ABSTRACT

Two distinctly different mechanisms operate within caves to produce concentrically laminated calcareous oolite, pisolite, and concretion grains. The first, a splash cup occurrence, produces grains under agitated conditions so that both abrasion and carbonate precipitation take place. The second mechanism, the rimstone dam and pool concretion occurrences, produces grains under non-agitated conditions so that carbonate precipitation alone controls grain morphology. The two mechanisms result in laminated grains with distinctively different characteristics.

Agitated grains are characterized by distinct, compact laminations which display a pseudo-uniaxial cross caused by an oriented crystal structure. The grains commonly have a nucleus, smooth polished surfaces, a low insoluble residue content, and with continued growth tend to approach a spheroidal shape. In contrast, non-agitated grains generally have indistinct, porous laminations lacking an oriented crystal structure. They commonly lack nuclei, have rough unpolished surfaces, are high in insoluble residue content, and with continued growth develop irregular shapes.

The above grain characteristics are applied to more extensive shallow marine deposits. The Bahamian oolite grains show characteristics of agitated grains whereas West Texas Permian Reef pisolite grains are quiescent in character.