The Lower Cave is filled with caymanite, which is formed of laminated, varicolored dolomitized mudstones, and grainstones that contain scattered marine fossils (e.g., foraminifera, red algae). This cave, connected to the Cayman Unconformity by a small-diameter tunnel, evolved as part of the karst system that developed during the Messinian lowstand (7.3–5.3 Ma). The cave was filled and dolomitized prior to deposition of the Pedro Castle Formation. The Upper Cave is filled with a wide spectrum of lithotypes, including dolostones, calcareous mudstones, terra rossa, gastropod coquina, coated grains, and speleothems. U/Th dating indicates that some of the flowstones are > 500,000 years old whereas others are only ~ 21,000 years old. Dolostones and mudstones in the basal part of the Upper Cave contain marine fossils (foraminifera, red algae) whereas the younger deposits are devoid of such fossils.
The Upper Cave and its deposits developed after the sediments of the Pedro Castle Formation had been deposited and lithified. Development of the cave filling deposits, which includes a clear transition from marine to non-marine influences, was controlled by eustatic sea-level changes and/or westward tectonic tilting of Cayman Brac that occurred after the Pedro Castle Formation became exposed, probably during the Late Pliocene.
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