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Hole 398D is located 200 km off the coast of Portugal (west of Oporto), in a small bathyal platform on the lower continental rise on the southern margin of Vigo Seamount. The hole was drilled on the western flank of a deep northeast-southwest trough in a region considered part of the continental passive margin of the eastern North Atlantic. Drilled in a water depth of 3910 meters, the hole bottomed at 1740 meters and was cored almost continuously downwards from Core 19 (585 m), with especially good recovery, in the Mesozoic series between Core 41 (800 m) and the basal Core 138. This report attempts to date the formations encountered between 800 meters and the bottom of the hole at 1740 meters (Figure 1), and to reconstruct their sedimentary history. Sampling and methods have been organized accordingly. We sampled extensively because of the unique opportunity afforded by the sequential nature of the deposits, in order to provide a statistical basis for these studies. Multiple samples were obtained from the same or a similar lithologic interval in a sequence; certain sequences were closely sampled several times. A total of 1073 samples was collected. The various components, organic and inorganic, found in the washed residues (on a 63-micron sieve) were estimated semiquantitatively as to their concentration (absent, trace, rare, common, abundant, and very abundant) and their frequency (sporadic, frequent, and permanent). This applies to calcareous benthos (0), agglutinated benthos (AP), planktonics (π), radiolarians (Rad), quartz, and mica. A more elementary scale (absent, present, abundant) was used for some other components (organic debris, aptychus, inoceramus, fish remains, plant debris, pyrite, and glauconite). Only the "presence" of ammonites, ostracodes, or spicules was noted. Lastly, the hydrochloric acid reaction of small fragments of sediments discerned under the microscope was tested (calcareous, argillo-calcareous, and noncalcareous). All these data have been entered on the left (Column B) and the right (Columns H, J) sides of a large stratigraphic range chart (Chart 1A, microfiche in back pocket, this volume). On its left border (Column A), this chart provides a complete listing of the samples examined. In the middle of this chart, the identified species and/or genera were recorded in the stratigraphic order of their first occurrence (with a larger black dot if particularly abundant). From left to right: the first column (Column C) corresponds to the so-called "primitive arenaceous foraminifers" (AP), which are generally considered residual forms after dissolution processes beneath the CCD; the second large column (Column D) corresponds to the main or most interesting species which serve to establish the biozonation and the age; the third column (Column E) corresponds to a certain number of genera which were not noted in the true biostratigraphic Columns D or C, but whose presence serves to reconstitute the biocoenoses; some of them, on the left side of Column E, also belong to the residual agglutinated group. Two other columns give the results of the analysis of the foraminiferal assemblages (F) and the sedimentary lithofacies (G). Foraminiferal assemblages were classified according to the presence, absence, or predominance of their three main components: ß, π, and AP (as noted above). To visualize the nature of these assemblages and to shorten our text, we propose the following abbreviations:

Chronostratigraphy and Ecostratigraphy of Cretaceous Formations Recovered on DSDP Leg 47B, Site 398