In a second study, profiler records from the Galapagos spreading centre were used to
assess sediment transport rates. The method essentially involved
quantifying the amount of material eroded from (or not deposited on) the
crests of fault scarps, and dividing this value by the age of the scarp which
is well known from the seafloor spreading history. Due to the method used,
the result was an upper bound on rates of surficial sediment movement. (Abstract and full article (PDF)*.)
Accumulation ratesSediment on ridge flanks commonly thicken with distance from the spreading axes, reflecting the increasing age of the volcanic seafloor. Complications to this simple picture occur where there is substantial sediment transport or varied dissolution of carbonate. High resolution sediment profiler records collected on the Mid-Atlantic Ridge in 1996 (CD99) show that this simple picture is not applicable there, which has implications for attempting to use the thickness of the sediment cover as a dating tool on slow-spreading ridges (abstract.). However, sediments on the Galapagos spreading centre (figure right) do show a simple systematic trend, partly because the ridge lies beneath the equatorial zone of high pelagic productivity causing very high accumulation rates relative to rates of sediment redistribution and dissolution. Accumulation rates are higher on the south flank, closest to the centre of the high productivity zone. Abstract.
Mapping lava flowsDue to the high accumulation rates on the Galapagos spreading centre relative to sediment redistribution rates, the thickness of sediment is a useful proxy for seafloor age. The ridge flanks have areas of near uniform sediment thickness which correspond to flat basement topography and are bounded by fault scarps. These areas are highlighted by horizontal bars in the figure (left) and were interpreted as regions of uniform age due to large lava flows. As a consequence of the flows, the surficial oceanic crust is slightly younger than might be predicted by simple seafloor spreading and distance of the seafloor from the ridge axis. Hence the sediment does not thicken monotonically away from the ridge axis but begins to thicken from a point away from it (e.g., as shown in the figure (above), from around 5 km). Using these sediment thickness data, the crustal age anomaly was estimated to be approximately 120-150 ky for the Galapagos spreading centre. Abstract
See also work on sonar penetration
into marine sediment and the possible use of variations in backscatter to
infer variations in the sediment cover over young seafloor.
Funding for the above work was provided by Research Fellowships from the Royal Society and the NERC. This research was primarily based on data collected with the Deep Tow system of Scripps Institution of Oceanography.
*The American Geophysical Union owns the copyright to these documents. Further reproduction or electronic distribution of them is not permitted.
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