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Phanerozoic Tethys region (view source)

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In the Tethys region, the evolution of North Africa and the Arabian Plates are intimately involved with the occurrence of hydrocarbons in both regions. In the Early Paleozoic, paleogeography was characterized by the breakup of Rodinia and by the re-arrangement of the major continental plates in the Pangea supercontinent. During the assemblage of Pangea, a major role was played by the transformation from Pangea B to Pangea A during Permian time by means of dextral motion of Laurasia relative to Gondwana, which changed the relative position of the Paleozoic and Mesozoic domains facing the east-west oriented Tethys Gulf ~~(Muttoni et al., 2009a, b)~~.

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In the Tethys region, the evolution of North Africa and the Arabian Plates are intimately involved with the occurrence of hydrocarbons in both regions. In the Early Paleozoic, paleogeography was characterized by the breakup of Rodinia and by the re-arrangement of the major continental plates in the Pangea supercontinent. During the assemblage of Pangea, a major role was played by the transformation from Pangea B to Pangea A during Permian time by means of dextral motion of Laurasia relative to Gondwana, which changed the relative position of the Paleozoic and Mesozoic domains facing the east-west oriented Tethys Gulf.<ref name=Muttonietal_2009a /> <ref name=Muttonietal_2009b />

Since late Paleozoic time, the southern margin of the Tethys was affected by the time-transgressive opening of the Neo-Tethys, which gave origin to a complex mosaic of peri-Gondwanan terranes. They gradually collided, during Mesozoic and Cenozoic times, with the northern margin of the Tethys, as the oceanic lithosphere of the Paleo-Tethys Ocean was subducted below Laurasia. Collisions were distributed irregularly along the northern margin of the Tethys. The spreading of the Neo-Tethys balanced the subduction of the oceanic lithosphere along the northern margin of the Paleo-Tethys, preserving the Tethys Ocean until the beginning of Cenozoic time. The subduction of the Paleo-Tethys led to the accretion of microplates that today characterize the Middle East outside of Arabia. Accretion started in Triassic time with the Cimmerian orogeny and persisted up to today, with the collision of Arabia along the Zagros suture. The present day relationships among orogenic belts are further complicated by the presence of important strike-slip movements, which accommodated the different convergence rates among plates, from the Alps to the Himalayas.

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Late Ordovician paleogeography ([[:file:M106Ch01Fig03.jpg|Figure 3]]) is represented by Cocks and Torsvick,<ref name=Cocksandtorsvik_2002 /> Robardet,<ref name=Robardet_2003>Robardet, M., 2003, The Armorica “microplate": Fact or fiction? Critical review of the concept and contradictory palaeobiogeographical data: Palaeoeography, Palaeoclimatology, Palaeoecology, v. 195, p. 125–148.</ref> and Ruban et al.,<ref name=Rubanetal_2007>Ruban, D. A., Al-Husseini, M. I., and Yumiko, I., 2007, Review of Middle East Palaeozoic plate tectonics: GeoArabia, v. 12, no. 3, p. 35–56.</ref> and shows that most continental blocks/terranes were located in the southern hemisphere except for Siberia and Tarim, which were entirely within the northern hemisphere. South China lay across the equator. The major oceans were not too large to prevent biotic exchange; thus the biota is quite cosmopolitan.

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The collision of Avalonia and Baltica occurred during Late Ordovician time, as documented by paleomagnetic, tectonic, isotope, and faunal data.<ref name=Cocksandtorsvik_2002 /> <ref name=Robardet_2003 /> Baltica, after the accretion of Avalonia, was positioned at intermediate latitudes NW of the Northern Gondwana margin and could have deflected the South Equatorial current southward. The Iapetus Oceanic lithosphere was subducting beneath the Laurentian active margin and its width was decreasing. The Rheic Ocean was several thousands of km wide with Perunica in the northern part, having probably detached from NW Gondwana in mid-Ordovician time. According to von Raumer and Stampfli,<ref name=Vonraumerandstampfli_2008 /> the Rheic Ocean was subducting beneath the Peri-Gondwanan blocks placed along the northern margin of Gondwana. The Panthalassic Ocean was very large and mostly covered the northern hemisphere. Cocks and Torsvik<ref name=Cocksandtorsvik_2002 /> suggest this ocean was comparable in size to today’s Pacific. Peri-Gondwanan blocks were located along the Gondwanan margin at high to intermediate southern latitudes. However, some faunal data ~~(e.g., Villas et al.~~<ref name=Villasetal_2002>Villas, E., Hammann, W., and Harper, D. A. T., 2002, Foliomena fauna (Brachiopoda) from the Upper Ordovician of Sardinia: Palaeontology, v. 45, p. 267–295.</ref>) suggest lower latitudes, as well as the existence of peripheral blocks detaching from North Gondwana. The position and the architecture of the Armorica composite plate is still discussed ~~(e.g~~.~~, Robardet~~<ref name=Robardet_2003 />). Nysæther et al.<ref name=Nysætheretal_2002 /> suggested that by the Late Ordovician, it is possible that part of Armorica had rifted off the NW Gondwanan margin; however, Robardet<ref name=Robardet_2003 /> casted doubts on the reliability of the paleomagnetic data on which the evolution of the Armorica was based and proposed a different scenario in which the southern European blocks remained attached to the northern Gondwanan margin from Ordovician to Devonian<ref name=Robardet_2003 /> ([[:file:M106Ch01Fig09.jpg|Figure 9]]).

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The collision of Avalonia and Baltica occurred during Late Ordovician time, as documented by paleomagnetic, tectonic, isotope, and faunal data.<ref name=Cocksandtorsvik_2002 /> <ref name=Robardet_2003 /> Baltica, after the accretion of Avalonia, was positioned at intermediate latitudes NW of the Northern Gondwana margin and could have deflected the South Equatorial current southward. The Iapetus Oceanic lithosphere was subducting beneath the Laurentian active margin and its width was decreasing. The Rheic Ocean was several thousands of km wide with Perunica in the northern part, having probably detached from NW Gondwana in mid-Ordovician time. According to von Raumer and Stampfli,<ref name=Vonraumerandstampfli_2008 /> the Rheic Ocean was subducting beneath the Peri-Gondwanan blocks placed along the northern margin of Gondwana. The Panthalassic Ocean was very large and mostly covered the northern hemisphere. Cocks and Torsvik<ref name=Cocksandtorsvik_2002 /> suggest this ocean was comparable in size to today’s Pacific. Peri-Gondwanan blocks were located along the Gondwanan margin at high to intermediate southern latitudes. However, some faunal data<ref name=Villasetal_2002>Villas, E., Hammann, W., and Harper, D. A. T., 2002, Foliomena fauna (Brachiopoda) from the Upper Ordovician of Sardinia: Palaeontology, v. 45, p. 267–295.</ref> suggest lower latitudes, as well as the existence of peripheral blocks detaching from North Gondwana. The position and the architecture of the Armorica composite plate is still discussed.<ref name=Robardet_2003 /> Nysæther et al.<ref name=Nysætheretal_2002 /> suggested that by the Late Ordovician, it is possible that part of Armorica had rifted off the NW Gondwanan margin; however, Robardet<ref name=Robardet_2003 /> casted doubts on the reliability of the paleomagnetic data on which the evolution of the Armorica was based and proposed a different scenario in which the southern European blocks remained attached to the northern Gondwanan margin from Ordovician to Devonian<ref name=Robardet_2003 /> ([[:file:M106Ch01Fig09.jpg|Figure 9]]).

