Site 508

Abstract

Principal results: Six holes were drilled at Site 508. In Hole 508 we cored 35 meters of siliceous foraminifer nannofossil ooze with 99% recovery using the hydraulic piston corer. Semilithified sediment was recovered immediately overlying the basement in Holes 508 and 508C. The sediments do not show a decrease in biogenic silica content with depth and microfossil preservation is better than at the mounds sites. The sedimenfs pore-water chemistry suggests that there is little input of formation waters in this area of presumed recharge. At Hole 5O8B, basement drilling penetrated 10 meters with 5.1 % recovery before drilling was terminated. The basalts recovered are fine-to medium-grained aphyric to sparsely Plagioclase phyric. Alteration rims are common and contain smectites, zeolites(?), and iron-oxyhydroxides. Some samples are slight- ly altered throughout, but no evidence was found of unequivocal hydrothermal alteration.Heat-flow measurements and pore-water sampling were conducted at Hole 5O8A. Principal results: The major purpose was to drill into basement. Sediments were washed to basement, but unfortunately drilling was slow. We abandoned the hole after 10.1 meters of basalt had been drilled with a meager recovery of 5.1 %. A mudline core was taken. Total recovery of sediment plus basalt was 21.4%. HOLE 508BHOLES 508C, 508D, 508E Principal results: Ten meters of sediment were cored above the basement in Hole 508C. This interval was inadvertently washed during Hole 508B drilling. Heat-flow measurements and pore-water sampling were conducted at Holes 5O8D and 508E.