Sands and sandstones from Leg 66 of the Deep Sea Drilling Project can be grouped into three general categories based upon textural and diagenetic similarities. Early Miocene upper slope sandstones from Sites 489 and 493 are cemented either by calcite, or by gypsum. Calcite is volumetrically the most important cement; it occurs as a void-filling cement in foraminifer chambers, as a micritic to sparry pore-filling cement, and as a replacement mineral in framework grains. The gypsum cement has a patchy distribution and appears to have been introduced along fractures in upper slope sands. Quaternary lower slope sands from Sites 488 and 486 are either weakly consolidated or totally unconsolidated. Framework grains in finer-grained sands are surrounded by thin, discontinuous films of chlorite and illite, which originated largely from the in situ alteration of biotite. Coarser-grained sands have thicker, more continuous clay films that consist of altered detrital biotite and of mechanically dispersed illite and chlorite. Subsequent burial diagenesis could totally obscure these differences in the origin of matrix between the finer- and coarser-grained sands. Middle to late Miocene slope sands from Site 492 have a complicated diagenetic history. There is a pervasive network of fractures throughout the sands, yet there has been no rotation of grain fragments. Either the sands were fractured tectonically following compaction or they were fractured as a result of compaction subsequent to decementation. Interbedded shales from this site are also intensively fractured, which suggests that the possibility of tectonic fracturing is more likely.

Supplement to: Lopez, Cynthia M (1982): Petrography and diagenesis of sands and sandstones, Deep Sea Drilling Project Leg 66. In: Watkins, JS; Casey Moore, J; et al. (eds.), Initial Reports of the Deep Sea Drilling Project (U.S. Govt. Printing Office), 66, 505-520