Correction of non-intrusive drill core physical properties data for variability in recovered sediment volume

Published in Geophysical Journal International, 2015, with M.H. Walczak, A.C. Mix, et al.
(academic.oup.com)

Abstract

Non-intrusive track-based physical properties measurements of sediment cores recovered during ocean drilling are often biased by imperfect recovery within sediment core liners, particularly in heterogeneous and/or partially lithified sediments. These biases result in misrepresentation in measurements of true sediment physical properties, and can complicate integration of the composite site records assembled from recovered cores with borehole logs of the stratigraphic section. Here we develop a strategy utilizing gamma ray attenuation (GRA) density to generate mass-specific magnetic susceptibility (MS) and natural gamma radiation (NGR) data. Shipboard GRA density is collected in all cores that comprise a site at equivalent or higher resolution than the corresponding MS and NGR data. All instruments are calibrated assuming a volume of sediment in their detector windows equivalent to that present in a perfectly full core liner; changes in sediment bulk density related to compaction, and/or imperfect sediment recovery resulting in a partially filled core liner thus influence all three measurements proportional to their detector sensitivities. In principle it may be possible to correct MS or NGR data for variable sediment volume by normalizing them to GRA measured at equivalent depth on a sensing track, assuming that the volumetric bias is comparable in all three datasets. Because GRA is measured in much greater detail, it must be smoothed by the known measurement windows of the other parameters for the assumption of comparable analytical sediment volume to be true. Normalizing MS or NGR by the equivalently smoothed GRA in down-hole records should thus remove the bias associated with variable sediment volume in the detector windows, allowing for robust mass-specific determination of these volume-based sediment physical properties.