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91-800: 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. 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. The region's structure comes from four main tectonic phases:

182-626: A carbonate-siliclastic regime. By the Middle Toarcian-Aalenian, the Azilal Formation expanded eastward, with isolated carbonates forming in the Amezraï basin, surrounded by terrigenous sediments. 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. Marine fossils like brachiopods and ammonites help date the sediment layers and confirm

273-412: A coastal platform. The formation is mainly made of sandstones, marls, and ooid limestones, different from older layers. Common fossils include bivalves, brachiopods, gastropods, corals, and echinoderms, with plant remains in some sandstones. The rocks formed in environments ranging from supratidal to subtidal, characterized by tropical conditions akin to those observed on Andros, Bahamas . The upper part of

364-618: A global value of around -3% to -4%. In addition, numerous smaller scale carbon isotope excursions are globally recorded on the falling limb of the larger negative δ C excursion. Although the PTo-E is not associated with a decrease in δ C analogous to the TOAE's, volcanism is nonetheless believed to have been responsible for its onset as well, with the carbon injection most likely having an isotopically heavy, mantle-derived origin. The Karoo-Ferrar magmatism released so much carbon dioxide that it disrupted

455-419: A higher diversity ecological assemblage of lycophytes , conifers , seed ferns , and wet-adapted ferns is observed in the palaeobotanical and palynological record over the course of the TOAE. The coincidence of the zenith of Classopolis and the decline of seed ferns and spore producing plants with increased mercury loading implicates heavy metal poisoning as a key contributor to the floristic crisis during

546-598: A large Mesozoic rift system. Triassic to Cretaceous layers are confined within basins, controlled by extensional rift structures. Sedimentation in these basins varied, with marine shales and limestones in the east and fluvial deposits in the west. Several tectonic events during the Triassic-Jurassic boundary reactivated normal faults, leading to the dominance of marls during the Middle Liassic to Toarcian. "Amezraï" Formation This formation, found in

637-492: A mitigating factor that ameliorated to a degree the oppressively anoxic conditions that were widespread across much of the Tethys. The enhanced hydrological cycle during early Toarcian warming caused lakes to grow in size. During the anoxic event, the Sichuan Basin was transformed into a giant lake, which was believed to be approximately thrice as large as modern-day Lake Superior . Lacustrine sediments deposited as

728-715: 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. Two main stages mark the area's evolution: during the Lower Toarcian, deposition patterns from

819-443: A proximal delivery area and the peak of the regression, with many microlagoons that formed between the large coral patch reefs are documented by micrite and partially leached micrite. 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

910-664: A result of this lake's existence are represented by the Da’anzhai Member of the Ziliujing Formation . Roughly ~460 gigatons (Gt) of organic carbon and ~1,200 Gt of inorganic carbon were likely sequestered by this lake over the course of the TOAE. The TOAE and the Palaeocene-Eocene Thermal Maximum have been proposed as analogues to modern anthropogenic global warming based on the comparable quantity of greenhouse gases released into

1001-674: A return to warmer conditions. The eastern and northeastern High Atlas saw the development of carbonate sedimentation, with reefs and marine fossils indicating tectonic activity during the Late Toarcian. The central High Atlas region features long diapirs and minibasins formed during early Jurassic rifting, with the Tazoult Ridge being a key example. Diapir movement shaped the surrounding rock layers, while local sedimentation reflects changes in climate, including wetter periods linked to increased erosion. Sharp geological boundaries mark

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1092-541: A shift to transgressive conditions even with the expansion of W continental facies. On the Amezraï Formation basin the fauna is composed by brachiopods such as Soaresirhynchia bouchardi , S. babtisrensis and Pseudogibbirhynchia jurensis that corroborate the Earliest Toarcian age for it and adjacent layers. Meanwhile, the presence of Aalenian ( Bradfordernsis-Murchinsonae ) Branchiopods in

1183-411: A sparse Pliensbachian marine vertebrate fossil record. The TOAE is suggested to have caused the extinction of various clades of dinosaurs, including coelophysids , dilophosaurids , and many basal sauropodomorph clades, as a consequence of the remodelling of terrestrial ecosystems caused by global climate change. Some heterodontosaurids and thyreophorans also perished in the extinction event. In

