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doi:10.2204/iodp.proc.313.102.2010 PaleontologyThree microfossil groups were examined for biostratigraphic purposes: calcareous nannofossils, planktonic foraminifers, and dinoflagellate cysts (dinocysts). Pollen and other palynomorphs, together with palynofacies, provided information on paleoenvironments (both marine and terrestrial) and on sediment provenance and transport. Benthic foraminifers were used to estimate paleobathymetry and to establish preliminary paleoenvironment interpretations. Most planktonic foraminifer and dinocyst age assignments were made using core catcher samples collected during offshore operations; a select few foraminifer analyses were performed on samples from cores split at the OSP. By contrast, nearly all calcareous nannofossil determinations were made on samples taken from split cores during the OSP. Sample positions and the abundance, preservation, chronostratigraphic age or biozone, and/or paleoenvironments for these microfossil groups were entered into the ExpeditionDIS. Unless otherwise noted, biostratigraphic zonations and datums used in this work are tied to the Berggren et al. (1995) integrated magnetobiochronologic timescale (BKSA95), which is based on the geomagnetic polarity timescale (GPTS) of Cande and Kent (1995), and are summarized in Figure F12. References for these biostratigraphic age assignments are given in Tables T1 and T2. Biostratigraphic and taxonomic references for each microfossil group are further discussed in the following sections and given in part for QA/QC purposes. Despite some uncertainties in age control and correlations, the assumption is made that first and last appearance datums (FADs and LADs, respectively) are globally synchronous and accurately dated and that these can be correlated over large distances and across different environments. The absence of a fossil may indicate that the sediments were deposited prior to that organism's FAD or following its LAD, that the organism did not inhabit that environment, or that its fossil remains were not preserved. Geographic and ecological variations can result in regional differences among zonations of all taxa, and dinoflagellate cysts in particular. Calcareous nannofossil and planktonic foraminifer zonations erected in deep-sea environments are sometimes difficult to use in inner neritic environments such as the New Jersey shelf, as some marker taxa may be rare or absent in this setting. Problems can also arise when reworking occurs, as reworked specimens can look well preserved. This is particularly critical above sequence boundaries, and for this reason LADs should be applied with caution to sediments immediately overlying sequence boundaries. Calcareous nannofossilsCalcareous nannofossil assemblages are primarily tied to the zonation scheme of Martini (1971) and secondarily to additional biohorizons within each zone. The zonal scheme and biohorizons are tied to the BKSA95 integrated magnetobiochronologic timescale and shown in Figure F12. Age estimates for these datums are taken from the literature and tied to the BKSA95 unless otherwise noted (Table T1). Taxonomic concepts are those given in Perch-Nielsen (1985) and Bown (1998). Core catcher samples from all three holes were sent ashore during the offshore phase of Expedition 313 for preliminary nannofossil age assignments by Shijun Jiang (former Expedition 313 Science Party member who was unable to attend the OSP). Additional analyses performed on samples from core split during the OSP supersede those preliminary age assignments. Preliminary age assessments were made during the OSP by examining one sample per every three cores (approximately one sample every 10 m). Additional samples were taken to refine age estimates as time permitted. All samples were prepared using standard smear slide techniques (e.g., Bown, 1998) and examined on an Olympus BX51 light microscope using cross-polarized and plane-transmitted light. Abundance estimates were done at 1000×, with lower magnification used to scan for rare biostratigraphic marker taxa. Qualitative assessment of calcareous nannofossil preservation was recorded as follows:
A qualitative assessment of the total abundance of calcareous nannofossils for each sample was estimated as follows:
The abundance of individual species for each sample was estimated as follows:
ForaminifersApproximately 300 samples were processed for Sr isotopes and foraminifers prior to the OSP. An additional ~20 core catcher samples were processed during the OSP. All samples (pre-OSP and OSP) that were examined for foraminifers were soaked in a sodium metaphosphate solution, washed through a 63 µm sieve, and oven dried. Planktonic and benthic foraminifers were examined from these coarse fractions (>63 µm). For both the planktonic and the benthic foraminifers, preservation characteristics were divided into five categories:
Planktonic foraminifersThe >150 µm fraction was examined for planktonic foraminifers and the 63–125 µm fraction was studied for zonal markers if they were absent in the larger size fractions. The total number of planktonic foraminifers encountered in each sample was noted for Hole M0027A. Presence/absence data were collected for all species observed. Species identification was made by reference to Blow (1969), Bolli et al., (1985), and Kennett and Srinivasan (1983). The zonation schemes of Berggren et al. (1995) for the Neogene and Berggren and Pearson (2005) for the Paleogene were used to assign biostratigraphic ages based on planktonic foraminifers. In addition, the zonations of Blow (1969), Shackleton et al. (1995), and Lourens et al. (2004) for the Neogene and Berggren and Miller (1988) for the Paleogene are also referred to in this study to enable comparison of planktonic foraminifer data to results from previous scientific ocean drilling legs. These zonation schemes are tied to the BKSA95 integrated magnetobiochronologic timescale and shown in Figure F12. Age estimates for important biohorizons are given in Table T2 and tied to the BKSA95 unless otherwise noted. In cases where key marker species were rare or absent, secondary markers were used whose ranges were calibrated by Berggren et al. (1995), Bolli et al. (1985), and Shackleton et al. (1999). Benthic foraminifersBenthic foraminifers were examined primarily from the >150 µm size fraction. The >63 µm size fraction was checked in barren samples and spot-checked