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Phanerozoic Tethys region (view source)
Revision as of 23:48, 17 February 2016
, 23:48, 17 February 2016no edit summary
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 />
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 />
In Pennsylvanian–Early Permian times, an extensive glaciation affected much of Gondwana (e.g., Stephenson et al.,<ref name=Stephensonetal_2007 /> Frank et al.<ref name=Franketal_2008 />), 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.
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.
[[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).]]
===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 (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).
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.
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 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).
[[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).]]
===Norian (about 205 Ma)===
The Norian represents a key interval in the evolution of the Paleo-Tethys Ocean (Figure 7). During this stage the first evidence for the closure of the Paleo-Tethys Ocean was recorded by the onset of the Cimmerian orogeny along the southern margin of Asia, due to the collision of the Iran blocks with the active margin of Turan. This collisional episode is known as the “Eocimmerian” event, which was followed during Jurassic time by additional collisions of other microplates (Zanchi et al., 2009).
All the microplates that detached from Gondwana were approaching Southern Asia, which was an active margin situated above a north-dipping subduction zone. The Neo-Tethys Ocean was widely open. The paleogeographic situation is clear in the central part of the Tethyan Gulf, but the geodynamic setting was extremely complex close to the triple junction located in the western part of the Tethys. Intense extensional to strike slip tectonics (likely transtension) was recorded along the southern margin of Europe, close to the future axis of the Alpine Tethys. This tectonic activity was connected westward with the Central Atlantic, where rift basins were forming during Norian time (Newark Basins). Among the different small plates in the Mediterranean region (Apulia, Greece, Turkey), minor deep-water seaways, partly floored with oceanic crust, have been recognized. Northern Africa and Arabia acted as the southern passive margin of the Neo-Tethys, with extensional basins in Lybia and Egypt (Schandelmeier and Reynolds, 1997). Extensional tectonics (Palmiryde Basin) was recorded along the Lebanon-Northern Israel shelf. Emplacement of basalts, probably related to local rifting, is documented in Israel. Intraplate alkaline magmatic activity (intrusive and subvolcanic) occurred in Sudan and S-E Egypt (Schandelmeier and Reynolds, 1997).
Frequent unconformities associated with extension along the Neotethyan margin (from Syria to Libya through Arabia) can be interpreted as far-field effects of the Cimmerian orogeny. Alternatively, they can be interpreted as local extensional events that preceded late Triassic-Liassic breakup between Apulia (sensu lato) and northern Gondwana (Robertson et al., 2003).
During Norian time, climate was generally arid at Tethyan latitudes: Carbonate facies that were deposited along the Tethys margin were bordered by evaporitic facies and coastal and continental fluvial to playa environments. Arid climate conditions probably favored the early, widespread, and pervasive dolomitization observed on most of the Norian carbonate platforms (Frisia, 1991; Iannace and Frisia, 1993). The arid belt probably extended beyond 40° latitude north and south, as reflected by the distribution of climatically sensitive facies. Climate reconstructions (Ziegler et al., 2003; Sellwood and Valdes, 2006) indicate that, during most of Triassic time, the arid belt extended to the equator, and a humid equatorial belt was probably absent. Pervasive dolomitization of carbonate platforms ended close to the Norian-Rhaetian boundary in the Western Tethys due to a shift to humid conditions (Berra et al., 2010; Berra, 2012), reflected also by the increase of siliciclastic deposits, which can be traced along part of the northern margin of the Tethys.
[[file:M106Ch01Fig08.jpg|thumb|300px|{{figure number|8}}Global paleogeography (top) and major depositional settings in the southern margin of the Tethys (below) during Callovian time (about 164 Ma).]]
