Previous   |    Next

doi:10.2204/iodp.proc.322.206.2014

Methods and materials

Samples used for this research were collected from Hole C0012A at an interval of 1–2 samples per core. We treated 51 samples ranging in age from middle Miocene to Pliocene. The stratigraphy of the studied site is divided into seven units; Unit I (0.0–150.86 m CSF-A) is upper Shikoku Basin deposits mainly composed of hemipelagic silty clay to silty claystone with thin interbeds of volcanic ash. Unit II (150.86–219.81 m CSF-A) is middle Shikoku Basin deposits consisting of silty claystone alternating with volcanic sandstone. Unit III (219.81–331.81 m CSF-A) is lower Shikoku Basin hemipelagites characterized by bioturbated silty claystone. Unit IV (331.81–418.29 m CSF-A) is lower Shikoku Basin turbidites consisting of alternations of silty claystone, clayey siltstone, and siltstone. Unit V (415.58–528.51 m CSF-A) is volcaniclastic-rich sediment composed of silty claystone alternating with tuff. Unit VI (528.51–537.81 m CSF-A) consists of pelagic claystone. Unit VII (537.81 m CSF-A to the bottom) is the Kashinosaki Knoll basement and is mainly composed of basalt. Each microfossil sample was collected from undisturbed hemipelagic sediment from Unit I to Unit VI.

Sediment samples of 0.5–1.0 g dry weight were disaggregated through the sodium tetraphenylborate method (Hanken, 1979). After the samples became macerated, each was wet-sieved through a 63 μm screen. Dried residues were then divided into suitable volumes yielding around 200 planktonic foraminiferal specimens with the use of a sample splitter. Planktonic foraminiferal specimens larger than 125 μm were picked up under a binocular microscope. Scanning electron microphotographs of selected index species were obtained with a JCM-5000 (JEOL Co. Ltd., Japan). To calculate foraminiferal flux (number/cm²/k.y.), we used the onboard data set of dry density and accumulation rate (see the “Site C0012” chapter [Expedition 322 Scientists, 2010]).

The quality of each biohorizon was determined on the basis of the criteria of Hayashi et al. (2013) as follows (Fig. F2):

• Quality A = biohorizons recognized by continuous occurrences above their lowest occurrence and below their highest occurrence.
• Quality B = biohorizons showing discontinuous occurrence above their lowest occurrence and below their highest occurrence.
• Quality C = biohorizons characterized by both rare and sporadic occurrences of the marker taxa.

Taxonomic names in this study generally follow Wade et al. (2011) and Hayashi et al. (2013) except for Paragloborotalia siakensis. This species has previously been regarded as a junior synonym of Paragloborotalia mayeri by many workers (e.g., Bolli and Saunders, 1982). On the basis of scanning electron microphotographs of both holotypes newly redrawn by Zachariasse and Sudijono (2012), we identified all of our specimens as P. siakensis rather than P. mayeri.

We used the planktonic foraminiferal zonation defined by Berggren et al. (1995) and revised by Wade et al. (2011). The astronomically tuned timetable of planktonic foraminiferal biohorizons in the current timescale (ATNTS2004; Lourens et al., 2004) has been revised in part by Wade et al. (2011). Independent of this, Tian et al. (2008) presented an astronomically tuned timescale over the past 23 Ma at Ocean Drilling Program (ODP) Site 1148 in the South China Sea. We considered both ages for biohorizons of this study.

Top of page   |    Previous   |    Next