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Pink Grotto (San Salvador Island, Bahamas) 3 | by James St. John
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Pink Grotto (San Salvador Island, Bahamas) 3

Pink Grotto, southwestern San Salvador Island, eastern Bahamas.

 

Pink Grotto is an erosional recess with overhanging rocks, hosted in aragonitic, oolitic calcarenite limestones of the Cockburn Town Member of the Grotto Beach Formation (Upper Pleistocene). This cave is likely a breached flank margin cave. Flank margin caves form at the flanks of carbonate islands and at the margins of fresh-groundwater lenses. As such, flank margin caves are phreatic features. In the vicinity of the seawater-freshwater mixing zone (halocline) of a groundwater lens (see diagram - www.carbonatecreek.com/caves/images/carbisland.gif), relatively rapid dissolution of limestone occurs due to the high aggressivity of the water. If this feature is a breached flank margin cave, limestone dissolution at Pink Grotto would have occurred during the MIS 5e highstand (early Late Pleistocene ~119-131 ka).

 

Flank margin caves have no surface entrances. Access to them occurs only after surficial erosion intercepts chambers or passages. Pink Grotto occurs along a wave-cut, paleo-sea cliff formed during the mid-Holocene. The pinkish coloration of the ceiling is due to algae. The projecting-downward structures are travertine dripstone (stalactites).

 

The basal walls of Pink Grotto have herringbone cross-stratified aragonitic calcarenite limestones (shallow subtidal facies), overlain by a unit having beach boulder paleorubble clasts cemented into beach facies calcarenites. The upper walls and ceiling have calcarenitic eolianite limestones.

 

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Taken on March 13, 2013