Consistency Check I: The Mediterranean Area and the Vøring Basin

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Fig15Herodotus

Strike-slip fault system of the South Mediterranean area (Matruh and Herodotus Basin), extracted from composite seismic profile published by Tari et al., 2012. Two different fault systems can be identified; the primary one is the regional strike-slip system. The secondary deformation events, materialized as listric faults and thrustings, are also triggered by strike-slip tectonics: 1) gravitational sliding in the transtensional stress field sector, 2) and contractional vertical and lateral duplexing in the transpressional stress field sector.

The thinning of the Mediterranean crust below the Sirte Basin and the Ionian Sea  has been evidenced recently by gravity inversion (Cowie and Kusznir, 2012). Cowie and Kusznir have also noted that the nature of the crust could be either oceanic or thinned continental. On their second profile, which transects the Herodotus Basin the transform nature of the basin margin i.e the sudden increase of crustal thickness is more prominent, as a consequence most probably the masterfault of basin opening was localized on the southern basin margin of the Mediterranean Sea.

In our interpretation, gravity profile from Fig.20 is showing additional arguments for the transtensional origin of the Mediterranean crust. Here, contrary to the southern margin, crustal thinning was enabled by overstepping strike-slip faults. The crustal thinning mechanism cannot be understood solely from the published profiles, but certainly must be sought in those of transtensional strike-slip basins.

Southern transform margin of the Mediterranean Basin (Matruh-Herodotus Basin)

An ENE-ESE opening of the East Mediterranean area related to a transform margin was documented by several authors (Longacre et al., 2007; Walley, 1998, 2001) in (Tari et al., 2012), and indeed strike-slip tectonics suggested by gravity profiles (Cowie and Kusznir, 2012) is supported by seismic profiles as well. Reinterpreting a composite profile across the Matruh-Herodotus Basin margin, we have concluded that  it is likely, that an important amount of the structural traps identified in the Matruh Basin were generated by the local Neogene transpressional stress regime. Actually, down-dip contractional horses interpreted by (Tari et al., 2012) might originate partly in strike-slip deformation than solely in gravitational sliding on a Cretaceous shale detachment, as indicated by the presence of numerous antithetic faults. The NNE-SSW Matruh Canyon itself, described by Tari as an aborted syn-rift basin, it is overlaying a Jurassic(?)-Cretaceous transtensional shear zone, most probably initiated as a plate-scale tension fracture, which is depicting the whole coeval North African stress regimes. Interestingly, the main strike of the basin is parallel with those of the NOSA zone in Tunis, which also belongs to the Sirte Microplate in our plate tectonic subdivision.

Eratosthenes Seamount

The Eratosthenes Sea Mount of the Levantine basin was reimaged recently with modern processing techniques (Peace et al., 2012). Around the Eratosthenes seamount, two sets of strike-slip faults can be differentiated highlighting the transpressional origin of the seamount. This crustal fragment initially it constituted a footwall segment of the Levantine Basin, related to a major transtensional fault, which later got inverted  with the evolution of the local stress-regime along the main displacement zone. Stratigraphy given in Fig. 22 is very uncertain; layering is rather reflecting seismic packages than established stratigraphic units.

Northern margin of the Mediterranean Basin

The Corinth Trough (Fig. 26) can be described as a 1-2 Ma old, ~100X30km high-strain band, which shows 5-15mm/year N-S extension (Bell et al., 2009), and segmented, overstepping boundary faults in plain view. Bell is referring to three prevailing theories which are used to explain basin extension: 1) back-arc extension related to the Hellenic Trench, 2) westward propagation of the North Anatolian fault (Dewey and Şengör, 1979), 3) gravitational collapse of the Hellenide orogeny lithosphere (Jolivet, 2001).

In the frame of GSST, the Corinth Trough is interpreted as an internal shear zone of the South Anatolian Nanoplate, which has developed internally an overstepping fault network in the principal displacement zone (PDZ), instead of a continuous masterfault. Given the significant space created in the releasing bend of the PDZ, gravitational collapse proposed by Jolivet (2001) is regarded as a complimentary effect of the regional strike-slip tectonic deformation.

