Thick intervals of early Pliocene subtidal carbonate sediments in the subsurface of northwestern Great Bahama Bank were lithified by submarine cement. This cementation, subsequently altered by meteoric diagenesis, occurred over a broad expanse of the platform interior. It shows that submarine cements can lithify thick packstone and grainstone intervals in the interior of large shallow-water carbonate shelves and platforms given open circulation, moderate to slow sedimentation rates, and minimal accumulation of fine sediments. A submarine origin for these cements is inferred from direct and circumstantial evidence, including: (1) regional depositional and diagenetic setting; (2) fabric and habit similar to modern submarine cements; (3) alteration of cements from mineralogically unstable precursors indicated by (a) abundant inclusions, (b) relict precursor fabric, and commonly (e) yellowish coloration, (d) undulose crystal extinction, and (d) selective leaching of specific generations of cement or cement types; (4) sutured mid-pore crystal contacts; (5) precipitation coeval with accumulation of internal marine sediment; and (6) association with organisms requiring a firm substrate for attachment. These considerations may help other workers recognize submarine cements in ancient carbonate rocks.