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Today's plate-tectonic boundaries in the Mediterranean area are delineated on the basis of earthquake hypocenters, faults, ophiolites, intermediate volcanic rocks, paleomagnetic data, linear gravity anomalies, and magnetic anomalies. These plate boundaries are subdivided into subduction zones, zones of oceanic crust formation, and transform or strike-slip faults.
The thickness and facies of Pliocene to Holocene sediments, both onshore and offshore, have been compiled from many sources, which include measured surface sections, well data, offshore sparker and other seismic surveys, and cores from JOIDES Leg XIII drilling sites. A prominent, subbottom, acoustic reflector is present on almost all marine-seismic sections. This reflector was proved to be the top of an upper Miocene evaporite sequence in cores from JOIDES site 134, where late Miocene Foraminifera are present in marine shales intercalated with halite. Evaporites from the same reflecting horizon were cored at 5 other JOIDES sites. On this evidence the prominent acoustic reflector has been identified as marking the Miocene-Pliocene boundary. The subsea Pliocene to Holocene sediments cor elate with post-Messinian onshore sediments.
A comparison of the postulated Mediterranean geometry with the Pliocene to Holocene sediment distribution shows the following correlations.
1. Thick, linear accumulations may occur along subduction zones, as in Italy, the eastern Carpathians, and the southern Caspian Sea-Caucasus area, but may also be thin or virtually absent, as offshore south of Crete and north of Algeria.
2. Sediment fans occur at the mouths of larger rivers as the Nile, Rhone, and Ebro; and where sea currents emerge from a constriction as south of the Strait of Messina. Some fans are related to plate-rift margins.
3. Thin sediment sheets or patches characterize the interior areas of both continental and oceanic plates.
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