Une Zonation du Crétacé à l'aide des Foraminifères planctoniques est proposée pour les régions méditerranéennes. L'attention est attirée particulièrement sur cette limitation géographique de la validité de l'échelle, ainsi que sur le degré de précision que l'on peut attendre dans la corrélation entre ces zones de microfossiles et les autres échelles (zones de macrofossiles, étages, échelle linéaire des âges, renversements magnétiques).

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Some sedimentary units (I to V) or sub-units will be discussed in the ecostratigraphy section of this report. The designation of sedimentary units and sub-units described in this report are unique to this study and do not apply to the designations provided by the shipboard sedimentologists. These sedimentary units comprise lithologic entities (here called lithoterms) which were partially described onboard ship and upon which we further elaborated at Lamont-Doherty Geological Observatory. The different lithoterms in a given unit roughly correspond to the successive intervals, which are usually distinguished in a sedimentary graded sequence. They have been designated differently, depending on the different units (1, 2, 3 . . . , I, II, III . . . , A, B, C. . .). In the caption of Column G of Chart 1A (back pocket, this volume), these letters and Arabic or Roman numbers have been inserted from one unit to 287

A survey of DSDP black shales from the North Atlantic has been carried out in order to study the evolution of Cretaceous palaeoenvironments in the region. The study involved a reappraisal of the biostratigraphy of the Cretaceous formations and considered accumulation rate, mineralogical and organic geochemical data. Special attention was paid to distinguishing between redeposited and autochthonous sediments. Three main phases of deposition are recognized which are separated by two unconformities:The Blake-Bahama phase (Valanginian-early Aptian (Bedoulian)) corresponds to relatively uniform depositional conditions over the whole of the North Atlantic with periods of anoxia. The clay mineral assemblages reflect different sedimentary influxes from the continents into the eastern and western parts of the basin which were separated by the midocean ridge.The transition to the Hatteras phase (Event El) is marked by a drastic fall in sediment accumulation rate and by a rapid rise in the CCD but not by any appreciable change in clay mineral fluxes.The Hatteras phase (late Aptian-late Cenomanian) is characterized by distinctly diverse depositional conditions. In the southeastern part of the basin anoxic conditions were persistent, while in the northeast along the European margin there is no, or only very rare, evidence of anoxia. In the west, periods of oxia and anoxia alternated. Over the mid-ocean ridge conditions were oxic. A 'barrier' in the region of the present-day Bermuda Rise separated two areas of distinct clay mineral deposition.The transition to the Plantagenet phase (Event E2) corresponds to low sedimentation rates. It was immediately preceded by, or was coincident with, deposition of a black shale rich in marine organic matter.The Plantagenet phase (Turonian-Senonian) was a period of uniform sedimentation under oxic conditions.Possible causes of these changes in sedimentation are outlined.

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