EFFECTS OF DIFFERENTIAL CEMENTATION ON THE SONIC VELOCITIES OF UPPER CRETACEOUS SKELETAL GRAINSTONES (SOUTHEASTERN NETHERLANDS)

P-wave velocities measured in Cretaceous skeletal grainstones from Lim burg, southeastern Netherlands, are significantly high er in moderatel y cemented samples than in poorly cemented samples from similar deposi tional facies, Petrography suggests that this relationship is due to d ifferences in the extent of development of intergranular cementation a s influenced by original grain mineralogy, rather than a significant d ifference in primary porosity, The time average velocity equation for a calcite matrix fails to predict the cementation effect an sonic velo city at high porosities. Linear and nonlinear time average regressions show strong correlation between velocity and porosity. Whether the un derlying trend is linear or nonlinear is a fundamental question that c annot be determined with this data set. Comparison between carbonate g rainstones and siliciclastic sandstones reveals that: (I) the grainsto nes have gradients in velocity-porosity space similar to those in sili ciclastic arenites but have velocities that are up to 0.3 km/s higher than those in clean arenites and up to 0.8 km/s higher than in argilla ceous arenites; and (2) grainstones develop a rigid framework that tra nsports elastic waves at significantly higher porosities than arenites , 40-50% compared to 30-40%. Higher sonic velocity presumably results from the higher matrix velocity of calcite versus quartz, and the high er elastic moduli created by the effective cement bridges connecting g rains.