29 D22. Sediments, Carbonates

Monday, 26 October 2020
5:30 PM - 8:00 PM
Meeting Rooms

EOLIAN ADHESION STRUCTURES PRESERVED IN QUATERNARY CALCARENITES, SAN SALVADOR ISLAND, THE BAHAMAS

Paper number: 29-11
Program: Technical Sessions
Time: 7:30 PM – 7:40 PM

Authors

Abstract

Quaternary carbonate rocks on San Salvador Island, Bahamas preserve signature eolian ripple-, grainflow-, and grainfall-strata reported previously by other workers. This study documents newly discovered adhesion ripples and resulting stratification that lend support to an eolian interpretation for these rocks.

In the Pleistocene Cockburn Town Member, Grotto Beach Formation on southern San Salvador, locally exposed bedding surfaces display wavy, ripple-like microridges, with amplitudes less than 1 cm and spacing between 1 and 2 cm. They trend NW-SE and are asymmetrical to the NE. In the Holocene North Point Member, Rice Bay Formation on northern San Salvador, localized bedding surfaces display strongly irregular microridges that also trend NW-SE. An exposure in a rocky-beach cove that corresponds with an interdune (dome dune) swale, displays thin, lenticular sets of pseudo-crosslaminae that dip up to 53o SW. These observed features suggest the occurrence of eolian adhesion ripples, especially when they are compared to those of modern and ancient adhesion ripples in siliciclastic eolian sand and sandstones.

Published studies indicated that eolian adhesion ripples form when dry wind-blown sand grains are captured at the depositional surface by damp or wet grains by adhesion and capillary attraction. Consequently, eolian adhesion ripples, like subaqueous antidunes, migrate and climb into the current. For the Quaternary eolianites studied here, the microridge trend to the NW-SE, microridge asymmetry to the NE, and pseudo-crosslaminae that dip steeply SW, corresponding with bedform climb to the NE, are consistent with Northeast Trade Winds that prevailed during Quaternary time at the latitude of the Bahamas. Interdune swales of the Holocene coastal dome-dune system are likely places where sediment was wetted by either sea spray or pooling rain water and adhesion ripples formed by wind. R. E. Hunter shared unpublished photographs of adhesion structures in Holocene carbonate eolianites on Eleuthera Island, Bahamas. Those studied here are the first reported for Quaternary carbonate eolianites on San Salvador Island, Bahamas.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-360076

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