Stratal architecture of Western Mediterranean Margins as the result of the stacking of Quaternary lowstand deposits below "glacio-eustatic fluctuation base-level.

Through a comparison of high-resolution seismic stratigraphy of seven Western Mediterranean Margins, similarities and differences in stratigraphic architecture were highlighted, and a hierarchy of controlling factors was established. The areas are: northwestern Alboran, Ebro, and northern Catalonia in the Spanish margin, Rhone in the French margin, and Tuscany, Latium, and Calabria in the Italian Tyrrhenian margin. Despite their different tectonic, physiographic and depositional setting, the seismic facies and growth pattern of the middle-late Pleistocene deposits are comparable. The margins are in fact the result of the stacking of lowstand systems tracts of 4th-order depositional sequences, bounded by polygenetic unconformities on the shelf and condensed sections on the upper slope. This lowstand nature results from the high frequency (100 ka), high amplitude (similar to 100 m), asymmetry (falling 65% of the time) and stationariness (between +10 and -120 m with respect to the present) of the glacio-eustatic sea-level curve. If eustasy directly controls the types of deposits making up the margins, tectonism conditions their growth pattern as it is the only factor accounting for similarities and differences in the external geometry, stratal pattern and distribution of the middle-late Pleistocene depositional sequences. An evolutionary model for the Quaternary growth of young passive continental margins is proposed. Zn this model, tectonics determines the degree of preservation of lowstand deposits, because it conditions the accommodation space left below the erosional profile produced by each glacio-eustatic cycle. Thus, some of the sequence stratigraphy principles (widely used to set up the model) have been modified and adjusted to take into consideration the peculiar nature of Quaternary glacio-eustasy.