Compressional-wave velocity in siliciclastic rocks is known to be a function mainly of porosity, and secondarily of mineralogy. We investigate the effect of cementation on velocity, using core-plug and whole-core measurements of velocity and porosity. The case study area is a drillhole at Cape Roberts, Antarctica, an environment with a rapid downhole gradient in cementation. After removal of porosity effect from velocity, the change from incipient to intense carbonate cementation is seen to account for up to 50% of total velocity. Increased intergrain coupling, particularly increased frame bulk modulus, is the cause of this velocity increase.