Contrasts between wave- and tide-dominated oolitic systems: Holocene of Crooked–Acklins Platform, southern Bahamas

Abstract

As the stratigraphic record is neither homogenous nor isotropic, a fundamental challenge in sedimentary geology is characterizing and predicting the nature of variability. Although many nearshore to shallow-marine siliciclastic depositional systems have been grouped into wave-dominated and tide-dominated classes, many facies models of carbonate systems have not recognized or applied this distinction. To fill this gap, the purpose of this study is to compare and contrast the hydrodynamic processes, sedimentology, geomorphology, and stratigraphy of an oolitic tide-dominated shoal complex and an oolitic wave-dominated shoreline system from the same area (Crooked–Acklins Platform, southern Bahamas). Field, petrographic, granulometric, remote-sensing, and hydrodynamic data illustrate marked contrasts between the two end members. The wave-dominated shoreface system near French Wells on the leeward margin is influenced by small (Hs <30 cm) waves and only weak, wave-driven currents (<15 cm/s, net southward flow); the passage of Hurricane Irene (in 2011) had only a local impact on the shoreface. The low-energy setting favors generation and alongshore transport of ooids and peloids of fine- to medium-sized sand, and has facilitated nearly 1 km of shoreface progradation, forming geomorphic bodies with margin-parallel geometry. The stratigraphic record of the area includes a coarsening- and shoaling-upward succession. In contrast, the ~7-km-wide, tide-dominated shoal on the southwestern margin is dominated by vigorous tidal currents (in excess of 50 cm/s, and reversing twice daily). These currents generate margin-normal bars and channels consisting of oolitically coated grains of medium to coarse sand size. Stratigraphically, above a basal clast-rich deposit, sediment size and sorting vary across the shoal. The open-ocean and the platformward flanks of the shoal, most impacted by tide and wave energy, include the cleanest oolitic sand, with fines accumulating in the stabilized shoal interior. Overall, the oolitic shoal aggraded and expanded platformward over bioturbated peloid–ooid sand. These results reveal how sediment, geomorphology, and stratigraphy differ between tide- and wave-dominated end members, patterns broadly analogous to several ancient examples. These data collectively illustrate the processes that create multi-scale linkages among stratigraphic patterns, geological facies bodies, and granulometry (e.g., depositional porosity and permeability). These linkages provide information that could be used to predict sedimentological and geomorphical trends in ancient analogues.