Detrital modes of Albian and younger Cretaceous sandstones at Site 1276 are similar and suggest that there was one major source of sandy sediment. Because this site was within a narrow ocean basin at this time, an eastern Iberian source was considered. The few Albian data available from the Iberian margin are inconclusive, but when Mesozoic–Cenozoic detrital modes for both margins are considered as a whole, the Site 1276 detrital modes are more compatible with a Newfoundland margin source such as Avalon Uplift. Other studies (e.g., Hiscott, this volume) help to rule out more northerly sources such as the lesser known rocks of Flemish Cap. The Site 1276 sandstones have a recycled orogen (Dickinson, 1985) provenance, consistent with their being at least partly derived from the erosion and recycling of foreland basin sedimentary cover sequences.
The source(s) of the ~60-Ma volcanic debris at Site 1276 remains unknown. Although we found no additional volcanic-rich intervals in samples from this core, we did identify and document mafic to felsic debris from the ~60-Ma intervals at several sites drilled on the Iberian transect. This new information implies that magmatism was widespread across the North Atlantic during this time frame. The presence of volcaniclastic material off Iberia makes long-distance submarine transport from Greenland volcanic centers less feasible; we favor local basin margin or intrabasinal sources (reactivation?) with eruptions likely linked to rifting and plate reorganizations in the North Atlantic.
The upsection change to a more calcareous petrofacies (grainstones) was likely driven by the establishment of carbonate environments on Grand Banks. This appears to have been a regional North Atlantic phenomenon, with calcareous deposits characterizing both the western and eastern (Pyrenees) margins of the Iberian Peninsula as well. Shelf productivity and downslope distribution of calcareous debris was likely eustatically controlled.
The Newfoundland and Iberian margin rift-to-drift successions and associated petrofacies are part of a spectrum summarized in Figure F21. The nonparallel compositional evolution of these margins is linked to the asymmetry of basement terranes across the region associated with rifting along a former suture zone. The more mature sand compositions likely result from reworking of foreland basin sediments. This asymmetry may be present elsewhere along the margins of the Atlantic Ocean. As sand composition exerts a first-order control on diagenesis and ultimate sandstone reservoir character on passive margins, this model has important ramifications in petroleum exploration.