Changes

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.

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<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 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.

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.

The end Permian crisis is generally considered the most dramatic extinction of the last 600 million years (Erwin, 2006) 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, 2002; Hays et al., 2007); extraterrestrial impact (e.g., Becker et al., 2001); enormous volcanic eruptions and/or an extreme global warming (e.g., Kidder and Worsley, 2004; Svensen et al., 2008; Reichow et al., 2009); or ozone layer collapse (e.g., Beerling et al., 2007). The pattern of the latest Permian extinction evaluated statistically (Jin et al., 2000; Shen et al., 2006; Groves et al., 2007; Angiolini et al., 2010) 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., 1989; Retallack and Krull, 2006; Horacek et al., 2007).

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> <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 &Delta;13C 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 &Delta;13C 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).]]

[[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).]]