1274-468: A transition from icehouse to greenhouse conditions further retarded ocean circulation, aiding the establishment of anoxic conditions. Geochemical evidence from what was then the northwestern European epicontinental sea suggests that a shift from cooler, more saline water conditions to warmer, fresher conditions prompted the development of significant density stratification of the water column and induced anoxia. Extensive organic carbon burial induced by anoxia

1365-523: Is strongly fissured, particularly in a southerly direction. The Anti-Atlas area is a traditionally Berber region, inhabited by the Chleuh group. It is sparsely inhabited and there are no large cities in the area. The main town is Tafraoute , which has been described as "Morocco's Berber heartland". There are cave paintings in certain areas of the range. The eastern prolongation of the Anti-Atlas

1456-769: Is the Jbel Saghro range. The Jbel Sirwa is its northern prolongation, connecting with a section of the High Atlas range . The summit of Jbel Sirwa, of volcanic origin, reaches 3304 m. The Jbel Bani is a much lower range running along the southern side of the Anti Atlas. The basement rock of Africa (the African Plate ) was formed in the Precambrian , and is much older than the Atlas mountains. The Anti-Atlas range developed even later. A fraction of

1547-707: 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. 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

1638-653: The Azilal Formation coeval with Ammonites of the same age at the Ikerzi Area confirms the marine delimitation in the last stages of deposition. In the Azilal system, the "Tafraout Platform" saw a deepening towards the uppermost layers, teasing the transition to the Bin El Ouidane transgressive Carbonate Platform facies, while the lower sequences, with fine conglomerate layers and plant remains indicate

1729-648: The Alleghenian orogeny that also formed the Appalachians , formed when Gondwana (including Africa) and Euramerica (America) collided. There are indications they were once a chain of mountains far higher than the Himalayas are today. More recently, in the Paleogene and Neogene Periods (66 million to ~1.8 million years ago), the remaining mountain chains that today comprise the Atlas were uplifted as

1820-603: The Atlas Mountains in the northwest of Africa . The Anti-Atlas extends from the Atlantic Ocean in the southwest toward the northeast, to the heights of Ouarzazate and further east to the city of Tafilalt , altogether a distance of approximately 500 km. The range borders on the Sahara to the south. In some contexts, the Anti-Atlas is considered separate from the Atlas Mountains system, as

1911-606: The Avalonia microcontinent, the Anti-Atlas range formed in the Paleozoic ( c. 300 million years ago), as a result of continental collisions. North America, Europe and Africa were connected as part of two former continents , Euramerica and Gondwana , which ground against one another to create the former Central Pangean Mountains . Evidence shows that the Anti-Atlas Mountains were originally formed as part of

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2002-593: The Cleveland , West Netherlands, and South German Basins. Valdorbia, a site in the Umbria-Marche Apennines, also exhibited euxinia during the anoxic event. There is less evidence of euxinia outside the northwestern Tethys, and it likely only occurred transiently in basins in Panthalassa and the southwestern Tethys. Due to the clockwise circulation of the oceanic gyre in the western Tethys and

2093-645: The External Rif Chain . The Continental/Tidal Flat Azilal Formation , within this group, was deposited in coastal environments influenced by rivers, tidal flats, and paralic settings, rwith eworked material and in Toundoute unique interbedded Explosive eruption -type volcanic material, generally constituting more than half of the detrital components, showing clear carbonate recrystallization, suggesting that these fragments were still at high temperature during deposition and, therefore, contemporaneous with

2184-675: The Jenkyns Event , was an extinction event that occurred during the early part of the Toarcian age, approximately 183 million years ago, during the Early Jurassic . The extinction event had two main pulses, the first being the Pliensbachian-Toarcian boundary event ( PTo-E ). The second, larger pulse, the Toarcian Oceanic Anoxic Event ( TOAE ), was a global oceanic anoxic event , representing possibly

2275-517: The Karoo-Ferrar Large Igneous Province is generally attributed to have caused the surge in atmospheric carbon dioxide levels. Argon-argon dating of Karoo-Ferrar rhyolites points to a link between Karoo-Ferrar volcanism and the extinction event, a conclusion reinforced by uranium-lead dating and palaeomagnetism. Occurring during a broader, gradual positive carbon isotope excursion as measured by δ C values,

