Site 513

Abstract

Site 513 is located on the lower flank of the Mid- Atlantic Ridge to the east of the Argentine Basin at a water depth of 4383 meters, about 150 miles north of the present-day position of the Polar Front. It was drilled and continuously cored to the basement at a depth of 380.5 meters. Muddy diatomaceous ooze of early Miocene to Holocene age, 180 meters thick, is underlain by 53.9 meters of muddy diatomaceous nannofossil ooze and diatomaceous ooze spanning the early Miocene to late Oligocene. These sediments overlie 145.5 meters of nannofossil ooze ranging in age from late to early Oligocene with a white Porcellanite bed at the base. The Porcellanite rests on fine-grained phyric basalt interpreted to be a sill. Periods of nondeposition or erosion are identified within the middle Pliocene (~ 3.85-3.05 m.y.), bracketing the Miocene/Pliocene boundary (a few hundred thousand years), within the late Miocene (-8.6-6.5 m.y.), and between the early and late Miocene (_ 19.0-9.5 m.y.). The Oligocene sections of Site 513 and 511 partially overlap; the composite section represents the most complete upper Eocene-lower Miocene sequence in southern high latitudes. The age of the basal layers (lowermost Oligocene, 36.5 m.y.) corresponds closely to the age predicted by magnetic anomalies.