Sound Velocity and Related Physical Properties of Fine-Grained Abyssal Sediments from the Brazil Basin (South Atlantic Ocean)

Document Type

Article

Publication Date

9-1-1990

Department

Physics and Astronomy

School

Mathematics and Natural Sciences

Abstract

Empirical relationships between compressional wave (sound) velocity and selected physical properties have been determined for fine‐grained abyssal sediments from the east Brazilian continental margin and Pernambuco abyssal plain of the Brazil Basin (NW South Atlantic Ocean). Porosity and wet bulk density were found to be the best sedimentological indices to sound velocity. In agreement with numerous other studies, other sediment properties were lesser, but still very good, indices. In order of decreasing statistical significance, these properties include mean grain size and percent clay. Averaged values of sediment physical properties of the Brazil Basin were compared with the published results of Hamilton and Bachman [J. Acoust. Soc. Am. 72, 1891–1904 (1982)] and show good agreement. The observed differences between the two studies were insignificant and attributed to slight mineralogical differences that can be expected in light of the differing sedimentation processes of the Pacific and Atlantic Oceans. Velocities of the Brazil Basin study, converted to in situconditions from laboratory measurements, were compared with those previously reported by Hamilton and Bachman, which were converted to in situconditions using bottom water velocities of this study and their velocity ratios. A plot of the velocities showed good agreement, but those of the present study were about 20 m/s lower. This discrepancy is probably not mineralogical in origin, but instead results from a systematic difference in the sediment velocimeters used in the two studies. The exact cause of the discrepancy is not known, and a detailed system evaluation of the velocimeters is recommended.

Publication Title

Journal of the Acoustical Society of America

Volume

88

Issue

3

First Page

1536

Last Page

1542

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