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Global climate deteriorated at the end of Ordovician time, resulting in the Hirnantian glacial episode. The glaciation is documented by sedimentary evidence and isotopic data<ref name=Brenchleyetal_1994>Brenchley, P. J., Marshall, J. D., Carden, G. A. C., et al., 1994. Bathymetric and isotopic evidence for a short-lived Ordovician glaciation in a greenhouse period: Geology, v. 22, p. 295–298.</ref> and lasted about 0.5–1 million years. Peri-Gondwanan and Gondwanan glacial deposits occur in North Africa (where a N-S high was present in Egypt<ref name=Schandelmeierandreynolds_1997>Schandelmeier, H. and Reynolds, P. O., eds., 1997, Palaeogeographic-palaeotectonic atlas of north-eastern Africa, Arabia, and adjacent areas: Balkema, Rotterdam, 160 p. 17 pls.</ref>), South America, Arabia, and South Africa, and periglacial features are known also from Armorica and Avalonia. Several interpretations have been offered on the distribution of the ice caps during the Hirnantian glaciation (a single large ice cap vs. a number of smaller ice caps), as summarized in Veevers.<ref name=Veevers_2004 /> This glaciation followed a period of climatic amelioration along the Northern Gondwana margin, evidenced by deposition of temperate bioclastic limestones and pelmatozoan-bryozoan mud-mounds, which overlie a very thick terrigenous succession of Early-Middle Ordovician age. The change from pre-Hirnantian “greenhouse” climates to Hirnantian “icehouse” conditions was rapid and was not preceded by any climatic fluctuations, which might have helped acclimatize the biota to the climate change.<ref name=Brenchleyetal_1994 /> If the pre-Hirnantian benthos was widespread in epicontinental seas and inland basins, the Hirnantian shelly fauna ~~(e.g., Sutcliffe et al.;~~<ref name=Sutcliffeetal_2001>Sutcliffe, O. E., Harper, D. A. T., Salem, A. A., Whittington, R. J., and Craig, J., 2001, The development of an atypical Hirnantia-brachiopod Fauna and the onset of glaciation in the late Ordovician of Gondwana. Transactions of the Royal Society of Edinburgh: Earth Sciences, v. 92, p. 1–14.</ref> ~~Jin and Copper~~<ref name=Jinandcopper_2008>Jin, J., and Copper P., 2008, Response of brachiopod communities to environmental change during the Late Ordovian mass extinction interval, Anticosti Island, eastern Canada: Fossils and Strata, v. 54, p. 41–52.</ref>) was mostly restricted to the continental margins, due to the sea-level drop caused by the glaciations in the latest Ordovician. The Hirnantian glaciation seems to have occurred during times of very high levels of the greenhouse gas CO2 (14–18 times the present atmospheric value). Brenchley et al.<ref name=Brenchleyetal_1994 /> considered that the onset of glaciation was the result of an early Hirnantian increment in burial rates of organic carbon acting as a major sink for the atmospheric CO2. However, according to Villas et al.,<ref name=Villasetal_2002>Villas, E., Hammann, W., and Harper, D. A. T., 2002, Foliomena fauna (Brachiopoda) from the Upper Ordovician of Sardinia: Palaeontology, v. 45, p. 267–295.</ref> the accumulation of great volumes of carbonates in the pre-Hirnantian late Ordovician served as the sink of the atmospheric CO2. At the end of the Hirnantian, the ice cap melting caused a rapid, eustatic sea-level rise and the development of low-oxygen conditions on the shelves.<ref name=Rongandharper_1988>Rong, J.-Y., and Harper, D. A. T., 1988, A global synthesis of the latest Ordovician Hirnantian brachiopod faunas: Transactions of the Royal Society of Edinburgh Earth v. 79, p. 383–402.</ref> <ref name=Owenandrobertson_1995>Owen, A. W., and Robertson, D. B. R., 1995, Ecological changes during the end-Ordovician extinction: Modern Geology, v. 20, p. 21–39.</ref> The end of the glaciation was followed by the deposition of organic-rich shales (Lower Silurian “hot shales”) which represent the most important source rocks in North Africa and one of the major in the Arabian peninsula.<ref name=Luningetal_2000>Luning, S., Craig, J., Loydell, D. K., Storch, P. B., and Fitches B., 2000, Lower Silurian ‘hot shales’ in North Africa and Arabia: Regional distribution and depositional model: Earth Science Review, v. 49, p. 121–200.</ref>

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Global climate deteriorated at the end of Ordovician time, resulting in the Hirnantian glacial episode. The glaciation is documented by sedimentary evidence and isotopic data<ref name=Brenchleyetal_1994>Brenchley, P. J., Marshall, J. D., Carden, G. A. C., et al., 1994. Bathymetric and isotopic evidence for a short-lived Ordovician glaciation in a greenhouse period: Geology, v. 22, p. 295–298.</ref> and lasted about 0.5–1 million years. Peri-Gondwanan and Gondwanan glacial deposits occur in North Africa (where a N-S high was present in Egypt<ref name=Schandelmeierandreynolds_1997>Schandelmeier, H. and Reynolds, P. O., eds., 1997, Palaeogeographic-palaeotectonic atlas of north-eastern Africa, Arabia, and adjacent areas: Balkema, Rotterdam, 160 p. 17 pls.</ref>), South America, Arabia, and South Africa, and periglacial features are known also from Armorica and Avalonia. Several interpretations have been offered on the distribution of the ice caps during the Hirnantian glaciation (a single large ice cap vs. a number of smaller ice caps), as summarized in Veevers.<ref name=Veevers_2004 /> This glaciation followed a period of climatic amelioration along the Northern Gondwana margin, evidenced by deposition of temperate bioclastic limestones and pelmatozoan-bryozoan mud-mounds, which overlie a very thick terrigenous succession of Early-Middle Ordovician age. The change from pre-Hirnantian “greenhouse” climates to Hirnantian “icehouse” conditions was rapid and was not preceded by any climatic fluctuations, which might have helped acclimatize the biota to the climate change.<ref name=Brenchleyetal_1994 /> If the pre-Hirnantian benthos was widespread in epicontinental seas and inland basins, the Hirnantian shelly fauna<ref name=Sutcliffeetal_2001>Sutcliffe, O. E., Harper, D. A. T., Salem, A. A., Whittington, R. J., and Craig, J., 2001, The development of an atypical Hirnantia-brachiopod Fauna and the onset of glaciation in the late Ordovician of Gondwana. Transactions of the Royal Society of Edinburgh: Earth Sciences, v. 92, p. 1–14.</ref> <ref name=Jinandcopper_2008>Jin, J., and Copper P., 2008, Response of brachiopod communities to environmental change during the Late Ordovian mass extinction interval, Anticosti Island, eastern Canada: Fossils and Strata, v. 54, p. 41–52.</ref> was mostly restricted to the continental margins, due to the sea-level drop caused by the glaciations in the latest Ordovician. The Hirnantian glaciation seems to have occurred during times of very high levels of the greenhouse gas CO2 (14–18 times the present atmospheric value). Brenchley et al.<ref name=Brenchleyetal_1994 /> considered that the onset of glaciation was the result of an early Hirnantian increment in burial rates of organic carbon acting as a major sink for the atmospheric CO2. However, according to Villas et al.,<ref name=Villasetal_2002>Villas, E., Hammann, W., and Harper, D. A. T., 2002, Foliomena fauna (Brachiopoda) from the Upper Ordovician of Sardinia: Palaeontology, v. 45, p. 267–295.</ref> the accumulation of great volumes of carbonates in the pre-Hirnantian late Ordovician served as the sink of the atmospheric CO2. At the end of the Hirnantian, the ice cap melting caused a rapid, eustatic sea-level rise and the development of low-oxygen conditions on the shelves.<ref name=Rongandharper_1988>Rong, J.-Y., and Harper, D. A. T., 1988, A global synthesis of the latest Ordovician Hirnantian brachiopod faunas: Transactions of the Royal Society of Edinburgh Earth v. 79, p. 383–402.</ref> <ref name=Owenandrobertson_1995>Owen, A. W., and Robertson, D. B. R., 1995, Ecological changes during the end-Ordovician extinction: Modern Geology, v. 20, p. 21–39.</ref> The end of the glaciation was followed by the deposition of organic-rich shales (Lower Silurian “hot shales”) which represent the most important source rocks in North Africa and one of the major in the Arabian peninsula.<ref name=Luningetal_2000>Luning, S., Craig, J., Loydell, D. K., Storch, P. B., and Fitches B., 2000, Lower Silurian ‘hot shales’ in North Africa and Arabia: Regional distribution and depositional model: Earth Science Review, v. 49, p. 121–200.</ref>

