Azilal Formation

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Azilal Formation
Stratigraphic range: Toarcian-Middle Aalenian 182–172 Ma Polymorphum-Murchisonae
Panoramic of the High Atlas on Gorges du Dadés with Toarco-Aalenian Redbeds
TypeGeological formation
Unit ofTafraout Group
Underlies
Overlies
AreaHigh Atlas[1][2]
Thickness300-800 m[3]
Lithology
PrimaryArgillite, conglomerate (+quartz-dredge conglomerates)
OtherBrown-red marl, siltstones (micro-sandstones), sandstone-pelitic, breccias with liasic limestone elements, lagoonal shale, sandstone and volcanic minerals.[3]
Location
LocationAzilal Province
Coordinates31°18′N 6°36′W / 31.3°N 6.6°W / 31.3; -6.6
Approximate paleocoordinates26°36′N 3°24′W / 26.6°N 3.4°W / 26.6; -3.4
RegionHigh Atlas[4][5]
Country Morocco
Type section
Named forAzilal
Named by
  • Jenny et al. (Informally)[3][6][7]
  • Milhi (Formally)
LocationNorthwest side of Jbel Mesgounane, 10 kilometers east of Azilal
Year defined
  • 1985 (Informally)[1]
  • 1992 (Formally)
Thickness at type section~250 m (820 ft)
Azilal Formation is located in Morocco
Azilal Formation
Azilal Formation (Morocco)

The Azilal Formation, also known as Toundoute Continental Series and Wazzant Formation (Called Informally "Marnes chocolat"), is a geological unit in the Azilal, Béni-Mellal, Imilchil, Zaouiat Ahansal, Ouarzazate, Tinerhir and Errachidia areas of the High Atlas of Morocco, that cover the Early Toarcian to Middle Aalenian stages of the Jurassic Period.[8] While there have been atributions of it´s lowermost layers to the Latest Pliensbachian, the current oldest properly measured are part of the Earliest Toarcian regresion ("MRST10"), part of the Lower-Middle Palymorphum biozone.[8] The Azilal Formation consists mainly of claystones rich in continental plant debris and laminated microbial facies.[9] It is a continental deposit which overlies marine dolomites of equivalent age to the Rotzo Formation of Italy, mostly part of the Aganane Formation.[6] The formation is best assigned to an alluvial environment occasionally interrupted by shallow marine incursions (tidal flat setting) and marks a dramatic decrease of the carbonate productivity under increasing terrigenous sedimentation.[10] Dinosaur remains, such the sauropod Tazoudasaurus and the basal ceratosaur Berberosaurus are known from the unit, along with several undescribed genera.[11] The toarcian High Atlas is divided in 5 units: the continental layers with paralic deposits belong to the Azilal, along the shoreface layers of the Tagoudite Formation and Tafraout Formation, both connected with the offshore Ait Athmane Formation and the deeper shelf deposits of the Agoudim 1 Formation.[12]

Geology[edit]

Geological map of the Central High Atlas and main structural domains

The Central High Atlas of Morocco is part of a double-vergent mountain belt that originated due to Cenozoic shortening and inversion of a rift that developed between the Triassic-Jurassic periods.[1][13] Its geometry is distinctive due to the presence of several ENE–WSW narrow rift basins, derived from four major tectonic phases: pre-rift, that was linked with the Hercynian Orogeny and the union of Pangea in the Paleozoic; syn-rift, that was developed mostly between the Late Permian-Late Triassic with several NE–SW to ENE–WSW rift-basins, al derived from the almost coeval opening of the Atlantic Ocean and Tethys Sea.[14] This rift-derived basins ended filled with continental siliciclastic sediments, and latter towards the Rhaetian stage of the Triassic affected by emissions of the Central Atlantic magmatic province.[15] It was on the so-called Post-rift phase that the local tectonics had a thermal relaxation and allowed the deposition of the Jurassic-Cretaceous carbonate platforms.[14] The structure of the High Atlas can be defined by two main groups of faults, thrust and oblique-slip faults, that occur from W-E to NE-SW.[13] The presence of tectonic inversion in the Atlas Mountains has shown that are an intracontinental mountain belts that appeared from the uplift of pre-existing rift systems, where here is represented by a major rift system (~2000 km) originated on the Mesozoic, that was later uplifted and inverted in the Cenozoic.[13] The impact and convergence movements of the African-Iberian plates after the Mesozoic end with an inversion of the previous deposited strata, transporting the sediments of that and forming new low angle thrusts. Triassic, Jurassic and Cretaceous strata are confined within basins controlled by the extensional structures of the Mesozoic rift. The Jurassic basins can be grouped into two main provinces located on either side of an emerged Massif Ancien: west, where the basin was open to the Early Atlantic, being related to its passive margin, and east with several epicontinental troughs connected to the Tethys Ocean.[16] Across the Toarcian-Bajocian strata, there was a great deposition of marine shales as marls, calciturbidites and reefal limestones were accumulated in the E Central High Atlas, while on the west margin around the Massif Ancien terrestrial, specially fluvial sedimentation dominated.[16] The present Red Beds of Azilal and the yonger marls of Bin el Ouidane indicate various marine oscillations across the Toarcian-Bajocian boundary, ending its sedimentation with the major Bathonian redbeds.[17][16] A initial tectonic event on the Triassic-Jurassic boundary led to the formation of the Tigrinine-Taabast pull-apart basin, for example.[18] Following this event a major extensional tectonic activity (derived from the second Pangea rifting) occurred towards the end of the Pliensbachian and beginning of the Toarcian.[18] This second major tectonic event developed towards the E-W to NE-SW, reactivating trending normal faults, what led to the drowning of the Lower Liassic carbonate platform and the predominance of marls during the Middle Liassic to Toarcian.[18]

