The Middle Pleistocene Belmont Formation of Bermuda consists in part of beach-dune biocalcarenites which underwent intense contemporaneous cementation and diagenesis. The beach deposits were contemporaneously cemented by fibrous isophacous cement to form beachrock, whereas previously deposited eolianites further inland underwent intense meteoric phreatic diagenesis, resulting in coarse-grained cementation and stabilization of most of the metastable components of the rock. Above the Belmont water table, vadose diagenesis was relatively ineffective in cementing and altering the biocalcarenites. Phreatic meteoric diagenesis is interpreted to be a very rapid process, relative to vadose meteoric diagenesis, and to result in a much coarser-grained sparite.