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Tafraout Group
Geological formations in Morocco From Wikipedia, the free encyclopedia
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The Tafraout Group (Full name: Assif Tafraout Group, also known as "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, Tinejdad and Errachidia areas of the High Atlas (with the Tagoudite Fm reaching areas near Rich in the Middle Atlas[1]) of Morocco.[2][3] 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.[4][5][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.[2][3]
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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", as well includes part of the "Aguerd-nˈTazoult Formation"); the Tafraout Formation (deposited in a subtidal to inner platform environment, includes the "Amezraï Fm" and part of the "Aguerd-nˈTazoult Formation"[9]) and the Tagoudite Formation (including the "Tamadout Formation", platform to open pelagic).[7] They are connected with the offshore Ait Athmane Formation and the deeper shelf deposits of the Agoudim 1 Formation.[10] 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.[11] The strata of the group extend towards the central High Atlas, covering different anticlines and topographic features along the mountain range.[12][13]
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.[14]
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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.[15] 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.[16][17] 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.[3] Several tectonic events during the Triassic-Jurassic boundary reactivated normal faults, leading to the dominance of marls during the Middle Liassic to Toarcian.[18][19]
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Description
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Azilal Formation
Informally known as "Marnes chocolat" in the Azilal region, and represents a continental to marginal marine unit made up of red-brown marls, silts (microsandstones) and conglomerates with centimetric quartz dragees. More marine-influenced sections near Beni Mellal 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 N. Here, it evolves from lower sections with transition from sandstone to limestone and/or sandstone to clay, with a thin level of green marls locally rich in ostracods. Then is followed by subtidal term, represented by an oolitic limestone with fine lamellibranch bioclasts and variable percentages of quartz and sandstone with calcareous cement and rare oolites drawing on the surface mega-ripples of 3 to 5 m in wavelength.[20] It ends with supratidal deposits made of coarse sandstone gradually changing to red Marls with "fluer" structures and locally to paleosols with fluvial decametric channeling lenses.[20]
On the south-southwest edge of the basin towards west of Azilal (Jbel Til-Jbel Amersiaz basin and part of the M'Goun syncline), Demnate, Telouet, Toundoute and Marrakesh, under the Bajocian limestones 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 non dissolved Liassic limestone elements.[6] This sector reaches 800 m thickness 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.[6]
In Talmest-Tazoult (Zaouiat Ahansal), the "Aguerd-nˈTazoult Formation" is present, a local informal unit.[7] It represent the most recent marginal marine layers, dating from the Upper Toarcian-Aalenian periods and mark the E expansion of the Azilal Formation. It begins with layers that have many conglomerate lenses, part of the Azilal Formation. Sandstones, oolitic, and biodetritic limestones are also found throughout. Red and green marls appear in several layers.[21] In the Talmest-Tazoult area has red sandstones and marls in the lower part. Here the formation is part of a large +200 m thick yellowish limestone bar, with the transgressive "S10", whose end marks the major post Middle Toarcian transgressive event, composed of bioclaetic or oncolithic limestones, poorly developed low-marine-level prisms and marly limestones with oblique stratifications, while oolitic limestones mark smaller transgressive events, and then the major one towards the Bajocian with the Aït Abdi/Bin el Ouidane Formation, flooding again all the sector.[22]