Rift Vulcanism[edit]

Extent of the CAMP

Along the High Atlas Triassic-Jurassic boundary, and until the Bathonian stage of the Middle Jurassic (then again in the Lower Cretaceous), there is a record on vulcanism locally on the succession of different local formations, such as the Guettioua Formation and others, but also absent on others such as the Pliensbachian Aganane Formation.[19] Mostly of the north-African Rhaetian-Bathonian volcanic events are related to the open of the Atlantic Ocean, with parallel records found on the North American coast.[20] On some locations, such as Haute Mouluya towards the Middle Central High Atlas, it is even possible to delimitate a transitions between the major CAMP event, linked with the Triassic–Jurassic extinction event and other posterior Hettangian and/or Sinemurian volcanic events, notorious due to be based around explosive vulcanism (Belonging to the Tizi-n-Ghachou Formation).[21] Mostly of the effects of the volcanism occur on the main emerged terrestrial deposits as can be seen in the presence of basaltic intrusions in the younger Bathonian layers of the Beni-Mellal zone, some of them cutting older strata.[19][22]

The origin of the Central Atlantic magmatic province volcanism is related with the Geography of the zone, and has been registred to last until the Early Sinemurian (196.3 + 1.2 Ma).[23] On the Sinemurian-Pliensbachian, the tethys flooded the area and a post-rift carbonate platform developed flooding CAMP basalts. On the Middle Toarcian, subsiding basins appeared which isolated the Mesetas and Precambrian and Paleozoic massifs.[24][25] On the Central High Atlas two sections of lava flows and dikes yielded ages between 188-153 M.a and 199-178 M.a respectively, whose age, if true, overlapped with the eruption of the Karoo-Ferrar igneous province.[26] Yet evidence of volcanism contemporaneous with the deposition of the Azilal Formation is almost nonexistent, and where volcanic rocks have been assigned, they have been repositioned as either younger or CAMP. The only possible record is found associated with the outcrops at Toundoute, with Trachyandesitic materials from a explosive source, like in the older Mouluya outcrops.[27]

Description[edit]

Levêque called this unit "Marnes chocolat" in the Azilal region, made up of red-brown marls, silts (microsandstones) and conglomerates with centimetric quartz dragees. Locations at Adoumaz, Ghnim and Jbel Taguendouft (Béni-Mellal Province) are composed by a succession of reddish-brown tints with terrigenous dominance: sandstone, clays with paleosols and sandstone limestones sometimes dolomitized, with marmorized levels in paleosols towards the northern region of Ghnim and Adoumaz. The lowermost sections show a transition from sandstone limestone and/or sandstone to clay, with a thin level of green marls locally rich in ostracods. This initial layers are followed by a subtidal term, represented by an oolitic limestone, with fine lamellibranch bioclasts and variable percentages of quartz, that host also small sections of sandstone with calcareous cement and rare oolites, representing this last one is an oblique bedding, of metric dimensions, drawing on the surface mega-ripples of 3 to 5 m in wavelength.[28] The last major section represents a supratidal deposit, as shown by the presence of coarse sandstone gradually changing to red Marls with "fluer" structures and locally to paleosols. This section in Adoumaz has abundance of Paleozoic quartz grains, that are found organized in decametric channeling lenses evoking a predominantly fluvial dynamic.[28]

On the south-southwest edge of the basin towards west of Azilal (Jbel Til-Jbel Amersiaz basin and part of the M'Goun syncline), Guettioua, Demnate, Telouet, Toundoute & Marrakesh, under the Bajocian limestones (Tanant Formation) or directly under the Bajocian?-Bathonian Guettioua Formation, develops a thick a red detrital section in which pelites, sandstones and conglomerates with centimeter-sized quartz balls alternate and breccias (locally called " Wazzant Formation") with Liassic limestone elements, this last ones except near paleofaults, do not appear or have been dissolved. This sector reaches 800 m thickess in the Wazzant subasin, being very reduced to the south of it in Aït-Toutline or Aït-Iouaridène, recovering a variation of the sedimentary process formed by a complex sedimentary unit, terrigenously dominated, composed by the abundance of conglomeratic channels with quartz dragees and Paleozoic basement elements, sandstones organized in bars channeled lenticulars and red clays, the whole part of the facies is organized in metric sequences of filling and alluvial channels.[17] In addition, exceptionally, at the Wazzant area it rests in this place directly on massive dolomites, having eroded the marno-limestones of the Pliensbachian, with transitional layers. A transition between marine and continental deposits, is seen through carbonate palustrine levels and horizons of caliche, being continental layers superimposed in stratigraphic continuity on the marine carbonates of the Aganane or older Imi-n-Ifri Formation.[27] The Wazzant area river system was driven by several minor freshwater currents, likely temporal and related to the rainy seasons. It has a notorious proximal character compared to the other sections of the Azilal formation.[29]

Strata[edit]

The layers at Azilal evolved along the central high Altas Toarcian-Aalenian Siliclastic-Carbonate Platform, and consist mostly on a succession of detritic rocks with Red Marls, deposited on an alluvial environment occasionally interrupted by shallow marine incursions, a Mudflat setting.[1][17] The unit represents a major sea regression measured in the central High Atlas, specially after the Lower Toarcian, proven by sections such as "Tarhia n’Dadès", where the Pliensbachian Choucht Formation marginal marine layers are overlain by one meter of red silt/bioclastic limestone alternations, that start a local paralic to continental environments, assigned to the Domerian Aganane Formation. Over this unit the limit with the Azilal formation is marked with a karstified subaerial exposure surface, that wears also great abundance of plant material, what overall implicates prograding terrestrial facies and a shrinking of the local carbonate platform width.[30] The base of the East Azilal Formation is not clear, there is a gradual passage between the underlying limestones of the Aganane Formation and the red pelites of the Azilal Formation. The upper limit is marked by a progressive transition to Bin-el-Ouidane limestones with the limit fixed at the base of the first massive limestones, generally “birds eyes”.[2]

In the west it rests conformably and with progressive passage either on the Aït-Bazzi Formation, or on its lateral equivalent the Aganane, as can be seen at Ait Blal and Tacht where limestone banks are gradually interspersed in the red pelites.[2] In other places is clearly discordant on the sediments of the Sinemurian-Pliensbachian which can be found barely blunted blocks in its conglomeratic levels, as can be seen in places like the N of Wazzant or Ait Bou Oulli. The western upper limit is marked by greenish clayey levels are interspersed between the red pelites, then limestone banks, gradually changuing into the Bajocian Tanant Formation, as can be seen at Tizi-n-Takiout on Aït-Blal.[2]


Stratigraphy of the Azilal Formation on the Mizaguène Hill (Termier, 1942)
Unit Lithology Thickness (metres) Fossils
14) Red, Bluish and Green Pelites, disposed on lenticular bands over yellow Breccia marls, parallel deposited with bodies of Calcite 10–15 m Non present
13) Very finely lit bistrated limestone, with green and purple grains 0.2-0.3 m Non present
12) Pelite and Bluish sandstones 0.7 m Non present
11) Yellowish marno-conglomeratic Sandstone 0.7 m Vertebrate remains indet.; Macroflora Indet.
10) Bluish sandstones of fairly variable composition: fine particles of Angular Quartz, Plagioclases, abundant Chlorite, clastic Andalusite and Iron Oxide; The coarse parts consisting of Quartz and Moscovite, over Cemented Calcite; Overall urface impregnations of Malachite 2 m Non present
9) Yellowish marno-conglomeratic sandstone, with bones and remains of plants, which, when not transformed into Lignite, show traces of preserved structure; this lenticular layer, which does not seem to exceed 80 cm, locally contains regions of sandstone and Calcite Geodes 0.8 m Sauropoda indeterminate; Vertebrate remains indet.; Macroflora Indet.
8) Sandy red pelites 8–10 m Non present
7) Red pelites passing through Leafy sandstone 2 m Non present
6) Sandy red pelites 2 m Non present
5) Coarse red sandstone (pebbles of 1 cm with other pebbles, many less than 2 to 3 cm) 0.8–4m Non present
4) Lithified red Pelite 2 m Non present
3) Red Sandstone composed by grains of 1/2 mm in benches of 10 to 20 cm 1 m Non present
2) Red Pelites: these levels form the horizontal table of the Summit 4–5 m Non present
1) Sandstone with a wine tone, composed by grains that range from 1/4 to 1 mm 0.2 m Non present
Stratigraphy at Toundoute
Unit Lithology Thickness (metres) Dinosaur fossils
Alluvium Holocene conglomerate
H Clay-sandstone series ≥ 100 Non present
G Clay-sandstone series, with gypsum layer present at the top, just below this a second dinosaur bearing horizon is present with very similar lithology to unit F. 50 Tazoudasaurus, Berberosaurus[31]
F Greenish grey clay-marl, detrital gravel to pebble-sized clasts with lignite and bones. ≤ 5 Present, indeterminate
E Alternation of red-brown clay, fine sandstone and sandstone coarse conglomerates 100 Non present
D Clay, fine sandstone and conglomerate, large volcanic rocks present. 80 Non present

