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...