A very important event at the end of the Ordovician was the first of the Big Five Mass Extinctions<ref name=Raupandsepkoski_1982>Raup, D. M., and Sepkoski, J. J., 1982, Mass extinctions in the marine fossil record: Science, v. 215, p. 1501–1503.</ref> of the Phanerozoic, with disappearance of 85% of species, 61% of genera, and 12–24% of families.<ref name=Sepkoski_1997>Sepkoski, J. J., 1997, Biodiversity: Past, present, and future: Journal of Paleontology, v. 71, p. 533–539.</ref> The close correlation between the Ordovician extinction and the glaciation suggests climatic change as the proximate cause. However, the extinction was probably a complex event.<ref name=Brenchleyetal_1995>Brenchley, P. J., Carden, G. A. F., and Marshall, J. D., 1995, Environmental changes associated with the “first strike” of the late Ordovician mass extinction: Modern Geology, v. 20, p. 69–82.</ref> A sea-level fall and rise, changes in oceanic structure,<ref name=Wildeandberry_1984>Wilde, P., and Berry, W. B. N., 1984, Destabilization of the oceanic density structure and its significance to marine ‘extinction’ events: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 48, p. 143–162.</ref> nutrient fluxes,<ref name=Brenchleyetal_1995 /> and development of anoxia<ref name=Fortey_1989>

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===Early Devonian (about 400 Ma)===

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During Early Devonian time Gondwana was centered on the Southern Pole, with northern Africa and Antarctica located toward the equator ([[:file:M106Ch01Fig04.jpg|Figure 4]]). The continental plates that would form future Laurasia were located immediately to the south of the equator, so that most of the continental masses were in the southern hemisphere. The Iapetus Ocean had been closed by the collision between North America and Baltica, giving rise to the Caledonian orogeny. The Avalonia Ocean between southern England and Scotland was still present, and other minor oceanic seaways separated different blocks. These blocks would later form the components of Europe, assembled during the Carboniferous Variscan orogeny, with the closure of the Rheic Ocean. The width of the Rheic Ocean is still questioned, but the paleobiogeographic distribution of different groups of fossil organisms between Laurasia and Gondwana suggests that this ocean was relatively narrow during Early Devonian.<ref name=Wehrmannetal_2010>Wehrmann, A. et al., 2010, Devonian shallow-water sequences from the North Gondwana coastal margin (central and eastern Taurides, Turkey): Sedimentology, facies and global events: Gondwana Research, v. 17, p. 546–560.</ref> The Paleo-Tethys Ocean was opening along northern Gondwana, generating a fringe of microplates (e.g., Armorica, Adria, Pontides, Hellenic, and Moesia terranes). We follow the interpretation of Torsvik and Cocks,<ref name=Torsvikandcocks_2004>Torsvik, T. H., and Cocks, L. R. M., 2004, Earth geography from 400 to 250 Ma: A palaeomagnetic, faunal and facies review: Journal of the GSL v. 161, p. 555–572.</ref> who considered Adria and Apulia as separate microplates split apart by the opening of Paleo-Tethys. The width of the Paleo-Tethys Ocean at this time is still a matter of discussion. According to Robardet et al.,<ref name=Robardetetal_1990>Robardet, M., Paris, F., and Racheboeuf, P. R., 1990, Palaeogeographic evolution of southwestern Europe during Early Palaeozoic times, in W. S. McKerrow and C. R. Scotese, eds., Palaeozoic palaeogeography and biogeography: GSL Memoirs 12, p. 411–419.</ref> the detachment of Armorica from Gondwana is not older than Late Devonian, and Robardet<ref name=Robardet_2003 /> considers a fiction even the concept of an Armorica microplate. Other reconstructions<ref name=Stampfliandborel_2002 /> <ref name=Torsvikandcocks_2004 /> <ref name=Vonraumerandstampfli_2008 /> suggest that the opening of the Paleo-Tethys occurred before Early Devonian, and this is more certain for the eastward extension of this ocean.<ref name=Metcalfe_2002>Metcalfe, I., 2002, Tectonic history of the SE Asian-Australian region: Advances in Geoecology, v. 34, p. 29–48.</ref> Besides the strongly debated concepts of Armorica ~~(e.g., Cocks and Torsvik~~,<ref name=Cocksandtorsvik_2002 /> ~~Nysæther et al.,~~<ref name=Nysætheretal_2002 /> ~~Robardet,~~<ref name=Robardet_2003 /> ~~Torsvik and Cocks~~<ref name=Torsvikandcocks_2009 />), also the relative position of the microplates detached from Gondwana with the opening of the Paleo-Tethys differs in several reconstructions: Stampfli and Borel<ref name=Stampfliandborel_2002 /> and von Raumer and Stampfli<ref name=Vonraumerandstampfli_2008 /> identify a major continental block (Hun superterrane), whereas Torsvik and Cocks<ref name=Torsvikandcocks_2004 /> suggest the presence of different independent microplates. In fact, the separation of these various microplates may have been diachronous.

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During Early Devonian time Gondwana was centered on the Southern Pole, with northern Africa and Antarctica located toward the equator ([[:file:M106Ch01Fig04.jpg|Figure 4]]). The continental plates that would form future Laurasia were located immediately to the south of the equator, so that most of the continental masses were in the southern hemisphere. The Iapetus Ocean had been closed by the collision between North America and Baltica, giving rise to the Caledonian orogeny. The Avalonia Ocean between southern England and Scotland was still present, and other minor oceanic seaways separated different blocks. These blocks would later form the components of Europe, assembled during the Carboniferous Variscan orogeny, with the closure of the Rheic Ocean. The width of the Rheic Ocean is still questioned, but the paleobiogeographic distribution of different groups of fossil organisms between Laurasia and Gondwana suggests that this ocean was relatively narrow during Early Devonian.<ref name=Wehrmannetal_2010>Wehrmann, A. et al., 2010, Devonian shallow-water sequences from the North Gondwana coastal margin (central and eastern Taurides, Turkey): Sedimentology, facies and global events: Gondwana Research, v. 17, p. 546–560.</ref> The Paleo-Tethys Ocean was opening along northern Gondwana, generating a fringe of microplates (e.g., Armorica, Adria, Pontides, Hellenic, and Moesia terranes). We follow the interpretation of Torsvik and Cocks,<ref name=Torsvikandcocks_2004>Torsvik, T. H., and Cocks, L. R. M., 2004, Earth geography from 400 to 250 Ma: A palaeomagnetic, faunal and facies review: Journal of the GSL v. 161, p. 555–572.</ref> who considered Adria and Apulia as separate microplates split apart by the opening of Paleo-Tethys. The width of the Paleo-Tethys Ocean at this time is still a matter of discussion. According to Robardet et al.,<ref name=Robardetetal_1990>Robardet, M., Paris, F., and Racheboeuf, P. R., 1990, Palaeogeographic evolution of southwestern Europe during Early Palaeozoic times, in W. S. McKerrow and C. R. Scotese, eds., Palaeozoic palaeogeography and biogeography: GSL Memoirs 12, p. 411–419.</ref> the detachment of Armorica from Gondwana is not older than Late Devonian, and Robardet<ref name=Robardet_2003 /> considers a fiction even the concept of an Armorica microplate. Other reconstructions<ref name=Stampfliandborel_2002 /> <ref name=Torsvikandcocks_2004 /> <ref name=Vonraumerandstampfli_2008 /> suggest that the opening of the Paleo-Tethys occurred before Early Devonian, and this is more certain for the eastward extension of this ocean.<ref name=Metcalfe_2002>Metcalfe, I., 2002, Tectonic history of the SE Asian-Australian region: Advances in Geoecology, v. 34, p. 29–48.</ref> Besides the strongly debated concepts of Armorica,<ref name=Cocksandtorsvik_2002 /> <ref name=Nysætheretal_2002 /> <ref name=Robardet_2003 /> <ref name=Torsvikandcocks_2009 /> also the relative position of the microplates detached from Gondwana with the opening of the Paleo-Tethys differs in several reconstructions: Stampfli and Borel<ref name=Stampfliandborel_2002 /> and von Raumer and Stampfli<ref name=Vonraumerandstampfli_2008 /> identify a major continental block (Hun superterrane), whereas Torsvik and Cocks<ref name=Torsvikandcocks_2004 /> suggest the presence of different independent microplates. In fact, the separation of these various microplates may have been diachronous.

