décollement level. However, this décollement is folded during the activation of a deeper detachment level in the Visean flyschs and cut out by late basement faults. A basal rigid group is distinguished, including Precambrian rocks and locally Paleozoic and Triassic rocks. Finally, we propose the first complete balanced cross-section of the belt in the MHA. The timing of the deformation is addressed: two main compressive tectonic events are highlighted and their relative importance is discussed.

Distinguishing eustatic and epeirogenic controls on Lower–Middle Cambrian boundary successions in West Gondwana (Morocco and Iberia)

AbstractMajor eustatic fall has been invoked to explain Lower–Middle Cambrian boundary sandstones and faunal replacements on a number of Cambrian palaeocontinents. This proposal has been tested on the Moroccan and Spanish margins of West Gondwana and found to be inadequate to explain stratigraphical developments. In these regions, sandstone intervals long presumed to be regressive and late Early Cambrian in age are now shown to be early Middle Cambrian, and composed of a lower regressive and an overlying transgressive sandstone separated by a regional unconformity. Only the lower tidalites (i.e. Tazlaft Formation in Morocco and lower Daroca sandstones in Spain) record the Hawke Bay eustatic regression in West Gondwana. The Tazlaft is overlain by a newly recognized, unconformably overlying sandstone (Talelt Formation) that onlapped southern Morocco with reactivation of a pull‐apart or transcurrent regime. Up to 150 m of erosion on uplifted blocks in the High Atlas range and foundering of the Souss Basin to the south preceded onlap and deposition of the volcanic‐rich Tatelt, the correlative and depositional analogue of the upper Daroca and lower Valdemides Formations in northern Spain. With folding and erosion, a type 1 depositional sequence boundary also caps the Tatelt at its contact with an overlying, lower Middle Cambrian mudstone‐dominated succession. This unconformity probably occurs in Spain within the Valdemiedes Formation and corresponds to a faunal discontinuity called the ‘Valdemiedes geoevent’. The Iberian ‘Daroca regression’ and Moroccan ‘Asrir regression’ are misnomers, as the sandstones on which they are based are composite units with a lower regressive interval that records eustatic fall and an upper transgressive unit that records epeirogenically driven onlap.

New continental Carboniferous and Permian faunas of Morocco: implications for biostratigraphy, palaeobiogeography and palaeoclimate

Abstract Late Palaeozoic sediments in central Morocco and the High Atlas Mountains document the development of this area during the formation of the Mauretanide part of the Hercynian orogeny. Continental basins formed during the Stephanian and Permian. Although scattered in time, they provide valuable biogeographical and climatic information for the Mauretanides as a link between the Variscides in the east, the Appalachians in the west and the Karoo in the south. New blattid insects in the Souss Basin enable correlation to Early Stephanian B. Furthermore, we document the oldest African tetrapod tracks ( Batrachichnus, Dromopus ). Litho- and biofacies indicate seasonally wet and dry phases. Wet red beds of the Khenifra Basin have produced tetrapod bones and the tracks Limnopus, Batrachichnus and Dromopus . Macrofloras give a transitional Autunian/Saxonian age. This fits well into the Artinskian wet phase. Similar facies pattern in the Tiddas Basin are correlated by tetrapod tracks as transitional Artinskian to Kungurian. Advanced tetrapod tracks of Synaptichnium and Rhynchosauroides were discovered in the Ikakern Formation of the Argana Basin, dated by pareiasaur remains as Wuchiapingian. Red beds of similar type are known in Europe, for example, from the Late Permian of the Lodève Basin. They originated during the Wuchiapingian wet phase.

Major geodynamic and sedimentary constraints on the chronostratigraphic correlation of the lower-middle Cambrian transition in the western Mediterranean region

The sedimentary rocks of the lower-middle Cambrian transition in the western Mediterranean region have recorded a superposition of extensive tectonic, volcanic, epeirogenic, and eustatic events that led to a complex sequence framework that, in some cases, makes detailed chronostratigraphic correlations difficult. This paper summarizes and updates the relationships between event stratigraphy, fluctuations of relative sea level, setting of major stratigraphic discontinuities, unconformities, and condensed levels, and succession of benthic community replacements displayed by outcrops located in the Iberian Peninsula (Iberian, Cantabrian and Cordoba platforms), Moroccan Atlas (Souss Basin), and the Montagne-Noire and Sardinian platforms. The resulting mosaic of inter-related geodynamic processes is correlated by trilobite, archaeocyath-and acritarch-based chronostratigraphic scales, taking as reference for the base of the Middle Cambrian in West Gondwana the immigration of paradoxidid trilobites.

Contrasting late Neoproterozoic to Ordovician successions of the Taoudeni Basin, Mauritania and Souss Basin, Morocco

The Souss Basin of the Anti-Atlas, Morocco is located on the northwestern margin of the West African Craton and preserves a thick early Palaeozoic, predominantly marine, succession recording rift basin development and subsidence following Pan-African arc accretion. In contrast, the Taoudeni Basin of southern Mauritania is located within the craton interior and preserves a comparatively condensed, continental and marine succession. This study contrasts the sedimentological relationships of the Cambrian and Ordovician successions of these two contemporary basins in the light of our current understanding of global eustatic sea-level fluctuations and the regional tectonic framework.

