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doi:10.2204/iodp.proc.323.201.2013

Materials and methods

Site U1341 is one of three sites drilled on the Bowers Ridge during Expedition 323. Hole U1341B reached a maximum depth of 600.0 meters below seafloor (mbsf), and its bottom was preliminarily dated to ~5 Ma. Onboard results showed that calcareous nannofossils were present along the entire record, although they were a minor component of the microfossil assemblage, with frequent barren intervals below 200 mbsf (see the “Site U1341” chapter [Expedition 323 Scientists, 2011b]).

For this study, samples were selected from Cores 323-U1341B-35H through 60X (Table T1). For each core, a small amount of sediment was picked with a toothpick or small spatula at a set horizon in each section and saved in a labeled plastic sample bag. Once ashore, sample bags were carefully opened and sediment was left to dry. For most samples, sediment was weighed once dried and slides were prepared for nannofossil counts following the decantation technique of Flores and Sierro (1997), which allows the calculation of numbers of calcareous nannofossils per gram. For the remaining samples, smear slides were carefully prepared following a standard smear slide preparation technique. In both cases, Canada balsam was used to seal the slides.

All samples were studied using a Zeiss polarized light microscope at 1250× magnification. A variable number of fields of view (FOV; always >150) were observed in each sample.

For every sample, we estimated the total abundance of calcareous nannofossils and the abundance of each calcareous nannofossil taxon as follows:

• D = dominant; more than half of the specimens in FOV belong to this taxon.
• A = abundant; >1 specimen per FOV.
• C = common; ≥1 specimen per FOV.
• F = few; <1 specimen per 2–10 FOV.
• R = rare; <1 specimen per 11–100 FOV.
• B = barren; no calcareous nannofossils present.

As to preservation, etching and overgrowth are the main features. In order to establish a ranking of preservation, we followed the code provided by Raffi and Flores (1995), who proposed four categories depending on the “average” state of preservation of the specimens examined in the smear slides:

• G = good; little or no evidence of dissolution and/or overgrowth, and specimens are identifiable to the species level.
• M–G = moderate to good; minor to moderate dissolution and/or overgrowth, but most specimens are identifiable to the species level.
• M = moderate; moderate dissolution and/or overgrowth, and identification to the species level is difficult.
• P = poor; extreme dissolution and/or overgrowth.

Calcareous nannofossil core catcher samples from this interval analyzed onboard for biostratigraphic purposes (see the “Site U1341” chapter [Expedition 323 Scientists, 2011b]) are also included in Table T1.

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