Site 884

Abstract

Beginning at 0900 hr on 24 August, we pulled up the drill pipe to the seafloor, offset 20 m, and began piston coring in Hole 884C; Core 145-884C-1H was recovered at about noon that day. Hole 884C was continued to a depth of 357.8 mbsf with 82.3% recovery to duplicate the upper portion of the section and to fill in the coring gaps left in Hole 884B. We were largely successful in achieving these objectives. Hole 884D, consisting of two APC cores extending 0 to 14.8 mbsf with 94.1% recovery, was intended for continuous sampling to determine paleointensity variations of Earth's magnetic field. Drilling was completed late in the evening of 25 August. On 26 August, the drill pipe was pulled up and the bit and BHA changed for rotary drilling; Hole 884E was washed down to 842.8 mbsf, and basalt drilling began at 0600 hr on 27 August. The last basalt core, 145-884E-10R, was recovered at about 0300 hr on 29 August; 87 m of basalt had been penetrated in 45 hr with a recovery of 66.78 m (76.8%). Logging operations followed on 29 and 30 August. Logging was hindered by a bridge at about 750 mbsf, presumably a swelling ash layer, but all five tool systems (the geochemical tool, formation microscanner, Quad combo, magnetic susceptibility, and magnetometer tools) made reasonably to completely successful runs above that depth. Logging operations were completed about 0545 hr on 31 August. Both beacons returned to the surface upon command, so for the first time during Leg 145 no unintended metal was left behind at the drill site. The JO1DES Resolution started southeast toward proposed Site NW-4A just before 1300 hr later the same day.Drilling at Site 884 penetrated 854 m of Cenozoic sediment and 87 m of the underlying basalt. The sediment column was divided into two main lithologic units, each with subunits. Lithologic Subunit IA (0-128 mbsf) is a Quaternary to upper Pliocene clay with diatoms. Vitric ash layers, some more than 1 m in thickness, and a few dropstones occur in this unit. .2 mbsf) is an upper Pliocene to upper Miocene clayey diatom ooze. A pure dolomite concretion occurs at 172 mbsf, and a piece of wood approximately 6 cm across is found at 214 mbsf in sediments of early Pliocene age. Lithologic Subunit IC (440.2-546.1 mbsf) is an upper Miocene to middle Miocene claystone with accessory diatoms and some chalk. Bladed and twinned crystals of native copper occur within the gray claystones of Subunit IC. Subunit ID (546.1-604.8 mbsf) is a middle Miocene to lower Miocene diatomite with clay. Unit II is differentiated from the overlying materials by the clear presence of reworked materials. Subunit .7 mbsf) is a lower Miocene to lower Oligocene claystone with minor chalk. This subunit shows evidence of downslope reworking and contains native copper as discrete grains. Subunit HB (694.7-771 mbsf) is an upper Eocene claystone conglomerate. Diatoms are no longer present in this part of the section, which is dominated by downslope reworking. Ash layers are present in the lower part of this subunit. Subunit HC (771-854 mbsf) is...