Ocean Drilling Program, United States

During Leg 149, a transect of five sites (Sites 897 to 901) was cored across the rifted continental margin off the west coast of Portugal. Lithologic and seismostratigraphical studies, as well as paleomagnetic, calcareous nannofossil, foraminiferal, and dinocyst stratigraphic research, were completed. The depositional history of the Iberia Abyssal Plain is generally characterized by downslope transport of terrigenous sediments, pelagic sedimentation, and contourite sediments. Sea-level changes and catastrophic events such as slope failure, triggered by earthquakes or oversteepening, are the main factors that have controlled the different sedimentary facies. We propose five stages for the evolution of the Iberia Abyssal Plain: (1) Upper Cretaceous and lower Tertiary gravitational flows, (2) Eocene pelagic sedimentation, (3) Oligocene and Miocene contourites, (4) a Miocene compressional phase, and (5) Pliocene and Pleistocene turbidite sedimentation. Major input of terrigenous turbidites on the Iberia Abyssal Plain began in the late Pliocene at 2.6 Ma.