Right side valley of Assif Tafraout flowing in a northerly direction. The village of Tafraout lies about 1 km to the north
Year defined
1992
Thickness at type section
~550 m (1,800 ft)
Tafraout Group (Morocco)
The Tafraout Group (Also "Tafraoute Group" or Zaouiat Ahançal Group) is a geological group of formations of Toarcian-Aalenian (Lower Jurassic-Middle Jurassic) age in the Azilal, Béni-Mellal, Imilchil, Zaouiat Ahansal, Ouarzazate, Tinerhir and Errachidia areas of the High Atlas of Morocco.[5] The Group represents the remnants of a local massive Siliciclastic-Carbonate platform ("Tafraout Platform"), best assigned to succession W-E of alluvial environment occasionally interrupted by shallow marine incursions (tidal flat setting) and inner platform to open marine settings, and marks a dramatic decrease of the carbonate productivity under increasing terrigenous sedimentation.[6] Fossils include large reef biotas with richness in "lithiotid" bivalves and coral mounts ("Patch reef", Tafraout Formation[7]), but also by remains of vertebrates such as the sauropod Tazoudasaurus and the basal ceratosaur Berberosaurus, along with several undescribed genera.[8] While there have been attributions of its lowermost layers to the Latest Pliensbachian, the current oldest properly measured are part of the Earliest Toarcian regression ("MRST10"), part of the Lower-Middle Palymorphum biozone.[5] This group is composed of the following units, which extend from west to east: the Azilal Formation (continental to subtidal, including its synonyms the "Wazzant Formation" and the "Continental Series of Toundoute"); the "Amezraï" Formation (intertidal environment); the Tafraout Formation (deposited in a subtidal to inner platform environment) & the Tagoudite Formation (including the "Tamadout Formation", shallow subtidal to open pelagic).[7] They are connected with the offshore Ait Athmane Formation and the deeper shelf deposits of the Agoudim 1 Formation.[9] Overall, this group represents a mixed carbonate-siliciclastic system of several hundred meters thick, dominated by deposits of shallow marine platforms linked to a nearby hinterland dominated by conglomerates.[10] The strata of the group extend towards the central High Atlas, covering different anticlines and topographic features along the mountain range.[11]
The after-effects of the Toarcian Oceanic Anoxic Event are also very present in the marginal marine strata of the Tafraout Group, with the Toksine Section recording a dramatic collapse on the scale of the Tethys of the neritic carbonate system.[12]
Geology
The Central High Atlas of Morocco is part of a mountain belt formed by the inversion of a rift from the Triassic-Jurassic periods, due to Cenozoic tectonic activity.[13] The region's structure comes from four main tectonic phases: the pre-rift phase tied to the formation of Pangaea, the syn-rift phase during the Late Permian to Late Triassic, influenced by the opening of the Atlantic Ocean and Tethys Ocean, and the post-rift phase, where Jurassic-Cretaceous carbonate platforms formed.[14][15] The High Atlas has thrust and oblique-slip faults from W-E to NE-SW. It is an intracontinental mountain range resulting from the uplift of a large Mesozoic rift system. Triassic to Cretaceous layers are confined within basins, controlled by extensional rift structures. Sedimentation in these basins varied, with marine shales and limestones in the east and fluvial deposits in the west. Several tectonic events during the Triassic-Jurassic boundary reactivated normal faults, leading to the dominance of marls during the Middle Liassic to Toarcian.[16][17][18]
Description
Geological map of the Central High Atlas and main structural domains
"Amezraï" Formation
This formation, found in the Amezraï minibasin and linked to the Tazoult Ridge, dates to the Earliest Toarcian and is identified by brachiopod fossils. It includes sandstones, marls, and biodetrital or oolitic limestones, with layers varying from centimeters to up to 6 meters thick. The lower part consists of conglomerates, sandstones, and clays, transitioning to limestones and marls at the top.[19] Ripple structures and cross-bedding are common in sandstone layers, while reworked horizons appear in the limestone. The formation reflects a subtidal to supratidal environment, with some layers suggesting lagoonal conditions and reduced carbonate content compared to older formations.[7] Local tectonic activity, mainly due to seismic events in the Tethyan region, influenced the formation, causing erosion of older Paleozoic layers.[20]