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Most of the Asian terranes, mainly located immediately north of the equator, were still separated by seaways before their collision with and incorporation into Pangea. The position and vergence of subduction among these blocks is not clear, and different models have been proposed (e.~~g., Stampfli and Borel,~~<ref name=Stampfliandborel_2002 /> ~~Torsvik and Cocks,~~<ref name=Torsvikandcocks_2004 /> ~~Ruban et al.,~~<ref name=Rubanetal_2007 /> ~~von Raumer and Stampfli~~<ref name=Vonraumerandstampfli_2008 />).

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Most of the Asian terranes, mainly located immediately north of the equator, were still separated by seaways before their collision with and incorporation into Pangea. The position and vergence of subduction among these blocks is not clear, and different models have been proposed.<ref name=Stampfliandborel_2002 /> <ref name=Torsvikandcocks_2004 /> <ref name=Rubanetal_2007 /> <ref name=Vonraumerandstampfli_2008 />

During Early Devonian time, a global sea-level fall was responsible for the reduction of the neritic belts. The occurrence of a wide depositional hiatus close to the Early Devonian in most of the Middle East is ascribed to this sea-level low-stand, probably enhanced by a tectonic uplift.<ref name=Rubanetal_2007 />. The middle latitude position of North Africa and part of Arabia favored the development of alluvial deposits. Tectonic activity was weak and limited volcanic flows are documented<ref name=Meneissy_1990>Meneissy, M. Y., 1990, Vulcanicity, in R. Said, ed., The Geology of Egypt: Balkema, Rotterdam, p. 157–172.</ref> mainly in Sudan and in the southern area of the Eastern Desert of Egypt.<ref name=Schandelmeierandreynolds_1997 />

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===Early Permian (about 290 Ma)===

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The late Paleozoic was a period of major plate tectonic reconfiguration ([[:file:M106Ch01Fig05.jpg|Figure 5]]). The Variscan orogeny led to the assembly of Gondwana and Laurasia into one supercontinent, Pangea. Adria and Apulia, previously separated, are from here onward assembled as a microplate that is referred to as Adria in the Early Permian and subsequent maps. The opening of the Neo-Tethys Ocean along the eastern margin of Gondwana, from Arabia to Australia, created the Cimmerian terranes (Iran, Central Afghanistan, Karakorum, Qiangtang). These migrated northward across the Tethys Ocean from southern Gondwanan paleolatitudes in Early Permian time to subequatorial paleolatitudes by the ~Middle Permian–Early Triassic times (e.~~g., Sengör~~<ref name=Sengör_1979>Sengör, A. M. C., 1979, Mid-Mesozoic closure of Permo-Triassic Tethys and its implications: Nature, v. 279, p. 590–593.</ref> ~~Dercourt et al.,~~<ref name=Dercourtetal_1993>Dercourt, J., Ricou, L. E., and Vrielynck, B., 1993, Atlas Tethys palaeoenvironmental maps: Paris, Gauthier-Villars, p. 307.</ref> ~~Besse et al.,~~<ref name=Besseetal_1998>Besse, J., Torcq, F., Gallet, Y., Ricou, L. E., Krystyn, L., and Saidi, A., 1998, Late Permian to Late Triassic palaeomagnetic data from Iran: Constrains on the migration of the Iranian block through the Tethyan Ocean and initial destruction of Pangea: Geophysical Journal International, v. 135, p. 77–92.</ref> ~~Metcalfe,~~<ref name=Metcalfe_2006>Metcalfe, I., 2006, Palaeozoic and Mesozoic tectonic evolution and palaeogeography of East Asian crustal fragments: The Korean Peninsula in context: Gondwana Research, v. 9, p. 24–46.</ref> ~~Muttoni et al.~~<ref name=Muttonietal_2009a>Muttoni, G., Mattei, M., Balini, M., Zanchi, A., Gaetani, M., and Berra, F., 2009, The drift history of Iran from the Ordovician to the Triassic, in M.-F. Brunet, M. Wilmsen, and J. W. Granath, eds., South Caspian to Central Iran Basins: GSL Special Publications 312, p. 7–29.</ref>). According to Muttoni et al.,<ref name=Muttonietal_2003>Muttoni, G., Kent, D. V., Garzanti, E., Brack, P., Abrahamsen, N., and Gaetani, M., 2003, Early Permian Pangea ‘B’ to Late Permian Pangea ‘A’: Earth and Planetary Science Letters, v. 215, p. 379–394.</ref> <ref name=Muttonietal_2004>Muttoni, G., Kent, D. V., Garzanti, E., Brack, P., Abrahamsen, N., and Gaetani, M., 2004, Erratum to “Early Permian Pangea ‘B’ to Late Permian Pangea ‘A"’: Earth and Planetary Science Letters, v. 218, p. 539–540.</ref> <ref name=Muttonietal_2009b>Muttoni, G., Gaetani, M., Kent, D. V., Sciunnach, D., Angiolini, L., Berra, F., Garzanti, E., Mattei, M., and Zanchi, A., 2009, Opening of the Neo-Tethys Ocean and the Pangea B to Pangea A transformation during the Permian: GeoArabia, v. 14, no. 4, p. 17–48.</ref> the Neotethyan opening is in part coeval to a major dextral motion of Laurasia relative to Gondwana that takes place essentially during Permian time. This relative motion causes the transformation of Pangea from an Early Permian configuration of the B-type, where Africa is placed south of Asia and South America is placed south of Europe,<ref name=Irving_1977>Irving, E., 1977, Drift of the major continental blocks since the Devonian: Nature, v. 270, p. 304–309.</ref> <ref name=Morelandirving_1981>Morel, P., and Irving, E., 1981, Paleomagnetism and the evolution of Pangea: Journal of Geophysical Research, v. 86, p. 1858–1987.</ref> <ref name=Muttonietal_1996>Muttoni, G., Kent, D. V., and Channell, J. E. T., 1996, Evolution of Pangea: Paleomagnetic constraints from the Southern Alps, Italy: Earth and Planetary Science Letters, v. 140, p. 97–112.</ref> <ref name=Torqetal_1997>Torq, F., Besse, J., Vaslet, D., Marcoux, J., Ricou, L. E., Halawani, M., and Basahel, M., 1997, Paleomagnetic results from Saudi Arabia and the Permo-Triassic Pangea configuration: Earth and Planetary Science Letters, v. 148, p. 553–567.</ref> <ref name=Bachtadseetal_2002>Bachtadse, V., Zanglein, R., Tait, J., and Soffel, H., 2002, Palaeomagnetism of the Permo/Carboniferous (280 Ma) Jebel Nehoud ring complex, Kordofan, Central Sudan: Journal of African Earth Sciences, v. 35, p. 89–97.</ref> <ref name=Irving_2005>Irving, E., 2005, The role of latitude in mobilism debates: PNAS, v. 102, p. 1821–1828.</ref> <ref name=Angiolinietal_2007>Angiolini, L., Gaetani, M., Muttoni, G., Stephenson, M. H., and Zanchi, A., 2007, Tethyan oceanic currents and climate gradients 300 m.y. ago: Geology, v. 35, p. 1071–1074.</ref> to a Late Permian configuration of the Wegenerian A-type, where Africa is placed immediately south of Europe and South America is placed south of North America. The presence of a E-W trending trans-Pangean seaway (connecting the Paleo-Tethys to the Panthalassa oceans) persisting until the Late Permian is proposed by Vai<ref name=Vai_2003>Vai, G. B., 2003, Development of the palaeogeography of Pangaea from Late Carboniferous to Early Permian Palaeogeography, Palaeoclimatology, v. 196, p. 125–155.</ref> based on his interpretation of facies analyses and paleobiogeographic distribution of floral, reptile, and marine benthic organisms.

