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.

Miocene calcareous nannofossil abundance and events in sediments of ODP Leg 189 sites

During Ocean Drilling Program (ODP) Leg 189, five sites were drilled in the Tasmanian Seaway with the objective to constrain the paleoceanographic implications of the separation of Australia from Antarctica and to elucidate the paleoceanographic developments throughout the Neogene (Shipboard Scientific Party, 2001a, doi:10.2973/odp.proc.ir.189.101.2001). Sediments ranged from Cretaceous to Quaternary in age and provided the opportunity to describe the paleoenvironments in the Tasman Seaway prior to, during, and after the separation of Australia and Antarctica. This study will focus on postseparation distribution of calcareous nannofossils through the Miocene. Miocene sediments were recovered at all five Leg 189 sites, and four of these sites were studied in detail to determine the calcareous nannofossil biostratigraphy. Hole 1168A, located on the western Tasmanian margin, contains a fairly continuous Miocene record and could be easily zoned using the Okada and Bukry (1980, doi:10.1016/0377-8398(80)90016-X) zonation. Analysis of sediments from Hole 1169A, located on the western South Tasman Rise, was not included in this study, as the recovered sediments were highly disturbed and unsuitable for further analysis (Shipboard Scientific Party, 2001c, doi:10.2973/odp.proc.ir.189.104.2001). Holes 1170A, 1171A, and 1171C are located on the South Tasman Rise south of the modern Subtropical Front (STF). They revealed incomplete Miocene sequences intersected by an early Miocene and late Miocene hiatus and could only be roughly zoned using the Okada and Bukry zonation. Similarly, Hole 1172A, located on the East Tasman Plateau, contains a Miocene sequence with a hiatus in the early Miocene and in the late Miocene and could only be roughly zoned using the Okada and Bukry (1980, doi:10.1016/0377-8398(80)90016-X) zonation. This study aims to improve calcareous nannofossil biostratigraphic resolution in this sector of the mid to high southern latitudes. This paper will present abundance, preservation, and stratigraphic distribution of calcareous nannofossils through the Miocene and focus mainly on biozonal assignment.

Nannofossil biostratigraphy of ODP Hole 206-1256B sediments

Site 1256 of Ocean Drilling Program Leg 206 to the Guatemala Basin on the eastern flank of the East Pacific Rise yielded a near-complete, middle Miocene-Quaternary carbonate-rich section that provides an opportunity to study low-latitude biostratigraphic and paleoceanographic events. The sedimentary sequence in Hole 1256B has been zoned using calcareous nannofossils according to the biostratigraphic schemes by Martini of 1971 (modified by Martini and Müller in 1986) and Okada and Bukry of 1980. The nannofossil assemblage is characteristic of the low latitudes, with abundant Gephyrocapsa, Discoaster, and Sphenolithus, and is in general moderately to well preserved, depending on nannofossil abundance and the presence of diatoms. Age estimates for the first occurrence and last occurrence of Reticulofenestra rotaria were derived from biostratigraphy and magnetostratigraphy independently and assigned to 7.18 and 6.32 Ma, respectively. Linear sedimentation rates, calculated using 28 nannofossil datums and age estimates, are high in the middle Miocene, decrease from the late Miocene to the Pliocene, then increase upsection. The abrupt drop in carbonate mass accumulation rates during the early late Miocene is referred to as the "carbonate crash." This pattern reflects (1) the long-trend decrease of productivity as the site moves away from the upwelling system at the equatorial divergence as well as (2) fluctuation in the chemistry of the bottom waters associated with production of the North Atlantic Bottom Water and ventilation via the Panama Gateway. A basement age of 14.5 Ma was obtained by extrapolating the 39.1-m/m.y. rate in the middle Miocene to the basement at 250.7 meters below seafloor, and is consistent with the ~15-Ma age of the oceanic crust estimated from marine magnetic anomalies. Reworked nannofossils and lithologic changes were used to unravel postdepositional history, and three episodes were recognized, one of which in the latest Miocene can be widely correlated.