2366-764: 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 becames fully terrestrial/intertidal, at other areas like Beni Mellal , Dadès Gorges or Zaouiat Ahansal marine influences are seen in

2457-435: The elegantulum subzone of the serpentinum ammonite zone, during a marked, pronounced warming interval. The TOAE lasted for approximately 500,000 years, though a range of estimates from 200,000 to 1,000,000 years have also been given. The PTo-E primarily affected shallow water biota, while the TOAE was the more severe event for organisms living in deep water. Geological, isotopic, and palaeobotanical evidence suggests

2548-475: The mirabile subzone of the tenuicostatum ammonite zone, coinciding with a slight drop in oxygen concentrations and the beginning of warming following a late Pliensbachian cool period. This first pulse, occurring near the Pliensbachian-Toarcian boundary, is referred to as the PTo-E. The TOAE itself occurred near the tenuicostatum – serpentinum ammonite biozonal boundary, specifically in

2639-475: The Amezraï minibasin and linked to the Tazoult Ridge, dates to the Earliest Toarcian and is identified by brachiopod fossils. It includes sandstones, marls, and biodetrital or oolitic limestones, with layers varying from centimeters to up to 6 meters thick. The lower part consists of conglomerates, sandstones, and clays, transitioning to limestones and marls at the top. Ripple structures and cross-bedding are common in sandstone layers, while reworked horizons appear in

2730-632: The Azilal Province. Some of them are recovered in a " Bone bed " and others are associated with abundant plant remains. Marine, brackish or freshwater bony fish of the family Leptolepidae . Recovered from the Tagoudite Formation, represents a genus of cosmopolitan fish, common in the Toarcian Mediterranean area. Most specimens appear to come from lagoonal facies. Indeterminate Marine or brackish bony fish of

2821-401: The Early Toarcian diversity collapse. Belemnite richness in the northwestern Tethys dropped during the PTo-E but slightly increased across the TOAE. Belemnites underwent a major change in habitat preference from cold, deep waters to warm, shallow waters. Their average rostrum size also increased, though this trend heavily varied depending on the lineage of belemnites. The Toarcian extinction

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2912-563: The Hispanic Corridor into European seas after the extinction event, aided in their dispersal by higher sea levels. The TOAE had minor effects on marine reptiles, in stark contrast to the major impact it had on many clades of marine invertebrates. In fact, in the Southwest German Basin, ichthyosaur diversity was higher after the extinction interval, although this may be in part a sampling artefact resulting from

3003-410: The PTo-E and TOAE. In northeastern Panthalassa, in what is now British Columbia , euxinia dominated anoxic bottom waters. The early stages of the TOAE were accompanied by a decrease in the acidity of seawater following a substantial decrease prior to the TOAE. Seawater pH then dropped close to the middle of the event, strongly acidifying the oceans. The sudden decline of carbonate production during

3094-402: The TOAE is preceded by a global negative δ C excursion recognised in fossil wood, organic carbon, and carbonate carbon in the tenuicostatum ammonite zone of northwestern Europe, with this negative δ C shift being the result of volcanic discharge of light carbon. The global ubiquity of this negative δ C excursion has been called into question, however, due to its absence in certain deposits from

3185-402: The TOAE is widely believed to be the result of this abrupt episode of ocean acidification . Additionally, the enhanced recycling of phosphorus back into seawater as a result of high temperatures and low seawater pH inhibited its mineralisation into apatite, helping contribute to oceanic anoxia. The abundance of phosphorus in marine environments created a positive feedback loop whose consequence

3276-434: The TOAE, as shown by a positive δ S excursion in carbonate-associated sulphate occurs synchronously with the positive δ C excursion in carbonate carbon during the falciferum ammonite zone. This positive δ S excursion has been attributed to the depletion of isotopically light sulphur in the marine sulphate reservoir that resulted from microbial sulphur reduction in anoxic waters. Similar positive δ S excursions corresponding to

