Micro-Organisms and Crystal Fabrics in Cave Pisoliths from Grand Cayman, British West Indies

Abstract

Cave pisoliths, up to g cm long, from terraced rimstone pools in a cave near Old Man Village on Grand Cayman have nuclei such as bird or bat hones or clusters of dendrite calcite crystals that are surrounded by cortical layers of(l) micrite, (2) dendrite calcite crystals, and (3) prismatic trigonal calcite crystals. The micrite laminae formed through calcification of filamentous microorganisms (algae and/or fungi). Recognition of dendrite calcite crystals can be difficult because later growth filled the spaces between branches, thereby disguising the diagnostic branches of this crystal type. Many large, seemingly homogeneous, spar calcite crystals are probably filled-in dendrite crystals. Some trigonal crystals lost their distinctive outline as they grew because their corners became rounded. Although the laminae formed of dendrite calcite crystals or prismatic trigonal calcite crystals formed from cave waters supersaturated with respect to CaCO 3 , the reason why one formed rather than the other is not yet known. The complexity of cave pisoliths, however, indicates that crystal growth was probably controlled by microenvironmental conditions around the surfaces of pisoliths.