Lithology[edit]

The lithology of the Azilal Formation recovers a Claystone-dominated interval, incised by metric dolomitized beds of Mudstones, Peloid-rich Packstones, Ooid-rich Grainstones, and Polymictic Conglomerates, all rich in Terrestrial plant debris, with faunal content very poor and mostly dominated by microbial facies.[1][3] This unit brings together sandstones, sometimes coarse or conglomeratics, especially red silts and some irregularly bedding carbonate horizons (lacustrine limestones?) as well as rarer coal beds.[2]

At the west this unit consists of conglomerates, sandstones and red pelites.[2] The sandstone and conglomeratic levels are lenticular with frequent oblique stratifications. While it can be complex to differenciate from the Guettioua Formation or the Oukaïmeden Sandstone, conglomerates with multicolored quartz balls of centimeter diameter are the major unique trait of the Azilal Formation.[2] This sequences record predominance of quartz grains (> 50), the rest is made up of fragments of rocks, often quartzose and schistosose with presence of vitreous rocks and spongy Glauconite; calcite cements the elements and fills vacuoles. The absence of heavy minerals and Plagioclase clearly indicate that these sandstones come from the dismantling of a non-granite base. Other proximal areas show Sieve-Conglomerate lenticular channels of ~5 m (16 ft) thickness (≤ 5 m (16 ft)), composed of several materials, such as volcanic products in Toundoute (blocks of sands composed of Feldspars, black ferruginous grains, siliceous green fragments of veins, microgeods, hummocky concretions), limestone debris with traces of roots and cracks, where in some parts traces of fine, dark brushy algal filaments are still visible, similar to blue-green algae of the genus Girvanella.[27] Finally, there are intercalations of fine, often laminated sandstone which mark the inondation facies of the channels during flood periods, being composed solely of feldspars plagioclase and to a lesser extent of orthoclase, as well as small ferruginous grains or fine silts of quartz.[27]

Microfacies[edit]

Due to the strong Dolomitization affecting the strata of this formation, it is difficult to describe in detail the microfacies types, so it was necessary to work with isolated samples combined with ground observations.[32] Based on this, the following types of microfacies were distinguished:

The first include laminated algal boundstones, with broad areal are characterized by yellow dolomitized Stromatolites.[32] Characteristic of this type of microfacies are cavity channels, which are often arranged parallel to the layering.  The presence of peloids is an important facies indicator for the supratidal zone, being transported into the tidal flats by periodic storms and then covered in turn by Microbial mats.[32]

The oosparites/Wackestones along dolomitic grainstones occur rarely, usually only as sparsely massive, gray to yellow layers, which are often obliquely stratified. This layers have diverse but scarce biocomponents, some of which form ooid cores and consist of Foraminifera, Echinoderms, Lamellibranch, Gastropods and Algae. Intraclasts are usually rounded. Peloids occur in a subordinate form.[32]

Biogenic pelmicrites and oomicrites/wackestones are rare facies. In addition to individual Ostracods, Mussel shells, foraminifera and Scytonemataceae Cyanobacteria (Ortonella spp.), Bioturbation is present.[32]

Dolomites, whose components are either completely recognizable or only barely identifiable, depending on the degree of dolomitization.[32]

Sandstone/Conglomerate/Marl: The sandstones of the Azilal Formation are composed of quartz clay, some Feldspar and Glauconite. Pyrite, Malachite, as well as bone and plant remains are found. In the microconglomerate gullies there are also clasts (mainly quartz, quartzite, Granite, Basalt, clay, sandstone) from the Paleozoic and to a lesser extent from the Triassic and Jurassic.[32]

Hydrogeology[edit]

The Azilal Formation constitutes a depressed zone, often intensely cultivated, rich in springs and wells. This is explained by the alternation of permeable and impermeable levels. Springs spring up at the top of this unit, under limestones (Tanant or Bin-el-Ouidane Formations), as in Bernat.[2] The numerous wells dug on the northern edge of Guettioua testify to this unit aquifer qualities, with water accumulated in the sandstone-conglomeratic levels interstratified in the pelites.[2]

Paleogeography[edit]

Early Jurassic Paleogeography of the Sahara Craton, including source Highlands, Jurassic basins and CAMP outcrops. While the Central High Atlas basin in the N limit is represented as fully marine, it was partially filled by terrestrial sediments towards the W-NW-SW

The Azilal Formation was deposited in the Moroccan Carbonate Platform, at a palaeolatitude between 19°-20°N, around the same latitude as modern Mauritania or Cuba, and developed along a major drowning episode linked with the Toarcian Anoxic event, that led to the eustatic sea–level rise on the Early Toarcian in Europe and Africa.[33] The Azilal Formation was bracketed between several major geologically older hinterlands: the West Moroccan Arch on the W-NW, the Anti-Atlas and the Sahara craton in the S-SE.[34]