3367-466: The TOAE. Carbonate platforms collapsed during both the PTo-E and the TOAE. Enhanced continental weathering and nutrient runoff was the dominant driver of carbonate platform decline in the PTo-E, while the biggest culprits during the TOAE were heightened storm activity and a decrease in the pH of seawater. The recovery from the mass extinction among benthos commenced with the recolonisation of barren locales by opportunistic pioneer taxa. Benthic recovery

3458-445: The TOAE. Concentrations of phosphorus, magnesium, and manganese rose in the oceans. A -0.5% excursion in δ Ca provides further evidence of increased continental weathering. Osmium isotope ratios confirm further still a major increase in weathering. The enhanced continental weathering in turn led to increased eutrophication that helped drive the anoxic event in the oceans. Continual transport of continentally weathered nutrients into

3549-694: The TOAE; the increase in clastic sedimentation was synchronous with excursions in Os/ Os, Sr/ Sr, and δ Ca. Additionally, the Toarcian was punctuated by intervals of extensive kaolinite enrichment. These kaolinites correspond to negative oxygen isotope excursions and high Mg/Ca ratios and are thus reflective of climatic warming events that characterised much of the Toarcian. Likewise, illitic/smectitic clays were also common during this hyperthermal perturbation. The Intertropical Convergence Zone (ITCZ) migrated southwards across southern Gondwana, turning much of

3640-555: The Tafraout Group, the fossil record of units like the Azilal Formation is very restrictive compared to the marine coeval/underliying units like the Amezraï or Tafraout Formations. In the Dadés area Coral patch reefs rarely occur in the middle of the unit with associated echinodems ( Sea urchin spines, Crinoid fragments) lamellibranchs, gastropods, solitary corals and algae. Plant remains are very abundant in places such as

3731-431: The Toarcian mass extinction. Poisoning by mercury, along with chromium, copper, cadmium, arsenic, and lead is speculated to be responsible for heightened rates of spore malformation and dwarfism concomitant with enrichments in all these toxic metals. The TOAE was associated with widespread phosphatisation of marine fossils believed to result from the warming-induced increase in weathering that increased phosphate flux into

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3822-466: The abrupt warming interval associated with the TOAE. This global warming, driven by rising atmospheric carbon dioxide, was the mainspring of the early Toarcian environmental crisis. Carbon dioxide levels rose from about 500 ppm to about 1,000 ppm. Seawater warmed by anywhere between 3 °C and 7 °C, depending on latitude. At the height of this supergreenhouse interval, global sea surface temperatures (SSTs) averaged about 21 °C. The eruption of

3913-650: The approximate time intervals corresponding to the PTo-E and TOAE have likewise been invoked as tell-tale evidence of the ecological calamity's cause being a large igneous province, although some researchers attribute these elevated mercury levels to increased terrigenous flux. There is evidence that the motion of the African Plate suddenly changed in velocity, shifting from mostly northward movement to southward movement. Such shifts in plate motion are associated with similar large igneous provinces emplaced in other time intervals. A 2019 geochronological study found that

4004-517: The atmosphere in all three events. Some researchers argue that evidence for a major increase in Tethyan tropical cyclone intensity during the TOAE suggests that a similar increase in magnitude of tropical storms is bound to occur as a consequence of present climate change. Anti-Atlas The Anti-Atlas , also known as Lesser Atlas or Little Atlas , is a mountain range in Morocco , a part of

4095-700: The atmosphere. Carbon release via metamorphic heating of coal has been criticised as a major driver of the environmental perturbation, however, on the basis that coal transects themselves do not show the δ C excursions that would be expected if significant quantities of thermogenic methane were released, suggesting that much of the degassed emissions were either condensed as pyrolytic carbon or trapped as coalbed methane. In addition, possible associated release of deep sea methane clathrates has been potentially implicated as yet another cause of global warming. Episodic melting of methane clathrates dictated by Milankovitch cycles has been put forward as an explanation fitting

4186-1156: The bivalve pavements. The platform patch reefs in the Tafraout area are notable for their biodiversity, with some reaching heights of up to 40 m and lengths of up to 80 m, representing massive biostromes with a varied associated fossil assemblage, including bivalves, gastropods, echinoderm fragments, solitary corals, and bryozoans, found among the coral patchs. Massive reef pinnacles are recovered at Anergui and northern flank of Tassent, while rarer ones are know from Bou Zemou. Multiple Gasteropodan faunas are know, specially associated with coral patch reefs, but lack proper studies. 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. Several scales & teeth of fishes ( Lepidotes ?) are know from several locations, coming from freshwater/lagoonal layers. Indeterminate dinosaurian & other vertebrates are know from Mizaguène Hill, Taouja Ougourane, Aït Ouaridène, Oued Rzef & Jbel Remuai in

