Changes

The Norian represents a key interval in the evolution of the Paleo-Tethys Ocean ([[:file:M106Ch01Fig07.jpg|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.<ref name=Zanchietal_2009>Zanchi, A., Zanchetta, S., Berra, F, Mattei, M., Garzanti, E., Molyneux, S., Nawab, A., and Sabouri, J., 2009, The Eo-Cimmerian (Late? Triassic) orogeny in North Iran, in M.-F. Brunet, M. Wilmsen, and J. W. Granath, eds., South Caspian to Central Iran Basins: GSL Special Publications, 312, p. 31–56.</ref>

The Norian represents a key interval in the evolution of the Paleo-Tethys Ocean ([[:file:M106Ch01Fig07.jpg|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.<ref name=Zanchietal_2009>Zanchi, A., Zanchetta, S., Berra, F, Mattei, M., Garzanti, E., Molyneux, S., Nawab, A., and Sabouri, J., 2009, The Eo-Cimmerian (Late? Triassic) orogeny in North Iran, in M.-F. Brunet, M. Wilmsen, and J. W. Granath, eds., South Caspian to Central Iran Basins: GSL Special Publications, 312, p. 31–56.</ref>

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).

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.<ref name=Schandelmeierandreynolds_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).

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.<ref name=Robertsonetal_2003>Robertson, A. H. F., Poisson, A., and Akinci, O., 2003, Developments in research concerning Mesozoic-Tertiary Tethys and neotectonics in the Isparta Angle, SW Turkey: Geological Journal, v. 38, p. 195–234.</ref>

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.

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.<ref name=Frisia_1991>Frisia, S., 1991, Caratteristiche sedimentologiche ed evoluzione diagenetica della Dolomia Principale (Norico) del Lago d’Idro e delle Dolomiti di Brenta, PhD Thesis, Dip. Sc.Terra, Milano.</ref> <ref name=Iannaceandfrisia_1993>Iannace, A., and Frisia, S., 1993, Changing dolomitization styles from Norian to Rhaetian in the southern Tethys reals. Spec. Publs Int. Ass. Sediment, v. 21, p. 75–90.</ref> The arid belt probably extended beyond 40° latitude north and south, as reflected by the distribution of climatically sensitive facies. Climate reconstructions<ref name-Ziegleretal_2003>Ziegler, A. M., Eshel, G., McAllister Rees, P., Rothfus, T. A., Rowlet, D. B., and Sunderlin, D., 2003, Tracing the tropics across land and sea: Permian to present: Lethaia, v. 36, p. 227–254.</ref> <ref name=Sellwoodandvaldes_2006>Sellwood, B. W., and Valdes P. J., 2006. Mesozoic climates: General circulation models and the rock record: Sedimentary Geology, v. 190, p. 269–287.</ref> 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,<ref name=Berraetal_2010>Berra, F., Jadoul, F., and Anelli, A., 2010, Environmental control on the end of the Dolomia Principale/Hauptdolomit depositional system in the central Alps: Coupling sea-level and climate changes: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 290, p. 138–150.</ref> <ref name=Berra_2012>Berra, F., 2012, Sea-level fall, carbonate production, rainy days: How do they relate? Insight from Triassic carbonate platforms (Western Tethys, Southern Alps, Italy): Geology, v. 40, p. 271–274.</ref> 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).]]

[[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).]]