Azilal Formation

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, part of the Tafraout Group that covers the Early Toarcian to Middle Aalenian stages of the Jurassic Period. 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. The Azilal Formation consists mainly of claystones rich in continental plant debris and laminated microbial facies. It is a continental deposit which overlies marine dolomites of equivalent age to the Rotzo Formation of Italy, mostly part of the Aganane Formation. The formation is the continental part of a massive Siliciclastic-Carbonate platform ("Tafraout Platform"), 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. Dinosaur remains, such the sauropod Tazoudasaurus and the basal ceratosaur Berberosaurus are known from the unit, along with several undescribed genera. 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 & Aguerd-nˈTazoult Formation, connected with the offshore Ait Athmane Formation and the deeper shelf deposits of the Agoudim 1 Formation.

Description
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. 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.

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. 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. 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.

Strata
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. 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. 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”.

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. 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.

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 are explosive volcanic eruption beds found associated with the outcrops at Toundoute, maybe associated to premature activity of the mobile area along the line of the South-Atlasic Fault with Trachyandesitic materials from a explosive source, like in the older Mouluya outcrops like the Tizi-nGhachou sector.

Lithology
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. 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.

At the west this unit consists of conglomerates, sandstones and red pelites. 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. 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 thickness (≤ 5 m), 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. 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.

Microfacies
Due to the strong Dolomitization affecting the strata of this formation it is difficult to describe in detail the microfacies types, yet the following types of microfacies were distinguished:

The first include laminated algal boundstones, with broad areal are characterized by yellow dolomitized Stromatolites. 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.

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.

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

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

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.

Hydrogeology
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. 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.

Environment
The Azilal Formation, located on the Moroccan Carbonate Platform at a palaeolatitude of 19°-20°N, developed during a major drowning episode linked to the Toarcian Anoxic event. It is bounded by the West Moroccan Arch, Anti-Atlas, and Sahara craton. Initially, local laguno-marine facies were overlain by terrigenous deposits post-Toarcian regression, filling small basins in the Atlas of Afourer and Azilal. In Demnate and nearby areas, conditions became terrestrial, while to the east at Beni-Mellal, the sea regression occurred later. The Amezraï minbasin evolved as an isolated carbonate environment. The formation expanded eastward during the Middle Toarcian-Aalenian, marked by tectonic calm and sedimentation of terrigenous and carbonate layers. The Azilal Formation spans post-Polymorphum levels, with notable sea regression and specific faunal assemblages confirming its Toarcian age, Meanwhile the presence of Aalenian (Bradfordernsis-Murchinsonae) Branchiopods in the Aguerd-nˈTazoult 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.

The Azilal Formation, part of the Tafraout Group in the Western High Atlas, was deposited in a coastal environment with continental influence. It consists of terrigenous-dominated deposits, reflecting a deltaic environment with temporary emersions represented by a great variety of settings, including continental river/palustrine-dominated, paralic-tidal deposits, and tidal mudflat shorelines. 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 formation's sedimentary features include raindrop impacts and ripple marks indicating channel/floodplain type fluvial system, with sand-filled channels abundant in plant roots (mostly located in fine limestone, probably from the channel margins), along with evidence of 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. The high abundance of plant remains, either as fossil wood, cuticles, charcoal or Rhizoliths, reveals the presence of vegetated soils in the vicinity. 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. The formation also shows evidence of erosion from nearby highlands,as indicates 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, locally either 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. 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. The surrounding highlands 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.

There is also a local record of a Middle Toarcian Cold Snap at Jbel Akenzoud, 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.

Invertebrates
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. Plant remains are very abundant in places such as the north of Jbel Akenzoud and partly impregnated and/or carbonized by malachite. Gastropods have been discovered in several places, but none of the specimens have been studied nor identified. 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).

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

Vertebrates
Several scales & teeth of fishes (Lepidotes?) are know from several locations, coming from freshwater/lagoonal layers. Indeterminate dinosaurian & other vertebrates are known 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.

Plantae
The Major Vegetational distribution was compared with the modern inland of the Isle of Pines. In the Beni Mellal-Azilal areas paleosols show abundance of Rhizoliths of plants associated with heavily bioturbated layers. 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. Wood debris from the same locality showed affinity within the coniferophytes, resembling the abietoid Pinaceae or towards the Taxaceae. By quantity of material the vegetation was apparently dominated by ferns, maybe concentrated in punctual wetlands (spring tuffs), followed by cycads and conifers. 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).

Fossil Wood
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.