The Tafraout Formation consists of oolitic and biodetrital limestones with cross-stratifications, found in channels and bars, alongside greenish marls and micro-conglomerates.[7] These layers were deposited on a coastal platform. The formation is mainly made of sandstones, marls, and ooid limestones, different from older layers. Common fossils include bivalves, brachiopods, gastropods, corals, and echinoderms, with plant remains in some sandstones. The rocks formed in environments ranging from supratidal to subtidal, characterized by tropical conditions akin to those observed on Andros, Bahamas.[21] The upper part of the formation shows sediments filling an old Pliensbachian basin, moving from deeper marine conditions to a supratidal coastal plain. Fossils and sediment features suggest a challenging environment, with alternating sandstone and marl layers indicating changes in water depth and sedimentation patterns.[7]
Tagoudite Formation
The Tagoudite Formation marks a major shift in Liassic sedimentation, replacing the carbonate turbidites of the Ouchbis Formation with mostly siliciclastic layers. These layers alternate between gray and green sandstone, sandy marls, and siltstones, forming sequences up to 20 meters thick.[7] They show a decrease in grain size and an increase in marl content from bottom to top, with features like ripple marks and laminations. Microscopically, the turbidites are mainly fine silt, with varying amounts of quartz, feldspar, and carbonate detritus, and occasional pyrite. This formation suggests an open marine environment with sediment interruptions and materials coming from distant areas. It is widespread in the Central High Atlas, with thicknesses reaching up to 320 meters, and varies across different regions like Tounfite and Beni Mellal. In the Central Middle Atlas, sedimentation was interrupted by emersion before the formation's deposition.[7]
Paleogeography
Early Jurassic Paleogeography of the Sahara Craton, including source Highlands, Jurassic basins and CAMP outcrops.
The Tafraout Group was formed on the Moroccan Carbonate Platform during a sea-level rise in the Early Toarcian, linked to the Toarcian Oceanic Anoxic Event, at a palaeolatitude between 19°-20°N, around the same latitude as modern Mauritania or Cuba, situated between ancient geological regions like the West Moroccan Arch, the Anti-Atlas and the Sahara craton, developed after a major sea regression, with red clays and conglomerates filling small basins in the Atlas region.[22][23]
Two main stages mark the area's evolution: during the Lower Toarcian, deposition patterns from the earlier Pliensbachian continued, followed by terrigenous materials filling the basins and stopping temporally the carbonate production.[5] It evolved along several depocenters and associated accidents, the southern edge of the Tilougguit Syncline in the north to the axis of the Aït Bouguemmez Basin in the south, showed that the depocenter zone corresponded to the disposal area located between the Talmest-Tazolt Ridge to the North and the North-Atlasic accident to the South. This terrestrial lithology is mostly found in the small basins in tearing in the Atlas of Telouet, Toundoute, Afourer and Azilal, having the Demnat Accident as the major structural element in this last sector. While at this W areas it became fully terrestrial/intertidal, at other areas like Beni Mellal, Dadès Gorges or Zaouiat Ahansal marine influences are seen in a carbonate-siliclastic regime.[21] By the Middle Toarcian-Aalenian, the Azilal Formation expanded eastward, with isolated carbonates forming in the Amezraï basin, surrounded by terrigenous sediments.[5][21] This period is marked by the individualization of thein the center of the basin and by a relative tectonic calm in the other coeval sectors.[21]
Marine fossils like brachiopods and ammonites help date the sediment layers and confirm the transition from marine to expansive E terrestrial environments during the Middle Toarcian. The deposition starts with a marked break of the Carbonate production and a major regression in the Lowermost Toarcian, then oscilated Transgresive/Regresive cycles in the Laevisoni-Bifrons substages, followed finally by a post Bifrons major regression and full return to the Carbonate production.[5][23] The Tafraout Platform deepened over time, signaling a shift to transgressive conditions even with the expansion of W continental facies.[21] On the Amezraï Formation basin the fauna is composed by brachiopods such as Soaresirhynchia bouchardi, S. babtisrensis and Pseudogibbirhynchia jurensis that corroborate the Earliest Toarcian age for it and adjacent layers.[21] Meanwhile, the presence of Aalenian (Bradfordernsis-Murchinsonae) Branchiopods in the Azilal Formation coeval with Ammonites of the same age at the Ikerzi Area confirms the marine delimitation in the last stages of deposition.[7] In the Azilal system, the "Tafraout Platform" saw a deepening towards the uppermost layers, teasing the transition to the Bin El Ouidane transgressive Carbonate Platform facies, while the lower sequences, with fine conglomerate layers and plant remains indicate a proximal delivery area and the peak of the regression, with many microlagoons that formed between the large coral patch reefs are documented by micrite and partially leached micrite.[7]
Paleoenvironment