In the Dadés area the formation is present asynchronously, seen in the W in the Earliest Toarcian, yet in some areas like Boumardoul n’Imazighn doesn't reach until the Middle Toarcian onwards, here recovered under the "Tidrite section", made of fine terrigenous deposits interbedded with dolomitized limestone.[14][23] In the Ait Hani area at Tinejdad the "Aït Hani formation" has been suggested to be the upper part of the Azilal formation, but may be part of the Bajocian units instead.[24]
Tafraout Formation
The Tafraout Formation can be divided in 4 members and consists of oolitic and bioclastic limestones, wackestones, silt marls, and quartz-rich sandstones with minor feldspar and carbonate debris with cross-stratifications, found in channels and bars, alongside greenish marls and micro-conglomerates.[7]
The Lowermost member is also known in Talmest-Tazoult as "Amezraï Formation" and is an essentially terrigenous unit that overlies the Aganane Formation, reflecting a deltaic depositional environment with high sedimentation rates.[13] Local tectonic activity, mainly due to seismic events in the Tethyan region, influenced this section within the formation, causing erosion of older Paleozoic layers.[9][25] This lowermost sequence is made of alternating fine-grained sandstones with lignite debris, sandy marls, biodetrital/oolitic limestones in thin beds, with sporadic nodular limestone bars (up to 6 m) formed by compaction and capping limestones with oblique intersecting stratifications and asymmetrical current ripples.[13][21] Marls contain fossil debris (lamellibranchs, gastropods, brachiopods), while limestones are bioclastic grainstones or packstones with brachiopods and sea urchin debris. Some sections (e.g., Aguerd N´Wahmane, Timghissine) include oolitic limestones (oosparites) at the base, at others like Aguerd N´Igli, this term merges with the 2nd member, showing plant debris and azoic sandy marls.[13] The 2nd member transitions to green marl-dominated sequences (up to 40 m thick) with intercalated red sandstones with slumped structures and rare carbonate bars, channel fillings, and turbidite sequences (coarse bases grading to fine tops). Limestones, where present, are bioclastic grainstones with oncoliths, lamellibranchs, and crinoid debris (e.g., Aït Allal), or oolitic in some sections (e.g., Timghissine), with sedimentary polarity westward (Aït Allal) or northeast–southwest (Aguerd N´Igli), inferred from slump directions and ripples.[13] Member 3 marks a shift to supratidal-subtidal settings with sandstone marls with oblique stratifications and channel deposits, silt marls, limestone bars and ooid limestones with fossiliferous packstones or wackestones with brachiopods, gastropods, and lamellibranchs featuring biogenic-rich grainstones, wackestones, and quartz-rich sandstones. Some sections (e.g., Aguerd N´Wahmane) include micro-conglomerates at the base, as well condensation levels with fauna occur.[13] The 4th member is characterized by coral patch reefs, interspersed biodetrital limestones, finely bedded sandstones, green marls with calcareous nodules, and gravitational eventstones with bioclastic debris. Throughout, compaction, bioturbation, dissolution, and episodic emersion influenced facies development.[7] At Aït Allal, this term forms the Aït Allal reef complex with colonial polyps and brachiopods. Elsewhere (e.g., Aguerd N´Igli, Timghissine), it includes oolitic limestones or sandstone limestones with fossil condensation zones.[13] The uppermost sequences (marine "Aguerd-nˈTazoult Formation") overlies with a ferruginized, bioturbated surface and are carbonate-dominated, representing a shallow platform environment with high-energy zones, with oolitic, oncolithic, and bird's eye limestones (grainstones, micrites) with marly intercalations. Upper levels may show algal laminations or bioherms.[13]
Hypersalinity, emersion phases, and desiccation cracks suggest fluctuating conditions, while sandstone-marl alternations point to proximal turbidite deposition. The biota includes bivalves, brachiopods, gastropods, echinoderms, rare corals, and plant remains, with widespread bioturbation.[7]
The upper sequences mark a transition to a carbonate platform dominated by coral patch reefs, some reaching up to 40 m in height. Patch reefs developed in a subtidal lagoonal setting, with inclined beds and resedimented material indicating channelized transport. The biota is dominated by corals, bivalves, echinoderms, and bryozoans, with occasional gastropods, brachiopods, and foraminifera. Plant remains, including coalified fragments, are abundant in siliciclastic intervals.[7]
