A qualitative and quantitative study of the distribution of pelagic sediment in the Atlantic Basin
Webb, Helen F.
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KeywordSedimentation and deposition; Geomorphology; Submarine topography; Maurice Ewing (Ship) Cruise EW9208; Maurice Ewing (Ship) Cruise EW9011; Robert D. Conrad (Ship) Cruise RC2711; Robert D. Conrad (Ship) Cruise RC2802; Thomas Washington (Ship) Cruise
Pelagic sedimentation is the primary modifier of topography generated by ridge-associated volcanic and tectonic processes. This thesis represents an effort to understand the processes of, and the general distribution of, pelagic sedimentation on rough topography, particularly in the Atlantic Basin but with applications to the world ocean as a whole. This study utilizes a simple numerical model of sedimentation which, when applied to models of rough basement topography, allows us to study sedimentation effects in terms of commonly-measured stochastic parameters including seafloor RMS height, abyssal hill spacing, and slope distribution. We also address the effect of sediment compaction on seafloor morphology, and the impact of long-wavelength topography on stochastic measures of sedimented seafloor. Understanding gained allows the construction of inverse problems to obtain information about sediment distribution and basement morphology from multibeam bathymetric data in regimes where backscatter from rough, reflective basement highs obscures returns from wide-beam seismic systems. By using maximum likelihood estimation to compare slope distribution functions calculated from data to those from filtered model topographies, we estimate average sediment thickness L, basement RMS height H, and a measure of sediment mobility K. Using data from near-ridge surveys and off-axis transit lines, we invert for L, H, and K for 3-29 Ma seafloor from the western flank of the Mid-Atlantic Ridge (MAR) near 26°N, 2- 45 Ma seafloor from the western flank of the MAR near 26°S, 2-40 Ma seafloor from the eastern flank of the MAR near 25°S, and 1-38 Ma seafloor from the western flank of the MAR near 35°S. Variations in L with seafloor age allow us to constrain sediment rain rate and the corrosivity of bottom waters to calcite since the Oligocene. We hypothesize that sediment rain rates during much of the early and middle Miocene were only 10-50% of the average rate for the past -10 m.y. Variations in H suggest correlation between tectonic setting and topographic variability. A relatively narrow range of K is needed to describe intrahill sedimentation patterns.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1997
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