Clay content, porosity and velocity of Amazon Fan sediments determined from ODP Leg 155 cores and wireline logs

Abstract

We characterize variations in velocity and porosity as a function of clay content for different depositional units of the Amazon Fan (levees, sand-rich High-Amplitude Reflection Packets, or HARPs and mass-transport deposits, or MTDs) using core and log data. Younger fan sediments, including both HARP and levee turbidites, show an increase in porosity and a decrease in velocity with increased clay content, a relationship indicative of a matrix-supported regime. In contrast, older, more deeply buried overbank turbidites and MTDs, show opposite physical-property trends, which are indicative of a framework-supported regime. The changing behavior of physical properties within various fan units results from a combination of the nature of clay distribution within the sediment caused by different depositional processes, and to changes in sediment structure during early burial and diagenesis.