Attenuation changes due to diagenesis in marine sediments

Abstract

Cenozoic marine sediments were drilled and cored by the Deep Sea Drilling Project at Site 613 in the Baltimore Canyon Trough, and four‐channel sonic waveforms were recorded from 115 to 585 m below sea floor. Compressional wave velocities and spectra were calculated from the sonic waveforms. In situ porosity was estimated and compared to core measurements. As expected, velocity increased with depth as porosity decreased. However, the energy loss between near and far receivers increased and the peak crosspower frequency decreased with depth, suggesting that attenuation increases over the same interval. The large changes in energy and frequency cannot be explained solely by changes in the elastic propeties of the sediments. We model the observed compressional wave spectra using measured values of velocity and density. Reasonable fits to the observed spectra are obtained using either a constant Q (CO) or nonconstant Q model. For the CO model, O decreases from 100 to 20 over this depth interval. Diagenesis obs...