Site 1179 was drilled in the northwest Pacific during Ocean Drilling Program (ODP) Leg 191 (Fig. F1); it is located east of Japan between Japan and Shatsky Rise at 41°04.78´N and 159°57.78´E at a water depth of 5563.9 m (Kanazawa, Sager, Escutia, et al., 2001). The primary scientific objective was to drill into the basaltic ocean crust to emplace a seismometer that would allow subsequent retrieval of data. During this process, advanced piston coring recovered 249.9 m of sediment in Holes 1179B and 1179C with 98.8% recovery.
The sediments consist of clayey siliceous ooze, clay, and chert. The two holes included in this study overlap slightly in depth and were divided aboard ship into four lithostratigraphic units. Samples reported here are from the uppermost unit, lithostratigraphic Unit 1, a 221.5-m-thick clay- and radiolarian-bearing diatom ooze. The sedimentation rate derived for Unit 1 from magnetic stratigraphy and the magnetic polarity reversal timescale is high (29.29 m/m.y.), which has been attributed to high productivity in divergent waters northeast of the western boundary current (Shipboard Scientific Party, 2001; see in particular fig. F37).
The upper Miocene to Pleistocene diatom biostratigraphy of the northwest Pacific Basin has been previously described in the Initial Reports of the Deep Sea Drilling Project (DSDP) for Legs 6, 20, 32, 86, and 87 and more recently in the ODP Scientific Results for Legs 185 and 186. During DSDP Leg 86, specifically, six holes were drilled in the same geographic area as the sites from Leg 191; Koizumi and Tanimura (1985) report the diatom biostratigraphic record of those holes. Maruyama (2000), Ikeda and Koizumi (2000), and Barron (2000) provide a recent documentation of the diatom record of the northeast Pacific from their work with material from ODP Leg 167. Yanagisawa and Akiba (1998) give an excellent summary of the northwest Pacific Neogene diatom biostratigraphy. Diatoms are present in all cores studied for this report (Cores 191-1179B-1H to 6H and 191-1179C-2H to 19H). Overall, diatom preservation is generally good and abundance is moderate. Silicoflagellates are also often quite abundant in the sediments, although they never dominate the microfossil assemblage.