Pliocene-Pleistocene calcareous nannofossils from the Iberian Abyssal Plain

During Ocean Drilling Program Leg 149, five sites were drilled on the Iberia Abyssal Plain, west of the Iberian Peninsula. Five holes (Holes 897A, 897C, 898A, 899A, and 900A) yielded Pliocene-Pleistocene sediments, which consist mainly of turbidites. Among these, Holes 897C and 898A yielded significant Pliocene-Pleistocene sediments that provided a high-resolution nannofossil biostratigraphy essential for locating paleomagnetic polarity events and for interpreting the age and frequency of turbidite sedimentation in the Iberia Abyssal Plain. Pliocene-Pleistocene nannofossils recovered during Leg 149 are generally abundant and well to moderately preserved. Although reworking is evident in most samples, the Pliocene-Pleistocene nannofossils proved quite reliable for dating the sediments. Most Pleistocene zonal boundaries proposed by S. Gartner in 1977 and the Pliocene standard zonal boundaries proposed by E. Martini in 1971 were easily recognized. In addition, several other nannofossil events proposed by D. Rio et al. in 1990 and by T. Sato and T. Takayama in 1992 were recognized and proved valuable for improving the resolution of Pliocene-Pleistocene nannofossil biostratigraphy. The Pliocene-Pleistocene nannofossil biostratigraphic results of Holes 897C and 900A coincide rather well with the discerned paleomagnetic polarity events. As a result, the combination of nannofossil biostratigraphic and paleomagnetic studies provides important information for fulfilling the second objective of this leg: to determine the history of turbidite sedimentation in the Iberia Abyssal Plain. The general trend of sedimentation rates inferred by nannofossil biostratigraphy indicates that sedimentation rates increase from the continental margin to the deep sea along with increasing water depth.

Cenozoic calcareous nannofossils in DSDP Leg 77 holes

Three of the six DSDP Leg 77 sites drilled in the western approaches to the Straits of Florida yielded thick sequences of Cenozoic sediment rich in calcareous nannofossils. Hiatuses are prominent in each of these continuously cored intervals. A prominent upper Oligocene hiatus, observed at each of these three sites, can be correlated to a large-scale "global" regression event. Other disconformable horizons present in the study area cannot be positively related to sealevel fluctuations and may be caused by a number of factors including local tectonic activity. Paleogene sections are generally marked by thick accumulations within the upper Oligocene Sphenolithus ciperoensis Zone and by a pronounced braarudosphaerid-holococcolith bloom recorded in the lower Oligocene and upper Eocene. This bloom is particularly well developed at Site 540. All samples examined contain abundant nannofossils. Preservation fluctuates throughout the sections from good to poor.

Cenozoic benthic foraminifers from ODP Leg 134 holes

This paper discusses the Paleobathymetric and paleoenvironmental history of the New Hebrides Island Arc and North d'Entrecasteaux Ridge during Cenozoic time based on benthic foraminiferal and sedimentological data. Oligocene and Pliocene to Pleistocene benthic foraminiferal assemblages from Sites 827, 828, 829, and 832 of Ocean Drilling Program (ODP) Leg 134 (Vanuatu) are examined by means of Q-mode factor analysis. The results of this analysis recognize the following bathymetrically significant benthic foraminiferal biofacies: (1) Globocassidulina subglobosa biofacies and Bulimina aculeata-Bolivinita quadrilatera biofacies representing the upper bathyal zone (600-1500 m); (2) Gavelinopsis praegeri-Cibicides wuellerstorfi biofacies, indicating the Pacific Intermediate Water (water depth between 1500 and 2400 m); (3) Tosaia hanzawai-Globocassidulina muloccensis biofacies, Valvulineria gunjii biofacies, and the Melonis barleeanus-Melonis sphaeroides biofacies, which characterize the lower bathyal zone; (4) the Nuttallides umbonifera biofacies, which characterizes the interval between the lysocline (approximately 3500 m) and the carbonate compensation depth (approximately 4500 m); and (5) the Rhabdammina abyssorum biofacies representing the abyssal zone below the carbonate compensation depth. Benthic foraminiferal patterns are used to construct Paleobathymetric and paleogeographic profiles of the New Hebrides Island Arc and North d'Entrecasteaux Ridge for the following age boundaries: late Miocene/Pliocene, early/late Pliocene, Pliocene/Pleistocene, and Pleistocene/Holocene.

Occurrence of nannoplankton observed in Early Pliocene samples from Zanclean stratotype of Capo Rossello, Sicily (Table I)

Calcareous nannoplankton biostratigraphy has been worked out in the eastern Mediterranean utilizing deep-sea sediments recovered from DSDP Leg 42A Sites 375 and 376. These two drill sites were located approximately 55 km west of Cyprus on the Florence Rise. Sediments, ranging in age from early Miocene (Helicosphaera ampliaperta Zone) through Holocene, contain sufficient age-diagnostic species to recognize essentially all of the lowlatitude nannoplankton zones described by Bukry, although regional, secondary marker species are needed to define some zonal boundaries. Reworked Cretaceous and Paleogene nannoplankton occur throughout the stratigraphic interval studied, but not in quantities large enough to mask indigenous species. Sedimentation rates at Sites 375 and 376 were highest in the late Miocene and late Pleistocene. Open-marine, warm-water species of discoasters are present in significant numbers throughout the Miocene and Pliocene. Earliest Pliocene assemblages contain numerous specimens of ceratoliths. Nannoplankton in post-Messinian sediments at the drill sites and the Zanclean stratotype at Capo Rossello, Sicily, indicate that the base of the Amaurolithus tricorniculatus Zone (base of Triquetrorhabdulus rugosus Subzone) corresponds with the Miocene-Pliocene boundary.

