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doi:10.2204/iodp.proc.317.102.2011 BiostratigraphyThe primary focus of the Expedition 317 shipboard paleontological group was to provide robust age and paleodepth inputs to help constrain the timing and magnitude of global sea level perturbations during the late Eocene to Holocene. Ages were assigned based on core catcher samples using calcareous nannofossil, planktonic and benthic foraminifer, bolboformid, and diatom biostratigraphy; where fitting, additional section subsamples were taken to better define some bioevents and zonal boundaries. Whole and nearly whole macrofossils in split cores and in the coarse-sized faction of washed microfossil samples were also routinely sampled and identified. Other fossil material that was monitored in washed samples and/or smear slides included shell fragments from bivalves, gastropods, brachiopods, scaphopods, barnacles, and crabs, as well as ostracods, otoliths, fish teeth, bryozoan fragments, echinoid spines and plate fragments, radiolarians, and silicoflagellates. All micropaleontological data, including relative and total abundances and preservation, were uploaded to LIMS using the DESClogik application. The 2008 geological timescale (Ogg et al., 2008) was used during Expedition 317, and the base of the Quaternary and Pleistocene were placed at the top of the Gelasian (1.806 Ma). The Pleistocene and Pliocene were divided into early, middle, and late (Fig. F5). All bioevents, including highest occurrences (HOs), lowest occurrences (LOs), highest common occurrences (HCOs), and lowest common occurrences (LCOs), were calibrated to the astronomically calibrated timescale of Ogg et al. (2008). Correlations to the geological timescale will be improved by the integration of postcruise data from more detailed biostratigraphic and magnetostratigraphic analyses, oxygen isotope stratigraphy, and cyclostratigraphic studies of physical property data. Foraminifers and bolboformidsForaminifer and bolboformid biostratigraphy provided robust correlations with the New Zealand geological timescale (Cooper, 2004) shown in Figure F5. The ranges of selected foraminifer and bolboformid species are shown in Figure F6. The calibrated ages of planktonic foraminifer and bolboformid datums are given in Table T3, and the recalibrated ages of benthic foraminifer datums are given in Table T4. Foraminiferal criteria for the adopted marine paleoenvironmental classification, modified after Hayward et al. (1999), are shown in Figure F7. Microfossil preparationTo obtain planktonic and benthic foraminifers and bolboformids from core catcher samples, a 100–200 cm3 whole-round sample was soaked in tap water, disaggregated, and washed over a 63 µm sieve. Where disaggregation was incomplete, especially through cemented intervals, selected samples were rewashed to improve microfossil recovery and facilitate microfossil identification. All sieves were cleaned in an ultrasonic tank and rinsed with a methylene blue solution between successive samples as a precaution against cross-contamination. After being washed, all samples were dried at 100°C in a thermostatically controlled drying cabinet. The samples were then divided with a microsplitter into separate aliquots for examination by members of the shipboard micropaleontological team. In most cases, only the >150 µm size fraction was examined; however, for stratigraphic levels where bolboformids were likely to be present, the 125–150 µm size fraction was also examined. All age- and depth-diagnostic species of planktonic and benthic foraminifers and bolboformids were picked and mounted onto 60-division faunal slides and/or single-hole slides coated with gum tragacanth. As time allowed, other species and microfossils were also picked and mounted onto the same slides. Planktonic foraminifersThe taxonomy for Neogene planktonic foraminifers follows a modified version of the phylogenetic classification of Kennett and Srinivasan (1983), except subgenera were raised to the status of genera (e.g., Globorotalia [Globoconella] = Globoconella). Abbreviations for genera and species qualifiers are given in Table T5. Species concepts are primarily based on Hornibrook (1981, 1982), Hornibrook et al. (1989), Scott et al. (1990), Hornibrook and Jenkins (1994), and Crundwell and Nelson (2007). Planktonic foraminiferal biostratigraphy from DSDP Site 594 and ODP Site 1119, off the eastern South Island of New Zealand, showed that late Neogene planktonic assemblages were strongly influenced by cold subantarctic water and that many of the age-diagnostic temperate species were either absent or poorly represented. As a consequence, unpublished ages for recently calibrated bioevents at South Tasman Rise (ODP Site 1171, 50°S) (M.P. Crundwell, unpubl. data) were used during Expedition 317 to subdivide and correlate the late middle Miocene. These bioevents include the HO of Globoconella conica (12.98 Ma), the LCO of Paragloborotalia mayeri s.l. (13.33 Ma), and the LO of Truncorotalia juanai (13.72 Ma). During the shipboard examination of samples for planktonic foraminifers, the abundance of foraminifers, bolboformids, and other fossil groups in the 150–1000 µm grain-size fractions of washed microfossil samples was categorized as follows:
The percentage of planktonic foraminifers relative to all foraminifers was determined semiquantitatively for all samples from random counts of 100 foraminifers in the 150–1000 µm grain-size fractions of washed microfossil residues. Because planktonic foraminifers were often present in very low numbers, especially at the cored shelf sites, only the presence of each species was recorded using the following categories:
The preservation of planktonic foraminifers was categorized as follows:
BolboformidsBolboformids are an extinct group of microfossils that have generally been interpreted as phytoplanktonic organisms (Spiegler and von Daniels, 1991), although oxygen isotope data from the analysis of bolboformid shells (Poag and Karowe, 1986; Spiegler and Erlenkeuser, 2001) suggest that bolboformids spent at least part of their life cycles below the photic zone in the mid- to lower levels of the water column. Bolboformids are generally made up of a hollow, single-spheroidal or subspheroidal chamber with a wall composed of monocrystalline calcite. They have a simple aperture surrounded by a short neck or collar. Surface morphology ranges from smooth to highly ornamented, with spines, knobs, reticulations, ribs, ridges, and flanges. Shell sizes range from 70 to 240 µm, although most specimens are <150 µm. Because of their small size, simple form, and often highly ornamented shells, bolboformids have commonly been misidentified as simple single-chambered foraminifers. They are important index fossils that supplement calcareous nannofossil and planktonic foraminiferal zonations in mid- to high-latitude regions of Europe, the Atlantic, the southern Indian Ocean, and the southwest Pacific (Spiegler and von Daniels, 1991; Spiegler and Müller, 1992; Crundwell and Nelson, 2007). Bolboformid records from oceanic sites around New Zealand, including Site 594 (45.5°S) and ODP Site 1123 (42°S) off the east coast of the South Island, comprise a series of short-lived appearances and disappearances punctuated by intervals without bolboformids (Fig. F6). These occurrences are unusual in that they are generally associated with a single species, often in very large numbers, and each interval is typically associated with a different morphologically distinct species. Similar bolboformid occurrences have been noted in offshore petroleum exploration wells in the Canterbury Basin and at ODP Site 1120 (50°S) on Campbell Plateau (M.P. Crundwell, pers. comm., 2009). The taxonomic classification scheme for Neogene bolboformids adopted during Expedition 317 follows Spiegler and von Daniels (1991), Spiegler (1999), and the intraspecific morphological variation of Crundwell et al. (2005). All bolboformid events in the Southwest Pacific were age calibrated to the geomagnetic polarity timescale (GPTS) at Site 1123 (Crundwell and Nelson, 2007). The ages of bolboformid datums recalibrated to the timescale of Ogg et al. (2008) are given in Table T3. Benthic foraminifersBenthic foraminifers were the primary paleontological tool used for estimating changes in water depths during the shipboard examination of samples. Benthic foraminifers were also used for biostratigraphic dating, especially for the shallow-water sections of cored sites, where planktonic foraminifers and calcareous nannofossils were poorly represented (e.g., Site U1353). The individual benthic foraminiferal datums recognized were mostly regional datums established for onshore and near-shore New Zealand (e.g., Hornibrook et al., 1989). The benthic foraminiferal taxonomy adopted for Expedition 317 follows Vella (1957), Hornibrook (1961), Hornibrook et al. (1989), and Hayward et al. (1999). The depth distributions of extinct benthic foraminifers were approximated on the assumption that extant species belonging to the same evolutionary lineage occupy a similar depth range. Water depths were estimated for each sample using a qualitative approach based on the diagnostic assemblages listed in Table T6 and by comparing the fossil assemblages with extant New Zealand benthic foraminiferal assemblages with known depth distributions (Hayward et al., 1999, unpubl. data). The proportion of planktonic to benthic foraminifers was also used as a proxy for paleowater depths. The abundance of benthic foraminifers relative to the composite fossil group of all foraminifers, ostracods, otoliths, echinoid spines, and micro-mollusks was categorized as follows:
