Sediment Accumulation Rates From Deep Tow Profiler Records and DSDP Leg 70 Cores Over the Galapagos Spreading Centre


Neil C. Mitchell

Variations in pelagic input rates over abyssal hill areas cannot be inferred easily from sedimentation rate variations between cores because of redistribution by down-slope gravity processes and bottom currents. Some spatial averaging or adjustment for sediment transport is required. Relatively accurate mean sedimentation rates may be obtained, however, by regressing sediment thickness with distance from a mid- ocean ridge spreading centre, where the regression averages out the variations due to local redistribution. This is shown using sediment profiler records from the Galapagos spreading centre (SC) at 1û N in the eastern Pacific. Physical property data from Deep Sea Drilling Project (DSDP) Leg 70 are used to correct sediment thicknesses for compaction and to convert sedimentation rates to mass accumulation rates (MARs), which are ~2 g cm-2 Ka-1 in this region. These high MARs are due to enhanced equatorial productivity of pelagic organisms, which is also reflected in a ~6% higher MAR for the ridge flank closest to the equator, corresponding to a rate of change of MAR with latitude of ~16% per degree. The equatorial high productivity zone in the Panama Basin lies further south then in the central Pacific (Moore et al. 1973); peak sedimentation along the Ocean Drilling Program (ODP) Leg 138 transect (110û W) occurs near 1û N so has nearly zero gradient at this latitude, but has comparable gradient to the Galapagos SC north of 2û N. The zone of peak enhancement at 86û W in the Panama Basin may therefore be 1û or more further south than at 110û W. Some further sedimentation characteristics of the Galapagos spreading centre are also described, such as a scaling of thickness variability and the possibility of dating seafloor using sediment thickness.

Mitchell, N. C., Sediment accumulation rates from Deep Tow profiler records and DSDP Leg 70 cores over the Galapagos Spreading Centre, in: A. Cramp, C.J. MacLeod, S.V. Lee and E.J.W. Jones (Eds.) The Geological Evolution of Ocean Basins: Results From the Ocean Drilling Program, Spec. Publ. Geol. Soc. Lond., 131, 199-209, 1998.


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