GEOMORPHOLOGY AND STRATIGRAPHY OF CARBONATE COASTAL DUNE COMPLEXES

Holocene and Pleistocene wind-blown carbonate dunes are common across The Bahamas and Turks and Caicos Islands. Unique environmental conditions of carbonate platforms related to aeolian geomorphology include 1) sediment to supply dunes is produced when sea level floods the shallow platforms during interglacial periods and 2) carbonate landscapes rapidly (~10 years) cement and uniquely preserve morphology from the past 500,000 years. The geomorphology and sedimentology reveal the constructional processes affecting dune-field development, provide evidence of significant erosion on the stoss and lee faces, and record the construction of dune complexes prior to the maximum positions of the Last Interglacial and Holocene sea level.

Caribbean dunes have four principal morphologies: ridges, compound ridges, elongated parabolic dunes, and sandsheets. While Pleistocene dunes are widely distributed, Holocene ridges are largely restricted to the present-day, windward shoreline. Holocene dunes are frequently anchored by Pleistocene headlands and separated from older dune complexes by interdune lows that are now flooded lagoons. Single and compound dune ridges are interpreted as having remained beach-attached during construction, while elongate parabolic and sand sheet morphologies confirm significant wind-blown sand advanced kilometers across the platforms. Lee faces of most Holocene and Pleistocene dunes dip below sea level, indicating the dunes formed when sea level was lower than today.

Morphologic evidence indicates marine erosional processes acted on dunes while they existed as unconsolidated sand and cemented bedrock. Evidence for wave reworking includes reduced sinuosity of the stoss sides relative to lee surfaces and near angle of repose stoss slopes. Wave erosion and longshore transport of sand from weakly-consolidated, vegetated Holocene dunes is ongoing; however, many Pleistocene dune ridges that were similarly eroded are no longer in contact with marine processes. In well-cemented early-Holocene dune deposits, wave-cut platforms are common.

These new observations put constraints on sediment availability, relative sea level position, and landscape evolution on carbonate platforms in the Caribbean through multiple interglacial cycles; and learnings from the Caribbean have the potential to be exported to analogous carbonate aeolian landscapes found throughout the Tropics and Subtropics.