Paleogene calcareous nannofossil biostratigraphy of DSDP Hole 21-210

The major objectives of Leg 133 were (1) to define the evolution of the carbonate platforms on the northeastern Australian margin, including their relationship to adjoining basins; and (2) to understand the effects of climate and sea level on their development in space and time (Davies, McKenzie, Palmer-Julson, et al., 1991, doi:10.2973/odp.proc.ir.133.1991). Sixteen sites were drilled, and more than 5.5 km of Neogene core was recovered during Leg 133. However, recovery of Paleogene sediments was unexpectedly poor (a total of a few meters), and the sediments were poorly dated because of strong diagenesis. On the other hand, Site 210 drilled in this region during Leg 21 yielded an expanded Paleogene section, which contains abundant calcareous microfossils. Biostratigraphic information for this section given in Burns, Andrews, et al. (1973, doi:10.2973/dsdp.proc.21.1973) was based primarily on shipboard results. Detailed calcareous nannofossil and planktonic foraminifer biostratigraphies have not been published. Here we provide a detailed documentation of the calcareous nannofossil distribution in the section, biostratigraphically date the section using the modern nannofossil zonation of Okada and Bukry (1980. doi:10.1016/0377-8398(80)90016-X), and construct an age-depth curve based on current knowledge of nannofossil magnetobiochronology. This should provide a useful Paleogene biostratigraphic reference in the northeastern Australian sea, as Site 210 has apparently yielded the most complete Paleogene record in the region. The detailed biostratigraphy should provide a better age constraint for the regional Eocene-Oligocene hiatus recognized previously (e.g., Jenkins and Srinivasan, 1986, doi:10.2973/dsdp.proc.90.113.1986) and should be useful for future studies on various aspects of Paleogene history of the northeastern Australian sea.

Middle Eocene to late Oligocene calcareous nannofossils of ODP Hole 120-748B

A major deterioration in global climate occurred through the Eocene-Oligocene time interval, characterized by long-term cooling in both terrestrial and marine environments. During this long-term cooling trend, however, recent studies have documented several short-lived warming and cooling phases. In order to further investigate high-latitude climate during these events, we developed a high-resolution calcareous nannofossil record from ODP Site 748 Hole B for the interval spanning the late middle Eocene to the late Oligocene (~42 to 26 Ma). The primary goals of this study were to construct a detailed biostratigraphic record and to use nannofossil assemblage variations to interpret short-term changes in surface-water temperature and nutrient conditions. The principal nannofossil assemblage variations are identified using a temperate-warm-water taxa index (Twwt), from which three warming and five cooling events are identified within the middle Eocene to the earliest Oligocene interval. Among these climatic trends, the cooling event at ~39 Ma (Cooling Event B) is recorded here for the first time. Variations in fine-fraction d18O values at Site 748 are associated with changes in the Twwt index, supporting the idea that significant short-term variability in surface-water conditions occurred in the Kerguelen Plateau area during the middle and late Eocene. Furthermore, ODP Site 748 calcareous nannofossil paleoecology confirms the utility of these microfossils for biostratigraphic, paleoclimatic, and paleoceanographic reconstructions at Southern Ocean sites during the Paleogene.

Cenozoic calcareous nannofossils from the Lesser Antilles Forearc Region

During Leg 110 of the Ocean Drilling Program, sediment was recovered from six sites in the vicinity of the Lesser Antilles Forearc. Hole 671B, drilled near the toe of the Barbados deformation front, was the first-ever penetration of the decollement between the underthrusting Atlantic Plate and the off scraped Barbados accretionary prism. Stratigraphic repetitions in sequence associated with tectonic movement along the decollement zone, first observed on DSDP Leg 78A, were further documented at four ODP Leg 110 sites. A significant biostratigraphic inversion is present at Site 671 at 128 mbsf in which upper Miocene sediments rest atop lower Pleistocene strata. Smaller repetitions in sequence are recorded at Sites 671, 673, 674, and 676. Leg 110 sediments range from middle Eocene to early Pleistocene in age. Pliocene/Pleistocene assemblages are generally well preserved; however, Miocene assemblages have undergone extensive dissolution at all Leg 110 sites. Paleogene sediments are sometimes recrystallized and the nannofossils contained within exhibit a range in preservation from poor to good.