Radiolarians of the Izu-Bonin Region

Radiolarians occur at five Leg 126 sites. Well-preserved radiolarians were recovered from Miocene and Pliocene through Holocene sections. The results of this study may help to fill the informational gap on Quaternary radiolarian distribution at mid-latitudes in the western Pacific. Radiolarian preservation is discontinuous, and, although present in Oligocene sections, specimens are poorly preserved.

Calcareous nannofossils of ODP Leg 103 holes

Ocean Drilling Program Leg 103 occupied five sites on the Galicia margin, northwest of the Iberian Peninsula. Two holes (Holes 637A and 638B) yielded significant Cenozoic sedimentary sections ranging from late Miocene to late Pleistocene in age. From the nannofossil stratigraphy, one hiatus is recognized in Hole 637A (2.35-2.4 Ma), whereas two hiatuses (one at 1.9-2.6 Ma and another at 3.5-3.7 Ma) are recognized in Hole 638B. Sediment-accumulation rates for the Cenozoic portions of these two holes have been calculated based on the nannofossil datums. The abundance ratios of Coccolithus pelagicus to Discoaster brouweri for Hole 637A show relatively low values and small fluctuations from 2.5 to 6.5 Ma but sharply increase and then widely fluctuate beginning at about 2.5 Ma. This may indicate relatively warmer, more stable surface-water temperatures from 2.5 to 6.5 Ma and cooler, variable surface-water temperatures after 2.5 Ma at Site 637. C. pelagicus/D. brouweri ratios from Hole 638B also show a trend of increasing values with time from late Miocene to late Pliocene, but with more fluctuations and a different pattern from that of Hole 637A.

Calcareous nannofossils of the Soithern Coral Sea

Leg 90 of the Deep Sea Drilling Project drilled 18 holes at eight sites (Sites 587-594) on several shallow-water platforms in the southern Coral Sea, Tasman Sea, and southwestern Pacific Ocean. The results from an additional hole (Hole 586B) drilled at Site 586 during Leg 89 are included in this report. Together, these sites form a latitudinal traverse which extends from the equator (Site 586) to 45°S (Site 594) and includes all the major water masses from tropical to subantarctic. Samples recovered at these sites range in age from middle Eocene to late Quaternary. The calcareous nannoplankton biostratigraphy for Leg 90 has divided into two parts: part 1, the Neogene and Quaternary of Sites 586-594. (this chapter); and part 2, the Paleogene of Sites 588, 592, and 593 (Martini, 1986). A slightly modified version of the Martini (1971) standard Tertiary and Quaternary zonation scheme was used to make age determinations on over 700 samples. All of the relevant Neogene and Quaternary zone-defining nannoplankton are present at Sites 586-591 (0°-30°S) but become increasingly rare or are absent at Sites 592-594 (35°-45°S). Species diversity increases southward from the equator (Site 586) and reaches a peak at 20°S (Site 587). A decrease at 25°S (Site 588) and 30°S (Sites 589-591) is followed by an increase in species diversity at 35°S (Site 592). South of 35°S, species diversity again decreases and reaches a low at 45 °S (Site 594). Species diversity for all sites as a group generally increases through the early, middle, and late Miocene, reaches a peak in the early Pliocene, then gradually decreases through the late Pliocene and Quaternary

Calcareous-nannofossil biostratigraphy at DSDP Leg 57 Holes

As a continuation of the Japan Trench transect commenced by DSDP Leg 56, 10 holes were drilled and 273 cores were recovered while occupying Sites 438, 439, 440, and 441 during Leg 57. At Sites 438 and 439, near the top of the trench inner wall, a principal biostratigraphic objective was to establish a Neogene reference section overlying a pronounced acoustic basement thought to represent continental crust extending outward to this slope environment. At Sites 440 and 441, prime objectives were to distinguish, if present, admixtures of accreted oceanic and non-accreted slope materials, and to recognize repeated or missing sections resulting from the accretionary process. This report summarizes the nannofossil biostratigraphy of the upper lower Miocene to Pleistocene sequences of Leg 57 cores. Insufficient occurrences in the lowermost Miocene, presumed upper Oligocene, and upper Cretaceous sequences at Sites 438 and 439 precluded age determinations for these intervals based on nannoliths. All but a few samples from Site 441 were barren, and in general Leg 57 nannofossil assemblages were too modified by dissolution and diagenesis to permit meaningful paleoclimatologic or paleobiogeographic conclusions to be drawn.

Calcareous nannoplankton of DSDP Leg 43 holes

During Leg 43, six holes (Sites 382-387) were drilled in the western part of the North Atlantic Ocean; locations of sites are shown in Figure 1. Lower Cretaceous to Quaternary calcareous nannofossils were found in 127 of 189 cores recovered during the leg. The ages and zonal assignments of these fossiliferous cores based upon light-microscopical observation are given in Table 1. An almost continuous succession of nannofossil assemblages of the lower Maestrichtian to upper Paleocene is present at Site 384. A detailed investigation was conducted on samples at this site, and the evolution of approximately 50 species is documented through almost the entire Paleocene epoch.