Causes of compressional-wave anisotropy in carbonate-bearing, deep-sea sediments

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doi: 10.1190/1.1441688
Author(s): Carlson, R. L.; Schaftenaar, Carl Howard; Moore, R. P.
Author Affiliation(s): Primary:
Tex. A&M Univ., Dep. Geophys. Geodyn. Res. Prog., College Station, TX, United States
Volume Title: Geophysics
Source: Geophysics, 49(5), p.525-532. Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States. ISSN: 0016-8033 CODEN: GPYSA7
Note: In English. 25 refs.; illus. incl. 1 table
Summary: Indurated sediment samples from DSDP site 516 were studied to determine the cause of acoustic anisotropy in carbonate-bearing deepsea sediments. Recovered from sub-bottom depths between 388 and 1222 m, the samples have properties exhibiting the following ranges: wet-bulk density, 1.90 to 2.49 g/cm3; fractional porosity, 0.46 to 0.14; carbonate content, 34 to 88 percent; compressional-wave velocity (at 0.1 kbar), 1.87 to 4.87 km/sec; anisotropy, 1 to 13 percent. Velocity were measured in three mutually perpendicular directions through the same specimen in 29 of the 40 samples studied. Calcite fabric has been estimated by X-ray pole figure goniometry. The major findings of this study are. (1) Carbonate-bearing deep-sea sediments may be regarded as transversely isotropic media with symmetry axes normal to bedding. (2) Calcite c-axes are weakly concentrated in a direction perpendicular to bedding, but the preferred orientation of calcite does not contribute significantly to velocity anisotropy. (3) The properties of bedded and unbedded samples are distinctly different. Unbedded sediments exhibit low degrees of acoustic anisotropy (1 to 5 percent). By contast, bedded samples show higher degrees of anisotropy (to 13 percent), and anisotropy increases markedly with depth of burial. Thus, bedding must be regarded as the principal cause of acoustic anisotropy in calcareous, deep-sea sediments. Modified journal abstract.
Year of Publication: 1984
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 30 Engineering Geology; Acoustical methods; Anisotropy; Atlantic Ocean; Body waves; Carbonate sediments; Cores; DSDP Site 516; Deep Sea Drilling Project; Deep-sea environment; Elastic waves; Geophysical methods; IPOD; Leg 72; Marine environment; Marine sediments; Oceanography; P-waves; Physical properties; Properties; Sediments; Seismic waves; South Atlantic
Coordinates: S302000 S302000 W0352000 W0352000
Record ID: 1985010344
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