The rocks formed in environments ranging from supratidal to subtidal, characterized by tropical conditions akin to those observed on Andros, Bahamas.[20] 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] The deposits of the Tagoudite Formation are mostly restricted to the central High Atlas, with a thickness of approx. 200 m in the northwest vs at 30–70 m in the southeast, but retaining around 200 m at center areas like Foum Tillicht.[26] More at the E it starts to disappear like at the Cirque de Jaafar, SW of Midelt or more at the E at Bou Redine Gorges, were the Agoudim 1 Formation directly overlies the Pliensbachian.[1]
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Economical Resources
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.[6]
At the M'Goun geopark near the Bin el Ouidane Dam several locations and fossiliferous outcrops within the group have been suggested to be of geotourism interest, with some useful for educational excursions for different school and university levels.[27] Towards the Anergui rigde, the Tafraout Formation appears spreading out in an open fanshape in anomalous contact with the Triassic, being a potential geological panoramic.[28]
Paleogeography
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Early Jurassic Paleogeography of the Sahara Craton, including source Highlands, Jurassic basins and CAMP outcrops and Paleogeography of N Gondwana and the European Arquipelago
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.[9][29][30]
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.[2] 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.[20] By the Middle Toarcian-Aalenian, the Azilal Formation expanded eastward, with isolated carbonates forming in the Amezraï basin, surrounded by terrigenous sediments.[2][9][20] 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.[20]
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 Transgressive/Regressive cycles in the Laevisoni-Bifrons substages, followed finally by a post Bifrons major regression and full return to the Carbonate production.[2][30] The Tafraout Platform deepened over time, signaling a shift to transgressive conditions even with the expansion of W continental facies.[20] On the Lowermost Tafraout Fm ("Amezraï") the fauna is composed by brachiopods that corroborate the Earliest Toarcian age for it and adjacent layers.[20] Meanwhile, the presence of Aalenian (Bradfordernsis-Murchinsonae) Branchiopods in the "Aguerd-nˈTazoult Formation" coeval with Ammonites of the same age at the Ikerzi Area confirms the marine delimitation in the last stages of deposition.[7] The "Tafraout Platform" saw then a deepening towards the uppermost layers, teasing the transition to the Bin El Ouidane transgressive Bajocian Carbonate Platform facies.[9][7]
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Paleoenvironment
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Modern analogues of the Toarcian-Aalenian High Atlas Paleoenvironments: Anti-Atlas highlands with Moist forests (Ex. Araucaria moist forests); lowland trophopilous forested areas (ex. Point Lobos State Reserve); Sabkhas (ex. at Dakhla); mangrove-like lagoons (ex. with modern flora from San Salvador Island); Shallow Carbonate Sea with bivalve or coral reefs (ex. modern extant fauna reef in Florida Keys National Marine Sanctuary)
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.[32] The Continental section was deposited in environments influenced by rivers, tidal flats, and paralic settings, rwith reworked material and in Toundoute unique interbedded Explosive eruption-type volcanic material, with carbonate recrystallization suggesting were still at high temperature during deposition and, therefore, contemporaneous with the sedimentation, probably derived from early activity in the local South-Atlasic Fault.[33] The direction of the fluvial sediments take place in a E-NE direction, as well are found on fluviatile channels inside the own rocks of this unit.[2][20][30] This layers also saw high plant activity, with remains such as wood, charcoal, and rhizoliths, indicating nearby vegetated soils.[34] Other features include raindrop impacts and ripple marks indicating floodplains, with lateral sand channels abundant in plant roots, along with evidence of ephemeral palustrine (Sabkhas, Chotts) episodes in the form of carbonate bodies (Caliche or Calcrete levels), intercalated with conglomerates under an arid environment, as marks the development of gypsum, particularly in areas like Azilal, Toundoute and Telouet.[33][34]
