Botryoidal aragonite commonly rims and fills voids in Holocene reef-wall limestone of the seaward-facing margins of Belize (British Honduras) barrier and atoll reefs. The cavernous, well-cemented reef-wall limestone that occurs between 65 and 120 m on the barrier reef consists of reef corals encased in algal-plate (Halimeda) packstone-wackestone; the botryoidal aragonite occurs in cylindrical bivalve borings, in polygonal shelter cavities, and in laminar to amoeboid voids of unknown origin. Mamelons of the fibrous aragonite as much as 5 cm thick often rim void ceilings, occasionally grow from void floors, and frequently fill voids completely. In other cavities the mamelons overlie floors of cemented internal sediment, and in still others they have laminations of internal sediment.
The aragonite is clearly marine: (1) it occurs within an unaltered reef limestone less than 13,000 yr old; (2) benthic fora-minifera occur locally within mamelons, and in others there are laminations of marine sediment; and (3) the aragonite has an average Sr2+ content of 8,300 ppm, an 018 average of +1.0 0/00, and a C13 average of +4.2 00/0, all characteristic of marine precipitation. The mamelons of botryoidal aragonite are similar in shape, texture, and fabric to some of the common cavity-filling cements in Paleozoic reef limestones.