Calcareous nannofossils of ODP sites 177-1088 and 177-1090

During ODP Leg 177, a Miocene to Pliocene calcareous nannofossil record was recovered at Sites 1088 and 1090. Site 1088, located at 41°8'S, shows a continuous middle-upper Miocene to Pliocene carbonate sequence that was deposited at relatively high sedimentation rates (Shipboard Scientific Party, 1999a, doi:10.2973/odp.proc.ir.177.103.1999). Moreover, Site 1088 proved suitable for calcareous nannofossil analysis as a means to improve the biostratigraphy at this southern latitude. Site 1090 was drilled at 42°54'S; a tephra layer marks a significant disconformity at the Miocene/Pliocene boundary of this sequence (Shipboard Scientific Party, 1999b, doi:10.2973/odp.proc.ir.177.105.1999). Although nannofossil assemblages are poorly preserved at this site (Shipboard Scientific Party, 1999b), they may help in determining the age of the disconformity and its paleoceanographic significance.

Calcareous nannofossil biostratigraphy of ODP Leg 108 sediments

Calcareous nannofossils were examined from the 400 cores recovered at 12 sites during Ocean Drilling Program Leg 108 in the eastern equatorial Atlantic Ocean and along the northwest African margin, representing a transect spanning 24° of latitude. Thirty calcareous nannofossil biohorizons were recognized in the Neogene and Quaternary sequences; only Site 661, located in water depths of 3500 m, contains a fossiliferous record older than the Oligocene. At Site 661, a 200-m-thick sequence of Upper Cretaceous sediments yielded Maestrichtian and uppermost Campanian nannofossils, yet a continuous Cretaceous/Tertiary boundary was not recovered. Widespread sediment slumps and turbidites deposited at many sites interrupted the pelagic sedimentation. A careful study of calcareous nannofossil and foraminifer assemblages correlated to paleomagnetic records suggests that "slumped" units at most sites were added as extra sediments to rapidly deposited pelagic sediments, with minor disturbance of the surrounding layers. Nannofossils are generally common to abundant and moderately preserved at all sites except for those located in two upwelling areas, where placoliths are etched and discoasters overgrown. Typical low-latitudinal zonal markers were used during this study, yet some of them were considered to be of little biostratigraphic value because of their inconsistent stratigraphic ranges and low abundances. This is especially apparent for the intervals representing the Miocene/Pliocene and Oligocene/Miocene boundaries. Characteristic nannofossils of cool-water conditions and low discoaster abundances occur at the coastal African upwelling and along the south equatorial divergence sites, signifying a stronger advection of cold waters toward the equator within the Canary and Benguela eastern boundary currents.

Tertiary and Quaternary calcareous nannoplankton biostratigraphy of ODP Leg 112 holes

Positions of all cores recovered during Ocean Drilling Program (ODP) Leg 112 off Peru are shown in the standard calcareous nannoplankton zonation. Stratigraphic and regional occurrences and preservation of calcareous nannoplankton are discussed for all sites, and fossil lists are presented for selected samples. Late Miocene to Holocene nannoplankton assemblages in the upwelling systems off Peru and scattered blooms, especially of Gephyrocapsa species and Helicosphaera carteri, are described. Scyphosphaera assemblages found in late Miocene Zone NN9 {Discoaster hamatus Zone) at Site 684 are compared with similar assemblages from Gabon on the west coast of Africa. Remarkable subsidence is indicated by early and middle Eocene nearshore and shallow-water nannoplankton assemblages for Sites 682, 683, and 688. Besides several local hiatuses, major regional hiatuses were noted at Site 682 (upper Eocene, uppermost middle Eocene, and part of the lower and middle Oligocene missing), Site 683 (uppermost middle Eocene to lower part of the middle Miocene missing), and Site 688 (part of the middle Eocene, uppermost middle Eocene to upper Oligocene, and parts of the lower and middle Miocene missing).