The fluvial displaced material was sourced from nearby highlands, indicated by abundant pebbles of metamorphic and igneous rocks from Paleozoic or Proterozoic beds emerged and subject to erosion and the effects of diagenesis, locally either to the south in the Anti-Atlas, to the west in the Massif Ancien and Jebilet, and to the north in the Central Meseta, all places exposed during the Jurassic.[35] 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.[30]
At Aït Bouguemez and adjacent sites (Aguerd N’Igli, Aguerd N’Wahmane, Tizi n-M’Barek, Timghissine, and La Cathédrale), intertidal sequences record sea-level fluctuations and tectonic influences.[36] The Lower Toarcian shows high-energy western deposits (sandstones, conglomerates, red marls) and eastern green marly-sandstones with coal and oolitic carbonates, with transgressive phases marked by bioclastic and dolomitized limestones that feature fossil-rich sandstones, marls, and limestones with slumping and reefs (Ait Allal), indicating a deltaic environment, and highstand/lowstand phases by red marly-sandstones and fluvial channels.[36] Younger layers show marly and oolitic limestones of a carbonate platform shifting from inter- to supratidal settings.[13] At Aguerd N’Igli and Aguerd N’Wahmane the deposition starts with sandy marls and oolitic limestones with NE–SW sediment supply, transitioning to a marly and oolitic facies, while at Tizi n-M’Barek's shows channels and marls, evolving into a low-energy facies with stromatolites. Finally Timghissine's and La Cathédrale's have conglomerates, red marls, microconglomerates and channels, leading to marly-oolitic with bird's-eye facies.[13]
The marine sectors were mostly part of the "Tafraout Platform". Initially, a shift to siliciclastic deposits occurred, marked by storm events and increased plant debris, indicating a warm, humid climate.[2][30] Sandstones, red marls, and oolitic carbonate sand bars, interpreted as deposits in a transitional subtidal to supratidal environment. High-energy shallow water conditions are indicated by oolitic and biodetrital limestones, while monospecific organism enrichments hint at restrictive lagoonal settings. Despite similarities with the Jbel Choucht and Aganane Formations, the carbonate content decreases, and sedimentation interruptions are marked by hardgrounds, with carbonate detritus linked to erosion of nearby platforms.[7] At the same time, the Tagoudite Fm siliciclastic turbidites were deposited in an open marine depositional environment, with sourced carbonates from the Platform and older formations. The second member reflects a significant environmental shift from shallow to deeper water conditions. Its basal part contains oolitic and biodetrital limestones and biostromes of large bivalves (Plicatostylidae), indicating high-energy shallow water deposition.[37] However, alternating grey and green marls with hemipelagic and ammonite-bearing sequences on the hanging wall suggest open marine conditions and distal turbidites, similar to the lowermost Agoudim 1 Formation.[7] The third member was deposited within the Toarcian Oceanic Anoxic Event and is characterized by a monotonous organism spectrum, pointing to restrictive living conditions, and its little thickness in Assif Tafraout indicates a high subsidence rate, estimated at 0.4 mm/year. Carbonate production stopped, causing local extinctions.[14][30] Sandstone/marl and limestone/marl alternations are interpreted as proximal turbidites with proximal source, with shallow water organisms, oolitic limestones, and plant remains suggesting sediment relocation via channels on submarine slopes and mudcracks further suggest periodic emersion. The Toarcian Oceanic Anoxic Event locally intensified Tropical storms, destroying older carbonate platforms and increasing siliciclastic deposits.[31][38] Finally, the fourth member records the return of the carbonate factory in the Middle Toarcian-Aalenian with a thickness of 680 meters in the Assif Tafraout profile, dominated by corals, bivalves, and echinoderms, reflecting deposition on a continuously deepening platform where subsidence outpaced sedimentation. A major fall of the sea level happened in the Middle Toarcian-Aalenian, re-activating the carbonate factory and the recovery of coral reefs.[2][14] The eastern and northeastern High Atlas saw the re-development of carbonate sedimentation along tectonic activity during the Late Toarcian.[2][23] Inclined layers, fine conglomerates, and plant remains in the lower part indicate a nearby supply area, while the depositional environment ranges from supratidal to subtidal, recording microlagoons between coral patch reefs marked by the presence of micrite.[7] There is also evidence of more smaller extinctions, like a Middle Toarcian (Variabilis/Gradata ammonite zone) cold snap, followed by a return to warmer conditions.[23] The last sequence is made up of the Azilal Formation were corals, benthic fauna, ooids and the observed structural features indicate deposition in shallow water, along with slanted layers, conglomeratic channel fillings and plant remains suggesting periodic emersions.[7]
