TRANSGRESSIVE SAND BODIES ON THE MARESME CONTINENTAL-SHELF, WESTERN MEDITERRANEAN-SEA

Three large-scale, elongate, asymmetrical sand bodies lie beyond the shoreface of the straight sandy coast of Maresme, Barcelona, in the northwestern Mediterranean Sea. They are found on the continental shelf at water depths of 15-30 m, 35-80 m and 95-113 m. They are typically 12-20 m thick, 1000-2000 m wide and trend parallel or subparallel to the coast for a distance of up to 24 km. Slopes on the steep offshore side vary between 3° and 20° while the shoreward slopes are gentler. The shallowest sand body is modern, in dynamic equilibrium with present conditions. The other two, however, are relict bodies built up during the last postglacial rise in sea level. Development of these sand bodies occurs in the shoreface environment and, in a space time evolution, they show a punctuated, but nearly continuous nature in the way that their preservation during the Holocene transgression occurs only in specific locations on the continental shelf. They begin growing on Pleistocene scarps with offshore slopes and their growth pattern is mostly controlled by the sediment supply, flow distribution and rate of sea-level rise. The formation of these sandy bodies is related to winter storms and southwesterly flows, which cause large volumes of sediment to be transported downshelf and offshore by downwelling bottom currents generated by coastal set-up. The result is sand movement onto and across the sand body surface down to water depths of 15-20 m. The thick sandy lenses of the Maresme shelf are interpreted as topographically induced lee-side sand bodies and not primarily as sand ridges in the classic sense. The occurrence of these bodies on a low-energy shelf may be significant for the interpretation of the geological record. © 1990.