Contrary to the popular notion that the Bahama Islands are built of eolianite deposits, at least New Providence Island consists principally of elevated marine sand-flat and protected lagoon deposits. Narrow eolianite ridges separate such deposits from reef-tract deposits capped by prograding beach deposits on the northern (bank-margin) side of the island.
All exposed depositional phases are Quaternary. The most extensively exposed deposits we correlate with the ∼125,000-yr high sea level, recognized world-wide. Elevations of keystone vugs in beach deposits of that depositional phase indicate paleo–mean sea levels of as high as +10 m.
Deposits of an earlier depositional phase suggest that there was then no island, but only a barrier sand shoal and reef tract. Holocene additions to the island's area have been minor and in the form of prograding beach deposits.
Classical superpositional stratigraphy has limited value in the elucidation of New Providence geology due to the nature of the deposits, which are partially overlapping thin facies sheets and lenses. Therefore, we have also used a morphostratigraphic approach and, as paleontological markers, species of Cerion, a very rapidly evolving genus of land snail. Limited radiometric dating is reported.
Islands on Bahama-type banks of earlier geologic periods were probably built almost entirely of beach deposits, rather than the eolianites and elevated marine deposits of which New Providence is built.