About the dating of Upper-Pleistocene fluvial deposits in the arid zone of Morocco: comparative data of radiocarbon, optic stimulation luminescence and uranium/thorium methods

In South Morocco Quaternary studies, one of the major tasks is to date the so-called ‘Soltanian’ alluvial terrace, which occurs widely and lies for its most part beyond the 14C limit [4]. This terrace was well identified in the Atlantic Atlas [7], in the Souss Basin [1,2,9], on the northern border of the Anti-Atlas [8], and more recently at its southern border [6,10] and also at its eastern side [3]. However, dates were limited at ca 35 kyr, often at the upper or at the middle part of the deposits, lock of adequate dating methods; a subsequent important question was the disagreement between the dating results and the presence of a Prehistoric industry of Mousterian tools throughout the sediments [8,11]. A first response is given by Thorp et al. [6] with recourse at the OSL dating method applied to alluvial quartz grains, which give an age of 45.0 ± 3.7 kyr for the bottom silts of the Soltanian terrace of Agadir Tissint and by Weisrock et al. [10]: OSL age of 49.1± 4.3 kyr for silts in a comparable stratigraphic section, and U/Th age of 55.9+ 9.3–8.6 kyr for an underneath travertine. New dating results, by OSL and U/Th, of the basal units underneath the bottom silts (calcreted alluvial conglomerates at Agadir Tissint, other silts and travertine sequences at Oued Noun) will be soon available [5,6]. Another important challenge in the Atlantic coastal area is to make reliable the bottom of the Soltanian terrace and the base level of the high

Dynamique sédimentaire comparative dans les bassins stéphano-permiens des Ida Ou Zal et Ida Ou Ziki, haut Atlas Occidental, Maroc

The intra-mountainous Ida Ou Zal Basin developed as a graben during the Stephanian (Carboniferous) and Lower Permian. Along its borders from east to west are the remnants of basal conglomerates. Passing laterally towards the centre of the basin are fine-grained fluvial-lacustrine sediments or flood-plain deposits. The important accumulation (1800 m) of sediments, associated with climatic and tectonic changes, caused substantial subsidence in a late orogenic setting. The remnants of sporadic volcanic products (shards) found in the Ida Ou Zal and the Ida Ou Zika Basins suggest nearby simultaneous magmatic activity. A comparison between the basins of Ida Ou Zal and Ida Ou Ziki suggest that the two basins formed a single unit, called the Souss Basin, ultimately terminated between the Lower Permian and Upper Permian times by a sinistral movement of the N70-80° Agadir Ou Anzizen Fault (west branch of the Tizi N'Test Fault) at the very end of the Hercynian Orogeny in Morocco.

Le bassin du Souss (Zone de Faille du Tizi n'Test, Haut Atlas occidental, Maroc): résultat d'une inversion tectonique contrl̂ée par une faille de détachement profonde

Analysis of seismic reflection profiles and boreholes performed in the Souss Basin, which constitutes the southern foreland of the western High Atlas and the western continuation of the Tizi n'Test Fault Zone, allows an accurate inventory of several structures related to the rifting and opening of the Central Atlantic, and inversion related to the collision of Africa and Europe to be made. The most conspicuous structure is a deep north-northwestward gently dipping detachment, from which the El Klee and Biougra Faults diverge, striking northeast with a northwesterly dip. These faults are normal, have a Triassic to Middle Jurassic age, and delimit half-graben structures tilted to the south-southeast. The amount of extension (β) is at least 1.19. The obliquity of the faults with respect to the trend of the final rift gives them appearance of transfer faults. The Tertiary to present-day inversion is outlined by the reactivation of the detachment and some associated former normal faults as the El Kléa Fault, and by the creation of new decollement levels at the base, or within, the Triassic evaporites. The present study supports the idea that most of the High Atlas structures may be largely controlled by upper to mid-crustal gently northward dipping detachment planes.

Surface magnetic survey of the Souss Basin, southwestern Morocco: Evaluation of the tectonic role postulated for the Agadir and Tarfaya fault zones and the South Atlas flexure

The results of a surface magnetic survey over the Souss Basin, the High Atlas and Anti-Atlas margins, combined with the gravity data of Van den Bosch (1971) and a review of the regional geology permits us to trace structures from the High Atlas into the Souss Basin. The South Atlas flexure is an east—west trending structure imposed during the Cenozoic upon an area with a northeast—southwest, Anti-Atlas structural grain. The major structure is the Tarfaya fault zone, whose location, projected by Choubert and Faure-Muret (1970), lies within a corridor of low residual magnetic anomalies. The continuation of this structure in the High Atlas is the Tizi n'Test fault zone. The Hercynian activity of the Tizi n' Test fault zone (Mattauer et al., 1972) was just one period of reactivation of an older, Precambrian, structure for we believe the Tarfaya fault zone was also active in post-late Triassic time. The Agadir earthquake occurred along a minor fault parallel to the Tarfaya-Tizi n' Test zone and is not related to the South Atlas flexure. Neither does it represent the entry into the African continent of a major ocean linked structure. The Tarfaya-Tizi n' Test fault zone is a much more likely candidate, for its offshore trend appears to match that of the Canary Fracture Zone.