Velocity and Density of Carbonate-Rich Sediments from Northeastern Australian Margin: Integration of Core and Log Data

Abstract

During Ocean Drilling Program (ODP) Leg 133, shipboard scientists obtained a remarkable quantity of both core and log measurements of the physical properties of carbonate-rich sediments. This suite of measurements provides a unique opportunity to evaluate the robustness of each measurement technique to variations in lithification , porosity, core disturbance (for core measurements), and hole conditions (for log measurements). Detailed quality-control, which often resulted in the deletion of erroneous data, was essential for the reliable integration of these core and log data. In common with several previous studies, our comparison between core and in-situ velocity and density data identified pervasive patterns of bias to the core measurements, caused by removal from in-situ conditions. Velocity is particularly sensitive to this change, because the frame modulus of unlithified sediments is decreased dramatically by even slight core expansion or disturbance. The much larger number of sites considered in this study allows us to distinguish between site-specific and regional patterns of differences between core and log data. Such a comparison suggests that we still cannot reliably predict the effects of core expansion, either for ODP cores or for ODP measurements of core physical properties. In general, Leg 133 index measurements of core density are approximately in agreement with log densities, but GRAPE measurements of core density may be lower or higher than log densities. This study has successfully integrated core and in-situ physical property measurements and developed merged velocity logs for 12 sites and merged density logs for nine sites. Each merged log extends from the seafloor to within a few meters of the bottom of the hole.