Neogene and Paleocene-Maestrichtian calcareous nannofossils in sediments of the upper continental rise off New Jersey

Maestrichtian to Holocene calcareous nannofossils from two closely spaced sites on the upper continental rise some 100 miles (161 km) southeast of Atlantic City, New Jersey, were zoned in order to help date a major canyon-cutting event in the late Miocene and to delineate and correlate other hiatuses with seismic stratigraphy. Mid-middle Eocene through middle Miocene sediments (Zones CP14 to CN6) were not recovered in these holes, but nearly all other zones are accounted for. The Eocene section is described in a companion chapter (Applegate and Wise, 1987, doi:10.2973/dsdp.proc.93.118.1987). Nannofossils are generally sparse and moderately preserved in the clastic sediments of Site 604. Sedimentation rates are extremely high for the upper Pleistocene (201 m/m.y. minimum) above a hiatus calculated to span 0.44 to 1.1 Ma. The associated disconformity is correlated with local seismic reflection Horizon Pr . Sedimentation rates continue to be high (93 m/m.y.) down to a second hiatus in the upper Pliocene dated from about 2.4 to 2.9 (or possibly 3.3) Ma. The disconformity associated with this hiatus is correlated with local seismic reflection Horizon P2 and regional Reflector Blue, which can be interpreted to mark either the onset of Northern Hemisphere continental glaciation or circulation changes associated with the closure of the Central American Seaway. Sedimentation rates in the pre-glacial lower Pliocene are only about a third those in the glacial upper Pliocene. A prominent disconformity in the upper Miocene marks a major lithologic boundary that separates Messinian(?) glauconitic claystones above from lower Tortonian conglomeratic debris flows and turbidites below. The debris flows recovered are assigned to nannofossil Zones CN8a and CN7, but drilling difficulties prevented penetration of the bottom of this sequence some 100 m below the terminal depth of the hole. Correlation of the lower bounding seismic reflector (M2/Merlin?) to a drift sequence drilled on the lower rise at DSDP Site 603, however, predicts that the debris flows began close to the beginning of the late Miocene (upper Zone CN6 time) at about 10.5 Ma. The debris flows represent a major canyon-cutting event that we correlate with the beginning of the particularly severe late Miocene glaciations believed to be associated with the formation of the West Antarctic Ice Sheet. The existence of these spectacular debris flows strongly suggest that the late Miocene glacio-eustatic low stand occurred during Vail Cycle TM3.1 (lower Tortonian) rather than during Vail Cycle TM3.2 (Messinian) as originally published. Beneath a set of coalesced regional disconformities centered upon seismic reflection Horizon Au, coccoliths are abundant and in general are moderately preserved at Site 605 in a 619-m carbonate section extending from the middle Eocene Zone CP13b to the upper Maestrichtian Lithraphidites quadratus Zone. Sedimentation rates are 37 m/m.y. in the Eocene down to a condensed interval near the base (Zone CP9). A disconformity is suspected near the Eocene/Paleocene boundary. Sedimentation rates for the upper Paleocene Zone CP8 are similar to those of the Eocene, but Zones CP7 and CP6 lie within another condensed interval. The highest Paleocene rates are 67 m/m.y. down through Zones CP5 and CP4 to a major disconformity that separates the upper Paleocene from the Danian. This hiatus spans about 2.6 m.y. (upper Zone CP3 to lower Zone CP2) and corresponds to the major sea-level drop at the base of Vail Cycle TE2.1. As the most prominent break in this Paleogene section, it may correspond to seismic reflection Horizon A* of the North American Basin. Sedimentation rates from this point to the Cretaceous/Tertiary boundary drop to 11 m/m.y., still high for a Paleocene DSDP section. No major break in deposition could be detected at the Cretaceous/Tertiary boundary.

Revision of the early-middle Pleistocene calcareous nannofossil biochronology

The extant nannofossil biostratigraphic and biochronologic framework for the early-middle Pleistocene time interval has been tested through the micropaleontological analysis of globally distributed high-quality low- to mid-latitude deep-sea successions. The quantitative temporal distribution patterns of relative abundances of selected taxa were reconstructed in critical intervals, and the following biohorizons were defined: first occurrence of medium-sized Gephyrocapsa spp. (bmG); last occurrence of Calcidiscus macintyrei (tCm); first occurrence of large Gephyrocapsa spp. (blG); last occurrence of large Gephyrocapsa spp. (tlG); first occurrence of Reticulofenestra asanoi (bRa); re-entrance of medium-sized Gephyrocapsa spp. (reemG) and last occurrence of Reticulofenestra asanoi (tRa). The detailed patterns of abundance change at these biohorizons were used to generate a detailed biostratigraphy, and the biostratigraphic data were transformed into a precise biochronology by means of correlation to isotope stratigraphies and astronomical timescales. The degree of isochrony or diachrony of the biohorizons was evaluated. Biohorizons tlG and tRa are isochronous occurring close to marine isotope stages (MIS)55 and MIS 22, respectively, and bmG and blG are slightly diachronous on the order of 30-40 kyr, whereas biohorizons tCm, reemG and bRa are confirmed as diachronous on the order of 100, 80 and 60 kyr, respectively. Some of the events are clearly controlled by environmental conditions, e.g. the last occurrence of R. asanoi, related to significant environmental changes associated with the first large-amplitude glaciation of the late Quaternary, MIS 22.

