Comparative Morphology of Oolitic Tidal Deltas

Stacy Lynn Reeder and Gene Rankey
University of Miami, RSMAS, Miami, FL

Although the shapes and formation of tidal deltas in siliciclastic systems are well understood, oolitic sands of carbonate tidal deltas remain unexplored. The purpose of this study is to characterize patterns and processes in the oolitic tidal deltas of the northern Abaco Island Chain of Little Bahama Bank.

Oolitic tidal shoals in the region are shaped by similar processes and share similar geomorphic forms, but the details of each tidal delta are diverse. The tidal delta lobes range in area up to 4 km2, and inlets can exceed 10 m deep. On ebb delta lobes, sand wave orientation and symmetries suggest a net outward flow near the inlet and net shore-parallel transport near the terminus. The flood lobes are generally less asymmetrical but contain similar facies patterns to the ebb lobes.

Quantitative measurements of tidal flows through the inlets indicate velocities up to 2 m/s. In the lobes, flow expansion occurs and the velocities decrease radially outward from the main channel to a point where wave energy dominates transport. The inlets with higher velocities through the main channel correspond to the larger sized lobes.

The results demonstrate that the oolitic tidal deltas include geomorphic characteristics similar to Hayes's (1979) model of siliciclastic deltas and that, like siliciclastics, there is a direct link between tidal flow velocities and the sizes and shapes of the oolitic lobes. Fundamental comparison between the shapes and processes of carbonate and siliciclastic tidal deltas provide enhanced predictive models of analogous oolitic reservoirs.