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The late Paleozoic was a period of major plate tectonic reconfiguration ([[:file:M106Ch01Fig05.jpg|Figure 5]]). The Variscan orogeny led to the assembly of Gondwana and Laurasia into one supercontinent, Pangea. Adria and Apulia, previously separated, are from here onward assembled as a microplate that is referred to as Adria in the Early Permian and subsequent maps. The opening of the Neo-Tethys Ocean along the eastern margin of Gondwana, from Arabia to Australia, created the Cimmerian terranes (Iran, Central Afghanistan, Karakorum, Qiangtang). These migrated northward across the Tethys Ocean from southern Gondwanan paleolatitudes in Early Permian time to subequatorial paleolatitudes by the ~Middle Permian–Early Triassic times.<ref name=Sengör_1979>Sengör, A. M. C., 1979, Mid-Mesozoic closure of Permo-Triassic Tethys and its implications: Nature, v. 279, p. 590–593.</ref> <ref name=Dercourtetal_1993>Dercourt, J., Ricou, L. E., and Vrielynck, B., 1993, Atlas Tethys palaeoenvironmental maps: Paris, Gauthier-Villars, p. 307.</ref> <ref name=Besseetal_1998>Besse, J., Torcq, F., Gallet, Y., Ricou, L. E., Krystyn, L., and Saidi, A., 1998, Late Permian to Late Triassic palaeomagnetic data from Iran: Constrains on the migration of the Iranian block through the Tethyan Ocean and initial destruction of Pangea: Geophysical Journal International, v. 135, p. 77–92.</ref> <ref name=Metcalfe_2006>Metcalfe, I., 2006, Palaeozoic and Mesozoic tectonic evolution and palaeogeography of East Asian crustal fragments: The Korean Peninsula in context: Gondwana Research, v. 9, p. 24–46.</ref> <ref name=Muttonietal_2009a>Muttoni, G., Mattei, M., Balini, M., Zanchi, A., Gaetani, M., and Berra, F., 2009, The drift history of Iran from the Ordovician to the Triassic, in M.-F. Brunet, M. Wilmsen, and J. W. Granath, eds., South Caspian to Central Iran Basins: GSL Special Publications 312, p. 7–29.</ref> According to Muttoni et al.,<ref name=Muttonietal_2003>Muttoni, G., Kent, D. V., Garzanti, E., Brack, P., Abrahamsen, N., and Gaetani, M., 2003, Early Permian Pangea ‘B’ to Late Permian Pangea ‘A’: Earth and Planetary Science Letters, v. 215, p. 379–394.</ref> <ref name=Muttonietal_2004>Muttoni, G., Kent, D. V., Garzanti, E., Brack, P., Abrahamsen, N., and Gaetani, M., 2004, Erratum to “Early Permian Pangea ‘B’ to Late Permian Pangea ‘A"’: Earth and Planetary Science Letters, v. 218, p. 539–540.</ref> <ref name=Muttonietal_2009b>Muttoni, G., Gaetani, M., Kent, D. V., Sciunnach, D., Angiolini, L., Berra, F., Garzanti, E., Mattei, M., and Zanchi, A., 2009, Opening of the Neo-Tethys Ocean and the Pangea B to Pangea A transformation during the Permian: GeoArabia, v. 14, no. 4, p. 17–48.</ref> the Neotethyan opening is in part coeval to a major dextral motion of Laurasia relative to Gondwana that takes place essentially during Permian time. This relative motion causes the transformation of Pangea from an Early Permian configuration of the B-type, where Africa is placed south of Asia and South America is placed south of Europe,<ref name=Irving_1977>Irving, E., 1977, Drift of the major continental blocks since the Devonian: Nature, v. 270, p. 304–309.</ref> <ref name=Morelandirving_1981>Morel, P., and Irving, E., 1981, Paleomagnetism and the evolution of Pangea: Journal of Geophysical Research, v. 86, p. 1858–1987.</ref> <ref name=Muttonietal_1996>Muttoni, G., Kent, D. V., and Channell, J. E. T., 1996, Evolution of Pangea: Paleomagnetic constraints from the Southern Alps, Italy: Earth and Planetary Science Letters, v. 140, p. 97–112.</ref> <ref name=Torqetal_1997>Torq, F., Besse, J., Vaslet, D., Marcoux, J., Ricou, L. E., Halawani, M., and Basahel, M., 1997, Paleomagnetic results from Saudi Arabia and the Permo-Triassic Pangea configuration: Earth and Planetary Science Letters, v. 148, p. 553–567.</ref> <ref name=Bachtadseetal_2002>Bachtadse, V., Zanglein, R., Tait, J., and Soffel, H., 2002, Palaeomagnetism of the Permo/Carboniferous (280 Ma) Jebel Nehoud ring complex, Kordofan, Central Sudan: Journal of African Earth Sciences, v. 35, p. 89–97.</ref> <ref name=Irving_2005>Irving, E., 2005, The role of latitude in mobilism debates: PNAS, v. 102, p. 1821–1828.</ref> <ref name=Angiolinietal_2007>Angiolini, L., Gaetani, M., Muttoni, G., Stephenson, M. H., and Zanchi, A., 2007, Tethyan oceanic currents and climate gradients 300 m.y. ago: Geology, v. 35, p. 1071–1074.</ref> to a Late Permian configuration of the Wegenerian A-type, where Africa is placed immediately south of Europe and South America is placed south of North America. The presence of a E-W trending trans-Pangean seaway (connecting the Paleo-Tethys to the Panthalassa oceans) persisting until the Late Permian is proposed by Vai<ref name=Vai_2003>Vai, G. B., 2003, Development of the palaeogeography of Pangaea from Late Carboniferous to Early Permian Palaeogeography, Palaeoclimatology, v. 196, p. 125–155.</ref> based on his interpretation of facies analyses and paleobiogeographic distribution of floral, reptile, and marine benthic organisms.

