Ocean Drilling Program Leg 103 recovered Lower Cretaceous sediments from the Galicia margin off the coast of Iberia. The high diversity and abundance of assemblages makes this excellent material for the study of Early Cretaceous calcareous nannofossils. With the exception of a hiatus between the upper Hauterivian and lower Barremian, nannofossil distributions form a continuous composite section from the lower Valanginian to lower Cenomanian sediments recovered at the four sites. The sedimentation history of this rifted continental margin is complex, and careful examination of the nannofossil con tent and lithology is necessary in order to obtain optimum biostratigraphic resolution. The Lower Cretaceous sequence consists of a lower Valanginian calpionellid marlstone overlain by terrigenous sand stone turbidites deposited in the Valanginian and Hauterivian during initial rifting of this part of the margin. Interbed ded calcareous marl and claystone microturbidites overlie the sandstone turbidites. Rifting processes culminated in the late Aptian-early Albian, resulting in the deposition of a calcareous, clastic turbidite sequence. The subsequent deposi tion of dark carbonaceous claystones (black shales) represents the beginning of seafloor spreading, as the margin con tinued to subside to depths near or below the CCD. The diversity, abundance, and preservation of nannofossils within these varied lithologies differ, and an attempt to distinguish between near shore and open-marine assemblages is made. Genera used for this purpose include Nannoconus, Micrantholithus, Pickelhaube, and Lithraphidites. In this study, six new species and one new subspecies are described and documented. Ranges of other species are ex tended, and an attempt is made to clarify existing, yet poorly understood, taxonomic concepts. A technique in which a single specimen is viewed with both light and scanning electron microscopes was used extensively to aid in this task. In addition, further subdivisions of the Sissingh (1977) zonation are suggested in order to increase biostratigraphic resolu tion. Retecapsa angustiforata Zone (CC2) Definition. Interval from the first occurrence of Retecapsa angusti forata to the first occurrence of Calcicalathina oblongata. Authors. Thierstein, 1971. Age. Late Berriasian to early Valanginian. Tubodiscus verenae Subzone (CC3a) of the Calcicalathina oblongata Zone (CC3) Definition. Interval from the first occurrence of C. oblongata to the first occurrence of Eiffellithus windii. Authors. CC3: Thierstein (1971), modified by Sissingh (1977) and Perch-Nielsen (1979). CC3a: this paper. Age. Early Valanginian. Remarks. The subdivision of CC3 is suggested here based on the first occurrence of E. windii n. sp. Although described here as new, it is illustrated as Eiffellithus sp. in earlier reports (see Appendix A). Al
During Leg 78A of the Deep Sea Drilling Project, six holes were drilled at three sites in the fore-arc region of the Lesser Antilles. Samples taken from sediments recovered west of the deformation front of the Barbados Ridge at Sites 541 and 542 contain upper Miocene through upper Pleistocene nannofossil assemblages. Comparable states of preservation in age-equivalent sediments indicate similar depositional histories at these two sites. Samples recovered from Site 543, an oceanic reference site east of the deformation front, contain poorly preserved nannofossils dated as early Pliocene through early Pleistocene. The sequence of nannofossil zones in the continuously cored sections at Sites 541 and 543 is similar. Differences in preservation of the calcareous nannoplankton in age-equivalent sediments at these two sites indicate that since the Miocene, sediments at Site 543 have been deposited at greater depths.A major stratigraphic inversion is present in Hole 541 at a depth of 276 m below the seafloor. At this horizon, upper Miocene muds of the Amaurolithusprimus Subzone (CN9b) overlie upper Pliocene marly nannofossil oozes of the Discoaster tamalis Subzone (CN12a). About 117 m of section are repeated above this level, as determined by the calcareous nannoplankton. This horizon is thought to be a reverse fault formed by imbricate underthrusting during the formation of an accretionary prism at the active margin. This is the first time this type of structure has been dated biostratigraphically at a modern convergent margin drilled by the Deep Sea Drilling Project. Three smaller repetitions of section occur above this fault in Hole 541. They begin at 262, 172, and 77 m sub-bottom. Strong evidence of faulting was also observed in sediments recovered at Site 542, as the last occurrence of Amaurolithus tricorniculatus lies at 180 m sub-bottom in Hole 542 and 211.5 m in Hole 542A. Poorly preserved nannofossil assemblages of the Discoaster berggrenii Subzone (CN9a) in a very thick section in the bottom of Hole 542A also suggest faulting of these upper Miocene muds.
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