Calcareous nannofossil during the Paleocene Eocene Thermal Maximum in sediments of Walvish Ridge

Compositions and abundances of calcareous nannofossil taxa have been determined in a ca 170 kyrs long time interval across the Paleocene/Eocene boundary at 1-cm to 10-cm resolution from two ODP Sites (1262, 1263) drilled along the flank of the Walvis Ridge in the South Atlantic. The results are compared to published data from ODP Site 690 in the Weddell Sea. The assemblages underwent rapid evolution over a 74 kyrs period, indicating stressed, unstable and/or extreme photic zone environments during the PETM hyperthermal. This rapid evolution, which created 5 distinct stratigraphic horizons, is consistent with the restricted brief occurrences of malformed and/or weakly calcified morphotypes. The production of these aberrant morphotypes is possibly caused by major global scale changes in carbon cycling in the ocean-atmosphere system, affecting also photic zone environments. No marked paleoecologically induced changes are observed in abundances of the genera Discoaster, Fasciculithus and Sphenolithus at the Walvis Ridge sites. Surprisingly, there is no significant correlation in abundance between these three genera, presumed to have had a similar paleoecological preference for warm and oligotrophic conditions.

Oligocene-Miocene calcareous nannofossils in ODP Leg 149 holes

During Ocean Drilling Program (ODP) Leg 149, five sites were drilled on the Iberia Abyssal Plain in the northeastern Atlantic Ocean. Both Mesozoic and Cenozoic sediments were recovered. Oligocene to Miocene sediments were cored at deepwater Sites 897, 898, 899, and 900. Except for a few intervals, occurrences of generally abundant and well-preserved calcareous nannofossils suggest that the deposition of the turbidite-type sediments occurred above the calcite compensation depth (CCD). One major unconformity in the middle late Miocene is present. Detailed quantitative analyses of calcareous nannofossils are used to determine the changes occurring among the nannoflora in relation to sea-level variation. A succession of 89 biohorizons from the early Oligocene to the late Miocene are defined by combining the biostratigraphic results of the four sites studied in the Iberia Abyssal Plain. One new genus and eight new species are described: Camuralithus, Camuralithus pelliculatus, Ericsonia detecta, Helicosphaera limasera, Sphenolithus akropodus, Sphenolithus aubryae, Sphenolithus cometa, Reticulofenestra circus, and Syracosphaera lamina. Two new variations and seven new combinations are also introduced.

Calcareous nannoplankton from the Southwest Pacific Ocean

The positions of all cores recovered during Leg 90 in the southwest Pacific are shown within the standard calcareous nannoplankton zonation. The stratigraphic and regional occurrences and preservation of Paleogene calcareous nannoplankton found at Sites 588, 592, and 593 are discussed, and fossil lists are given for selected samples. Data on the Eocene/Oligocene boundary found in Holes 592 and 593 and on the Oligocene/Miocene boundary in Hole 588C are presented. Regional unconformities are noted in Hole 588C, where the upper Eocene to middle Oligocene interval (Zones NP17 to NP23) is missing, and in Hole 592, in which the middle Oligocene to lowest Miocene interval (Zones NP23 to NN1) is not represented.

(Table 1) Biomass per area of picoplankton algae, cyanobacteria, and total picoplankton and their contribution to total phytoplankton biomass in 0-200 m layer

Abundance of picophytoplankton in the Subantarctic and subtropical frontal zones was found to be 10**6-10**7 cells/l. Biomass of eucaryotes and procaryotes reached 2 g/m**2 and accounted for 1-15% of total phytoplankton biomass. A deep peak in the distribution of phytoplankton abundance was found at 40-120 m. Maximum number of dividing cyanobacteria cells occurred at depths of 40-60 m. An estimate of picophytoplankton production shows that picophytoplankton accounts for 30-40% of total primary production.

Calcareous nannofossil abundance of ODP Sites 174A-1071, 174A-1072 and 174A-1073

Calcareous nannofossil range charts for Leg 174A sites on the New Jersey continental margin are presented in this report, and nannofossil biostratigraphy is established. Nannofossil biostratigraphic resolution is low in shallow-water Sites 1071 and 1072, where nannofossils are generally rare or frequently absent. Site 1073 yields generally common to abundant nannofossils, which allows a fairly detailed nannofossil biostratigraphy for the entire Pleistocene through upper Eocene sequence. Quantitative and semiquantitative nannofossil data for the upper Pleistocene section from Site 1073 reveal an average sedimentation rate of about 80 cm/k.y. The unusually high sedimentation rate makes this calcareous section very valuable for high-resolution studies.