Towards the west (Afourer and Azilal province maps) the local laguno-marine facies of the Aganane Formation are directly overlain by terrigenous deposits of the Azilal Formation after the initial major Toarcian regression: red clays, conglomerates with paleozoic elements.[8] This deposits fill many small basins in tearing in the Atlas of Afourer and Azilal, having the Demnat Accident as the major structural element in this last sector. While at Demnate, Telouet, Azilal, Skoura or Toundoute the conditions did become fully terrestrial, towards the east at Beni-Mellal the Lower Toarcian the ongoing sea regression happened latter, marked by oscillations between the Azilal Formation and the marly marine Tagoudite Formation or the carbonate Tafraout, ending both fully overlain by the terrigenous layers towards the Middle-Late Toarcian.[8] The Amezraï minbasin evolved as an isolated lateral equivalent, composed of intertidal to open marine carbonate environments, hosting also layers of the Tagoudite Formation, that end first overlain by the Tafraout Formation, and then in the westernmost sectors by the Azilal Formation while remaining in the central East marine-based as marks the Aguerd-nˈTazoult Formation.[28]

The Azilal Formation co-evolved with several staggered sections from 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. At Talmest-Tazoult ridge, the siliclastic-carbonate series of the Toarcian-Aalenian form a clear progressive unconformity above the carbonates of the Sinemurian-Pliensbachian, building an individualized ridge oriented NE-SW, limiting two local depressions to the South-East (Amezraï and Wahmane). The North Altas accident shows variations of thickness and facies, testifying a weak activity of the latter, in particular during the deposition of the Azilal Formation, with the reliefs created during the previous phase covered by the terrigenous layers of this last one.[28]

Two main stages can be then distinguished in the paleogeographic evolution of the western border of the High Atlas Basin during the Toarcian-Aalenian: during the Lower Toarcian, this sector presented the same paleogeographic characteristics as those seen during the uppermost Pliensbachian, being latter followed by a reduction in the deposition areas and a filling of the Pliensbachian basins by terrigenous material from the Tagoudite & Azilal Formations.[28] Then, with the Middle Toarcian- Aalenian, the Azilal Formation expanded towards the east as the sedimentation resumed throughout the region, where coeval layers in the Amezraï subsiding basin was filled by carbonates from the internal platform of the Tafraout and Agrd N'Tazolt Formations, being surrounded to the north, east and south by a coastal area with dominant terrigenous sedimentation of the own Azilal Formation. This period is marked by the individualization of the Talmest-Tazolt Ridge in the center of the basin and by a relative tectonic calm in the other coeval sectors.[28]

Despite being claimed to have Latest Pliensbachian layers, the Azilal Formation is measured in post Polymorphum (Earliest Toarcian) levels, and impacts in the sedimentation (especially of the Béni-Mellal Province, Zaouiat Ahansal, or the Dadès Gorges) in the Middle Toarcian-Lower Aalenian, marked by a notorious sea regresion, distributed in at least 6 sequences, that overlie layers with the ammonite genus Eodactylioceras and Hildoceras bifrons allow a precise localization of this initial progradation of the terrestrial settings around the Bifrons substage of the Toarcian (that can be either considered the uppermost Lower Toarcian of the lower Middle Toarcian).[8] The layers are, at the oldest sections of this initial phase, represented by marly and silty marls and limestones as well as marginal-littoral sandstones testifying to the siltation of this sector by sandy sheets of deltaic origin. At the same time on the Amezraï basin the fauna is composed by brachiopod fauna such as Soaresirhynchia bouchardi, S. babtisrensis and Pseudogibbirhynchia jurensis that corroborate the Toarcian age and the connection between both locations.[28] Meanwhile the presence of Aalenian (Bradfordernsis-Murchinsonae) Branchiopods in the Agrd N'Tazolt Formation coeval with Ammonites of the same age in the easternmost Azilal formation at the Ikerzi Area confirms the marine delimitation in the last stages of deposition.[32]

Environment[edit]

The Azilal Formation represents mostly fluvial-aluvial under arid to humid climate similar to the Yaté coast in New Caledonia. Surrounding highlands hosted ecosystems with alternating tundra and moist forests (ex. Brazilian Araucarian Uplands)

The Azilal Formation 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.[35] It represented a variety of settings, including continental river/palustrine-dominated, paralic-tidal deposits, and tidal mudflat shorelines.[34] The terrigenous-dominated deposits of the Azilal Formation were deposited in a coastal environment with continental influence. On this facies, the fauna (composed of rare Brachiopods, poorly diversified black Bivalves or vertebrates) and the sedimentary figures (impacts of raindrops, soft pebbles, crisscrossed stratifications and "ripplemarks") reflect a confined to continental/marine deposition environment, with temporary emersions, where conditions met in a deltaic environment with saltwater/brackish influences. This terrigenous deposition can be seen from north to south as a lateral transition from a coastal facies to a fluvial facies (at Adoumaz) to a foreshore facies (Ghnim "fining up" type sequences) to a beach facies (Jbel Taguendouft "coarsening up" type sequences). The relatively small thicknesses found at the Jbel Taguendouft section would testify to the tectonic activity of the Jbel Abbadine ridge.[28]

The flow of the fluvial-washed sediments take place in a E-NE direction, being moved to the layers of the Tafraout Formation and other coeval marine units, as well are found on fluviatile channels inside the own rocks of this unit.

