This study of cementation and porosity trends also revealed gradual changes in diagenetic maturity of the rocks and progressive evolution of the pore systems with increasing depth of burial. Subsurface cementation and secondary porosity development occurred primarily during emergence and subaerial exposure of the bank top. Three diagenetic stages were recognized, and were related to changing diagenetic environments regulated by changing Pliocene-Pleistocene sea level and slow bank subsidence. Stage I, dominated by vadose diagenesis, commenced with initial subaerial exposure
of metastable sediments, and ended with development of an induratedsurface breached locally by vertical solution pipes. In Stage II, with shallow burial (surface to variably 12 to 20 m) and under ephemeral freshwater phreatic conditions, metastable carbonate sediments completed alteration to low-Mg calcite, and porosity inverted from primary interparticle and intraparticle to moldic. Relatively uniform cementation by equant calcite also occurred. In Stage III (depths to 150 to 200 m), subjection of deeper subsurface rocks to prolonged episodes of corrosive bank-wide freshwater phreatic and mixing-zone conditions during bank emergence resulted in extensive dissolution. Because GBB is comprised of carbonate rock and lacks siliciclastic aquitards, freshwater lenses and underlying mixing zones fluctuated