Jurassic to Cretaceous calcareous nannofossils from the Argo Abyssal Plain

A summary of calcareous nannofossil biostratigraphy performed for Late Jurassic (Kimmeridgian) to Early Cretaceous (Hauterivian) cores of Site 765 (Cores 123-765C-58R to -55R) and Site 261 (Cores 27-261-33 to -27), Argo Abyssal Plain, off northwestern Australia is presented. Precise age determinations were limited by variable preservation and the exclusion of a number of marker species due to provincialism. However, the presence of species, such as, Stephanolithion bigotii bigotii, Watznaueria manivitae, Tubodiscus verenae, and Cruciellipsis cuvillieri results in a reasonably good degree of biostratigraphic control. Biogeographic interpretation of the nannofossil data suggests that the Argo Basin occupied a position transitional between the Tethyan and Austral nannofloral realms. A cooler water regime is suggested by the absence of thermophyllic Tethyan forms, such as Nannoconus, and the presence of taxa that display bipolar distribution, such as Crucibiscutum salebrosum. Two new species, Zeugrhabdotus cooperi and Cyclagelosphaera argoensis, and one new combination, Haqius ellipticus are described.

Neogene calcareous nannofossil abundances and biostratigraphy of the Ontong Java Plateau

A total of 35 calcareous nannofossil datums were found in the Neogene sediments recovered at five sites (Sites 803-807) on the Ontong Java Plateau in the equatorial Pacific during Ocean Drilling Program Leg 130. Among them, 12 datums in the Pleistocene-upper Pliocene sequences were correlated with magnetostratigraphy. Pliocene and Miocene calcareous nannofossil assemblages in 289 samples obtained from Holes 804C, 805B, 805C, and 806B were studied. Reticulofenestra coccolith size distribution patterns in these Pliocene-Miocene sediments were also revealed through the present investigation.

Calcareous nannofossil biostratigraphy of ODP Leg 134 sites

Seven sites drilled in the central New Hebrides Island Arc during Ocean Drilling Program Leg 134 yielded varying quantities of upper Eocene through Pleistocene calcareous nannofossils. Most of the Miocene and Pliocene strata were absent from Sites 827-831 drilled along the collisional boundary between the Australia and Pacific plates where the North d'Entrecasteaux Ridge and Bougainville Guyot are being subducted. Sites 832 and 833, drilled in the intra-arc North Aoba Basin, contained upper Miocene through Pleistocene and early Pliocene through Pleistocene nannofossils, respectively. Detailed range charts displaying species abundances and age interpretations are presented for all of the sites. Despite problems of reworked assemblages, poor preservation, overgrowths and/or dilution from volcaniclastics, the nannofossil biostratigraphy delineates several repeated sections at Site 829 in the accretionary prism adjacent to Espiritu Santo Island. Paleogene pelagic sediments equivalent to those in a reference section at Site 828 appear to have been scraped from the downgoing North d'Entrecasteaux Ridge and accreted onto the forearc during the Pleistocene. Other sediments in the forearc include Pleistocene olistostromal trench-fill deposits containing clasts of various ages and compositions. Some of the clasts and olistoliths have affinities to rocks exposed on the neighboring islands and environs, whereas others are of uncertain origin. The matrix of the olistostromes is predominately Pleistocene, however, matrices of mixed nannofossil ages are frequently encountered. Comparisons of the mixed nannofossil ages in the matrices with sedimentological and structural data suggest that sediment mixing resulting from fault movement is subordinate to that occurring during deposition.

Calcareous nannofossils, pollen and spores from ODP Leg 178 sites

Calcareous nannofossils, pollen, and spores were examined on samples from Ocean Drilling Program Leg 178 Site 1095 on the continental rise and Sites 1097, 1100, and 1103 on the outer continental shelf of the western Antarctic Peninsula. Stratigraphically useful specimens of calcareous nannofossils occur in Site 1095 sediments assigned to Zones CN15, CN13b, and CN11. Calcareous nannofossils are rare but occur throughout the sedimentary sequences from seismic Units S1 to S3 on the continental shelf. Most of the calcareous nannofossils in Units S1 and S2 are composed of Cretaceous specimens that have been recycled by glacial processes. The occurrence of Dictyococcites in samples within Unit S3 upper Miocene sediments without any reworked specimens suggests those sediments are deposited in an open-ocean environment. These results are consistent with those from foraminifer and radiolarian studies. Pollen and spores including Nothofagidites, the genus for fossil pollen referred to as Nothofagus, are also observed in Unit S3 sediments. The sparse occurrence of pollen and spores, however, makes it difficult to assess the nature of the Antarctic terrestrial vegetation.