Ocean Drilling Program, United States

During Leg 149 a transect of holes (Sites 897 to 901) was drilled across the rifted continental margin off the west coast of Portugal at the edge of the Iberia Abyssal Plain. The upper part of the sedimentary sequence revealed the history of turbidite sedimentation on the plain. The sequence consists of thin terrigenous turbidites (0.1 to 1.0 m thick) separated by pelagic clay, marl, and ooze layers (0.01 to 1.89 m thick). Most of the turbidites consist of ungraded massive silts and clays, with sporadic coarser bases. Major input of terrigenous turbidites on the Iberia Abyssal Plain began in the late Pliocene at 2.6 Ma, but at Site 898 the lower part of the turbidite sequence is missing because of a hiatus. A large number of turbidites was deposited in the last 2.6 m.y., at an average of one turbidite per 3200 years at Hole 898A. It appears that sedimentation in the Iberian Basin is controlled at least partially by climatic changes.