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doi:10.2204/iodp.proc.331.104.2011

Biostratigraphy

At depths shallower than ~10 mbsf, core catcher samples from Site C0014 generally contain microfossils. Paleontological (PAL) samples from core catchers at depths greater than ~10 mbsf contain no microfossils (Table T4). Core catcher samples also include glass at shallow depths near the seafloor; at intermediate depths they contain pumice clasts and fragments with varying amounts of weathered white clay, transitioning to gray clay above a second white clay-anhydrite zone near the bottom of the deepest Hole C0014G. Microfossils are also abundant in sediment samples from Hole C0014A at 0.01 mbsf, Hole C0014B at 0.06 and 6.04 mbsf, and Hole C0014F at 2.04 mbsf. In contrast, no microfossils were observed in any material from Holes C0014C, C0014D, C0014E, or C0014G (Table T5; Fig. F10).

The foraminifers observed are dominated by planktonic species, suggesting either that there is a large input of foraminifers from the overlying water column or that the environment surrounding Site C0014 is preferentially dissolving benthic foraminifers, which are typically more prominent in South China Sea samples (Saidova, 2007). Although some fragmentation occurred, preservation of foraminiferal microfossils is generally good, with little or no evidence of dissolution and/or overgrowth; diagnostic characteristics are preserved, and many species can be identified. Consistent with good preservation, microfossils from Site C0014 represent foraminifers that are observed in modern surface waters. The greater relative abundance of Neogloboquadrina pachyderma dextral (e.g., right-hand coil sense) versus the sinistral (e.g., left-hand coil sense) variant demonstrates the influence of the warmer Kuroshiro Current at this site (Bandy, 1960; Ericson, 1959).

A sediment sample from Hole C0014A at 4.1 mbsf contained a large fraction of pyritized foraminifers (Fig. F11A–F11C). These pyritized foraminifers are extremely well preserved, allowing species identification. Pyritization in these samples differs from those in previous reports with respect to infilling of the foraminiferal tests and the preservation of pseudomorphs (Kohn et al., 1998). The broken, pyritized foraminifers are hollow (Fig. F11C), highlighting complete replacement of the carbonate wall with fine-grained iron sulfide. Preliminary observations suggest that they are coated in fine-grained framboidal pyrite (Fig. F11E); at high resolution, framboids were shown to consist of well-ordered acicular iron sulfide crystals (Fig. F11F). Smaller foraminifers are also pyritized within more classically structured framboidal pyrite aggregates (Fig. F12), suggesting that the foraminiferal carbonate tests were controlling iron sulfide crystallization during pyrite replacement (Fig. F11).

Only a few coccolithophorids were recovered at Site C0014. One sample from Hole C0014A at 0.01 mbsf was processed as a surface (i.e., modern) sample (Table T6; Fig. F13A–F13C) and compared to a core catcher sample from Hole C0014B from ~7.0 mbsf. The coccolithophorid diversity of this deeper sample is generally consistent with the shallow modern mud sample (Winter and Siesser, 1994; Raffi et al., 2006), as Emiliania huxleyi is the predominant species. Coccolith preservation at ~7.09 mbsf is poor (Fig. F13D). Damage to coccoliths at such a shallow depth suggests they may have been reworked or deposited under more energetic conditions; in addition, pore water at this depth is corrosive to coccolithophorids (see “Geochemistry”).

Small numbers of radiolarians were observed in the 63–150 µm sieved fraction recovered from 0.01 mbsf in Hole C0014A. Radiolarian fragments were commonly observed in samples that contain abundant foraminifers (Fig. F14).

Based on their relatively high abundance and enhanced preservation, foraminifers were targeted for paleontological examination during Expedition 331. The restriction of microfossils to one or two samples (when they occur at all) and to only the upper few meters of sediment limits biostratigraphic interpretation at this site using core catcher material. The recovery of as much as 5 m of sediment containing foraminifers from Holes C0014A and C0014B, along with the 50 cm/k.y. average sedimentation rate described by Chang et al. (2008), suggests a maximum of 10 k.y. of sediment accumulation at Site C0014. This estimate does not account for the contribution of pumice clasts and fragments (Table T4), which represent a major part of the sediment accumulating in the upper stratigraphic units at this site. The microfossils may therefore be even younger (i.e., essentially modern and encompassing only the earliest paleontological unit described by Xiang et al., 2003).

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