Facies Architecture and Processes of Post-Messinian Prograding Basin Fill, Valencia Trough, Western Mediterranean

Michael E. Field, James V. Gardner, Belen Alonso

The eastern margin of the Valencia Trough is underlain at sediment depths of 400 to 1,200 m by a prominent, mappable seismic reflector. This reflector, which marks the top of the evaporitic facies that culminated in latest Messinian, provides a marker bed for evaluating post-Miocene deposition on the margin. We recognize a facies architecture in the deposits that overlie the Messinian reflector. This architecture is composed of four distinct sediment facies: distal (isolated) basin, basin plain, base of slope, and shelf. A submarine-fan style of sedimentation per se is not evident. The composite sediment body is a prograded, upward-shallowing, offlap sequence controlled by the influx of terrigenous sediment from the Rio Ebro during the Quaternary.

The lower 400-600 m of the post-Messinian section is dominated by flat-lying, laterally extensive reflectors (distal basin) overlain by a similar facies that includes low-relief, shallow channels (basin floor). The upper 200-600 m is a basinward-thinning sequence of high-energy slope and base-of-slope deposits. The base-of-slope deposits are composed of amalgamated sediment lobes, each 5 to 10 km wide, formed by channel and overbank deposition. The overlying slope deposits primarily formed by levee construction adjacent to vertically prograding canyons. The entire sequence is capped by prograded Pleistocene delta lobes of the Rio Ebro. Levees and canyon walls on the slope appear to have undergone erosion through sediment failure, a condition probably related to the present high sea le el stand.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.