The Tafraout Group records multiple environments: surrounded by alternating tundra-moist forests highlands; fluvial-alluvial under arid to humid (See Azilal Formation); Shabkas; Mangrove-like lagoons (ex. with modern flora from Bahamas or Indonesia); Shallow Carbonate Sea with reefs (ex. modern Bahamas)
The Tafraout Group covers most of the W High Atlas, surrounded by highlands that probably hosted dry cool (10.6 °C) to humid climate (12.30 °C), with a succession rain tundra to wet forest environments, as proven by samples from coeval layers in the External Rif Chain.[24] The Continental/Tidal Flat Azilal Formation, within this group, was deposited in coastal environments influenced by rivers, tidal flats, and paralic settings, rwith eworked material and in Toundoute unique interbedded Explosive eruption-type volcanic material, generally constituting more than half of the detrital components, showing clear carbonate recrystallization, suggesting that these fragments were still at high temperature during deposition and, therefore, contemporaneous with the sedimentation, probably as a result of early activity in the local South-Atlasic Fault.[25] Fauna, including rare brachiopods and bivalves, alongside sedimentary features like ripple marks and rain imprints, indicate a mix of marine and continental conditions, with evidence of emersions. The environment shifted from coastal facies in the north to fluvial facies in the south, and tectonic activity affected sediment deposition.[23][21] The flow of the fluvial-washed sediments take place in a E-NE direction, being moved to the layers of the Amezräi, Tagoudite & Tafraout Formations and other coeval marine units, as well are found on fluviatile channels inside the own rocks of this unit.[5]
The Azilal Formation also saw high plant activity, with remains such as wood, charcoal, and rhizoliths, indicating nearby vegetated soils.[26] Fluvial systems transported sediment from Paleozoic and Triassic sources, with volcanic material also present, suggesting active volcanic processes during deposition.[25] The warm, alternating wet and dry climate led to the formation of soils with calcareous nodules and gypsum in arid zones, particularly in areas like Toundoute and Telouet.[25]
During the Lower Toarcian, a shift to siliciclastic deposits occurred, marked by storm events and increased plant debris, indicating a warm, humid climate.[23] Some areas, especially near the coast, resembled modern Sabkha (like those in the Persian Gulf). The Tafraout Formation, meanwhile, represented marginal marine environments with diverse marine fauna, including coral reefs and "lithiotid" (Plicatostylidae aberrant reef-forming) bivalves.[27]
The Toarcian Oceanic Anoxic Event (T-OAE) intensified Tropical storms, destroying older carbonate platforms and increasing siliciclastic deposits, which contributed to the formation of the Tafrout environment.[28][29] Additionally, after the T-OAE, ecosystems in areas like Jebel Toksine began to recover with new carbonate activity and diverse marine life, including bivalves and other reef organisms.[5][12]
The aftermath of the T-OAE is visible in the lower Azilal Formation, showing a slow recovery of marine environments. There is also evidence of a Middle Toarcian cold snap, followed by a return to warmer conditions.[30] The eastern and northeastern High Atlas saw the development of carbonate sedimentation, with reefs and marine fossils indicating tectonic activity during the Late Toarcian.[5][30]
The central High Atlas region features long diapirs and minibasins formed during early Jurassic rifting, with the Tazoult Ridge being a key example.[31] Diapir movement shaped the surrounding rock layers, while local sedimentation reflects changes in climate, including wetter periods linked to increased erosion. Sharp geological boundaries mark the closure of salt walls during diapir growth, and ancient environments here resembled modern shallow waters like the Red Sea.[32] Charcoal remnants suggest coastal forests or mangroves existed during wetter times.[33]
In the Tafraout Group, the fossil record of units like the Azilal Formation is very restrictive compared to the marine coeval/underliying units like the Amezraï or Tafraout Formations. In the Dadés area Coral patch reefs rarely occur in the middle of the unit with associated echinodems (Sea urchin spines, Crinoid fragments) lamellibranchs, gastropods, solitary corals and algae.[7] Plant remains are very abundant in places such as the north of Jbel Akenzoud and partly impregnated and/or carbonized by malachite.[7] Gastropods have been discovered in several places, but none of the specimens have been studied nor identified.[39] Beds with large accumulations of unidentified Ostracod valves on an endemic thin level of green marl are found at the Beni-Mellal area (Adoumaz & Col de Ghnim outcrops).[40][41] The tubes of serpulid worms are known from Jbel Toksine, in relation to the bivalve pavements.[27]
Structures fouisseuses de Thalassinoides, avec une faune moderne apparentée, montrant la convergence écologique et la variété des animaux qui ont quitté cet Ichnogenus.
