SEDIMENTATION ON YOUNG OCEAN-FLOOR AT THE MID-ATLANTIC RIDGE, 29-DEGREES-N

Measurements of the sediment cover over mid-ocean ridges are potential ly useful for tectonic and volcanic problems because sediment thicknes s variations may reflect variations in seafloor age. In profiler recor ds recently collected with the deeply towed TOBI system, however, we f ind that sediments on 0-2.5 Ma seafloor do not thicken systematically with distance from the spreading axis as would be expected from increa sing seafloor age. Average sedimentation rates calculated from the thi cknesses show some tendency to increase with depth as found elsewhere on the Mid-Atlantic Ridge. Many of the deposits drape basement topogra phy and occur on outlying promontories, so sediment is probably deposi ted from suspension in the bottom nepheloid layer rather than from tur bidity currents or other gravity flows. Enhanced sedimentation rates i n deeper areas, therefore, occur because of enhanced suspended load wi thin the bottom nepheloid layer or reduced bottom movement which allow particles to settle from suspension. The profiler records reveal a va riation in the style of sedimentation from draping and localised pendi ng on young seafloor, to accumulation in large turbidite ponds farther off-axis, which probably reflects the progressive accumulation in sou rce areas and, due to sedimentation, progressively smoother pathways f avourable to turbidity currents. (C) 1998 Elsevier Science B.V. All ri ghts reserved.