EOLIAN DOME DUNES DISCOVERED IN CARBONATE SEDIMENTARY ROCKS, HOLOCENE OF SAN SALVADOR ISLAND, THE BAHAMAS

Pleistocene and Holocene history of San Salvador Island, Bahamas is recorded in marine and nonmarine carbonate rocks. Nonmarine rocks were identified in earlier studies by their signature eolian ripple-, sandflow-, and grainfall-strata, terrestrial fossils, and paleosols. However, little attention has been given to identifying the type of dune that deposited eolian calcarenites on the island. This study documents surface and internal structure of mounds and swales, the topographic expression of the Holocene North Point Member, Rice Bay Formation at North Point, a peninsula at the northern limit of the island. The study concludes with an interpretation of eolian dome dunes, a rarely reported dune type in sediment and sedimentary rocks.

In the North Point Member, wind-ripple laminae comprise windward-set, topset, brinkset, foreset, and toeset strata that preserve the entire dune form. Such strata dominate over slipface crossbeds composed of mixed sandflow, wind-ripple, and local grainfall strata. Dome-shaped dunes are recognized here by: 1) circular and oval plan-view of bedrock mounds towering up to 10 m; 2) nearly 360^o dip azimuths of bounding and reactivation surfaces, wind-ripple laminae and slipface crossbeds, and mound flanks; 3) dominance of wind-ripple laminae over slipface crossbeds; 4) modern mound-swale landscape that likely mimics the Holocene landscape; and 5) mound surfaces and bedding that extend laterally and connect with swale surfaces and bedding. During Holocene time on San Salvador, mature dome dunes evolved in variable storm and Northeasterly Trade winds from juvenile lobate and shadow dunes as precursor bedforms. Confined to a small depositional area, dome dunes grew vertically in phases marked by surfaces armored with plant-stem traces and calcareous crusts. Coastal moisture, cohesive sand, and insufficient supply of grainfall sand enhanced dune-slope stability so that grainflows were infrequent. This is the first to report dome dunes in eolian calcarenites.