Relation of bank-margin fractures to sea-level change, Exuma Islands, Bahamas

Abstract

Data from carbonate bank-margin fractures in the southern Exuma Islands, Bahamas, in the vicinity of Lee Stocking Island show that these fractures have a preferred bank-margin-parallel orientation. Fractures that showed evidence of pedogenic alteration to micrite (calcretization) had an even more pronounced orientation preference. Calcretization is associated with a well-defined paleosol believed to have formed within the last glacial period and the transition to the present interglacial (∼20-13 ka). Horizontal laminations within the paleosol continue as vertical laminations within some fracture traces. Analysis of thin sections revealed root tubules and fabrics characteristic of pedogenic alteration within the calcretized parts of fracture zones. The association of bank-margin-parallel fractures with the last interglacial suggests that fracture development is related to a eustatic process. I suggest that fractures formed in response to undercutting of the bank margin during the last sea-level low. A fracture-controlled submarine cave extending to >100 m below present sea level provides additional evidence supporting a eustatic link to fracture development.