Calibration of marine sediment core loggers for quantitative acoustic impedance studies

Accurate density and P-wave velocity measurements on marine sediment cores are needed for quantitative acoustic impedance studies. An increasing numbe r of international marine laboratories routinely measure P-wave velocity an d bulk density, the product of which gives the acoustic impedance, on marin e sediment cores using automated core loggers (MSCLs). Despite the progress ive standardisation of MSCLs in recent years, no standard calibration techn ique has been decided that will enable datasets from different marine labor atories to be validated and compared with confidence. This problem is parti cularly acute for bulk density measurements because systematic MSCL errors are typically much greater than 10%. One solution is to use a calibration t ube (comprising a stepped aluminium insert inside a water-filled core liner ) that mimics marine sediment porosities and velocities, and that can be: u sed during normal core logging. The calibration tube enables a reliable gam ma ray reference intensity to be measured, and an apparent Compton mass att enuation coefficient to be derived that is suitable for most marine sedimen ts and that simplifies data processing. The calibration tube results show t hat the MSCL belonging to Southampton Oceanography Centre (SOC), used as pa rt of the standard analysis procedure of the British Ocean Sediment Core Re pository (BOSCOR) gives measurement accuracies of better than +/-0.07 g/cm( 3) for bulk density and +/-0.3% for P-wave velocity. (C) 1999 Elsevier Scie nce B.V. All rights reserved.