Kyushu Univ., Japan

One of the most surprising results of ODP Leg 110 was the discovery of a 220 m-thick sequence of anomolously coarse-grained sediments on the slope of the Tiburon Rise, an area in which we expected to encounter only hemipelagic and pelagic deposits. This middle Eocene-upper Oligocene sequence consists of 37% South American-derived silt/sand terrigenous turbidites, 10% marl turbidites derived from higher on the Tiburon Rise, and 53% hemipelagic 'background' clays deposited below the CCD. The terrigenous beds occur several hundred meters above the abyssal plain and represent an exceptional example of upslope flow of distal turbidity currents. Two major sediment pulses (late middle Eocene and late early Oligocene) in this interval corellate closely with eustatic sea level high stands, the opposite relationship from that predicted by most models of deep-sea terrigenous sedimentation. Because similar terrigenous deposits do not occur in association with later sea level high stands, we propose that the two pulses resulted from increased sediment supply caused by tectonic movements of the northern South American borderland. The oil-bearing Scotland Group sandstones of Barbados are approximately the same age as the Leg 110 terrigenous silts/sands and may have been deposited in response to the same tectonic events. However, the Scotland Group sandstones had a predominantly cratonic source whereas the Leg 110 deposits were probably derived from a more easterly mixed cratonic-shelfal source.