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The western North Atlantic section consists mainly of gray, black, and bluish white hemipelagic sediments which were deposited and subjected to early diagenesis under reducing conditions. Authigenic (diagenetic) minerals in these sediments with bivalent iron manganese include pyrite, siderite, glauconite, rhodochrosite, and manganic siderite. Authigenic iron and manganese oxides are virtually absent in the reduced layers. In contrast to the reduced sediments, several brown, red, and variegated layers occur. They indicate the presence of oxidized iron and manganese and obviously represent oxidizing conditions of sedimentation and early diagenesis. Two distinct intervals of this oxidized sediment were described from the western North Atlantic on the basis of DSDP Leg 11 drilling: (1) Upper Jurassic red and variegated limestone, marly limestone, calcareous claystone; (2) Upper Cretaceous to Paleocene (?) variegated clay stones (Hollister, Ewing, et al., 1972). Both intervals were drilled at Site 391 of Leg 44 (this volume). The Upper Cretaceous sequence was also cored at Sites 382, 385, 386, and 387 of Leg 43 (Tucholke, Vogt, et al., in press). In addition, Cretaceous (Aptian to Albian) variegated and brown chalks were drilled at Site 390 (Leg 44). Analogies may be drawn with the Maestrichtian nannofossil chalk in Hole 384 (Leg 43). Intervals of similar red and variegated sediments have also been drilled in the eastern Atlantic continental margins during several DSDP legs (14, 40, 41). We conducted geochemical and mineralogical investigations on several tens of samples from Legs 43 and 44 and also utilized published data by Lancelot et al. (1972), and X-ray determinations by Zemmels et al. (1972), Koch and Rothe (in press), and Flood (this volume). On the basis of these data I discuss lithologic, geochemical, and mineralogic aspects of these peculiar variegated and red sediments in order to compare the sediments from different locations.

Mesozoic Variegated and Red Sediments of the Western North Atlantic, DSDP Legs 43 and 44