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doi:10.2204/iodp.proc.307.102.2006

Biostratigraphy

Shipboard age assignments were determined based on calcareous nannofossils and planktonic foraminifers. The microfossil assemblages were examined from core catcher samples of each core. Additionally, some critical horizons were selected to refine placement of datum levels and assemblage boundaries. Sample position, group abundance, group preservation, and species frequencies as well as age or zone of each fossil group were recorded for each sample in the Janus database.

Correlation of the nannofossil and foraminiferal zonal schemes to magnetostratigraphy are summarized in Figure F5. Datum levels are listed in Tables T2 and T3. The timescale and datum ages of planktonic foraminifers and nannofossils follow those of Berggren et al. (1995b).

Details of the shipboard methods for each microfossil group are described as follows.

Planktonic foraminifers

We applied the zonal schemes of Berggren et al. (1995a, 1995b) and Jenkins (1985, 1993). Ages of species datum levels are largely from Berggren et al. (1995a, 1995b, and references therein).

Taxonomic concepts for Neogene taxa were adopted from Kennett and Srinivasan (1983).

Sample preparation methods varied according to the degree of lithification. Unlithified sediment samples were soaked in tap water and then washed over a 63 µm sieve. Partially lithified material was soaked in a 3% H₂O₂ solution before washing. Washed samples were dried at 60°C and then sieved into the >125 µm fraction. The >125 µm fraction is used for examination of planktonic foraminifers. Planktonic foraminiferal abundances were quantitatively estimated using the following categories:

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

Preservational characteristics were determined as follows:

• VG = very good (no evidence of breakage or dissolution).
• G = good (dissolution effects are rare; >90% of specimens unbroken).
• M = moderate (dissolution damage, such as etched and partially broken tests, occurs frequently; 30%–90% of the specimens unbroken).
• P = poor (strongly recrystallized or dominated by fragments and broken or corroded specimens).

Calcareous nannofossils

The zonal scheme of Bukry (1973, 1975) with zonal code numbers added and modified by Okada and Bukry (1980), was used for Cenozoic calcareous nannofossils. The zonation scheme of Gartner (1977) was used for Pleistocene biostratigraphy, with reference to Okada and Bukry (1980), in order to obtain higher resolution for biostratigraphic correlation. This scheme is presented in Figure F6. The Cenozoic zonal schemes of Martini (1971) and Okada and Bukry (1980), together with the geomagnetic polarity timescale, are presented in Figure F5. Cenozoic biostratigraphic events, including but not limited to the zonal/​subzonal indicators of Martini (1971) and their proxies, are listed in Table T2.

Standard smear slides were made of all soft lithologies. Smear slides of indurated lithologies were prepared by the traditional double-slurry smear slide method. Calcareous nannofossils were examined by means of standard microscope techniques, under cross-polarized and transmitted light at 1000×. We adopted a simple system to characterize preservational states:

• VG = very good (all specimens are in pristine condition and can be identified with certainty).
• G = good (little or no evidence of dissolution and/or secondary overgrowth of calcite; diagnostic characters fully preserved; all specimens can be identified).
• M = moderate (dissolution and/or secondary overgrowth; partially altered primary morphological characteristics; however, nearly all specimens can be identified at the species level).
• P = poor (severe dissolution, fragmentation, and/or secondary overgrowth with primary features largely destroyed; many specimens cannot be identified at the species level and/or generic level).

Relative abundance estimates for individual species were categorized as follows:

• D = dominant (>100 specimens of a species per field of view).
• A = abundant (10–100 specimens of a species per field of view).
• C = common (1–10 specimens per field of view).
• F = few (one specimen per 10 fields of view).
• R = rare (fewer than one specimen per 10 fields of view).
• B = barren (no calcareous nannofossils found).

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