Paleomagnetic results from sediments acquired from the continental margin at DSDP Sites 548, 549, 550, and 551 are described. Where possible, the results were used to construct a polarity reversal stratigraphy for the sections sampled, thus enabling the biostratigraphic dating of the sediments to be refined. Several sections in this study were found to be suitable for magnetostratigraphic work, in particular the upper Paleocene to middle Eocene sediments from Site 549, which contained rich faunal assemblages. These sediments are underlain by a thick sequence of Cretaceous sediments that formed during the Long Cretaceous normal polarity interval. Sediments that formed during the later part of this magnetically quiet interval were also recovered at Site 550. Three short reverse polarity intervals were also recovered at this site; they lie directly over basement and are thought to represent a mixed-polarity interval of late Albian age. They may therefore provide important evidence concerning the age of the earliest sediments at this site.In addition, measurements of the magnetic susceptibility and intensity of remanent magnetism proved to be of interest. A significant decrease in the susceptibility and intensity values close to the early/middle Eocene boundary was noted at Sites 548 and 549. This decrease may be correlated with the results from Holes 400A and 401, which were drilled on DSDP Leg 48 in the northeast Bay of Biscay. The decrease may represent an abrupt reduction in the supply of terrigenous material at the end of the early Eocene, reflecting, perhaps, a change in sediment transport processes at that time.
A composite stratigraphic section based on the four DSDP-IPOD Leg 80 drill sites provides a nearly complete record of syn-rift and post-rift events in the vicinity of Goban Spur. Syn-rift sediments were deposited in marginal marine to outer shelf environments. Above the "breakup" unconformity (hiatus spanning most of the Aptian), post-rift Albian sediments indicate the development of a deep-water seaway in the Goban Spur region. The latest Campanian/Maestrichtian interval records the initiation of rather uniform, widely distributed marine sedimentation throughout the region. Climatic changes, rather than changes in water depth, became conspicuous during the Tertiary. Widespread, nearly synchronous periods of nondeposition or erosion occurred in the Paleocene, middle Eocene, middle Oligocene, and late Miocene. Differences in the sediment record among sites are due to their varying positions (1) along the margin of the developing Atlantic seaway and (2) within their respective half-graben depositional basins.
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