4277-417: The carbon cycle disruption. It has also been hypothesised that the release of cryospheric methane trapped in permafrost amplified the warming and its detrimental effects on marine life. Obliquity-paced carbon isotope excursions have been interpreted as some researchers as reflective of permafrost decline and consequent greenhouse gas release. The TOAE is believed to be the second largest anoxic event of

4368-682: 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. 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

4459-468: The closure of salt walls during diapir growth, and ancient environments here resembled modern shallow waters like the Red Sea . Charcoal remnants suggest coastal forests or mangroves existed during wetter times. the Pliensbachian-Toarcian interval. Tasmanites Cysts A member of Prasinophyceae . The presence of this genus indicates fresh or brackish water inputs in the depositional environment In

4550-473: The distances between one village and another are great, without any human presence in between. There are Neolithic cave paintings in certain areas of the range. The landscape of the Anti-Atlas is marked by picturesque kasbah (small castles) in many places in the region. During former times, the kasbah was important as a place of shelter and as a supply depot for kinsmen. Close to these settlements, terraced fields with dry-stone retaining walls cover

4641-541: The earlier Pliensbachian continued, followed by terrigenous materials filling the basins and stopping temporally the carbonate production. 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

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4732-684: The emplacement of the Karoo-Ferrar large igneous province and the TOAE were not causally linked, and simply happened to occur rather close in time, contradicting mainstream interpretations of the TOAE. The authors of the study conclude that the timeline of the TOAE does not match up with the course of activity of the Karoo-Ferrar magmatic event. The large igneous province also intruded into coal seams, releasing even more carbon dioxide and methane than it otherwise would have. Magmatic sills are also known to have intruded into shales rich in organic carbon, causing additional venting of carbon dioxide into

4823-535: The family Leptolepidae. The vegetation in the Toundoute area is compared to that of the Isle of Pines . Paleosols in these regions show many plant roots ( Rhizoliths ) and heavily disturbed layers. Plant remains include coal, leaves, woody roots, rhizoliths, fossil wood, and other plant debris. In Toundoute, small plant fragments, mostly fern leaflets and some cycad leaves, were found, with wood debris resembling conifers like Pinaceae or Taxaceae. Ferns seem to have dominated

4914-662: The fluvial-washed sediments take place in a E-NE direction, being moved to the layers of the Amezräi, Tagoudite & Tafraout Formations and other coeval marine units, as well are found on fluviatile channels inside the own rocks of this unit. The Azilal Formation also saw high plant activity, with remains such as wood, charcoal, and rhizoliths, indicating nearby vegetated soils. Fluvial systems transported sediment from Paleozoic and Triassic sources, with volcanic material also present, suggesting active volcanic processes during deposition. The warm, alternating wet and dry climate led to

5005-810: The formation of soils with calcareous nodules and gypsum in arid zones, particularly in areas like Toundoute and Telouet. During the Lower Toarcian, a shift to siliciclastic deposits occurred, marked by storm events and increased plant debris, indicating a warm, humid climate. Some areas, especially near the coast, resembled modern Sabkha (like those in the Persian Gulf ). The Tafraout Formation , meanwhile, represented marginal marine environments with diverse marine fauna, including coral reefs and "lithiotid" ( Plicatostylidae aberrant reef-forming) bivalves. The Toarcian Oceanic Anoxic Event (T-OAE) intensified Tropical storms , destroying older carbonate platforms and increasing siliciclastic deposits, which contributed to

5096-520: The formation of the Tafrout environment. Additionally, after the T-OAE, ecosystems in areas like Jebel Toksine began to recover with new carbonate activity and diverse marine life, including bivalves and other reef organisms. The aftermath of the T-OAE is visible in the lower Azilal Formation, showing a slow recovery of marine environments. There is also evidence of a Middle Toarcian cold snap, followed by

