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At the uppermost continental rise off Cape Bojador, 153 meters of upper Hauterivian, laminated, gray, silty claystones were penetrated below a 1300-meter-thick Neogene section. These claystones are rich in terrigenous components (quartz, mica, plant debris), fish remains, and organic carbon, but poor in carbonate and microfossils. The sequence contains many thin layers and some nodules of siderite which was precipitated during early diagenesis after the formation of pyrite and may have replaced earlier calcite. Locally, a few thin layers of well-sorted silt to fine sand occur, and also marls with a well-preserved nannoflora. Within a three-dimensional facies model for the Early Cretaceous continental margin, the upper Hauterivian sediments of Site 397 are interpreted as being distal prodelta muds, rapidly deposited (75 to 150 m/m.y.) in an oxygen-depleted environment and in a water depth of a few hundred to thousand meters. They are comparable to deposits from recent (e.g., Niger) and Early Cretaceous (e.g., Nova Scotian shelf) deltaic environments. Coeval sediments from a nearby commercial shelf well and from outcrops in the Aaiun-Tarfaya coastal basin represent the landward (neritic, intertidal-lagoonal, alluvial plain) subenvironments of a widespread delta system. The source area of the rapidly deposited deltaic sediments were uplifted Precambrian and Paleozoic rocks of the Requibat Massif, Mauritanides, and/or Anti-Atlas Mountains. Heavy minerals suggest a plutonic source area; plant fragments and clay mineral associations indicate weathering under a temperate, humid climate. After the "Wealden-type" phase of a prograding delta, the Middle Cretaceous transgression initiated a landward facies migration. This lead to a fining-upward "megacycle" and a decrease of the terrigenous and a relative increase of the biogenic input. An expanded oxygen-minimum zone and/or regional upwelling during the late Cenomanian/Turonian generated laminated bituminous marls in the coastal basin. The present coastline is situated between the Early and mid-Cretaceous strandlines. The present outer shelf edge was not formed before about the Cenomanian/Turonian. INTRODUCTION One of the objectives of Leg 47A was to study the Early Cretaceous paleoenvironment and sedimentary history of the Cape Bojador continental margin. However, not before a 1300-meter-thick Neogene section had been penetrated, did the core barrel first reveal an enigmatic Lower Cretaceous sequence of medium gray, partly laminated, and almost barren mudstones with thin yellowish brown "dolomite" intercalations. Because of time constraints and extremely low penetration rates, only 153 meters of the more or less homogeneous formation were penetrated. This was insufficient to reach the base of the Cretaceous which, due to the apparently increasing accumulation rates, may occur at considerably greater depth. Although the recovered sediments may represent less than 2 per cent of Cretaceous time, they revealed a remarkable facies forming the hitherto unknown seaward equivalent of the well-surveyed Aaiun Basin sequence (AUXINI, 1969; Ratschiller, 1970). The strange facies of the Lower Cretaceous strata of Site 397 raises a number of important questions concerning sedimentation and paleoenvironment of these deposits. We will try to tentatively answer some of these questions in the context of the Early Cretaceous evolution

Facies Paleoenvironment of Lower Cretaceous Sediments at DSDP Site 397 and in the Aaiun Basin (Northwest Africa)