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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 52 (1982)No. 3. (September), Pages 733-753

Acoustic and Related Properties of Calcareous Deep-Sea Sediments

Edwin L. Hamilton, Richard T. Bachman, Wolfgang H. Berger, Thomas C. Johnson, Larry A. Mayer

ABSTRACT

Three expeditions to the Ontong-Java Plateau and the eastern equatorial Pacific obtained unusually good samples of calcareous sediment from box and piston cores; water depths ranged from 1600 m to 4900 m. Two sedimentary environments are represented. Dissolution, dilution, and winnowing cause reductions (with increasing water depth) of CaCO3, percent sand, mean grain size, sediment rigidity, and sound velocity. The best indices to predict sound velocity are percent sand, mean grain size, and the velocity ratio; this ratio varies from about 1.05 on top of the Plateau to about 1.00 at 4400 m. Hollow tests of Foraminifera act as solid particles in transmitting sound. Density and porosity are good predictors of velocity in the east Pacific but not in the Plateau area because of large amounts of hollow Foraminifera. There is no significant increase in sound velocity as CaCO3 increases from 35 to about 75 percent; above that percent, increases in velocity are mainly due to increases in sand-size particles. Eastern Pacific sediment has higher Previous HitporositiesNext Hit and lower Previous HitdensitiesNext Hit (than the Plateau samples) because of less CaCO3 and more biogenous silica. Biogenous silica content causes good correlation between density and CaCO3 content in the eastern Pacific but not in the Plateau sediment; density or impedance cannot be used to determine CaCO3 content in sediment lacking significant amounts of biogenous silica. As water depth increases from 1600 m to 4900 m, percent sand and mean grain size decrease markedly but total porosity increases only 1 to 3 percent. This is due to dissolution and breakdown of hollow tests of Foraminifera and transfer of intraparticle porosity (within the tests) to interparticle porosity between the grains. New estimates of intraparticle porosity range from 13 percent in clayey sand to zero in silty clay. New relations between the frame bulk modulus and porosity allow computations of elastic properties which indicate very small differences in bulk moduli or Previous HitdensitiesNext Hit over wide ranges of grain sizes and water depths, but large changes in dynamic rigidities cause both shear and compressional wave Previous HitvelocitiesTop to decrease with increasing water depth.


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