The proposed Early Permian reconstruction is from Muttoni et al.,<ref name=Muttonietal_2009b /> which is based on Early Permian poles that support a Pangea B configuration essentially similar to that originally proposed by Irving<ref name=Irving_1977 /> and confirmed by subsequent analyses.<ref name=Morelandirving_1981 /> <ref name=Muttonietal_1996 /> <ref name=Torqetal_1997 /> <ref name=Bachtadseetal_2002 /> <ref name=Muttonietal_2003 /> <ref name=Muttonietal_2004 /> <ref name=Angiolinietal_2007 /> The Cimmerian terranes (alternatively named Cimmeria Superterrane) are placed close to the Gondwanan margin in Early Permian time on the basis of geological, paleontological, and paleomagnetic evidences.<ref name=Stöcklin_1968>Stöcklin, J., 1968, [http://archives.datapages.com/data/bulletns/1968-70/data/pg/0052/0007/1200/1229.htm Structural history and tectonics of Iran: A review]: AAPG Bulletin, v. 52, p. 1229–1258.</ref> <ref name=Stöcklin_1974>Stöcklin, J., 1974, Possible ancient continental margins in Iran, in C. A. Burk and C. L. Drake, eds., The geology of continental margins: Springer-Verlag, p. 873–887.</ref> <ref name=Berberianandking_1981>Berberian, M., and King, G., 1981, Toward a paleogeography and tectonic evolution of Iran: Canadian Journal of Earth Sciences, v. 18, p. 210–265.</ref> <ref name=Wendtetal_2005>Wendt, J., Kaufmann, B., Belka, Z., Farsan, N., and Bavandpur, A. K., 2005, Devonian/Lower Carboniferous stratigraphy, facies patterns and palaeogeography of Iran Part II. Northern and central Iran: Acta Geologica Polonica, v. 55, no. 1, p. 31–97.</ref> <ref name=Muttonietal_2009b />

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Neotethyan rifting along the eastern Gondwana margin from India<ref name=Garzantiandsciunnach_1997>Garzanti, E., and Sciunnach, D., 1997, Early Carboniferous onset of Gondwanian glaciation and Neo-Tethyan rifting in Southern Tibet: Earth Planetary Science Letters, v. 148, p. 359–365.</ref> to Oman<ref name=Albelushietal_1996>Al-Belushi, J., Glennie, K. W., and Williams, B. P. J., 1996, Permo-Carboniferous glaciogenic Al Khlata Formation, Oman: A new hypothesis for origin of its glaciation: GeoArabia, v. 1, p. 389–403.</ref> started in Carboniferous times and was followed by continental breakup and formation of oceanic crust in Early Permian time (mid-Sakmarian<ref name=Garzanti_1999>

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Garzanti, E., 1999, Stratigraphy and sedimentary history of the Nepal Tethys Himalayan passive margin, in B. N. Upreti and P. Le Fort, eds., Advances on the geology of the Himalaya - focus on Nepal: Journal of Asian Earth Sciences, v. 17, p. 805–827.</ref> <ref name=Angiolinietal_2003>Angiolini, L., Balini, M., Garzanti, E., Nicora, A., and Tintori, A., 2003, Gondwanan deglaciation and opening of Neotethys: Palaeontological and sedimentological evidence from interior Oman: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 196, p. 99–123.</ref> <ref name=Metcalfe_2006 />). In the same time interval, a major zone of northward subduction of Paleotethyan oceanic crust was active along the Eurasian margin and persisted through most of Permian–Triassic times (e.~~g., Dercourt et al.,~~<ref name=Dercourtetal_1993 /> ~~Alavi et al.,~~<ref name=Alavital_1997>Alavi, M., Vaziri, H., Seyed Enami, K., and Lasemi, Y., 1997, The Triassic and associated rocks of the Nakhlak and Aghdarband areas in central and northeastern Iran as remnants of the southern Turanian active continental margin: GSA Bulletin, v. 109, p. 1563–1575.</ref> ~~Besse et al.,~~<ref name=Besseetal_1998 /> ~~Metcalfe~~<ref name=Metcalfe_2006 />). Transpressive strike-slip tectonics was responsible for basin inversion in Lybia and Egypt.<ref name=Schandelmeierandreynolds_1997 />

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Garzanti, E., 1999, Stratigraphy and sedimentary history of the Nepal Tethys Himalayan passive margin, in B. N. Upreti and P. Le Fort, eds., Advances on the geology of the Himalaya - focus on Nepal: Journal of Asian Earth Sciences, v. 17, p. 805–827.</ref> <ref name=Angiolinietal_2003>Angiolini, L., Balini, M., Garzanti, E., Nicora, A., and Tintori, A., 2003, Gondwanan deglaciation and opening of Neotethys: Palaeontological and sedimentological evidence from interior Oman: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 196, p. 99–123.</ref> <ref name=Metcalfe_2006 />). In the same time interval, a major zone of northward subduction of Paleotethyan oceanic crust was active along the Eurasian margin and persisted through most of Permian–Triassic times.<ref name=Dercourtetal_1993 /> <ref name=Alavital_1997>Alavi, M., Vaziri, H., Seyed Enami, K., and Lasemi, Y., 1997, The Triassic and associated rocks of the Nakhlak and Aghdarband areas in central and northeastern Iran as remnants of the southern Turanian active continental margin: GSA Bulletin, v. 109, p. 1563–1575.</ref> <ref name=Besseetal_1998 /><ref name=Metcalfe_2006 /> Transpressive strike-slip tectonics was responsible for basin inversion in Lybia and Egypt.<ref name=Schandelmeierandreynolds_1997 />

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In Pennsylvanian–Early Permian times, an extensive glaciation affected much of Gondwana ~~(e.g., Stephenson et al.~~,<ref name=Stephensonetal_2007>Stephenson, M. H., Angiolini, L., and Leng, M. J., 2007, The Early Permian fossil record of Gondwana and its relationship to deglaciation: A review, in M. Williams, A. Haywood, J. Gregory, and D. Schmidt, eds., Deep time perspectives on climate change: Marrying the signal from computer models and biological proxies: London, Publication of The Micropalaeontological Society, Special Publications. GSL p. 103–122.</ref> ~~Frank et al.~~<ref name=Franketal_2008>Frank, T. D., Birgenheier, L. P., Montañez, I. P., Fielding, C. R., and Rygel, M. C., 2008, Late Paleozoic climate dynamics revealed by comparison of ice-proximal stratigraphic and ice-distal isotopic records, in C. R. Fielding, T. D. Frank, and J. L. Isbell, eds., Resolving the late Paleozoic Ice Age in time and space: GSA Special Paper 441, p. 331–342.</ref>), leaving widespread glacial deposits at high to intermediate southern latitudes. The tropical belt was thus restricted to very low latitudes, which benefited from a warm westward-flowing equatorial current, which, upon reaching the continental shelves of the western Tethys Gulf, deflected southeastward, bringing warm surface waters toward the northern corner of Arabia.<ref name=Angiolinietal_2007 /> This compressed tropical current gyre was bounded to the south by the thermal effects of the Gondwanan glacial climate, which directly controlled the distribution of cold biota in most other peri-Gondwanan terranes.

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In Pennsylvanian–Early Permian times, an extensive glaciation affected much of Gondwana, <ref name=Stephensonetal_2007>Stephenson, M. H., Angiolini, L., and Leng, M. J., 2007, The Early Permian fossil record of Gondwana and its relationship to deglaciation: A review, in M. Williams, A. Haywood, J. Gregory, and D. Schmidt, eds., Deep time perspectives on climate change: Marrying the signal from computer models and biological proxies: London, Publication of The Micropalaeontological Society, Special Publications. GSL p. 103–122.</ref> <ref name=Franketal_2008>Frank, T. D., Birgenheier, L. P., Montañez, I. P., Fielding, C. R., and Rygel, M. C., 2008, Late Paleozoic climate dynamics revealed by comparison of ice-proximal stratigraphic and ice-distal isotopic records, in C. R. Fielding, T. D. Frank, and J. L. Isbell, eds., Resolving the late Paleozoic Ice Age in time and space: GSA Special Paper 441, p. 331–342.</ref> leaving widespread glacial deposits at high to intermediate southern latitudes. The tropical belt was thus restricted to very low latitudes, which benefited from a warm westward-flowing equatorial current, which, upon reaching the continental shelves of the western Tethys Gulf, deflected southeastward, bringing warm surface waters toward the northern corner of Arabia.<ref name=Angiolinietal_2007 /> This compressed tropical current gyre was bounded to the south by the thermal effects of the Gondwanan glacial climate, which directly controlled the distribution of cold biota in most other peri-Gondwanan terranes.

[[file:M106Ch01Fig06.jpg|thumb|300px|{{figure number|6}}Global paleogeography (top) and major depositional settings in the southern margin of the Tethys (below) at the time of the Permian-Triassic boundary (about 251 Ma).]]

