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doi:10.2204/iodp.proc.330.102.2012

Paleontology

Preliminary age assignments were based on calcareous microfossils (nannofossils and planktonic foraminifers) in core catcher samples, with additional samples from core sections, as required. The Quaternary, Neogene, and Paleogene timescale constructed for IODP Expedition 320/321 was used for this study (Expedition 320/321 Scientists, 2010). Biostratigraphic events were correlated to the geomagnetic polarity timescale, which is based on a composite of several timescales (Cande and Kent, 1995; Lourens et al., 2004; Pälike et al., 2006) (Fig. F4A–F4D). The timescales of Gradstein et al. (1995) and Channell et al. (1995) were applied for the early Paleocene (older than 60 Ma) and Late Cretaceous (Fig. F4E). Preservation, abundance, and zonal assignments for each microfossil group were entered into the LIMS database via DESClogik software.

Calcareous nannofossils

Calcareous nannofossils were examined in smear slides prepared with standard microscope slides and coverslips and mounted with Norland optical adhesive. Slides were observed using standard light microscope techniques on a Zeiss Axiophot with crossed polarizers and transmitted light at 1000× magnification. Following the methods used during ODP Leg 144, the zonation of Okada and Bukry (1980) was used during Expedition 330 for Cenozoic calcareous nannofossils (Table T1, modified from Expedition 320/321 Scientists, 2010). In the upper Cretaceous the zonation of Sissingh (1977) was applied (Table T2, modified from Shipboard Scientific Party, 2004). Taxonomy follows that of Bowen (1998) and Perch-Nielsen (1985), where full taxonomic lists can be found.

Estimates of the abundance of calcareous nannofossils were determined as follows:

  • D = dominant (>100 specimens per field of view).

  • A = abundant (>10–100 specimens per field of view).

  • C = common (1–10 specimens per field of view).

  • F = few (1 specimen per 1–10 fields of view).

  • R = rare (<1 specimen per 10 fields of view).

  • B = barren.

Preservation of calcareous nannofossils was classified as follows:

  • VG = very good (no evidence of dissolution and/or recrystallization, no alteration of primary morphological characteristics, and all specimens identifiable to the species level).

  • G = good (little or no evidence of dissolution and/or recrystallization, primary morphological characteristics only slightly altered, and specimens identifiable to the species level).

  • M = moderate (some etching and/or recrystallization, primary morphological characteristics somewhat altered, and most specimens identifiable to the species level).

  • P = poor (severe etching or overgrowth, primary morphological characteristics largely destroyed, fragmentation has occurred, and specimens often unidentifiable at the species and/or generic level).

Planktonic foraminifers

The planktonic foraminiferal zonal scheme used for the Cenozoic follows Berggren et al. (1995), except for the Eocene and Oligocene, which are based on Berggren and Pearson (2005). The mid–late Paleogene, Neogene, and Quaternary age estimates (0–60 Ma) used in this study follow those used during Expedition 320/321 (Expedition 320/321 Scientists, 2010). Those ages and sources are listed in Table T3. The zonation used for Cretaceous planktonic foraminifers is based on the zonal schemes of Caron (1985), Sliter (1989), and Robaszynski and Caron (1995). The early Paleogene (>60 Ma) and Late Cretaceous age estimates, obtained from Erba et al. (1995), Bralower et al. (1997), and Premoli Silva and Sliter (1999), are based on those used during ODP Leg 207 (Shipboard Scientific Party, 2004) (Tables T3, T4).

Cenozoic taxonomic concepts used selectively follow those of Kennett and Srinivasan (1983), Bolli and Saunders (1985), Toumarkine and Luterbacher (1985), Loeblich and Tappan (1988), Spezzaferri and Premoli Silva (1991), Chaisson and Leckie (1993), Leckie et al. (1993), Spezzaferri (1994), Pearson (1995), Chaisson and Pearson (1997), Pearson and Chaisson (1997), and Pearson et al. (2006). Cretaceous taxonomic concepts used are based on Robaszynski and Caron (1979), Robaszynski et al. (1984), Caron (1985), Nederbragt (1991), and Petrizzo (2000).

Foraminifers from ooze were spray-washed over a 63 μm sieve. Semilithified ooze and chalk were first partly fragmented by hand and then soaked in a 3% solution of hydrogen peroxide (H2O2) before washing. Hard chalk and limestone were pounded with a hammer into pea-size fragments and boiled on a hot plate for 1–2 min in a 3% H2O2 solution. Species identification for planktonic foraminifers was made on >250 µm and >150 μm size fractions for the Neogene and Paleogene–Cretaceous, respectively.

The following group abundance categories were estimated from visual examination of the dried sample for foraminiferal group abundance:

  • A = abundant (>50%).

  • C = common (>25%–50%).

  • F = few (>10%–25%).

  • R = rare (1%–10%).

  • T = trace (only a few broken specimens).

  • B = barren (no specimens).

The following species abundance categories were used for foraminiferal species abundance:

  • D = dominant (>30%).

  • A = abundant (>10%–30%).

  • F = few (>5%–10%).

  • R = rare (1%–5%).

  • P = present (<1%).

The preservation status of planktonic foraminifers was estimated as follows:

  • VG = very good (no evidence of overgrowth, dissolution, or abrasion).

  • G = good (little evidence of overgrowth, dissolution, or abrasion).

  • M = moderate (calcite overgrowth, dissolution, or abrasion are common but minor).

  • P = poor (substantial overgrowth, dissolution, or abrasion).

In many cases during Expedition 330, foraminifers from consolidated sediments were also examined in thin section. Species identification was made only for axially sectioned specimens, whereas general morphologies were described for all other individuals. Group abundance, species abundance, and preservation were not recorded for thin section analyses.

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