Radiolaria: Leg 31 of the Deep Sea Drilling Project

Comments: a Drilling in this hole was conducted during two visits (see text).Ingle, J. C, Jr., Suyehiro, K., von Breymann, M. T., et al., 1990. Proc. ODP, Init. Repts., 128: College Station, TX (Ocean Drilling Program).2 Shipboard Scientific Party is as given in list of participants preceding the contents. Core recovery (%): 106 HOLE 799CDate Oldest sediment cored:Depth (mbsf): 252.5 Nature: diatom clayey mixed sedimentComments: This was a "dedicated" hole to test the sonic core monitor.Principal results: Our objectives at Site 799, located in the KitaYamato Trough were (1) to determine the depositional and tectonic history of the trough as a sedimented failed-rift environment thought to be ideal or typical for the occurrence of volcanogenic massive sulfide deposits of the Kuroko or perhaps shale-hosted type and (2) to obtain information about the paleoceanographic history of the Yamato Rise area and the Sea of Japan as a whole.Results at Site 799 are summarized below, and a stratigraphic summary is presented in Figure 1. 1. Before drilling, seismic estimates of the thickness of sediment in the Kita-Yamato Trough indicated up to 1300 m of Miocene to Holocene sediments might be present in the axis of this narrow graben structure. Drilling in the trough, we penetrated 1084 m of lower Miocene through Holocene sediments before an increase in hydrocarbon gases and a fluorescent cut forced us to stop drilling. Post-drilling vertical seismic profile (VSP) analysis indicated that acoustic basement was present about 120 m below the base of Hole 799B (1084 mbsf T.D.), indicating a total sediment thickness of about 1200 m.2. The sedimentary column at Site 799 can be divided into five lithologic units that correspond to variations in composition and depositional style and major post-depositional diagenetic changes. Benthic foraminifers indicate that the entire sediment column at Site 799 was deposited at lower to middle bathyal water depths that were approximately equivalent to the presentday water depth at this site (2084 m). Coarse turbidite sands mark early Miocene deposition in the trough area and indicate close proximity to an insular or continental littoral area and associated terrestrial environments. Middle and upper Miocene intervals are dominated by siliceous claystones, porcellanites, and biosiliceous sediments that include common authigenic carbonate layers and nodules, indicating high surface productivity of both siliceous and calcareous plankton during this period. organic matter indicate episodic deposition under low-oxygen bottom-water masses. Lower Pliocene sediments are rich in diatoms, with higher amounts of fine-grained terrigenous sediment appearing in late Pliocene through Pleistocene time, accompanied by slump deposits, redeposited foraminiferal sands, and volcanic ashes. There are hints of a causal relationship between the appearance of the slump deposits and the occurrence of volcanic ashes.3. The opal-A/opal-CT transition occurs at about 435 mbsf and forms a major lithologic and geochemical bound...

Section: Radiolarianssupporting

confidence: 49%

Site 799

1990

“…In general, radiolarian preservation is good in Site 292 sediments (Ling, 1975). The D. ateuchus and T. tuberosa Zones are well represented and most of the radiolarians described by Ling from Site 292 are present in Sites 767 and 770 in the Celebes Sea.…”

Section: Discussionmentioning

confidence: 69%

“…The most notable difference between Celebes and Philippine basin sediments is the apparent lack of strong dominance of abundant and diverse Dorcadospyris species in Philippine sediments, as is found in the Celebes Sea sediments. While diverse Dorcadospyris species are reported by Ling (1975), he does not indicate that they are abundant in his samples. In contrast, a nearly identical assemblage, strongly dominated by Dorcadospyris species, has been described from similar-aged sediments of tropical Atlantic Site 628, on the Little Bahama Bank (Palmer, 1988).…”

Section: Discussionmentioning

confidence: 93%

See 1 more Smart Citation

Radiolarians of the Celebes Sea, Leg 124, Sites 767 and 770

Scherer¹

1991

Two sites were drilled in the Celebes Sea as part of Ocean Drilling Program Leg 124; Site 767 and Site 770. Radiolarians are preserved in Paleogene pelagic claystones with minor occurrences in certain Neogene successions. The brown clays that immediately overlie basalt at both sites contain radiolarians of the late middle Eocene Podocyrtis chalara Zone. Late Eocene radiolarians are not found, due to dissolution and probable hiatus. The Oligocene is represented by the Theocyrtis tuberosa and Dorcadospyris ateuchus Zones. Oligocene sediments are strongly dominated by abundant and diverse radiolarians of the TristylospyrislDorcadospyris lineage. Preservation of Paleogene radiolarian assemblages ranges from good to very poor. Late Miocene radiolarians of the Didymocyrtis antepenultima Zone are found only in Site 770. Other Neogene sediments are barren of radiolarian remains, with the exception of latest Pleistocene and Holocene sediments.

“…During deposition of the upper Paleogene-lower Neogene, this difference in depth may have been significant for distribution of radiolarian populations. However, such assemblage differences are not apparent elsewhere (e.g., Philippine Basin, Deep Sea Drilling Program Leg 31; Ling, 1973). It is also possible that the topographic rise led to very localized variation in circulation and upwelling, which influenced the radiolarian assemblage at Site 770.…”

Section: Foraminifersmentioning

confidence: 97%

Site 770

1990

Core recovery (%): 14.7 Oldest sediment cored:Depth (mbsf): 10. Principal results: Three holes were drilled at Site 770 (5°08.7'N, 123°40.1 'E; Table 1). Hole 770A did not properly spud in, so it was abandoned after two cores. Hole 770B was spot cored every 50 m to 340 meters below seafloor (mbsf) and then was cored continuously to 474 mbsf, including 53 m of basement. We had to abandon Hole 770B to remove 7 km of polypropylene rope that was wrapped around the drill pipe. Hole 770C was washed to basement, then cored to 529 mbsf, including 106 m of basement. We achieved excellent results in three Schlumberger logging runs and a borehole televiewer (BHTV) downhole run. The hole was reentered for an attempted packer experiment, but we could not penetrate a bridge at 56 mbsf, at which time the site was abandoned and we proceeded to Site 771 on the Cagayan Ridge. The objectives of Site 770 were to obtain basement and logs within basement at a location close to Site 767, which had been abandoned just after hitting basement. Except for the lack of a packer run, the objectives were very well satisfied here.Site 770 consists of two main lithologic units:Unit I (0-296 mbsf) is middle(?) Miocene to Holocene in age, with dominant rock types composed of volcanogenic silty clay and clay with sparse thin beds of marl and volcanic ash.Unit II (296-421 mbsf) is late middle Eocene to middle(?) Miocene in age, consisting of claystone and calcareous claystone, with sparse interbeds of silty to sandy claystone and porcellanite clay mixed sediment. The unit is divided into 3 subunits mainly on the basis of carbonate content.Subunit IIA (296-388 mbsf) is late Oligocene to middle(?) Miocene in age. Claystone is the dominant lithology, but the subunit also contains minor interbeds of volcanogenic claystone with silt, sand, and porcellanite-mixed sediment. The claystone is grayish brown in the upper part, becoming brown to yellowish brown in the lower part.