Estructura de las sales messinienses y de los depósitos sincinemáticos asociados en el sector Noreste del surco de Valencia

M. SANS, F. SÀBAT

Abstract


Three main types of messinian salt accumulation structures are described from the interpretation of the ENIEPSA-MAP77 (1977) and WESTERN GEOPHYSICAL COMPANY OF AMERICA-MEDS (1973) seismic profiles of the northern area of the Valencia Trough (3'30'-5'30'E, 42'30'-40'00'N). Salt rollers, pillows and diapirs form three belts parallel to the contour of the Messinian salt limit. Salt rollers are located in the margin of the evaporitic basin, where the base of the salt has a dip of up to 5'. The extension achieved in the salt rollers area is accommodated by the roll-overs and the small pillows that develop basinward. The instability processes of the slope start the raft tectonics observed in this area. In the center of the basin, on the other hand, where the salt base is horizontal, bigger structures (pillows and diapirs) develop due to differential loading processes linked to the growing of the Valencia fan. Pillows are the most common structures and are separated from the diapirs of the deepest part of the basin by a syncline under which there is a salt weld. The diapirs are very scarce and show, as a main characteristic, the absence of secondary nm synclines. The evolution model for the whole basin, inferred from the study of the syn-hnematic sediments related to al1 the structures and the correlation of six guide reflectors through out the basin, is complex. The western margin oE the basin, where the salt rollers develop, shows that the salt rollers migrate upward in the slope and that the small pillows (sector 1) have a direction of migration from the bottom of the slope toward the basin. On the other han4 the big pillows (sector 11) and the scarce diapirs of the center of the basin show a landward migration from the deepest parts of the basin. The two pillow areas, sector 1 and sector 11, are separated by an area of no defonnation where the salt is 800 m thick which confirms the idea of no linkage between the two zones and two different origins for the margin and deep salt accumulation structures.

The age of formation of these structures is lower Pliocene. Salt rollers are the first ones and the big pillows start growing later on. At present, the marginal salt rollers are inactive whereas the big pillows are still active as can be seen by the deformation they create at the sea bottom topography.



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