Cretaceous sediments encountered in Hole 603B contain a 17 Å smectite as the principal clay mineral, with lesser amounts of illite, kaolinite, and randomly interstratified illite/smectite (I/S). No evidence of smectite to I/S transformation with depth is seen in the interval between 1040 and 1570 m below the sediment surface. Although the presence of some volcanic ash suggests a volcanic origin for the smectite, the nature of associated organic matter together with prevailing sedimentological models for Cretaceous sedimentation on the lower continental rise argue more strongly for a dominantly terrestrial origin for the clays.

Supplement to: Huff, Warren D (1987): Cretaceous clay mineralogy of the continental rise off the east coast of the United States, Site 603, Deep Sea Drilling Project 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, 985-988