Changes

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=Nys&aelig;theretal_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]]).

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=Nys&aelig;theretal_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]]).

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>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> 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>

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>

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>

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>

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

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

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=Seng&ouml;r_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., 2009b, 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>

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=Seng&ouml;r_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.

 

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=St&ouml;cklin_1968>St&ouml;cklin, 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=St&ouml;cklin_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 />

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=St&ouml;cklin_1968>St&ouml;cklin, 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=St&ouml;cklin_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 />

===Permian-Triassic Boundary (251 Ma)===

===Permian-Triassic Boundary (251 Ma)===

The beginning of the Mesozoic was marked by the end of the transitional stage from the Pangea B to Pangea A configurations (Irving, 1977; Morel and Irving, 1981; Muttoni et al., 1996; Torq et al., 1997; Bachtadse et al., 2002; Irving, 2005; Angiolini et al., 2007). The change in the configuration of Pangea required a west to east translation of Laurasia of some 3000 km (1864 mi) with respect to Gondwana ([[:file:M106Ch01Fig06.jpg|Figure 6]]). The dextral movement was accommodated along a lithospheric shear zone which runs from the subduction zone of Panthalassa eastward to a triple junction joining this shear zone, the Neo-Tethys ridge, and the subduction of Paleo-Tethys below the southern margin of Laurasia. This triple junction was located along the northern margin of the Tethys, close to southern Europe (Muttoni et al., 2009b).

The beginning of the Mesozoic was marked by the end of the transitional stage from the Pangea B to Pangea A configurations.<ref name=Irving_1977 /> <ref name=Morelandirving_1981 /> <ref name=Muttonietal_1996 /> <ref name=Torqetal_1997 /> <ref name=Bachtadseetal_2002 /> <ref name=Irving_2005 /> <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> The change in the configuration of Pangea required a west to east translation of Laurasia of some 3000 km (1864 mi) with respect to Gondwana ([[:file:M106Ch01Fig06.jpg|Figure 6]]). The dextral movement was accommodated along a lithospheric shear zone which runs from the subduction zone of Panthalassa eastward to a triple junction joining this shear zone, the Neo-Tethys ridge, and the subduction of Paleo-Tethys below the southern margin of Laurasia. This triple junction was located along the northern margin of the Tethys, close to southern Europe.<ref name=Muttonietal_2009b />

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 (Al-Belushi et al., 1996; Garzanti and Sciunnach, 1997). Oceanic crust began forming as early as Early Permian time (Garzanti, 1999; Angiolini et al., 2003; 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 (Ruban et al., 2007). In detail, Iran was crossing the equator (Muttoni et al., 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 Sengor (1990), who interpreted the peri-Gondwanan blocks as three independent ribbons migrating northward.

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 Seng&ouml;r,<ref name=Seng&ouml;r_1990>Seng&ouml;r, 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.

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; Schandelmeier and Reynolds, 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., 2000; Stampfli and Borel, 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; Schandelmeier and Reynolds, 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., 2000; Stampfli and Borel, 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.