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ABSTRACT: Physical and Chemical Properties of Sediments in the Izu-Bonin Forearc Basin, ODP Leg 126

Kathleen A. Dadey, M. Lovell, A. Klaus

Laboratory and downhole techniques were used to characterize the sediments in the Izu-Bonin forearc basin at two sites during Leg 126 of the Ocean Drilling Program. Sedimentary sections of 723 and 1403.9 meters were recovered at sites 792 and 793, respectively. In situ measurements at both sites include physical (sonic, density, and electrical) and chemical (K, U, Th, H, Cl, Si, Al, Ca, Fe, Gd, Ti) characteristics. The resulting logs are of variable quality owing to logistic difficulties in certain depth zones. Laboratory data include acoustic, thermal conductivity, shear strength, electrical, and index property measurements at discrete intervals, generally 1-2 m apart. Results for each site indicate the importance of careful calibration of both the physical and chemical ata. The difference in scale between laboratory and downhole measurements, as well as the sampling bias between them, effectively produce two complementary but distinctly different datasets.

The physical and chemical properties vary spatially between sites as well as with depth at each site. These variations are attributable to depositional and post-depositional processes. Processes of sedimentation, particularly volcanic and pelagic (biogenic) sedimentation, as well as post-depositional diagenetic and authigenic mineral formation contribute to the sediment properties. The laboratory measurements are used to constrain the in situ log data and derive a more complete and continuous description and interpretation of the physical state of the deposit. These are then evaluated using the physical and chemical characteristics to better determine the controls of the different signatures exhibited by individual sedimentary units.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990