Site 647

Abstract

Core recovery (%): 62Srivastava, S. P., Arthur, M., Clement, B., et al., 1987. Proc, Init. Repts. (Pt. A) Principal results: Holes 647A and 647B, Site 647, were drilled in a water depth of 3858.5 m, at 53°19.876'N, 45°15.717'W, in the southern Labrador Sea. The total depth of penetration was 736 mbsf; average recovery during rotary drilling at Hole 647A was 62% and during APC coring at Hole 647B, 90%. Four major sedimentary units were encountered between the seafloor and 699 mbsf, and basalt was re covered from 699 to 736 mbsf. The lithologic units are as follows: Lithologic Unit I (Cores 105-647A-1R to 105-647A-12R; 105-647B-1H to 105-647B-11H) 0-116 mbsf. Age: late Pliocene to Holo cene. Description: consists of interbedded gray to light brownish gray silty clays, clayey muds, and clayey silts containing highly varia ble amounts of biogenic carbonate (foraminifers, nannofossils) to a maximum of 40%-50%. Lithologies are interbedded on a scale of from 10 cm to 3 m, having both sharp and gradational contacts. Silty clays, clayey muds, and clayey silts are structureless to color mottled. Foraminifer-nannofossil silty clays or clayey silts are homo geneous, but pockets within or at the tops of beds are enriched in foraminifers; the tops of such thin beds have sharp contacts with overlying beds. Detrital (nonbiogenic) carbonate occurs as dissemi nated silt-sized grains (as much as 50%) and as concentrations of as much as 75% in thinly laminated silty clay to clayey silt layers. Some of these layers have sharp bases and exhibit grading. All facies except the laminated detricarbonate silty clay layers contain variable amounts of sand-and gravel-sized material to cobble size. The upper 675 SITE 647 50 m of Unit I are coarser grained than the lower part, but no sys tematic trend to the biogenic content exists. However, intervals con taining gravel and those relatively rich in biogenic constituents alter nate in a cyclical but irregular pattern.Lithologic Unit II (Cores 105-647A-13R to 105-647A-14R) 116.0-135.4 mbsf. Age: early Miocene to late Miocene. Description: pri marily mottled olive-yellow to yellowish brown silty mud, clay, and nannofossil clay (Subunit IIA, 116-119 mbsf) and olive-yellow to grayish green silica-bearing (as much as 25%) clays lacking calcare ous nannofossils (Subunit IIB, 119-135.4 mbsf). Subunit IIA con tains quartz silt (as much as 25%) and scattered iron/manganese micronodules that increase in abundance toward the base; the sediment is bioturbated to homogeneous. Subunit IIB is marked by diatomand spicule-bearing silty clay; biogenic silica (as much as 15%) con tents increase toward the base. Dark-gray bands of iron/manganese micronodules occur in the upper part, and larger iron/manganese nodules appear near the base of the subunit. Subunit IIB is biotur bated and mottled.Lithologic Lithologic Unit IV (Cores 105-647A-56R to 105-647A-71R) 530.3-699.0 mbsf. Age: middle Eocene to early Eocene. Description: pre dominantly greenish gray claystone and foraminifer-nannofossil-bearing claystone with...