Eolian Dune Depositional Environments

Carbonate eolianites are deposited as coastal dunes immediate landward of high-energy beaches (McKee and Ward, 1983). They commonly form a transverse ridge parallel to the shoreline with the windward side facing the open sea and the leeward side facing inland (see below). As with beaches, eolian dunes can form in several areas of the platform.

Isla Cancun barrier island off Yucatan Peninsula, Mexico with Holocene eolian dune development. From Loucks and Ward (2001).

A diagrammatic depositional model of a beach/eolian dune system is presented below (Loucks and Ward, 2001). Diagnostic sedimentary structures and rock types include large-scale crossbedded, well-sorted, fine-grained grainstones with rare fossils. Crossbedding will be strongly oriented in a landward direction and can be tens of meters thick. Caliche and large clasts may be associated features.

Carbonate Eolian Dune Stratification Types Hunter (1977) and Loucks and Ward (2001) have described the stratification and other features of coastal dunes. Climbing Translatent Stratification (Wind-Ripple Laminations): The laminae are generated as wind ripples migrate across the dune. The ripples produce thin, isopachous laminae on low-angle slopes.

Schematic diagram showing the development of wind ripple laminations. Modified from Hunter (1977).         example: Isla Cancun   example: Jamaica

Grainfall Lamination: They develop on leeward sides of dunes. The airborne grains fall onto the foreset slope, forming relative high-angle and uniform, but diffuse laminae that commonly pinch out downdip.

Schematic diagram showing the development of grain-fall laminations. Modified from Hunter (1977).

example: Isla Cancun   example: Jamaica

Sandflow Cross-Stratification: They are generated by avalanching of tongue-shaped and cone-shaped masses of non-cohesive sand down foreset slip faces whose inclination is at the angle of repose.

example: Isla Cancun   example: Jamaica

Dune-Front Conglomerates: Deposits of eroded eolianite clasts produced where storm waves erode the seaward side of weakly to well lithified dunes.

Dune-front conglomerate formed by erosion of the toe of the dune. From Loucks and Ward (2001).

Intradune Marine Storm Deposits: As a dune is decapitated during a storm, reworked marine sediments are deposited on the eroded surface. Boulder-sized material can be transported onto this surface

Isla Cancun outcrop showing intradune marine storm deposits composed of corals and clasts. From Loucks and Ward (2001).

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