13. Grape Density Records and Density Cyclicity

The gamma-ray attenuation porosity evaluator (GRAPE) component of the multisensor track (MST) unit on board the JOIDES Resolution measures the saturated bulk density of sediments by relating the attenuation of gamma rays in a core sample to that of a standard with known density (aluminum). After reaching thermal equilibrium, unsplit core sections are routinely run through the MST system. The sampling density chosen for the MST during Ocean Drilling Program (ODP) Leg 130 (about 2-3 cm) provides a near-continuous measurement of sediment density by means of the GRAPE equal to a resolution of 0.53 k.y, depending on the sedimentation rate. Comparisons of GRAPE density values with discrete laboratory density measurements and downhole density logs show that absolute GRAPE density estimates are higher than both laboratory and logging density measurements; however, the downhole trends in the density data are very coherent. The constant offset between the GRAPE data and density measurements made by other means indicates that the offset is a function of the calibration of the GRAPE system. The extremely high sample resolution of the GRAPE makes it possible to use these data for a number of purposes: