Biogenic structures and micrite in stalactites from Grand Cayman Island, British West Indies

Abstract

Stalactites from modern and old caves developed in the Bluff Formation of Grand Cayman Island contain laminae and bulbous masses of micrite intercalated with sparry calcite. The micrite, as well as some of the sparry calcite around it, contains small (up to 25 μm long) ovate to spherical bodies that have a high concentration of either manganese or iron. Such bodies may be of bacterial origin. The micrite contains numerous calcified filaments that are probably of algal origin. Calcification of the filaments occurred either during life or shortly after death of the algae. The algae played an important role in trapping and binding the micrite. Furthermore, the algae may be directly or indirectly responsible for the formation of much of the micrite.