Calcareous nannofossils are primarily the skeletal remains of golden-brown unicellular algae called coccolithophores. These nannofossils have proven useful for marine biostratigraphy in sediments ranging from the Late Triassic to the Holocene in age. Nannofossil biostratigraphic zones are defined by first appearances, extinctions, or acmes and must be recognizable over large regions of the world in order to be useful.
During Ocean Drilling Program (ODP) Leg 173, six sites were drilled in the Iberia Abyssal Plain (IAP), which is located off the western coast of the Iberia peninsula (Fig. F1). We recovered Upper Cretaceous sediments from Sites 1068 and 1069 and Paleocene sediments from Sites 1067, 1068 and 1069. Leg 173 was intended as a follow-up to Leg 149; thus, it had similar objectives of sampling oceanic and continental crusts to determine their origin and history (Whitmarsh, Beslier, Wallace, et al., 1998). However, its important secondary objective was to determine the sedimentary history of the passive margin.
Site 1067, drilled over a high buried basement block (Fig. F2), yielded only uppermost Paleocene sediments. Site 1068 was drilled farther down the flank of the same basement block; from it we recovered Upper Cretaceous sediments and the most complete Paleocene section in the area. The only other reasonably complete Upper Cretaceous to Paleocene section in the IAP was recovered adjacent to the nearby Vigo Seamount at Deep Sea Drilling Project (DSDP) Site 398 (Fig. F1) (Sibuet, Ryan, et al., 1979). An uppermost Paleocene section was recovered at Site 900 of Leg 149 (Sawyer, Whitmarsh, Klaus, et al., 1994).
Of the three Leg 173 sites discussed here, Site 1069 was the farthest from the continent and was drilled over the next westward basement block from Sites 1067 and 1068. Site 1069 contained a fairly continuous record of nannofossils from the upper Campanian through the Paleocene but was the most difficult to zone because of the absence of key biostratigraphic marker species.
Much of the sedimentation during the Cretaceous to Paleocene on the IAP was made up of carbonate-bearing turbidites. The main purpose of this study is to describe the abundance, preservation, and biostratigraphic distribution of Cretaceous to Paleocene calcareous nannofossils recovered from these sediments during Leg 173. Using these data, we will determine sedimentation rates and mass accumulation rates to help elucidate the sedimentation history of the IAP.
We believe that a reliable biostratigraphic model can be constructed, despite the fact that the nannofossils are found in turbidites. Weaver (1994) demonstrated that most turbidites in the Canary Basin were essentially nonerosive and generally consisted of a mixture of sediments that ranged from 200 to 500 ka in age. A working hypothesis in this paper will be that the turbidites found on the IAP are similar to the turbidites found in the Canary Basin and that they can yield a usable nannofossil biostratigraphy.
Calcareous nannofossils species considered in this report are listed in the "Appendix," where they are arranged in alphabetical order by genera. Bibliographical references for these taxa can be found in Perch-Nielsen (1985) and Bown (1998); any references not listed therein are cited in the references of this paper.