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doi:10.2204/iodp.proc.320321.218.2014

Results

Foraminifer SEM

The SEM images show that the benthic foraminifer C. mundulus from Site U1338 generally shows good preservation (Fig. F2). The umbilical and spiral sides of the specimens from 87.13, 129.17, 148.20, and 164.93 m CCSF-A (Fig. F2A, F2E, F2F, F2G, respectively) show only very minor calcite overgrowth, the original pores are still well preserved, and the apertures and individual chambers are well defined. The specimens from 89.53 and 101.38 m CCSF-A (Fig. F2B, F2C, respectively) show very similar levels of overgrowth as the specimens in Figure F2A, F2E, F2F, and F2G; however, these specimens have possibly experienced very minor dissolution (red arrows in Fig. F2B, F2C) around some of the edges of a few pores on the umbilical side. The umbilical specimens from 115.49 and 176.60 m CCSF-A (Fig. F2D, F2H umbilical side, respectively) show some evidence of dissolution and large calcite overgrowths that disguise the original pores and chamber structure (red arrows in Fig. F2D, F2H umbilical side). The specimens examined on their spiral sides from both 115.49 and 176.60 m CCSF-A are relatively well preserved (Fig. F2D, F2H spiral side, respectively).

The planktonic foraminifer SEM images indicate that the specimens are not pristine and that preservation is variable (Fig. F3). All specimens show some levels of recrystallization, ranging from very minor (Fig. F3F, F3K) to high (Fig. F3I, F3J). However, even in the worst recrystallization cases, the original pore structure remains visible, occasionally with the spine bases intact. Blockier, gametogenic calcite is present on the final chamber of all imaged specimens (blue arrows in figure). Specimens from 105.50 and 117.87 m CCSF-A (Fig. F3F, F3K) show the best preservation. The latter specimen was mechanically broken to expose the wall structure and the inside of the test (Fig. F4). Minor recrystallization of the outer test has occurred in both specimens, and many spine bases remain visible (Fig. F3). The inner wall of the specimen at 117.87 m CCSF-A only shows minor overgrowth and has retained a smooth surface (Fig. F4). The internal growth structure is still largely retained. However, the microgranular texture of the test wall has recrystallized throughout, as indicated by large calcite crystals visible throughout the wall (Fig. F4). Nonetheless, there is no infilling seen in the specimen, as the internal wall has remained smooth. Specimens from 63.64, 96.73, 111.70, 125.74, 171.51, and 178.70 m CCSF-A (Fig. F3A, F3E, F3H, F3M, F3N, F3O, respectively) show more recrystallization, although the spine bases are still frequently visible. The specimens from 74.58, 87.35, 91.23, 110.70, and 118.87 m CCSF-A show still more recrystallization, which masks most of the spine bases (Fig. F3B, F3C, F3D, F3G, F3L, respectively). The worst recrystallization was found on specimens from 112.77 and 116.87 m CCSF-A (Fig. F3I, F3J, respectively). Here the spine bases have mostly disappeared and the original pore structure is almost entirely obscured by recrystallization.

Fine fraction SEM

The BSE SEM images of the Sample c1 and c2 <63 µm fractions show the presence of many heterococcolith plates (green circles in Fig. F5) and large fragments of radiolarians and foraminifers (Fig. F5A–F5B). There are also large numbers of whole diatoms present. Higher resolution SE SEM images show that the dominant sedimentary components are coccoliths, coccolith plate and diatom fragments, and small fragments (Fig. F5C–F5D). The small fragments are sometimes distinguishable as very small coccolith or foraminifer fragments (red circles in Fig. F5C–F5D). The fragments are frequently too small to accurately identify their origin but could potentially be fragmented holococcoliths and heterococcoliths. No holococcoliths are identifiable on the higher resolution images, although some of the smaller fragments of calcite may be disintegrated holococcoliths (Fig. F5E). The central structures of the heterococcoliths have not been retained, which suggests slight to moderate dissolution/etching occurred. Most imaged heterococcoliths show minor overgrowths of single calcite cells (red arrows in Fig. F5E, F5G, F5H). However, as a large number of small fragments is present, some of this potential overgrowth could simply be a small fragment attached to the coccolith surface (Fig. F5G). The resolution of the SE SEM micrographs is not sufficiently high to judge whether there is any recrystallization. The original coccolith growth structures are also retained in some of the heterococcoliths (green arrows in Fig. F5F, F5H). However, the absence of holococcoliths and original structures in all heterococcoliths, together with the minor overgrowths and large number of fragments, suggests that the preservation of these samples is moderate, perhaps even moderate to poor.

Qualitative EDS maps (Fig. F6) show that the main chemical components are biogenic calcite (CaCO₃ represented by the red-colored calcium map) and biogenic silica (SiO₂ represented by the green-colored silicon map) (lower section Fig. F6). The lower EDS maps also show some large euhedral to subspherical barite crystals are present (BaSO₄ represented by the blue-colored barium map), which are most likely marine barite. The red areas of the four EDS overlays show that much of the smaller (<2 µm) fragments and particles, which are sometimes distinguishable as coccolith plate fragments, are all calcite.

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