The depositional environment of the Azilal formation was dominantly fluvial or alluvial, with large sandstone channels cutting through detrital conglomerate deposits. The high abundance of plant remains, either as fossil wood, cuticles, charcoal or Rhizoliths, reveals the presence of vegetated soils in the vicinity.[6] There is also evidence ephemeral Palustrine (Sabkhas, Chotts) episodes in the form of carbonate bodies (Caliche or Calcrete levels), intercalated with conglomerate under an arid environment, as marks the development of gypsum.[36] This is recorded specially in the Telouet and Demnate-Wazzant area, but also seen in more detail at Toundoute: the deposits present a channel/floodplain type fluvial system, with sand-filled channels abundant in plant roots (mostly located in fine limestone, probably from the channel margins), developed in the near E-W direction of transit. The channel lithology shows notable enrichment of material from the Paleozoic basement and Triassic cover, with interbedded volcanic material (sand to pebbles), 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.[27] Lithic elements or isolated crystals found locally show no evidence of prolonged transport, probably from relatively nearby Springs, being these collected and transported by a poorly developed river system during episodic floods.[27]

The overall local climate was warm with alternating wet and dry periods have generated soils with differentiated calcareous profiles (pedogenetic nodules, Caliche), hosting active erosion on sparsely vegetated soils.[6][27]

Modern Sebkha of Imlily, near Dakhla. Some areas of the Azilal Formation have layers derived from a similar deposition

The environment of the Azilal Formation becomes notorious after the Middle Toarcian, with a clear major regression that ends with a slowdown of the local sedimentary filling. The paralic deposits of this phase contain clay intervals rich in continental organic matter such as wood debris, but a rare fossil fauna consisting of abundant algae, benthic foraminifera, common oncoids, gastropods, and bivalve bioclasts.[34] As the Lower Toarcian started, over the region, the carbonate platform was abruptly replaced by siliciclastic deposits fed by a greater surrounding hinterland weathering, measured thanks to increased plant debris and the absence of evaporite-rich intervals and semi-arid paleosols, with alternating shoreline-forest depositional contexts.[34] This initial layers are overlied by storm-dominated deposits, with a depauperate fauna and very common occurrence of plant debris, which with the increase in ooid-rich facies suggest deposition on a warm, wet climate belt.[34] Some of these areas, particularly the more coastal ones located in the Azilal region, have an appearance similar to that of modern Sebkhas, for example those of found in the modern Persian Gulf. These intervals have increased nutrient levels locally, as evidenced by the high amount of Phosphorus along the entire Atlas Basin.[37] These siliciclastic beds have abundant pebbles of metamorphic and igneous rocks, implying that the material must have been derived from the Paleozoic or Proterozoic, implying a hinterland that is frequently emerged and subject to erosion and the effects of diagenesis. The only ones of this nature in Morocco, that on the Atlas are located to the south in the Anti-Atlas, to the west in the Ancient Massif and the Jebilet, and to the north in the Central Meseta, all places that were subaerially exposed during the Jurassic.[37][38] Specifically, the Anti-Atlas shows processes of tectonic uplift, overburden erosion, which, combined with the concentration of coarse siliciclastic material in the western part of the central High Atlas (absent in the east), suggest that this area was the source of the altered Lower Toarcian sediments, allowing the tracing of the fluvial channels that developed towards the Azilal Formation.[34]

At the same time towards the South-East the sister and connected Tafraout Formation in the Amezraï basin represents a marginal marine environment, with wave ripples, cross-bedding, the Amphipoda ichnofossil Arenicolites isp. and the calcareous algae Cayeuxia sp., all deposited on diagenetic mudstone.[34] Concretely, on Taguendouft, towards the Middle Toarcian the carbonate producers recovered locally, with the ooid grainstone replaced by wackestone to packstone beds, where heterotrophic faunal bioclasts increase, such as cephalopods, brachiopods, echinoderms, and gastropods, with occasional coral patch reefs.[34]

The Azilal formation recovers, as seen on worldwide units an increase of weathering due to the Pl/To and T-OAE events, with increase of the siliciclastic sediment supply and increased dissolved material to the oceans. This occurred along an intensification of tropical storm events (as well Hurricane action) on the T-OAE, destroying the older carbonate platform organisms locally.[34] This allowed to set the Azilal Formation environments, that range from a series of continental settings with river influence, increased during the T-AOE with more amounts of flora being washed, to nearshore deposits, paralic and subtidal, subject of storm and tropical storm events, all set on a warm humid climate.[34]