The Vøring Basin, offshore Norway

Within the Vøring Basin, several compressional (Cenomanian-Turonian, Maastrichtian-Paleocene, Middle Miocene) and extensional collapse phases (Paleozoic, Late Jurassic, Early Cretaceous hyperextension, Late Paleocene, Early Eocene) have been documented (Lundin et al., 2013). Overviewing Lundin’s data, we have noted that the ‘early’ (Permian–Jurassic) tension fractures in many places have evolved into overstepping strike-slip faults and several isolated subbasins formed. It should be also noted, that main (SSW-NNE trending) sedimentary trenches, are cut by  further W-E striking strike-slip systems in the continuation of mid-oceanic transforms, giving birth to complex structural patterns. During  periods of inversion, i.e. when structural blocks have arrived into restraining phase, some fault blocks evolved into push-up ranges, like the Vema Dome (Fig. 24), which has been formed in the Middle Miocene.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.

Accommodation Space Budget in the Mediterranean Area During the Messinian Salinity Crisis

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Recent shoreline  with uplifted Pleistocene sediments in Antalya, Turkey. History has recorded that the Manavgat River was navigable several centuries ago. While Venice is tectonically subsiding, Manavgat is rising.

The motor of basin opening mechanisms and subsequent subsidence in the Mediterranean Basin is best described in terms of strike-slip tectonics, related to the plate-velocity contrast of the African and Eurasian Plates during their eastward journey. In this approximation, the Mediterranean area represents an intercontinental mega-shear zone,  obviously with numerous transtensional zones, which evolved into isolated, small subbasins (Martínez-Garcia et al., 2013), featuring transform margins Tari et al. (2012), internal strike-slip zones (our experience in the Pantelleria Island area), and several push-up ranges, which in many parts of the Mediterranean area evolved into orogens, like in the case of the Atlas, Apennine, Alpine, Carpathian orogens. This continental scale tectonic evolution was enabled by several microplates and even nanoplates, in GSST wording.

The Atlas Microplate is found at the northern margin of the African Plate. Besides the High Atlas Nanoplate, which underlies the Atlas orogene, it includes two other, smaller nanoplates, the Gibraltar and Sicily Nanoplates. This microplate shows particularly intense strike-slip tectonics, and at the same time, we believe that it holds the main responsibilities for the accommodation space budget in the Mediterranean area, what has as a direct consequence that strike-slip tectonics should be considered as the main controlling factor for the Messinian Salinity Crisis, obviously exploiting the existing background climate factors.

According to Salé et al. (2012), the Mediterranean basins are showing very similar depositional trends and sedimentary architecture. They found however that the Late Messinian cyclicity of non-marine and fully marine sediments is related to climate changes, admitting that cyclicity is enhanced by tectonic activity in their study area, which is located over the Serrata-Carboneras strike-slip zone in Spain.

Looking after clues in the sedimentary record, we found that Late Messinian sediments are evidencing sedimentary intervals described as seismicites (Fortuin and Dabrio, 2008) and explosive fluid expulsion events (Bertoni and Cartwright, 2015).

In conclusion, it is more likely that causes of the Messinian Salinity Crisis should be attributed to the joint management of the Mediterranean accommodation space budget. Whatever is the subsidence of the individual subbasins, the total volume of available sea water counts in desiccating subbasins. It should be also noted that not every subbasin contains Messinian Salt, just those which met the desiccation criteria of the communicating vessels (subbasins).

Given the strike-slip related deformations recorded by the Atlas orogene, it is not hard to believe that the Atlas Microplate, certainly accompanied by the other microplates and orogens involved,  had a significant impact on  driving the vertical basin-floor oscillation, and ultimately changes in basin volume, all orchestrated by the regional strike-slip stress field.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.