The Plicatostylidae-Scleractinia bioherms are found in multiple locations during the Lower Toarcian, recording a series of dynamic shallow marine environments, with fluctuating energy levels and diverse marine life, indicating periods of stable reef-like conditions and intercalated sedimentary layers recording environmental stress, as well tidal and storm influences. Bivalve and coral species thrived in different settings, contributing to a complex benthic community.[37] After the TOAE, horizons of enormous coral patch reefs, reef-like occurrences of bivalves (tought barely few Plicatostylidae), echinoderms accumulations, algal mounds, bivalve enrichments, gastropods, decapodan coprolites, solitary corals and bryozoans in the area between bioherms.[7]
Diapirism
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The central High Atlas region features long diapirs and minibasins formed during early Jurassic rifting, know as The Central High Atlas Jurassic Diapiric Province.[39] Local diapiric sequences are distributed across five distinct areas: First, the Northern Atlassic Front transitions from a foreland basin (Tadla Plain) to the Jbel Ighnayene culmination, characterized by a thick succession of Jurassic-Eocene sediments affected by thrust tectonics and faulting, were the Azilal Formation is widely present with relatively homogeneous continental sedimentation.[40] Next is the Abbadine diapiric complex, with multiple minibasins (Ouaouizaght, Taguelft, and Tilougguite) separated by salt walls (Abbadine and Addendoum) that influenced local sedimentation, with progressive thinning and truncation of Toarcian-Aalenian facies near diapirs.[40] At the Amezraï Minibasin and Tazoult/Jbel Azourki salt walls thick Toarcian-Aalenian sequences formed wedge and hook structures as they adjusted to salt movement.[40] The Ikerzi diapir is surrounded by minibasins with contrasting facies, at the N the Takrakart minibasin hosts subtidal marine sediments, while the S M'Semrir minibasin shows more restricted intertidal deposits of the Azilal Formation. The last sequence, the Southern Atlassic Front represents a transition towards less halokinetically influenced settings, connecting the diapiric structures to broader sedimentary basins.[40]
The SE-verging Talmest allochthonous salt sheet formed due to regional slope and thinner Pliensbachian carbonates. The period also saw the development of a megaflap structure. Comparable diapirs exist in the Dead Sea, Red Sea (specially on Gubal Straits and Farasan Banks), and Gulf of Suez.[41] Charcoal remnants suggest coastal forests or mangroves existed nearby during wetter times.[42] The Talmest-Tazoult ridge and Amezraï minibasin locally evolved through varying subsidence phases, more rapid in Early Pliensbachian and Aalenian, separated by a quiescent Toarcian period. The Earliest Toarcian saw rapid "Amezraï Formation" deposition, triggering allochthonous salt sheets. Increased Toarcian sedimentation led to burial of Pliensbachian carbonates and calcite precipitation. Karstic sediments were replaced by dolomites from high-temperature Magnesium-rich fluids, while limited exchange occurred between the diapir flanks and core.[43] The Tazoult salt wall rise drove continued burial diagenesis. This structural evolution shaped the final depositional and diagenetic framework of the region.[44] The diapirs remained as emerged islands within shallow sea to lagoons during the deposition of the Tafraout Group, evidenced by decreasing deep water deposits towards them and with coral reefs and oolitic shoals forming near their walls.[21]
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Biota
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Color key
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Notes Uncertain or tentative taxa are in small text; |
Foraminifera
Phytoplankton
Ichnofossils
The tubes of serpulid worms are known from Jbel Toksine, in relation to the bivalve pavements.[37]
Porifera
Anthozoa
