Interactions between tidal flows and ooid shoals, northern Bahamas

摘要

Oolitic strata are common through the geologic record. Ooids generally form in high-energy environments, but it remains unclear how ooids remain in such systems and form geomorphic features such as bars and shoals. Integrating remote sensing, hydrodynamic, bathymetric, granulometric, and field observations of modern tidal systems in the Bahamas provides insight into this fundamental question. Oolitic tidal sands in the northern Abacos display a geomorphic pattern in which bedrock islands restrict and focus tidal flow down a main channel. Within the channel, a shallow shoal separates an ebb-dominated subchannel from a flood-dominated subchannel. Tidal velocities in these subchannels can exceed I m/s, enough to transport the oolitic sediments. Hydrodynamics and bathymetry in these subchannels produce a net circular hydrodynamic pattern around the shoal (the "spin cycle"), allowing the sands to remain in motion without being transported out of the ooid "factory." This general pattern is apparent in several other ooid shoal complexes. This concept provides integrated insights into the physical influences impacting the formation, suspension, transport, and deposition of ooids and the resulting geomorphic forms. These results represent first steps toward developing more comprehensive and predictive analogs of spatial heterogeneity in ancient tidally dominated oolitic shoals.