elsewhere. Paleobathymetric estimates were based on qualitative assemblages, although in some samples the total number of specimens encountered was recorded. Bathymetric zones were defined as inner neritic (0–50 m), middle neritic (50–100 m), and outer neritic (100–200 m). Taxonomic concepts, paleobathymetric estimates, and paleoenvironment interpretations were based on multiple references (Culver and Goshorn, 1996; Cushman and Cahill, 1933; Gibson, 1983; Katz et al., 2003; Miller et al., 1997; Olsson et al., 1987; Schnitker, 1970; Snyder et al., 1989), with the general paleobathymetric model following Miller et al. (1997) for coeval onshore New Jersey sections. In general, Elphidium-dominated biofacies were interpreted as upper inner neritic (<10 m), Hanzawaia concentrica–dominated biofacies as middle inner neritic (10–25 m), Nonionella pizarrensis–dominated biofacies as outer inner neritic (25–50 m), Buliminella gracilis–dominated biofacies as upper middle neritic (50–80 m), Uvigerina juncea–dominated biofacies as lower middle neritic or deeper (>75 m), and high-diversity, low-dominance assemblages with key indicator taxa (e.g., Hanzawaia mantaensis and Oridorsalis) as outer neritic (>100 m). Paleobathymetric estimates within this framework have a high degree of confidence. Within a depth zone, a sample may be noted to be, for example, "slightly deeper than the previous sample" based on minor abundance changes of key depth-indicator species, but this cannot be quantified to the meter level. In addition, assemblages dominated by infaunal taxa such as Uvigerina, Rectuvigerina, and Bulimina, especially with diatom and radiolarian co-occurrences, can indicate low-oxygen, high–organic carbon environments typically associated with upwelling zones. In contrast, assemblages dominated by epifaunal taxa such as Gyroidinoides, Cibicidoides, and Hanzawaia can indicate better oxygenated, low–organic carbon oligotrophic environments. PalynomorphsSamples (mainly from core catchers collected offshore and prepared onshore before the OSP) of 5 mL volume were processed for palynological analysis by disaggregating samples in a warm, weak (0.02%) sodium metaphosphate solution prior to sieving using 15 µm Nitex mesh. Samples were centrifuged for 4 min at 3000 rpm, washed with distilled water, and then treated with warm 10% HCl, dissolving a tablet containing 10,500 ± 300 Lycopodium spores, which allows for calculation of absolute abundances of palynomorphs in the sediment. Samples were centrifuged, rinsed with water, centrifuged again, and treated with 48% HF. After a third centrifugation and rinsing, the samples were sieved again prior to mounting in glycerine jelly. DinocystsSlides were examined at 400× and 1000× magnification for dinoflagellate cysts. Dinocyst assemblages were tied to the biostratigraphic zonations of de Verteuil and Norris (1996), Van Simaeys et al. (2005), and Eldrett et al. (2004) for the Miocene, Oligocene, and Eocene sequences, respectively. These zonations are correlated to the BKSA95 integrated magnetobiochronologic timescale. Reference was also made to several other sources in the literature, such as Williams and Manum (1999), Louwye et al. (2000), Sluijs et al. (2003), Munsterman and Brinkhuis (2004), Dybkjær (2004), and Van Simaeys et al. (2004). Biostratigraphic zones were assigned to the Pleistocene sequence based on dinocyst assemblages and ranges following McCarthy and Gostlin (2000). The relative abundance of dinocysts versus pollen and plant spores was determined to facilitate sea level reconstructions, as described in McCarthy et al. (2003), together with an approximation of palynofacies following the criteria of Batten (1996). Dinocyst assemblages were used to make inferences regarding surface water conditions (temperature and salinity) to accompany paleoenvironmental interpretations based on the observation of terrestrial palynomorphs in the same slides. Terrestrial palynomorphsThe slides used for the examination of dinoflagellate cysts were also used for the analysis of terrestrial palynomorphs. Slides were examined for terrestrial palynomorphs mainly under plane-transmitted light at 400× and 1000× magnification, with additional use of phase-contrast illumination. Slides were examined for pollen grains, plant spores, and fungal spores (morphotypes only). Pollen and plant spores were identified using McAndrews et al. (1973), Pazzaglia et al. (1997), Beug (2004), and Traverse (2007). In addition, foraminifer test linings, dinocysts, and other algal remains were counted to achieve a direct land-sea correlation and to compare with results from the analyses of marine palynomorphs. Characteristics of different pollen types affect their transport and resistance to degradation, resulting in alteration of the original pollen assemblage during transport. For instance, bisaccate pollen is generally overrepresented in marine pollen assemblages because of its transport properties and high resistivity to oxidation (e.g., Traverse, 2007). It was therefore excluded from the sum used for calculation of pollen percentages. Additionally, the pollen production rates of different plant taxa were incorporated into the ecosystem reconstructions for the hinterland of the New Jersey shallow shelf. As an example, the overrepresentation of certain nonsaccate pollen types, such as oak/birch pollen (because of the high pollen production of these taxa) and hickory/linden pollen (mainly because of the extraordinary thickness of their exines), was taken into account for paleoenvironmental reconstruction. When bisaccate pollen grains dominated the pollen assemblages, 75–150 nonsaccate pollen grains were counted per slide. When nonsaccate pollen grains dominated the pollen assemblages, 100–200 pollen grains (normally ~150) were counted per slide. Obviously degraded/reworked pollen grains were excluded from the pollen sums for percentage calculations. With this approach, statistical relevance could be guaranteed to a reasonable degree even with bisaccate pollen being excluded from the pollen reference sums. Lycopodium spores added to the samples during processing (see "Palynomorphs") were counted to allow for calculation of pollen content per core catcher. Around 60 pollen types, 8 spore types, and 12 types of fungal remains were distinguished. Dinocysts were grouped into transparent chorate/proximate and brownish chorate/proximate dinocysts. |
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