- In the Dadés-Assif Tafraout areas large Coral patch reefs rarely occur in the middle of the unit with associated echinodems (Sea urchin spines, Crinoid fragments) bivalves, gastropods, Bryozoa, Serpulidae annelids, branchiopods, solitary corals and algae.[7]
- The Ait Allal reef complex appears in the form of lenticular constructed masses (10 to 30 m long, 10 to 15 m wide and 3 to 4 m high) which pass laterally, towards the South East and the North East, to sandstone horizons.[13]
- The upper platform patch reefs in the Assif Tafraout area are hovewer 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][53]
- Massive reef pinnacles are recovered at Anergui and northern flank of Tassent (Imilchil), while rarer ones are known from Bou Zemou.[47][53]
Brachiopoda
Bivalves
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Gastropoda
Multiple Gastropodan faunas are know, specially associated with coral patch reefs, but lack proper studies.[7][63]
Ammonites
Crustacea
Beds with large accumulations of unidentified Ostracod valves on an endemic thin level of green marl are found at the Beni-Mellal area (Adoumaz and Col de Ghnim outcrops).[66][67]
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][11][20][36] In the Tagoudite Formation rare Ophiuroid impressions can be observed.[30]
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Actinopteri
Several scales and teeth of fishes are know from several locations, coming from freshwater/lagoonal layers.[68]
Theropoda
Indeterminate dinosaurian and other vertebrates are know from Mizaguène Hill, Taouja Ougourane, Aït Ouaridène, Oued Rzef and Jbel Remuai in the Azilal Province. Some of them are recovered in a "Bone bed" and others are associated with abundant plant remains.[69]
Sauropodomorpha
Viridiplantae
Paleosols in regions like Beni Mellal, Azilal, Wazzant or Toundoute show many plant roots (rhizoliths) and heavily disturbed layers.[81] In Toundoute cuticles dominated by fern and cycad leaflets were found along with wood debris resembling conifers of the families Pinaceae or Taxaceae.[33][82] Other plant remains include coal beds, leaflets, cuticles, rhizoliths, fossil wood and other indeterminate plant debris.[6]
Non studied rich floral assamblages include:
- Top of the Azilal 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, considered root fragments.[27]
- At Mizaguène Hill (Azilal) lenticular marno-conglomeratic sandstone levels filled with plant remains are found, maybe derived from a lagoon.[69]
- At Taquat N'Agrd the uppermost Tafraout Fm is capped by a +10 m succession of coal beds intercalated with limestones.[20]
- North of Jbel Akenzoud and partly impregnated and/or carbonized by malachite.[7]
- At Aguerd n'Igli the Tafraout Fm starts with sandstone marls with plants, and in upper sections includes bioclastic limestones-sandstones and green-yellow marls in color also rich in plant debris.[13]
- At Tizi n-M'Barek a carbonate bar on top of marls with associated plant debris and bivalves.[13]
- At Jebel Azourki and Jebel Toksine, woody plant debris, including shales with coal streaks, bioclastic limestones-sandstones rich in debris, charcoal and cuticle fragments suggests vegetation in a humid, marginal marine environment, maybe a salt marsh.[36][37]
- At M'Semrir Pass, samples dominated by Pollen have been recovered in the Tafraout and Azilal Fms.[14]
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.[51] This interval is numerically dominated by Classopollis, which usually accounts for more than 60.95% of the palynomorphs present.[51]
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See also
- Toarcian turnover
- Toarcian formations
- Aganane Formation, Morocco
- Calcaires du Bou Dahar, Morocco
- Marne di Monte Serrone, Italy
- Podpeč Limestone, Slovenia
- El Pedregal Formation, Spain
- Mizur Formation, North Caucasus
- Sachrang Formation, Austria
- Posidonia Shale, Lagerstätte in Germany
- Irlbach Sandstone, Germany
- Ciechocinek Formation, Germany and Poland
- Krempachy Marl Formation, Poland and Slovakia
- Djupadal Formation, Central Skane
- Lava Formation, Lithuania
- Whitby Mudstone, England
- Fernie Formation, Alberta and British Columbia
- Whiteaves Formation, British Columbia
- Navajo Sandstone, Utah
- Los Molles Formation, Argentina
- Mawson Formation, Antarctica
- Kandreho Formation, Madagascar
- Kota Formation, India
- Cattamarra Coal Measures, Australia
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References
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