The relative abundances of individual benthic foraminiferal species were recorded as follows:
Preservation categories for benthic foraminifers follow those of planktonic foraminifers. Calcareous nannofossilsThe calcareous nannofossil zonation of Martini (1971; zonal code numbers NP–NN) was used as a general framework during Expedition 317 (Fig. F8). The biozonal markers of Gartner (1977) were also used to improve biostratigraphic resolution through the Pleistocene (Fig. F9), and the bioevents of Okada and Bukry (1980) were considered for their biostratigraphic utility through the Cenozoic. An exception to this is the base of NN2, defined as the LO of Discoaster druggii; because of the species' rarity, the datum was not considered reliable enough to be used as a zonal marker. The calcareous nannofossil biostratigraphy of ODP Leg 181, off the east coast of New Zealand, showed that Pleistocene nannofossil assemblages had mid-latitude characteristics, and marker species that define standard biostratigraphic zones were recognized; however, standard zonal markers for the Pliocene and late Miocene (i.e., Discoasters, Sphenoliths, Ceratoliths, and Amauroliths) were not always applicable, because these groups were either absent or occurred in such paucity as not to be useful (Shipboard Scientific Party, 1999). Calcareous nannofossil datums utilized during Expedition 317 were calibrated to the 2008 timescale (Ogg et al., 2008) and are given in Table T7. Taxonomic classification was based on Perch-Nielsen (1985) and Bown (1998, 2005). Samples were prepared as smear slides and analyzed using standard light microscope techniques under cross-polarized and plain light at 1000× magnification. The total abundance of calcareous nannofossils was defined as follows:
The relative abundances of individual calcareous nannofossil taxa were recorded relative to the field of view (FOV) at 1000× magnification:
Calcareous nannofossil preservation was categorized using the following criteria:
As time allowed, additional semiquantitative counts of calcareous nannofossils were made (where individual nannofossils were counted in five FOVs) in order to provide better insight into the cyclic nature of nannofossil abundance. DiatomsThere have been numerous biostratigraphic and taxonomic studies of diatoms in Southern Ocean sediments (McCollum, 1975; Schrader, 1976; Fenner et al., 1976; Ciesielski, 1983; Gersonde and Burckle, 1990; Gersonde, 1990; Baldauf and Barron, 1991; Harwood and Maruyama, 1992; Censarek and Gersonde, 2002; Zielinski and Gersonde, 2002; Winter and Iwai, 2002). The adopted Neogene diatom zonal scheme used during Expedition 317 follows Cody et al. (2008), and the Paleogene zonal scheme follows Harwood and Maruyama (1992). All diatom samples were prepared as smear slides using Pleurax as the mounting medium. Smear slides were set on a hot plate at 50°–60°C. Calcareous concretions were sieved with a 20 µm mesh after hydrochloric acid (HCl, 30%) was applied to dissolve the carbonate. This solution was kept in a 200 mL beaker for a few hours. The total abundance of diatoms and other biosiliceous components, together with assemblage composition, was recorded for all slides. For core catcher samples, wherever possible, 100 specimens (other than Chaetoceros resting spores) were counted. After counting, the slides were scanned to record the presence of other species missed in the original census. Between 100 and 1000 valves were observed in samples containing sufficient diatom remains. When <100 diatom valves were observed on a slide, all taxa were enumerated in a single count. Except for core catcher samples, the assessment of total diatom abundance was qualitative. Diatom abundances were recorded as follows:
Diatom preservation categories were described as follows:
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