===Callovian (about 164 Ma)===
The breakup of Pangea continued in Callovian time with spreading in the Central Atlantic and the complete detachment of Africa from North America (Figure 8). A rifting event along the future axis of the North Atlantic Ocean caused the development of a network of roughly parallel rift basins along the Iberian margin and Newfoundland. Oceanic crust was also forming between India and Arabia, following an Early Jurassic rifting stage. In the Tethys area the situation was more complex (Barrier and Vrielynck, 2008), due to the existence of an extensional regime in the west (spreading in the Alpine Tethys, also known as the Penninic Ocean) and to the south (spreading in the Mesogea Ocean) and to the onset of the Neo-Tethys subduction along the southern margin of Laurasia, which followed the docking of the peri-Gondwanan blocks with Laurasia in early Middle Jurassic time (Middle Cimmerian orogeny). The northward subduction of the Neo-Tethys was responsible for the development of a volcanic belt bordering to the north the subduction zone, whereas retro-arc basins formed between the margin of Laurasia and the volcanic arc. Sedimentation in the backarc basins ranged from deep to shallow marine carbonates and clastics. The opening of the Mesogea Ocean separated the margin of Arabia and North Africa from a major continental block, composed of a large carbonate platform and related peri-platform basins, which would later form part of the Turkish jigsaw and the Dinaride-Pelagonian blocks. The southern coast of the Mesogea Ocean was marked by coastal deposits along present-day northern Africa (Guiraud and Bosworth, 1999), whereas shelf carbonates were deposited on most of the eastern to southern Arabia. The latter, bordered to the north by the Mesogea Ocean, faced to the south the new oceanic seaway, which began to separate Arabia from India. This geodynamic position, between two extensional basins, probably favored the development of deep seaways (at least partially controlled by extensional tectonics, as the Arabian Basin) on the Arabian shelf.
[[file:M106Ch01Fig09.jpg|thumb|300px|{{figure number|9}}Global paleogeography (top) and major depositional settings in the southern margin of the Tethys (below) during Aptian time (about 120 Ma).]]
===Aptian (about 120 Ma)===
The major oceanic seaways that characterize the present-day configuration are readily recognized in the Aptian map (Figure 9). The North Atlantic Ocean was opening between Iberia and Newfoundland, whereas the northernmost part of the future Atlantic Ocean was characterized by the development of a network of rift basins seen between Canada, Greenland, and Scandinavia. Africa was separated from India and Antarctica by narrow seaways. The South Atlantic Ocean was opening between southern Africa and the southernmost part of South America. Continental South America and Africa were still connected along the future Equatorial Atlantic. The Alpine Tethys connected the Central Atlantic with the Neo-Tethys Ocean. The passive margin of North Africa and northernmost Arabia faced the Mesogea Ocean (Barrier and Vrielynck, 2008). The active southern margin of Laurasia was still characterized by the subduction of the Neo-Tethys Ocean beneath it. Along this margin it was still possible to recognize a volcanic arc with backarc basins. The central part of the Neo-Tethys was characterized by the slow northward motion of a complex puzzle of blocks, including parts of future Turkey, Greece, Dinarids, and Adria microplates. Within this block, bordered by passive margins facing to the north the Neo-Tethys Ocean and to the south the Mesogea Ocean, extensional tectonics were responsible for the development of a major basin (Pindos-Olonos basin). Albian time probably marked the beginning of the compressional regime in the Alpine Tethys, with the possible onset of its subduction. During Aptian time sea level was close to its Phanerozoic maximum, so the size of the continental shelves are very large. Along the uplifted shoulder of the southern coast of Mesogea the coastal deposits were represented by a narrow belt, whereas most of the eastern and southern part of the Arabian block were characterized by shallow to deep carbonate deposits. The future Red Sea area was uplifted and emergent, whereas in its surroundings (mainly in the present-day Libya and Egypt, where extensional basins were formed; Schandelmeier and Reynolds, 1997) fluvio-lacustrine deposits passed seaward to deltaic clastics and evaporites (Mesogea Ocean coast). Volcanic activity is recorded in Israel (alkali-basaltic lavas), whereas syenitic intrusions are reported from NE and S Sudan (Schandelmeier and Reynolds, 1997).
During Albian time the paleoceanographic setting was characterized by a major anoxic event that can be traced all across the Albian seas.
[[file:M106Ch01Fig10.jpg|thumb|300px|{{figure number|10}}