The platform patch reefs in the Tafraout area are notable for their biodiversity, with some reaching heights of up to 40 m and lengths of up to 80 m, representing massive biostromes with a varied associated fossil assemblage, including bivalves, gastropods, echinoderm fragments, solitary corals, and bryozoans, found among the coral patchs.[7] Massive reef pinnacles are recovered at Anergui and northern flank of Tassent, while rarer ones are know from Bou Zemou.[36]
A Brackish/marine Lissajousithyrididae (Brachiopod). Mostly benthonic specimens are known. The presence of this species indicates an upper Toarcian-Aalenian age for the layers where was discovered.
A brackish/marine Lobothyrididae (Brachiopod). Relatively abundant on seashore deposits. Includes juvenile forms of Telothyris jauberti, present on benthic deposit strata.
A brackish/marine Plicatostylidae (Bivalve). A large bivalve, with a subequivalent shell, reaching 60–70 cm high. It is one of the three main bivalves found on the Lithiotis Facies, whose accumulations generally cover megalodontid coquinas.
A brackish/marine Plicatostylidae (Bivalve). This genus was founded to be a bivalve with a byssate juvenile stage that developed different lifestyles as adults depending on the density of the individuals and the firmness of the bottom
A brackish Astartidae (Bivalve). Is considered a genus that evolved from shallow-burrowing ancestors, secondarily becoming an edge-prone semi-fauna adapted to photosymbiosis.
An Ammonite of the family Dactylioceratidae. The basis of this series is based on a regional discontinuity marked by a remarkable abundance of Eodactylites from the Lower Toarcian
A marine Ostracodan of the family Polycopidae. Present with large accumulations of specimens
Echinodermata
Multiple echinoderm remains, including Crinoid articulated and fragmentary specimens and indeterminate echinoid fragments, are know from several localities, usually associated with large coral bioherms or sea trangressions.[7][10][51][21]
Several scales & teeth of fishes (Lepidotes?) are know from several locations, coming from freshwater/lagoonal layers.[53] Indeterminate dinosaurian & other vertebrates are know from Mizaguène Hill, Taouja Ougourane, Aït Ouaridène, Oued Rzef & Jbel Remuai in the Azilal Province. Some of them are recovered in a "Bone bed" and others are associated with abundant plant remains.[54]
Marine, brackish or freshwater bony fish of the family Leptolepidae. Recovered from the Tagoudite Formation, represents a genus of cosmopolitan fish, common in the Toarcian Mediterranean area. Most specimens appear to come from lagoonal facies.
The vegetation in the Toundoute area is compared to that of the Isle of Pines.[55] Paleosols in these regions show many plant roots (Rhizoliths) and heavily disturbed layers.[56] Plant remains include coal, leaves, woody roots, rhizoliths, fossil wood, and other plant debris. In Toundoute, small plant fragments, mostly fern leaflets and some cycad leaves, were found, with wood debris resembling conifers like Pinaceae or Taxaceae.[25][57] Ferns seem to have dominated the vegetation, likely in wetlands, followed by cycads and conifers.[25] Similar plants have been found in Egypt's Mashabba Formation.[58] At Jebel Toksine, woody plant debris, including charcoal, suggests vegetation in a humid, marginal marine environment.[27] Jebel Azourki has layers of shales with coal streaks and plant fragments, possibly representing a marsh in a lagoon area.[51]
Palynology
Phytoclasts, spores, pollen and Tasmanites algae indicate that the palaeoenvironment of the lower Toarcian Amellago area was likely proximal continental shelf with a high terrestrial input, and notorious influence of brackish water in the depositional environment.[38]
Affinities with Cheirolepidiaceae inside Coniferae. This interval is numerically dominated by Classopollis, which usually accounts for more than 60.95% of the palynomorphs present
^ abcdeBodin, S.; Krencker, F. N.; Kothe, T.; Hoffmann, R.; Mattioli, E.; Heimhofer, U.; Kabiri, L. (2016). "Perturbation of the carbon cycle during the late Pliensbachian–early Toarcian: New insight from high-resolution carbon isotope records in Morocco". Journal of African Earth Sciences. 116 (2): 89–104. Bibcode:2016JAfES.116...89B. doi:10.1016/j.jafrearsci.2015.12.018.
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