A 300-m-thick, upper Valanginian to Barremian turbidite sequence, consisting of sandstone and organic-matter-rich claystone turbidites intercalated in pelagic marl and limestone, was discovered at Site 603, on the lower continental rise off North America. Many of the turbidites consist of clayey sandstone beds, 1 to 1.5 m thick, containing abundant claystone clasts and displaying no or incomplete Bouma sequences. Sedimentary structures suggest that such beds were dominantly emplaced by viscous flows (sandy debris flows). The turbiditic sequence is topped by 40 m of clean, uncemented sands of ?Barremian-Aptian age.The development of different turbidite facies and facies associations at Site 603 is related to regional geology, variations in the type and amount of sediment supplied, and changes in sea level. We consider that the Hauterivian-Barremian lower turbidite sequence was deposited at times of high or rising sea level in a sediment-starved, channel-dominated turbidite system. Sedimentological and seismic data favor the hypothesis of a structurally confined "channel-levee complex" characterized by an efficient network of channels for distributing sand to the deep sea. High-energy turbidite facies suggest that turbidity currents might have been confined within levees of major channels while passing by Site 603. Erosion at channel levees may explain the abundance of shale clasts within the turbidites. The claystone lithology of ripup clasts indicates a probable levee origin. The hummocky reflection configuration supports the channel-levee hypothesis. At the same time as the lower turbidites were deposited, large amounts of terrigenous sediments were trapped on the shelf (Wealden-type facies). The upper, unconsolidated sand unit reflects a sudden input of shelf sand, thought to correspond to a phase of shelf destruction after the sea level dropped in middle Aptian time. A late Aptian-early Albian sealevel rise terminated the turbidite deposition, caused the change from carbonate-rich to carbonate-free pelagic sedimentation (CCD rise), and promoted the development of anoxic bottom waters which enhanced preservation of organic matter ("black shales").
D = dominant (>25(50)%), A = abundant, C = common (> 10%), R = rare, + = traces (< 1%), ( + ) = ? traces.
Supplement to: Sarti, Massimo; von Rad, Ulrich (1987): Early Cretaceous turbidite sedimentation at Deep Sea Drilling Project Site 603, off Cape Hatteras (Leg 93). In: van Hinte, JE; Wise, SW Jr; et al. (eds.), Initial Reports of the Deep Sea Drilling Project, Washington (U.S. Govt. Printing Office), 93, 891-940