Line 81: Line 81:

Northern Gondwana was characterized by the development of a mature passive margin along the Neo-Tethys Ocean, which started to open with a time-transgressive trend beginning in Carboniferous time.<ref name=Albelushietal_1996 /> <ref name=Garzantiandsciunnach_1997 /> Oceanic crust began forming as early as Early Permian time.<ref name=Garzanti_1999 /> <ref name=Angiolinietal_2003 /> <ref name=Metcalfe_2006 /> The opening of the Neo-Tethys was responsible for the northward flight of the peri-Gondwanan blocks: in Early Triassic time these continental blocks were moving northward toward the southern margin of Asia. These blocks include a number of minor, semi-independent blocks such as Apulia, Taurides, Iran (NW and Central), Sanandaj Sirjian, Heland, and Northern Tibet.<ref name=Rubanetal_2007 /> In detail, Iran was crossing the equator<ref name=Muttonietal_2009b /> before its docking to Eurasia, which gave rise to the Cimmerian orogeny. In contrast, to the east most of the blocks were still located south of the equator. The different velocities of the peri-Gondwanan blocks were probably controlled by the presence of roughly N-S trending transform faults, which defined portions of the Neo-Tethys oceanic ridge characterized by different rates of spreading. The existence of a complex network of oceanic branches during the opening of the Neo-Tethys has been suggested by Sengör,<ref name=Sengör_1990>Sengör, A. M. C., 1990, A new model for the late Palaeozoic-Mesozoic tectonic evolution of Iran and implications for Oman, in A. H. F. Robertson, M. P. Searle, and A. C. Ries, eds., The geology and tectonics of the Oman region: GSL Special Publication 49, p. 797–831.</ref> who interpreted the peri-Gondwanan blocks as three independent ribbons migrating northward.

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The present-day North Africa was located along the southern passive margin of Neo-Tethys and was characterized by the development of extensional basins in Lybia and Levant (probably transtensional basins<ref name=Schandelmeierandreynolds_1997 />). Paleogeographic reconstructions are more complex in the western part of the Tethys, as the narrowing of the oceanic basin along with the closer proximity of the Neo-Tethys ridge and the Paleo-Tethys subduction zone complicate the definition and precise position of the numerous blocks which can be identified in this zone. Furthermore, the position and significance of blocks such as the Taurides and Apulia are still a matter of debate. Paleogeographic reconstructions in the western part of the Tethys Ocean are often contrasting (e.~~g., Dercourt et al.,~~<ref name=Dercourtetal_2000>Dercourt, J., Gaetani, M., Vrielynck, B., Barrier, E., Biju-Dural, B., Brunet, M. F., Cadet, J. P., Crasquin, S., and Sandulescu, M., 2000, Atlas PeriTethys, Palaeogeographical Maps. CCGM/CGMW, Paris: 24 maps and explanatory notes: I-XX, 269 pp.</ref> ~~Stampfli and Borel~~<ref name=Stampfliandborel_2002 />). Differences can be ascribed to the puzzle of small plates and to the complex history of aperture and closure of small oceanic branches which characterize, for most of the Mesozoic, the Alpine and Dinaric domains. There are also different interpretations of the significance of the multiple extensional events along northern Gondwana, which is the most likely to represent breakup and formation of the passive margin at any particular location.

+

The present-day North Africa was located along the southern passive margin of Neo-Tethys and was characterized by the development of extensional basins in Lybia and Levant (probably transtensional basins<ref name=Schandelmeierandreynolds_1997 />). Paleogeographic reconstructions are more complex in the western part of the Tethys, as the narrowing of the oceanic basin along with the closer proximity of the Neo-Tethys ridge and the Paleo-Tethys subduction zone complicate the definition and precise position of the numerous blocks which can be identified in this zone. Furthermore, the position and significance of blocks such as the Taurides and Apulia are still a matter of debate. Paleogeographic reconstructions in the western part of the Tethys Ocean are often contrasting.<ref name=Dercourtetal_2000>Dercourt, J., Gaetani, M., Vrielynck, B., Barrier, E., Biju-Dural, B., Brunet, M. F., Cadet, J. P., Crasquin, S., and Sandulescu, M., 2000, Atlas PeriTethys, Palaeogeographical Maps. CCGM/CGMW, Paris: 24 maps and explanatory notes: I-XX, 269 pp.</ref> <ref name=Stampfliandborel_2002 /> Differences can be ascribed to the puzzle of small plates and to the complex history of aperture and closure of small oceanic branches which characterize, for most of the Mesozoic, the Alpine and Dinaric domains. There are also different interpretations of the significance of the multiple extensional events along northern Gondwana, which is the most likely to represent breakup and formation of the passive margin at any particular location.

The Permian-Triassic boundary was characterized at a global scale by low sea level, reflected by widespread continental or shallow marine facies. The beginning of Triassic time was characterized by a sea-level rise that can be traced worldwide.

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The end Permian crisis is generally considered the most dramatic extinction of the last 600 million years<ref name=Erwin_2006>Erwin, D. H., 2006, Extinction: How life on Earth nearly ended 250 million years ago: Princeton University Press, 296 p.</ref> and led to the extinction of 75–96% of species. Some of the invoked mechanisms included rapid sea-level change and/or anoxia or euxinia ~~(e.g., Wignall and Twitchett,~~<ref name=Wignallandtwitchett_2002>Wignall, P. B., and Twitchett, R. J., 2002, Permian-Triassic sedimentology of Jameson Land, East Greenland: Incised submarine channels in an anoxic basin: Journal of the Geological Society, v. 159, p. 691–703.</ref> ~~Hays et al.~~<ref name=Haysetal_2007>Hays, L. E., Beatty, T., Henderson, C. M., Love, G. D., and Summons, R. E., 2007, Evidence for photic zone euxinia through the end-Permian mass extinction in the Panthalassic Ocean (Peace River Basin, Western Canada): Palaeoworld, v. 16, p. 39–50.</ref>); extraterrestrial impact ~~(e.g., Becker et al.~~<ref name=Beckeretal_2001>Becker, L., Poreda, R. J., Hunt, A. G., Bunch, T. E., and Rampino, M., 2001, Impact event at the Permo-Triassic boundary: Evidence from extraterrestrial noble gases in Fullerenes: Science, v. 291, p. 1530–1533.</ref>); enormous volcanic eruptions and/or an extreme global warming ~~(e.g., Kidder and Worsley,~~<ref name=Kidderandworsley_2004>Kidder, D. L., and Worsley, T. R., 2004, Causes and consequences of extreme Permo-Triassic warming to globally equable climate and relation to the Permo-Triassic extinction and recovery: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 203, p. 207–237.</ref> ~~Svensen et al.,~~<ref name=Svensenetal_2008>Svensen, H., Planke, S., Polozov, A.,G., Schimdbauer, N., Corfu, F., Podladchikov. Y. Y., and Jamtveit, B., 2008, Siberian gas venting and the end-Permian environmental crisis: Earth and Planetary Science Letters, v. 277, p. 490–500.</ref> ~~Reichow et al.~~<ref name=Reichowetal_2009>Reichow, M. K. et al., 2009, The timing and extent of the eruption of the Siberian Traps large igneous province: Implications for the end-Permian environmental crisis: Earth and Planetary Science Letters, v. 277, no. 1-2, p. 9–20.</ref>); or ozone layer collapse ~~(e.g., Beerling et al~~.<ref name=Beerlingetal_2007>Beerling, D. J., Harfoot, M., Lomax, B., and Pyle, J. A., 2007, The stability of the stratospheric ozone layer during the end-Permian eruption of the Siberian traps: Philosophical transactions of the Royal Society, Mathematical, Physical and Engineering Sciences, v. 365, p. 1843–1866.</ref>). The pattern of the latest Permian extinction evaluated statistically<ref name=Jinetal_2000>Jin, Y. G., Wang, Y., Wang, W., Shang, Q. H., Cao, C. Q., and Erwin, D. H., 2000, Pattern of marine mass extinction near the Permo-Triassic boundary in South China: Science, v. 289, p. 432–436.</ref> <ref name=Shenetal_2006>Shen, S. Z., Cao, C. Q., Henderson, C. M., Wang, X. D., Shi, G. R., Wang, Y., and Wang, W., 2006, End-Permian mass extinction pattern in the northern peri-Gondwanan region: Palaeoworld, v. 15, p. 3–30.</ref> <ref name=Grovesetal_2007>Groves, J. R., Rettori, R., Payne, J. L., Boyce, M. D., and Altiner D., 2007, End-Permian mass extinction of Lagenide foraminifers in the southern Alps (northern Italy): Journal of Paleontology, v. 81, p. 415–434.</ref> <ref name=Angiolinietal_2010>Angiolini, L., Checconi, A., Rettori, R., and Gaetani, M., 2010, The latest Permian mass extinction in the Alborz Mountains (North Iran). In press in Geological Journal.</ref> indicates that the extinction was a sudden event occurring during a sea-level rise. The evidence that the extinction was abrupt in different latest Permian paleogeographic settings is consistent with scenarios in which mass extinction resulted from climatic and environmental deterioration triggered by the Siberian Traps volcanism, which also increased greenhouse gas emissions into the atmosphere and thus global warming and ozone depletion. This is also supported by the pronounced negative δ13C excursion recorded worldwide near the latest Permian extinction event (e.g., Baud et al.,<ref name=Baudetal_1989>Baud, A., Magaritz, M., and Holser, W. T., 1989, Permian-Triassic of the Tethys: Carbon isotopes studies: Geologische Rundschau, v. 78, no. 2, p. 649–677.</ref> Retallack and Krull,<ref name=Retallackandkrull_2006>Retallack, G. J., and Krull, E. S., 2006, Carbon isotopic evidence for terminal Permian methane outbursts and their role in extinctions of animal, plants, coral reefs, and peat swamps, in Wetlands through time: S. F. Greb and W. A. Di Michele, eds., GSA Special Paper, v. 399, p. 249–268.</ref> Horacek et al.<ref name=Horaceketal_2007>Horacek, M., Richoz, S., Brandner, R., Krystyn, L., and Spotl, C., 2007, Evidence for recurrent changes in Lower Triassic oceanic circulation of the Tethys: The δ13C record from marine sections in Iran: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 252, p. 255–369.</ref>).

