Ebro Margin Sedimentary System in the Western Mediterranean Sea, from Delta to Deep Sea

C. Hans Nelson, Andres Maldonado

During Holocene high sea level, delta-front lobes of silty mud have deposited beside a lobate Ebro delta. Topset and foreset beds of these lobes extend up to 20 km offshore in up to 30 m of water. Geostrophic currents advect fine silt and clay from river discharge and storm wave resuspension in the delta front and deposit up to 20 m of bottomset beds in a distal prodelta clay belt formed on the inner to middle shelf for 70 km south from the delta. Intensified water circulation and increased bottom-current speeds inhibit prodelta progradation over the outer shelf and north of the delta and south of the clay belt, where the shelf narrows. Deposition of Holocene hemipelagic mud on the upper slope is restricted, but some modern Ebro sediment apparently bypasses to the deep ma gin.

During Pleistocene low sea level, a series of shelf-edge deltas resulted in extensive progradation of foreset mud beds over the continental slope east of the modern delta and south to the Columbretes Islands. In the north, rapid sediment progradation has resulted in large canyons (±5 km wide), unconfined sediment gravity flows, and deposition of large sediment aprons (50 km diameter) downslope from canyon mouths. In the south, narrow canyons (±2 km wide) have funnelled turbidity currents to side-by-side channel-levee complexes younger and smaller to the southwest. Subsidence of the Valencia trough has facilitated sediment transport from these channel-levee complexes into Valencia Valley and thence to the Valencia fan, 200 km to the northeast. Consequently, during low sea lev l stands a major portion of Ebro sediment is transported north to the Valencia fan, whereas the main progradational history of the Ebro margin has been offshore and to the south of the present delta.

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