Sedimentation on mid-ocean sediment drifts

Abstract

Summary The paper reports results from DSDP Leg 94, where holes were drilled in the Feni and Gardar sediment drifts, with particular emphasis placed on studying sediment waves that ornament the surfaces of the drifts. The Feni Drift is a 1500–1700 m thick accumulation of sediment constructed on an early Eocene to late Oligocene seismic reflector. The Gardar Drift is 1300–1600 m thick, and is probably built directly on late Eocene oceanic basement. At Site 610 on Feni Drift, the deepest hole penetrated to upper Miocene sediments at 720 m, and at Gardar Drift, to upper Miocene sediment at 500 m. Pre-site surveys showed that the sediment wave fields on the drift surfaces were more irregular than Gloria sidescan records suggest, consisting of interfingered en echelon mounds. The waves did not show any well-defined sense of migration. The sediments recovered at Sites 610 and 611 show that the drifts consist of pelagic ooze and calcareous mud, with very few primary sedimentary structures preserved. No significant differences were observed between lithologies on sediment wave crests and those in through locations. On the other hand, systematic differences in sedimentation rates between crest and trough holes at Gardar Drift support the hypothesis that the waves migrated during the Pliocene but were evenly draped during the Pleistocene.