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Sites 403 and 404, situated on the rifted margin of Rockall Plateau, have an incomplete Tertiary succession. Late Paleocene to Eocene clastic and volcaniclastic sediments were deposited in inner shelf, brackish to marine, and mid-shelf marine environments. By middle Eocene times the water had deepened to outer shelf or upper bathyal. The upper Eocene sediments at Site 403 were deposited in upper bathyal depths. Following a long stratigraphic break to late Miocene time, sedimentation resumed in a water depth of 2200 to 2600 meters. The record from then until the present day appears to be continuous. Sites 405 and 406, situated south of the transform fault that bounds the southern margin of Rockall Plateau, also have an incomplete Cenozoic record. Upper Paleocene to Eocene sediments accumulated in about 1000 meters water depth. In late Miocene to Recent time the depth was 2200 to 2500 meters at Site 406 and 1800 to 3000 meters at Site 405. Planktonic foraminifers are rare in Paleogene sediments of Sites 403 and 404; at Sites 405 and 406 they are more common but not diverse, and short-ranging stratigraphic marker species are rare. Neogene planktonic assemblages are moderately diverse, but are temperate assemblages often lacking the stratigraphic markers so valuable in tropical zonal schemes. Benthic foraminifers show great variety in the Paleogene successions because of the changing depositional environments. Those of the Neogene were of deep water habitat and are much more uniform; most belong to the Planulina wuellerstorfi association characteristic of the bathyal zone. INTRODUCTION AND OBJECTIVES Sites 403 and 404 were drilled on the rifted margin of Rockall Plateau (Figure 1). They provide a record of events during rifting and the subsequent opening of the North Atlantic between Rockall Plateau and Greenland. Sites 405 and 406 were drilled south of the transform fault that bounds the southern margin of Rockall Plateau. They provide a record of the evolution of a transform margin. The main objective of this study was to investigate the benthic foraminiferal assemblages in the Cenozoic sediments for the purpose of interpreting the subsidence history and the concomitant environmental changes. A further objective was to date the assemblages using the planktonic foraminifers. MATERIALS AND METHODS OF STUDY Shipboard scientists selected samples that represented intervals of approximately 1 m.y. (Table 1). Most of the Neogene sediments were soft and easily processed. Those that were hard were soaked in water or in a dilute solution of sodium hexametaphosphate. All samples were washed on a 240 mesh (63 μm) sieve and the residue dried at room temperature. When dry, the > 120 fraction was separated by sieving, spread on a picking tray and benthic foraminifers were picked until at least 100 had been collected; this was not possible in all cases. No attempt was made to pick assemblages of planktonic forms; instead, representative species were mounted. 25° 20° Figure 1. Location of Sites 403 to 406. The large number of species and the limited time available for study has meant that not all species could be identified; many have been left in open nomenclature. In some figures i.e., 12, 14, 16, 18 and 21 to 24) the species plotted are those present in excess of 4% in one or more core assemblages. Those present in less than 4% overall abundance have not been plotted and are not included in the faunal reference list.

Cenozoic Biostratigraphy and Paleoecology of Sites 403 to 406 Based on the Foraminifers