Elastic property corrections applied to Leg 154 sediment, Ceara Rise

Abstract

Sediments recovered from Ocean Drilling Program (ODP) holes undergo elastic rebound and physical expansion when recovered from great depths below the seabed (about 75 m). This expansion contributes to the artificial "growth" of the composite depth section (Hagelberg et al., 1992). Sediment elastic properties, derived from one-dimensional consolidation tests, are used to correct the expanded sediment column back to in situ values. The property that controls this effect is the sediment elastic rebound (C r), which is a simple function of the effective stress or depth below the seabed and sediment type. For Leg 154 sites, 90% to 95% of the composite section "growth" is attributed to elastic rebound of the sediment. The remaining "growth" is likely caused by intervals of sediment flow-in, identified in the visual description of the split cores. The composite depth scale, although artificially expanded, is an excellent tool for building a composite stratigraphy at one site. However, caution should be used when applying this depth scale for the construction of synthetic seismograms, for calculation of mass accumulation rates, and for any analyses that requires true sediment thickness. For these applications, corrections to the composite depth section are recommended.