The aftermath of the Toarcian Oceanic Anoxic Event is also highly present on the marginal marine strata of the formation, with the so-called Toksine Section, a succession of near shore marine strata disposed along the Toarcian boundary, where its last 40 m belong to the lower part of the Azilal Formation and are composed of dolomitized Mudstones and ooidal Grainstones, that show a slowly recovering a low-depth nearshore marine environment after in the Pliensbachian-Toarcian boundary a dramatic Tethys-wide collapse of the Neritic Carbonate System happened.[39]

At Tazouda Volcanic material from a possible coeval Explosive eruption is present (Tungurahua Volcano as example)

There is also a local record of a Cold Snap, where the Akenzoud section, that has 182 section meters on the Azilal Formation, and shows that after cold event that affect the local waters, related to the Karoo & the Atlantic Rift volcanism the present Brachiopods, based on their preserved oxygen isotope data show that warm seawater temperatures re-established during the early Late Toarcian.[9]

In the Middle Toarcian the eastern and north-eastern part of High Atlas of Todrha-Dadès, sedimentation carbonate with bioconstructions (patch-reef), develops with a thickening towards the East and a still thinning towards the West in the direction of the reef of Jbel Akenzoud, where the dew marine fossils of the formation are recovered.[40] The Coralline faunas suffered a significant collapse visible in the locality of Ouguerd Zegzaoune, showing that sedimentation at this time took place in a distensive tectonic context.[40] Then, towards the Late Toarcian-Aalenian boundary, the series corresponds to detrital deposits with carbonate intercalations with neritic fauna. The structural analysis shows that the sedimentation during the upper Toarcian was controlled by a tectonic game, always distensive, causing the tilting of blocks along the transverse fault of NW-SE direction, which leads to the creation of available space with openings always towards E and NE.[40]

Invertebrates[edit]

The fossil record of the Azilal Formation is very restrictive compared to the marine coeval/underliying units, like the Tafraout Formation. 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.[32] Plant remains are very abundant in places such as the north of Jbel Akenzoud and partly impregnated and/or carbonized by malachite.[32] Gastropods have been discovered in several places, but none of the specimens have been studied nor identified.[41] 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).[42][43]

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Ichnofossils[edit]

Genus Species Location Material Type Made by Notes Images

Rhizocorallium[9][44]

  • R. parallelum
  • R. ispp.
  • NW Dades Valley
  • Todrha–Dades
  • Jbel Akenzoud

Tubular Fodinichnia

Domichnia and/or fodinichnia.

  • Crustaceans
  • Annelids
  • Fishes

Dwelling and feeding burrow of a suspension-feeder or deposit-feeder, associated usually with shallow waters

Example of Rhizocorallium fossil

Brachiopoda[edit]

Genus Species Stratigraphic position Material Notes Images

Stroudithyris[9][40]

  • S.stephanoides
  • Jbel Akenzoud
  • E Boumardoul n’Imazighn

Isolated Shells

A Brackish Lissajousithyrididae Brachiopod. Mostly benthonic specimens are known. The presence of this species indicates an upper Toarcian-Aalenian age for the layers where was discovered.

Bivalves[edit]

"Dwarf black bivalves (Lucinidae?)" in great abundance where reported from the unit at it´s type section.[2]

Genus Species Stratigraphic position Material Notes Images

Coelastarte[45]

  • C. depressa
  • Jbel Mesgounane

Isolated Shells

A shallow marine/lagoon burrower Astartidae Bivalve. Is considered to be shallow infaunal burrowers

Lucina[45]

  • L. spp.
  • Jbel Akenzoud
  • Jbel Mesgounane
  • Jbel Taguendouft

Isolated Shells

A shallow marine/lagoon burrower Lucinidae Bivalve. A burrowing mollusc which lived in the low intertidal/shallow subtidal settings, with modern species known to be closely associated with mangroves

Specimen of the Genus

Ammonites[edit]

Genus Species Stratigraphic position Material Notes Images

Planammatoceras[32]

  • P. cf.spinosum
  • SW of Anergui

Isolated Shell

An Ammonite of the family Hammatoceratidae. Indicator of a Middle Aalenian age for the uppermost layers, as is found also on the Middle Atlas. As well evidence of greater marine influx in the easternmost outcrops.

Vertebrates[edit]

Several scales & teeth of fishes (Lepidotes?) are know from several locations, coming from freshwater/lagoonal layers.[7] 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.[46]

Theropoda[edit]

Genus Species Stratigraphic position Material Notes Images

Berberosaurus[47][31]

B. liassicus

  • Holotype: Neck vertebra, part of the sacrum, a metacarpal, a femur, and parts of a tibia and both fibulae. Part of another femur has been assigned to the genus as well.[47]
  • The axis, a postorbital, the endocranium and teeth are currently being studied.[48]

Described originally as a basal representative of the Abelisauroidea, it was recovered as a basal ceratosaur in later studies.[49] It was a medium-sized theropod, measuring 5.1 m (17 ft) long, with a weight of 200 kg (440 lb).

Berberosaurus life restoration and size comparison.

