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Foraminifer Biostratigraphy, North Philippine Sea, Deep Sea Drilling Project Leg 58
| Content Provider | Semantic Scholar |
|---|---|
| Author | Echols, Dorothy Anne Jung |
| Copyright Year | 1980 |
| Abstract | During Leg 58, part of the DSDP program of drilling on active ocean margins, five sites were drilled in the north part of the Philippine Sea — three in the central part of the Shikoku Basin, and two to the southwest, in the Daito Ridge and Basin province. Samples from the Shikoku Basin sites (442, 443, 444) represent Quaternary through middle-Miocene sediments. In this basin, water depths are believed to exceed the carbonate-compensation depth (CCD), for no carbonate organisms have been found in the surface sediments. Both planktonic and benthic foraminifers were very rare and poorly preserved in these samples, indicating that the depth of deposition fluctuated near the CCD. The few identified key planktonic species show general agreement with the nannofossil and radiolarian biostratigraphy. The autochthonous benthic assemblages at all three sites are characteristic of deep water. Samples from the two sites (445, 446) in the Daito Ridge and Basin province represent Quaternary through early-Eocene sediments. The autochthonous foraminifers of Site 445 are, over certain intervals, suitable for biostratigraphic and environmental study. Some foraminifer zones are recognized at Site 446. Although deposition at Site 445 is believed to have been above the CCD, foraminifers are rare or absent in certain intervals. At Site 446, the foraminifers indicate that the depth of deposition fluctuated near the CCD. At both sites, thick sequences of resedimented sandstones, siltstones, and mudstones in turbidites occur in the early and middle Eocene. In these sediments, abundant shallow-water larger and smaller benthic foraminifers were recovered in varying states of preservation. It is suspected that these deposits were derived from ridges fairly close to the depositional basin. SHIKOKU BASIN Introduction Three sites (442, 443, 444) were drilled in the Shikoku Basin in the north Philippine Sea (Figure 1). Primary objectives of drilling in the Shikoku Basin were to study the geological history and to test the validity of sea-floor-spreading models. The paleontological objectives were to determine basement ages, which might in turn indicate the age and kind of spreading; to infer paleocirculation and paleoenvironment; and, where possible, to establish biostratigraphic zonation (Table 1). The time scale used in the foraminifer biostratigraphy is adapted from Berggren and Van Couvering (1974), Saito (1977), van Andel et al. (1975), and Hardenbol and Berggren (1978). The preliminary Neogene and Paleogene planktonic-foraminifer zonations include those established by Bolli (1957, 1970), Banner and Blow (1965), Blow (1969), Jenkins (1966, 1967, 1971), Brönnimann and Resig (1971), Postuma (1971), Jenkins and Orr (1972), Kennett (1973, 1975), Vincent (1975), Stainforth et al. (1975), and Saito (1977). Site 442 The summary of Holes 442, 442A, and 442B is based on all samples collected aboard ship. Foraminifers were rare and at best only moderately well preserved, indicating proximity of the depositional surface to the CCD. In no case were more than a few specimens (2026) found on a tray; therefore, it is meaningless to establish relative abundances. A detailed tabulation of foraminifers recovered at Site 442, is found in Appendix 1. Sediments drilled in the Shikoku Basin span the Holocene through the middle or early Miocene. Foraminifer recovery was disappointing, but this was expected. As mentioned previously, the basin is now below the CCD, and it was anticipated that this situation might well prove to have been the case in the geological past. However, in a few instances rare key planktonic foraminifers were recognized that indicated ages in general agreement with the nannofossil and radiolarian determinations (Okada, this volume; Sloan, this volume). For example, in Core 442B-2, the few fragmented and partially dissolved forms related to the Sphaeroidinella group might be significant. At first it was believed |
| File Format | PDF HTM / HTML |
| DOI | 10.2973/dsdp.proc.58.108.1980 |
| Alternate Webpage(s) | http://deepseadrilling.org/58/volume/dsdp58_08.pdf |
| Alternate Webpage(s) | https://doi.org/10.2973/dsdp.proc.58.108.1980 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