5187-464: 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. Tagoudite Formation The Tagoudite Formation marks a major shift in Liassic sedimentation, replacing

5278-459: The imprint of the 9 Myr long-term carbon cycle that was otherwise steady and stable during the Jurassic and Early Cretaceous. The values of Os/ Os rose from ~0.40 to ~0.53 during the PTo-E and from ~0.42 to ~0.68 during the TOAE, and many scholars conclude this change in osmium isotope ratios evidences the responsibility of this large igneous province for the biotic crises. Mercury anomalies from

5369-545: The land masses of Europe and Africa collided at the southern end of the Iberian Peninsula . Erosion continued to reduce the Anti-Atlas range so that it is today less massive than the High Atlas range to the north. In the Anti-Atlas, the precipitation annually is typically below 200 mm, while the climatic conditions on the north and west slopes are locally more wet and agriculturally favorable. Climatically,

5460-562: The last 300 Ma, and possibly the largest of the Phanerozoic. A positive δ C excursion, likely resulting from the mass burial of organic carbon during the anoxic event, is known from the falciferum ammonite zone, chemostratigraphically identifying the TOAE. Large igneous province resulted in increased silicate weathering and an acceleration of the hydrological cycle , as shown by a increased amount of terrestrially derived organic matter found in sedimentary rocks of marine origin during

5551-414: The late Pliensbachian was an icehouse period. These ice sheets are believed to have been thin and stretched into lower latitudes, making them extremely sensitive to temperature changes. A warming trend lasting from the latest Pliensbachian to the earliest Toarcian was interrupted by a "cold snap" in the middle polymorphum zone, equivalent to the tenuicostatum ammonite zone, which was then followed by

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5642-582: The limestone. The formation reflects a subtidal to supratidal environment, with some layers suggesting lagoonal conditions and reduced carbonate content compared to older formations. Local tectonic activity, mainly due to seismic events in the Tethyan region, influenced the formation, causing erosion of older Paleozoic layers. Azilal Formation Tafraout Formation The Tafraout Formation consists of oolitic and biodetrital limestones with cross-stratifications, found in channels and bars, alongside greenish marls and micro-conglomerates. These layers were deposited on

5733-404: The methane released from ocean sediments was rapidly sequestered, buffering its ability to act as a major positive feedback, and that methane clathrate dissociation occurred too late to have had an appreciable causal impact on the extinction event. Hypothetical release of methane clathrates extremely depleted in heavy carbon isotopes has furthermore been considered unnecessary as an explanation for

5824-415: The most dire crises in their evolutionary history. Brachiopod taxa of large size declined significantly in abundance. Uniquely, the brachiopod genus Soaresirhynchia thrived during the later stages of the TOAE due to its low metabolic rate and slow rate of growth, making it a disaster taxon . The species S. bouchardi is known to have been a pioneer species that colonised areas denuded of brachiopods in

5915-515: The most extreme case of widespread ocean deoxygenation in the entire Phanerozoic eon. In addition to the PTo-E and TOAE, there were multiple other, smaller extinction pulses within this span of time. Occurring during the supergreenhouse climate of the Early Toarcian Thermal Maximum (ETTM), the Early Toarcian extinction was associated with large igneous province volcanism, which elevated global temperatures, acidified

6006-526: The mountains are separated from the Mediterranean 's influence by the High Atlas to its north, and therefore they belong to the Saharan climate zone. The driest area is the Jbel Saghro . In the least dry areas to the west and the north, much of the land is covered with thyme , rosemary and other drought tolerant plants, such as argan . The quilt-like cover is endangered by overgrazing , and in

6097-503: 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). The tubes of serpulid worms are known from Jbel Toksine, in relation to

6188-478: The northwestern Tethyan region. Ostracods also suffered a major diversity loss, with almost all ostracod clades’ distributions during the time interval corresponding to the serpentinum zone shifting towards higher latitudes to escape intolerably hot conditions near the Equator. Bivalves likewise experienced a significant turnover. The decline of bivalves exhibiting high endemism with narrow geographic ranges

