SUBMARINE CEMENTATION OF SUBSURFACE PLIOCENE CARBONATES FROM THE INTERIOR OF GREAT BAHAMA BANK

Thick intervals of early Pliocene subtidal carbonate sediments in the subsurface of northwestern Great Bahama Bank were lithified by submari ne cement. This cementation, subsequently altered by meteoric diagenes is, occurred over a broad expanse of the platform interior. It shows t hat submarine cements can lithify thick packstone and grainstone inter vals in the interior of large shallow-water carbonate shelves and plat forms given open circulation, moderate to slow sedimentation rates, an d minimal accumulation of fine sediments. A submarine origin for these cements is inferred from direct and circumstantial evidence, includin g: (1) regional depositional and diagenetic setting; (2) fabric and ha bit similar to modern submarine cements; (3) alteration of cements fro m mineralogically unstable precursors indicated by (a) abundant inclus ions, (b) relict precursor fabric, and commonly (c) yellowish colorati on, (d) undulose crystal extinction, and (d) selective leaching of spe cific generations of cement or cement types; (4) sutured mid-pore crys tal contacts; (5) precipitation coeval with accumulation of internal m arine sediment; and (6) association with organisms requiring a firm su bstrate for attachment. These considerations may help other workers re cognize submarine cements in ancient carbonate rocks.