LESSONS LEARNED FROM GREAT BAHAMA BANK – NEW MODELS AND PARADIGM SHIFTS

Recent studies of Great Bahama Bank (GBB), the largest isolated carbonate platform in the Bahamas, continue to refine stratigraphic, depositional, and diagenetic models in carbonate systems. These studies have provided additional insight into the details of sedimentation and diagenesis that were first developed in the Bahamas decades ago, while also establishing new models constrained within a sequence stratigraphic framework that, at times, transcend established dogmas.

On a regional scale, stratigraphic and depositional studies provide an understanding of the lateral growth potential and pulsed progradational nature of GBB and the significance of a windward versus leeward oceanographic setting. Ancestral isolated platforms coalesced to form GBB through progradation along leeward margins through highstand shedding of bank-top derived sediment. The role of antecedent topography on the platform top in initiating development of both marginal reefs and sand bodies is strongly coupled to a windward margin setting. Likewise, the sedimentary make-up (grain vs. mud dominated) of proximal slope facies is dependent upon the windward/leeward orientation of the margin. The growth and diagenesis of platform strata is also intimately linked to sea level variability. Details of the genesis of platform top shallowing-upward cycles on GBB have added to our understanding of ancient platform equivalent strata. For example, the realization that unfilled accommodation space is common, combined with the nature of cycle variability suggests limitations inherent to cyclostratigraphic correlation and explains many aspects of reservoir heterogeneity.

Syndepositional marine cementation clearly takes place to great depths down the flanks of GBB at rates that are instantaneous relative to geologic time, suggesting that paradigms associated with slope stabilization and architecture need to be revisited. Likewise, the presence of “meteoric-like” moldic porosity and cementation fabrics in the marine phreatic environment poses the dilemma of correctly interpreting the stratigraphic context of similar diagenetic features in ancient carbonates. Dolomite within this same deep marine phreatic environment corroborates a model for dolomite formation that is likely typical for isolated platforms.