22 Geomorphology (Posters)

A MORPHOLOGICAL COMPARISON OF TAFONI VS. FLANK MARGIN CAVES, SAN SALVADOR ISLAND BAHAMAS

Paper number: 22-22
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

The Glossary of Geology (p. 655) defines tafone as: “...one of the natural cavities in a honeycomb structure, formed by cavernous weathering on the face of a cliff in a dry region or along the seashore. The hole or recess may reach a depth of 10 cm, and is explained as the result of solution of free salts in crystalline rock (granite, gneiss) following heating by insolation.” The term is morphological in origin and not based on genesis. The term is poorly defined; the literature provided much contrast to this definition, varying in terms of shape and size of the void, mechanism of formation, orientation, climate, and rock type. Tafoni are present in eolian calacernites on several islands in the tectonically-stable Bahamas, including Long, Cat, Abaco, and San Salvador. San Salvador Island is on an isolated platform, its Quaternary carbonates include eolianites, beachrock, fossilized coral reefs, beach facies, and paleosols. San Salvador has a wide variety of karst features, including flank margin caves, pit caves, and banana holes.

Certain cave types, such as flank margin caves, are used as paleo sea-level indicators in carbonate islands. If tafoni are present, and have been misidentified as flank margin caves, then past sea-level interpretations could be in jeopardy. Measurements were taken of tafoni along sea cliffs, road cuts, and quarries. The tafoni analyses was done on Holocene eolianite sea cliffs in which no abandoned dissolution features, such as last interglacial flank margin caves, could exist. The analysis of 13 tafoni showed that tafoni could develop to a size of 30m wide by 7m high in a 5000-year time frame. Analyses of 5 tafoni in Late Pleistocene eolianites in a coastal setting showed a size maximum of 10m wide by 5 m high. Analyses were also conducted in a road cut and a quarry cut into Late Pleistocene eolianites. Analysis of 390 tafoni were done using five different measurements each, showed that tafoni could develop close to 2m wide by 1 meter high in 35 years. A morphological analysis completed on the tafoni present on San Salvador Island and compared to a previous analysis of flank margin caves indicates that tafoni had a far simpler morphology; therefore morphological analysis is a viable way to differentiate between the two features.