Coelophysidae[50][51][52][31]

Indeterminate

Two adults and one recently hatched juvenile. At least the posterior half of the skeleton is present: caudal, sacral, dorsal vertebrae, pelvis and both hind legs

A coelophysid coelophysoid. According to Mickey Mortimer: "Assigned to Coelophysidae based on the apparent fusion between distal tarsal III and metatarsal III". It has been also proposed as a possible tetanuran.[53] That was dismissed by Benson in 2010.[54] Includes at least three different individuals that have been collected in Wazzant: two adults and a newly hatched juvenile. The former foot material resembles the Cretaceous Australian genus Kakuru, that has been proposed as a basal tyrannoraptoran. Mortimer said that "I really don't see much resemblance to Kakuru in the astragalus" and labeled it as a possible dilophosaurid or coelophysoid.[55]

Theropoda[47][31][56][57]

Indeterminate

Phalanges and several non mentioned remains.[47][57]

Described as a "Large theropod of uncertain affinities"[47] and as an "enigmatic theropod".[56] To quote Allain: "Two theropods have been found on Toundoute. The first theropod hasn't been described but shows a size larger than any of the know theropods of the Triassic-Early Jurassic know by now, indicating that Toarcian theropods had sizes rivaling that of late Jurassic allosaurs".[58]

Sauropodomorpha[edit]

Genus Species Stratigraphic position Material Notes Images

Gravisauria[46][58]

Indeterminate

  • East of Azilal, at 1 km at the South of Dar Ou Hammou.[46]

Pubis and other indeterminate remains

A gravisaurian sauropod. Quoted to resemble Tazoudasaurus

Eusauropoda[50][46][31]

Indeterminate

  • Mizaguène Hill, 3 km at the Souhtwest of Azilal.[57][31]

5 dorsal & caudal vertebrae, fragmentary ribs, chevrons and several large badly determinable debris.[46][51][52]

A eusauropodan sauropod maybe related with Spinophorosaurus. Was collected on a freshwater lagoonal depositional setting.[46]

Sauropoda[50][51][52][31][57]

Indeterminate

Left ilium, a humerus and three vertebrae.[51][52]

A possible basal sauropod of uncertain affinities. Remains recovered represent a Juvenile

Sauropodomorpha[50][59]

Indeterminate

  • Sud d'Ait Bouzid

One or more vertebrae and other unidentified remains

A possible Sauropodomorpha of uncertain affinities. P. Lévêque brought these bones back from a hill which he placed in Cretaceous strata, but more recent work has shown that the deposit is in fact in Toarcian layers.

Tazoudasaurus[60]

T. naimi

Around 10 different specimens:Partially articulated skeleton and cranial material including complete left mandible with teeth, quadrate, jugal, postorbital, parietal, frontal and exoccipital. Associated remains of a juvenile skeleton.

A gravisaurian sauropod related to Vulcanodon. The most complete sauropod from the Lower Jurassic Found, with adult, sub adult and juvenile specimens.[47][56][57][31]

Representative vertebrae of Tazoudasaurus naimi.

Plantae[edit]

The Major Vegetational distribution was compared with the modern inland of the Isle of Pines.[61] In the Beni Mellal-Azilal areas paleosols show abundance of Rhizoliths of plants associated with heavily bioturbated layers.[62] While there is a great amount of plant remains in the form of coal, foliar debris, cuticles, woody roots, rhizolith and ghost roots, fossil wood and unidentified macrofoliar remains the only flora with some work on it was recovered at Toundoute, as abundant infra-centimeter plant debris composed mostly by Leaflets from ferns and, less frequently, cycad pinnulae, with common cuticles and no palynomorphs.[60] Wood debris from the same locality showed affinity within the coniferophytes, resembling the abietoid Pinaceae or towards the Taxaceae.[27] By quantity of material the vegetation was apparently dominated by ferns, maybe concentrated in punctual wetlands (spring tuffs), followed by cycads and conifers.[27] A possible correlative flora if found in the same age layers of the Mashabba Formation (North Sinai, Egypt) and is composed by the genera Equisetites (Equisetales), Phlebopteris and Piazopteris branneri (Matoniaceae).[63] Other coeval flora includes the plants recovered on the Budoš Limestone and specially the Rotzo Formation.[64][65]

Fossil Wood[edit]

At the top of the formation at the Idemrane geosite, unidentified pieces of wood fossils of variable sizes were recovered (largest over 20 cm in length) showing traces of iron oxides. This woody pieces are considered root fragments.[66]

Genus Species Stratigraphic position Material Habit Notes Images

Metapodocarpoxylon[67][68]

  • M. maurianum
  • Mount M’semrir
  • Isolated Logs
  • Isolated Branches
  • Stump remains

Arboreal, high canopy, linked with floodplain margins yet high aridity tolerant

Conifer fossil wood related with Podocarpaceae inside Pinales. Probably built evergreen tropophilous forests in alluvial plains together with Agathoxylon. A genus closely related with Dacrydium and Dacrycarpus.[69]

Extant Dacrydium

See also[edit]

References[edit]

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