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Albian/Aptian sediments from the Bay of Biscay, recovered during DSDP Leg 48, are characterized by a cyclicity in their lithology. This cyclicity generally consists of alternations of dark gray to black carbonaceous mudstones and greenish gray calcareous mudstones (see Site Chapters). The dark layers are similar, in their lithology, to the "black shales," a widespread facies in the Atlantic Cretaceous deposits, as established by previous DSDP Legs 14, 36, 40, and 41. In the deep-water sediments of Hole 400A, the dark layers are characterized by an organic carbon content value averaging 0.5 to 2 per cent of the sediment (Deroo et al., this volume); shipboard optical studies estimated a carbonaceous (' 'black material'') content ranging from 5 to 20 per cent of the sediment. It was thus obvious that an important part of the "black material" consisted of unidentified inorganic constituents; finely dividedpyrite or hydrotroilite were evoked. In order to try to resolve the problem, a detailed X-ray mineralogy study was carried on 122 samples taken every five cm in the following selected sequences: l>Hole 400A, Core 66 (lower Albian), Section 3: 27 samples. This hole was drilled at the foot of the Meriadzek Terrace, in 4473 meters of water; the lithologic sequence studied is interpreted as a deep sea-water deposit (see Site Chapter). 2)Hole 402A, Core 24 (lower Albian), Sections 1 through 5: 95 samples. This hole was drilled in a spur of the Armorican Slope, north of the Meriadzek Terrace in 2385 meters of water. Hole 402A Albian sediments are interpreted as shallow-water deposits (see Site Chapter). The samples were chosen in order to obtain a continuous control on the mineralogical assemblages throughout sedimentary cycles, and to compare the deepand the shallow-water depositional conditions, in sediments as contemporary as possible. Figure 1 shows the physiographic position of Sites 400 and 402 in the paleogeographic conditions thought to have prevailed during the Albian times. The position of the samples with regard to lithology appears on Figures 2 and 3.

Mineralogy and Geochemistry of Selected Albian Sediments from the Bay of Biscay, Deep Sea Drilling Project Leg 48