Calcareous nannofossil abundance and datum events of ODP Holes 181-1123C and 181-1124C, southwest Pacific

Seven sites were drilled off the eastern shore of New Zealand during Ocean Drilling Program Leg 181 to gain knowledge of southwest Pacific ocean history, in particular, the evolution of the Pacific Deep Western Boundary Current (DWBC). Holes 1123C and 1124C penetrated lower Oligocene to middle Eocene sediments containing moderately to poorly preserved calcareous nannofossils. Nannofossil assemblages show signs of dissolution and overgrowth, but key marker species can be identified. Nannofossil abundance ranges from abundant to barren. The lower Oligocene sediments are distinctly separated from the overlying Neogene sequences by the Marshall Paraconformity, a regional marker of environmental and sea level change. An age-depth model for Hole 1123C through this sequence was constructed using nine nannofossil age datums and three magnetostratigraphic datums. There is good agreement between the biostratigraphy and magnetostratigraphy, which indicates that the Marshall Paraconformity spans ~12 m.y. in Hole 1123C. The same sequence in Hole 1124C is disrupted by at least three hiatuses, complicating interpretation of the sedimentation history. The Marshall Paraconformity spans at least 3 m.y. in Hole 1124C. A 4- m.y. gap separates lower Oligocene and middle Eocene sediments, and a ~15 m.y. hiatus separates middle Eocene mudstones from middle Paleocene nannofossil-bearing mudstones. Nannofossil biostratigraphy from Holes 1123C and 1124C indicates that the Eocene-Oligocene transition was a time of fluctuating biota and intensification of the DWBC along the New Zealand margin.

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.

Calcareous nannofossil abundance estimates and datums of ODP Leg 189 sites

A major objective of Leg 189 was to date the opening of the Australia-Antarctic Gateway to shallow-water circulation and subsequently to deepwater circulation in the Paleogene. Calcareous nannofossils are the most consistently present, although not necessarily the most abundant fossil group in Paleogene sections, and the shipboard study (Exon, Kennett, Malone, et al., 2001, doi:10.2973/odp.proc.ir.189.2001) showed that they generally provided the most useful age information. This report presents documentation of the stratigraphic distribution of nannofossils in the Paleogene and summarizes useful nannofossil datums, which should facilitate construction of age-depth curves and contribute to an integrated chronology for Leg 189 sediments. Previous Paleogene nannofossil study in this area is that of Edwards and Perch-Nielsen (1975, doi:10.2973/dsdp.proc.29.113.1975).

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 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.

Calcareous nannofossils in ODP Sites 135-840 and 135-841

Ocean Drilling Program Leg 135 drilled at two sites on the Tonga Ridge. Calcareous nannofossils recovered at Site 840 on the Tonga Ridge date the sedimentary sequence as late Pleistocene or Holocene (CN15) through late Miocene (CN9) in age. A hiatus occurs in the mid Pliocene. Site 841 in the Tonga Trench yielded a sedimentary sequence with nannofossils from middle Pleistocene Subzone CN14b through the middle or late Eocene Subzones CP14a-CP15b overlying a rhyolitic volcanic basement. Part of the Eocene interval contains the shallow-water nannofossil taxa Braarudosphaera, Micrantholithus, and Pemma. A major unconformity separates lower Oligocene Zone CP 16 from lower middle Miocene Zone CN4 strata.