6279-440: The observed shifts in the carbon isotope record. Other studies contradict and reject the methane hydrate hypothesis, however, concluding that the isotopic record is too incomplete to conclusively attribute the isotopic excursion to methane hydrate dissociation, that carbon isotope ratios in belemnites and bulk carbonates are incongruent with the isotopic signature expected from a massive release of methane clathrates, that much of

6370-468: The ocean enabled high levels of primary productivity to be maintained over the course of the TOAE. Rising sea levels contributed to ocean deoxygenation; as rising sea levels inundated low-lying lands, organic plant matter was transported outwards into the ocean. An alternate model for the development of anoxia is that epicontinental seaways became salinity stratified with strong haloclines , chemoclines , and thermoclines . This caused mineralised carbon on

6461-585: The ocean. This produced exquisitely preserved lagerstätten across the world, such as Ya Ha Tinda, Strawberry Bank, and the Posidonia Shale . As is common during anoxic events, black shale deposition was widespread during the deoxygenation events of the Toarcian. Toarcian anoxia was responsible for the deposition of commercially extracted oil shales, particularly in China. Enhanced hydrological cycling caused clastic sedimentation to accelerate during

6552-476: The oceans, and prompted the development of anoxia, leading to severe biodiversity loss. The biogeochemical crisis is documented by a high amplitude negative carbon isotope excursions, as well as black shale deposition. The Early Toarcian extinction event occurred in two distinct pulses, with the first event being classified by some authors as its own event unrelated to the more extreme second event. The first, more recently identified pulse occurred during

6643-566: The onset of TOAE are known from pyrites in the Sakahogi and Sakuraguchi-dani localities in Japan, with the Sakahogi site displaying a less extreme but still significant pyritic positive δ S excursion during the PTo-E. Euxinia is further evidenced by enhanced pyrite burial in Zázrivá, Slovakia, enhanced molybdenum burial totalling about 41 Gt of molybdenum, and δ Mo excursions observed in sites in

6734-499: 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.   Toarcian Oceanic Anoxic Event The Toarcian extinction event , also called the Pliensbachian-Toarcian extinction event , the Early Toarcian mass extinction , the Early Toarcian palaeoenvironmental crisis , or

6825-466: 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. 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

6916-519: The prefix "anti" (i.e. opposite) implies. The summits of the Anti-Atlas reach average heights of 2,500–2,700 m (8,200–8,900 ft), with a few peaks reaching higher. To the north lies a plateau at 1700–1800 m in height. To the south lie the Sahara highlands at approximately 700 m. On the heights of Ouarzazate , the massif is cut through by the Draa valley , opening towards the south. The range

7007-633: The region more arid. This aridification was interrupted, however, in the spinatus ammonite biozone and across the Pliensbachian-Toarcian boundary itself. The large rise in sea levels resulting from the intense global warming led to the formation of the Laurasian Seaway, which enabled the flow of cool water low in salt content to flow into the Tethys Ocean from the Arctic Ocean . The opening of this seaway may have potentially acted as

7098-458: The rough, uneven bathymetry in the northward limb of this gyre, oxic bottom waters had relatively few impediments to diffuse into the southwestern Tethys, which spared it from the far greater prevalence of anoxia and euxinia that characterised the northern Tethys. The Panthalassan deep water site of Sakahogi was mainly anoxic-ferruginous across the interval spanning the late Pliensbachian to the TOAE, but transient sulphidic conditions did occur during

7189-498: The seafloor to be recycled back into the photic zone, driving widespread primary productivity and in turn anoxia. The freshening of the Arctic Ocean by way of melting of Northern Hemisphere ice caps was a likely trigger of such stratification and a slowdown of global thermohaline circulation. Stratification also occurred due to the freshening of surface water caused by an enhanced water cycle. Rising seawater temperatures amidst

7280-442: The sedimentation, probably as a result of early activity in the local South-Atlasic Fault. Fauna, including rare brachiopods and bivalves, alongside sedimentary features like ripple marks and rain imprints, indicate a mix of marine and continental conditions, with evidence of emersions. The environment shifted from coastal facies in the north to fluvial facies in the south, and tectonic activity affected sediment deposition. The flow of