+

The end Permian crisis is generally considered the most dramatic extinction of the last 600 million years<ref name=Erwin_2006>Erwin, D. H., 2006, Extinction: How life on Earth nearly ended 250 million years ago: Princeton University Press, 296 p.</ref> and led to the extinction of 75–96% of species. Some of the invoked mechanisms included rapid sea-level change and/or anoxia or euxinia; <ref name=Wignallandtwitchett_2002>Wignall, P. B., and Twitchett, R. J., 2002, Permian-Triassic sedimentology of Jameson Land, East Greenland: Incised submarine channels in an anoxic basin: Journal of the Geological Society, v. 159, p. 691–703.</ref> <ref name=Haysetal_2007>Hays, L. E., Beatty, T., Henderson, C. M., Love, G. D., and Summons, R. E., 2007, Evidence for photic zone euxinia through the end-Permian mass extinction in the Panthalassic Ocean (Peace River Basin, Western Canada): Palaeoworld, v. 16, p. 39–50.</ref> extraterrestrial impact;<ref name=Beckeretal_2001>Becker, L., Poreda, R. J., Hunt, A. G., Bunch, T. E., and Rampino, M., 2001, Impact event at the Permo-Triassic boundary: Evidence from extraterrestrial noble gases in Fullerenes: Science, v. 291, p. 1530–1533.</ref> enormous volcanic eruptions and/or an extreme global warming;<ref name=Kidderandworsley_2004>Kidder, D. L., and Worsley, T. R., 2004, Causes and consequences of extreme Permo-Triassic warming to globally equable climate and relation to the Permo-Triassic extinction and recovery: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 203, p. 207–237.</ref> <ref name=Svensenetal_2008>Svensen, H., Planke, S., Polozov, A.,G., Schimdbauer, N., Corfu, F., Podladchikov. Y. Y., and Jamtveit, B., 2008, Siberian gas venting and the end-Permian environmental crisis: Earth and Planetary Science Letters, v. 277, p. 490–500.</ref> <ref name=Reichowetal_2009>Reichow, M. K. et al., 2009, The timing and extent of the eruption of the Siberian Traps large igneous province: Implications for the end-Permian environmental crisis: Earth and Planetary Science Letters, v. 277, no. 1-2, p. 9–20.</ref>); or ozone layer collapse.<ref name=Beerlingetal_2007>Beerling, D. J., Harfoot, M., Lomax, B., and Pyle, J. A., 2007, The stability of the stratospheric ozone layer during the end-Permian eruption of the Siberian traps: Philosophical transactions of the Royal Society, Mathematical, Physical and Engineering Sciences, v. 365, p. 1843–1866.</ref> The pattern of the latest Permian extinction evaluated statistically<ref name=Jinetal_2000>Jin, Y. G., Wang, Y., Wang, W., Shang, Q. H., Cao, C. Q., and Erwin, D. H., 2000, Pattern of marine mass extinction near the Permo-Triassic boundary in South China: Science, v. 289, p. 432–436.</ref> <ref name=Shenetal_2006>Shen, S. Z., Cao, C. Q., Henderson, C. M., Wang, X. D., Shi, G. R., Wang, Y., and Wang, W., 2006, End-Permian mass extinction pattern in the northern peri-Gondwanan region: Palaeoworld, v. 15, p. 3–30.</ref> <ref name=Grovesetal_2007>Groves, J. R., Rettori, R., Payne, J. L., Boyce, M. D., and Altiner D., 2007, End-Permian mass extinction of Lagenide foraminifers in the southern Alps (northern Italy): Journal of Paleontology, v. 81, p. 415–434.</ref> <ref name=Angiolinietal_2010>Angiolini, L., Checconi, A., Rettori, R., and Gaetani, M., 2010, The latest Permian mass extinction in the Alborz Mountains (North Iran). In press in Geological Journal.</ref> indicates that the extinction was a sudden event occurring during a sea-level rise. The evidence that the extinction was abrupt in different latest Permian paleogeographic settings is consistent with scenarios in which mass extinction resulted from climatic and environmental deterioration triggered by the Siberian Traps volcanism, which also increased greenhouse gas emissions into the atmosphere and thus global warming and ozone depletion. This is also supported by the pronounced negative δ13C excursion recorded worldwide near the latest Permian extinction event (e.g., Baud et al.,<ref name=Baudetal_1989>Baud, A., Magaritz, M., and Holser, W. T., 1989, Permian-Triassic of the Tethys: Carbon isotopes studies: Geologische Rundschau, v. 78, no. 2, p. 649–677.</ref> Retallack and Krull,<ref name=Retallackandkrull_2006>Retallack, G. J., and Krull, E. S., 2006, Carbon isotopic evidence for terminal Permian methane outbursts and their role in extinctions of animal, plants, coral reefs, and peat swamps, in Wetlands through time: S. F. Greb and W. A. Di Michele, eds., GSA Special Paper, v. 399, p. 249–268.</ref> Horacek et al.<ref name=Horaceketal_2007>Horacek, M., Richoz, S., Brandner, R., Krystyn, L., and Spotl, C., 2007, Evidence for recurrent changes in Lower Triassic oceanic circulation of the Tethys: The δ13C record from marine sections in Iran: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 252, p. 255–369.</ref>).

[[file:M106Ch01Fig07.jpg|thumb|300px|{{figure number|7}}Global paleogeography (top) and major depositional settings in the southern margin of the Tethys (below) during Norian time (about 205 Ma).]]

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