Turbidites and Terrigenous Muds, DSDP, Leg 25

Abstract

Turbidites and/or terrigenous muds were recovered from eight sites along the southeast African continental margin during Leg 25 of the Deep Sea Drilling Project. Although these terrigenous deposits do not show equivalent facies between adjacent basins, they can be subdivided broadly by lithology. Biogenic and volcanic graded beds occur at five sites, whereas laminites (contourites?) are present at two sites.'The graded beds, usually less than 20 cm thick, range in age between Oligocene and Recent; the laminites are Late Cretaceous and Eocene. A Late Cretaceous turbidite sequence (with virtually every characteristic of an Alpine flysch) comprises a portion of the continental rise of the Somali Basin. Thick Eocene and Miocene massive sand units were cored from the Somali and Mozambique Abyssal plains. Detailed grain-size analyses of the graded beds and massive sands indicate up to 20 percent matrix of apparently primary origin. A C-M diagram suggests deposition of the graded beds and some of the massive sands by turbidity currents. The C-M diagram further suggests that portions of the massive sands may have been moved by a traction current, possibly as a "bed load" below a turbid flow. Regardless of the depositional process, the massive sands were transported between 750 and 1770 km over slopes as gentle as 1:1000.