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doi:10.2204/iodp.proc.340.102.2013

Paleontology and biostratigraphy

During Expedition 340, preliminary age assignments were based on biostratigraphic analyses of calcareous nannofossils and planktonic and benthic foraminifers from core catcher samples. At appropriate intervals, additional nannofossil samples were collected in sections requiring a more refined age determination. Paleodepth interpretations were based on the paleoenvironmental requirements of cosmopolitan benthic foraminifers. Biostratigraphic calibrations (Wade et al., 2011; Kameo and Bralower, 2000) were correlated to the geomagnetic polarity timescale (GPTS) of Cande and Kent (1995) to be consistent with the methods described in “Paleomagnetism.” Shipboard methods used to analyze and assess each microfossil group are detailed below.

Calcareous nannofossils

The calcareous nannofossil schemes of Okada and Bukry (1980) and Gartner (1977) were applied for the Neogene and Quaternary sequences, respectively. For the Quaternary sequences, the zonation of Gartner (1977) provides better resolution because of the use of the acme of small Gephyrocapsa sp. as a datum. For Zone CN14a, the species Emiliania ovata was considered to be Pseudoemiliania lacunosa, based on the discussion of Gartner (1977). Caribbean specific age calibrations (Table T1) for each zone were taken from Kameo and Bralower (2000).

Core catcher samples were prepared according to standard smear slide preparation techniques for examination with a light-polarizing microscope at 788× and 1250× magnification. A small amount of sediment was placed onto a coverslip with two drops of deionized water and smeared with a wooden toothpick. Norland optical adhesive was used to mount the samples, which were set to harden under an ultraviolet lamp for 10 min.

The overall preservation of each sample is evaluated in the following manner:

• G = good; specimens show little or no evidence of dissolution.
• M = moderate; specimens show some etching and/or recrystallization.
• P = poor; specimens are severely etched or overgrown.

The relative abundance of individual species proposed by Hay (1970) was used:

• HA = highly abundant; >100 specimens/field of view (FOV).
• VA = very abundant; 11–100 specimens/FOV.
• A = abundant; 1–10 specimens/FOV.
• C = common; 1 specimen/2–10 FOV.
• F = few; 1 specimen/11–100 FOV.
• R = rare; 1 specimen/101–1000 FOV.
• B = barren; no specimens.

Foraminifers

Biostratigraphic interpretations of planktonic foraminifers are based on the revised Cenozoic Tropical bioevents of Wade et al. (2011) (Table T2), specifically using those correlated to the GPTS of Cande and Kent (1995). Neogene planktonic foraminiferal taxonomy largely follows that of Kennett and Srinivasan (1983). For benthic foraminiferal taxonomic identification, the Ellis and Messina online catalogue (Ellis and Messina, 1940), Barker (1961), Poag (1981), Hayward and Kawagata (2005), and the generic classification scheme of Loeblich and Tappan (1988) were used. Paleodepth estimates were determined using depth ranges presented by Poag (1981) and Galluzzo et al. (1990).

Paleodepth nomenclature follows that of van Morkhoven et al. (1986):

• Neritic = <200 m.
• Bathyal = 200–2000 m.
• Abyssal = >2000 m.

For each core catcher sample, ~10 cm³ of sediment was processed for planktonic and benthic foraminifer analysis. All samples were first disaggregated with water and washed over a 63 µm sieve. Highly indurated samples were soaked in a solution of 30% hydrogen peroxide until washed over a 63 µm sieve. The >63 µm sediment fraction was then dried in an oven at ~60°C until dry and then split for separate benthic and planktonic foraminiferal analyses. The <63 µm sediment fraction was not retained. To minimize contamination of foraminifers between samples, sieves were briefly soaked in methylene blue stain to identify any trapped foraminifers. Sieves were also occasionally ultrasonicated. Faunal analysis was carried out using either a Zeiss Stemi SV11 or Zeiss Discovery V8 binocular microscope. Analysis of benthic and planktonic foraminifers was based on the >150 µm fractions. For benthic foraminifers, up to 125 specimens per 1 gram of sample were picked. The >63 µm fraction was analyzed for a few select samples to provide a better representation of the breadth of benthic foraminiferal diversity. Preservation, abundance, and faunal composition data were also collected.

Planktonic foraminiferal preservation is categorized as follows:

• VG = very good; no breakage or dissolution.
• G = good; only very minor dissolution and no recrystallization; <10% of specimens are broken.
• M = moderate; frequent etching and partial breakage; 30%–90% of specimens are unbroken.
• P = poor; much dissolution and recrystallization; broken specimens dominate.

Benthic foraminiferal preservation is categorized 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 = substantial overgrowth or infilling, dissolution, or fragmentation.

Planktonic foraminiferal abundance in relation to the total residue in the >150 µm fraction is defined as follows:

• D = dominant; >30%.
• A = abundant; >10%–30%.
• F = few; >5%–10%.
• R = rare; 1%–5%.
• P = present; <1%.
• B = barren; no planktonic foraminifers are present.

Benthic foraminifer abundance in relation to the total residue in the >150 µm fraction is defined as follows:

• D = dominant; >30 specimens.
• A = abundant; >10–30 specimens.
• F = few; >5–10 specimens.
• R = rare; >1–5 specimens.
• P = present; 1 specimen.
• B = barren; no benthic foraminifers present.

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