Vol. 39, n.4, December 1998
Thickness of the Plio-Quaternary sediments (IBCM-PQ)
M. Gennesseaux, P. Burollet, and E. Winnock
(Received July 2, 1998; accepted November 9, 1998)
The compilation of the maps of the thickness of the Plio-quaternary sediments, presented in 1 M. and 1/5 M. scale reduction map, was started in 1981 by E.Winnock, a geologist of ELF-Aquitaine. After his death, in 1985, his work was continued with a large contribution from GEMCO, an Unité de Recherche Associée au CNRS (URA 718) at Villefranche sur mer and Paris VI. E. Tzotzolakis, F. Burollet and P. Kouprine are major contributors. Russian geologists provided coverage of the Black Sea and greatly contributed to the compilation of sheet N° 10 (Levant Sea). Seismic surveys used in this mapping were mainly carried out by Oil Companies (CFP-Total, ELF Aquitaine, AGIP), a few Institutes (IFP, Ist. di Geof. di Trieste) and some Universities (Villefranche sur mer, Paris VI, Bologna). Because the velocities of Plio-quaternary sediments were not sufficiently known, E. Winnock selected an average velocity of 2 km/s (two way travel), which we have retained. To simplify the numbering of maps, we chose isochron intervals of tenths of a second. So, the values inscribed are approximatively hectometric (see on map the range of colours: white to yellow: 0 to 1 km, orange: 1 to 3 km, red: > 3 km). Generally, the Mio-Pliocene boundary is well defined, on continental slopes by aerial erosional surfaces and in deep parts of basins by high reflectivity of Messinian salt deposits (see their schematic distribution, after Rouchy, in the inset under the Black Sea on sheet 5). As D. J. Stanley underlined previously, the reduction map clearly shows that distribution of Plio-quaternary sediments results from two major factors, alluvial deposits rates near the mouth of a large river and/or in compressive and overthrusting movements. So, the Danube-Dnepr, the Nile, the Rhône and the Ebro submarine deltas are the largest accumulations of terrigeneous sediments, principally turbiditic. Elsewhere, post-miocene compressive tectonics explains Plioquaternary sediment thicknesses, as in southern Sicily and especially in front of the northern appenninic range. On the contrary, in young back-arc basins, (the Tyrrhenian and the Aegean Seas), irregular topographic relief induces a very complex and sparce Plio-quaternary sedimentation. Similary, on a strongly tectonized Mediterranean ridge, isolated from turbiditic terrigeneous supplies, pelagic sediments distribution was not known enough to provide an outline of isochrons. In the same way, owing to the lack of data, the thickness of sediments cannot be estimated along the Cyrenaic margin. The Black Sea is probably a old back-arc basin, where the Plio-quaternary sediment thickness reaches 4 km and whose NE margins are presently affected by strong compressive movements.
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