7371-489: The south little but thorn shrubs remain. The transition to the desert is gradual towards the south. The Moroccan citron is cultivated there, and used as Etrog in Jewish rituals. The Anti-Atlas area is a traditionally Berber region, inhabited by the Chleuh group. It is sparsely inhabited and there are no large cities in the area. The main town is Tafraoute , which has been described as "Morocco's Berber heartland." Often

7462-657: The time, such as the Bächental bituminous marls, though its occurrence in areas like Greece has been cited as evidence of its global nature. The negative δ C shift is also known from the Arabian Peninsula , the Ordos Basin , and the Neuquén Basin . The negative δ C excursion has been found to be up to -8% in bulk organic and carbonate carbon, although analysis of compound specific biomarkers suggests

7553-704: The transition from marine to expansive E terrestrial environments during the Middle Toarcian. The deposition starts with a marked break of the Carbonate production and a major regression in the Lowermost Toarcian, then oscilated Transgresive/Regresive cycles in the Laevisoni-Bifrons substages, followed finally by a post Bifrons major regression and full return to the Carbonate production. The Tafraout Platform deepened over time, signaling

7644-494: The vegetation, likely in wetlands, followed by cycads and conifers. Similar plants have been found in Egypt's Mashabba Formation . At Jebel Toksine, woody plant debris, including charcoal, suggests vegetation in a humid, marginal marine environment. Jebel Azourki has layers of shales with coal streaks and plant fragments, possibly representing a marsh in a lagoon area. Phytoclasts, spores, pollen and Tasmanites algae indicate that

7735-405: The wake of the extinction event, many derived clades of ornithischians, sauropods, and theropods emerged, with most of these post-extinction clades greatly increasing in size relative to dinosaurs before the TOAE. Eusauropods were propelled to ecological dominance after their survival of the Toarcian cataclysm. Megalosaurids experienced a diversification event in the latter part of the Toarcian that

7826-472: Was a negative feedback loop retarding the otherwise pronounced warming and may have caused global cooling in the aftermath of the TOAE. In anoxic and euxinic marine basins in Europe, organic carbon burial rates increased by ~500%. Furthermore, anoxia was not limited to oceans; large lakes also experienced oxygen depletion and black shale deposition. Euxinia occurred in the northwestern Tethys Ocean during

7917-615: Was particularly severe. At Ya Ha Tinda, a replacement of the pre-TOAE bivalve assemblage by a smaller, post-TOAE assemblage occurred, while in the Cleveland Basin , the inoceramid Pseudomytiloides dubius experienced the Lilliput effect . Ammonoids , having already experienced a major morphological bottleneck thanks to the Gibbosus Event, about a million years before the Toarcian extinction, suffered further losses in

8008-519: Was possibly a post-extinction radiation that filled niches vacated by the mass death of the Early Toarcian extinction. Insects may have experienced blooms as fish moved en masse to surface waters to escape anoxia and then died in droves due to limited resources. The volcanogenic extinction event initially impacted terrestrial ecosystems more severely than marine ones. A shift towards a low diversity assemblage of cheirolepid conifers, cycads , and Cerebropollenites -producers adapted for high aridity from

8099-597: Was slow and sluggish, being regularly set back thanks to recurrent episodes of oxygen depletion, which continued for hundreds of thousands of years after the main extinction interval. Evidence from the Cleveland Basin suggests it took ~7 Myr for the marine benthos to recover, on par with the Permian-Triassic extinction event . Many marine invertebrate taxa found in South America migrated through

8190-405: Was the further exacerbation of eutrophication and anoxia. The extreme and rapid global warming at the start of the Toarcian promoted intensification of tropical storms across the globe. The extinction event associated with the TOAE primarily affected marine life as a result the collapse of the carbonate factory. Brachiopods were particularly severely hit, with the TOAE representing one of

8281-582: Was unbelievably catastrophic for corals ; 90.9% of all Tethyan coral species and 49% of all genera were wiped out. Calcareous nannoplankton that lived in the deep photic zone suffered, with the decrease in abundance of the taxon Mitrolithus jansae used as an indicator of shoaling of the oxygen minimum zone in the Tethys and the Hispanic Corridor. Other affected invertebrate groups included echinoderms , radiolarians , dinoflagellates , and foraminifera . Trace fossils , an indicator of bioturbation and ecological diversity, became highly undiverse following

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