Site 444, Shikoku Basin, Deep Sea Drilling Project Leg 58

Abstract

Time on hole: 1 day Position (latitude; longitude): 28°38.25 N; 137°41.03 E Water depth (sea level; corrected m, echo sounding): 4843.0 Water depth (rig floor; corrected m, echo sounding): 4853.0 Bottom felt (m, drill pipe): 4852.0 Penetration (m): 91.5 Number of cores: 10 Total length of cored section (m): 91.5 Total core recovered (m): 41.49 Core recovery (%): 45 Oldest Sediment Cored: Depth sub-bottom (m): 91.5 Nature: clay and pumice Age: early Pliocene/late Miocene Measured velocity (km/s): 1.53 Basement: Depth sub-bottom (m): not reached Principal Results: Site 444 is in the east-central part of the Shikoku Basin, 45 nautical miles southeast of Site 443. The stratigraphic section consists of 48 meters of Pleistocene in-terbedded mud, vitric mud, ash, and clayey nannofossil ooze; 35.5 meters of Pleistocene and Pliocene mud, ash, and vitric mud; 75.5 meters of Pliocene and late-Miocene mud, ash, vit-ric mud, nannofossil ooze, radiolarian ooze, quartz sand, and siliceous mud; and 100.6 meters of late-and middle-Miocene mudstone, ash, nannofossil ooze, and radiolarian mudstone, cut by a 10-meter basalt sill. Next below are 19 meters of amygdaloidal phyric basalt flows, and another 19-meter aphanitic, aphyric basalt flow. An early-Pliocene to latest-Miocene hiatus occurs in the section. Mixed hemipelagic sediments and ash predominate. Basement age is 15 m.y., which is at variance with the magnetic-anomaly age for the site. Time on holes: 2 l days Position (latitude; longitude): 28°38.25 N; 137°41.03 E Water depth (sea level; corrected m, echo sounding): 4843.0 Water depth (rig floor; corrected m, echo sounding): 4853.0 Bottom felt (m, drill pipe): 4852.0 Penetration (m): 310.0 Number of cores: 27 Total length of cored section (m): 228.0 Total core recovered (m): 107.2 Core recovery (%): 47 Oldest Sediment Cored: Depth sub-bottom (m): 272.7 Nature: red clay Age: late early or middle Miocene Measured velocity (km/s): 1:72 Basement: Depth sub-bottom (m): 310.0 Nature: basalt Velocity range (km/s): 4.25-5.46 Principal Results: See Hole 444. BACKGROUND AND OBJECTIVES Background The background and objectives for Site 444 are complementary to the background and objectives reviewed for Sites 442 and 443. Site 444 is in the Shikoku Basin and was chosen for further testing of hypotheses about the origin of marginal basins. The marine geology of the Shikoku Basin was summarized in the site reports for 442 and 443, as well as by Karig, Ingle, et al. (1975), Tomoda et al.