Bowles, Frederick A. and Wood, Warren T. (1995): Diminished amplitude reflections (fadeout) in Bermuda Rise stratification

Leg/Site/Hole:
DSDP 43
DSDP 43 386
DSDP 43 387
Identifier:
1995-053275
georefid

Creator:
Bowles, Frederick A.
Naval Research Laboratory, Seafloor Sciences Division, Stennis Space Center, MS, United States
author

Wood, Warren T.
author

Identification:
Diminished amplitude reflections (fadeout) in Bermuda Rise stratification
1995
Marine Geology
Elsevier, Amsterdam, Netherlands
125
1-2
133-141
Single and multichannel deep-tow seismic records collected on the southwestern Bermuda Rise reveal areas within the acoustic layering where the intensity of reflectors fade or even disappear over lateral distances of 20-60 m. The fadeouts are conspicuously present in a highly stratified interval consisting of lower to middle Eocene siliceous turbidites and thin, cherty layers interbedded with hemipelagic/pelagic clays and oozes. Acoustic scattering at rough interfaces, gas pockets, and changes in geoacoustic properties do not readily account for the diminished amplitudes of the reflections. Detailed examination of the wave coda from selected fadeout areas reveal changes in reflector geometry due to faulting of the sediments. Strong reflections within the stratified sequence are thought to result from the thin, high impedance chert beds that occur within the turbidite layers. Secondary reflections (multiples) generated by the hard, chert interfaces are thought to interact constructively with primary reflections to generate strong interference reflections, but also destructively to cause fadeouts where the faulting has changed the layer configuration. Alternatively, the fadeouts may result from the dissolution of chert beds due to the upward migration of silica-deficient pore fluids along faults and fractures in response to excess pore pressures.
English
Serial
Coverage:Geographic coordinates:
North:32.1912
West:-67.4000East: -64.1456
South:31.1112

Applied geophysics; Oceanography; acoustical properties; amplitude; Atlantic Ocean; Bermuda Rise; Cenozoic; chemically precipitated rocks; chert; clastic sediments; clay; Deep Sea Drilling Project; deep-tow methods; DSDP Site 386; DSDP Site 387; elastic waves; Eocene; fadeouts; geophysical methods; geophysical surveys; impedance; interpretation; Leg 43; marine sediments; multichannel methods; North Atlantic; ooze; Paleogene; pore pressure; pore water; pressure; reflection; sedimentary rocks; sediments; seismic methods; seismic waves; single-channel methods; stratification; surveys; Tertiary; turbidite;

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