STUCK ON SPIN CYCLE: INTERACTIONS BETWEEN TIDAL FLOWS AND OOID SHOALS, BAHAMAS

Oolitic sands are ubiquitous through geologic history. Although it is widely recognized that ooids generally form in high-energy environments, 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 within a GIS and in a model provides insight to this fundamental question.

Oolitic tidal sands in Joulters Cays, Bahamas, and the tidal deltas of the northern Abaco Islands, Bahamas, display similar geomorphic themes where a main channel restricts and focuses flow. Within the channel, a shallow shoal separates an ebb-dominated subchannel from a flood-dominated subchannel. Tidal velocities in these subchannels reach up to 1 m/s, enough to transport the oolitic sediments, although details of velocity asymmetry are influenced by bathymetry and geomorphology. Flow and bathymetry in these mutually evasive subchannels produce a net circular hydrodynamic pattern around the shoal, allowing the sands to remain in motion without being transported out of the “ooid factory.”

This “Spin Cycle” concept provides integrated insights into the physical influences impacting the formation, suspension, transport, and deposition of ooids and the resulting geomorphic forms. These results can be used to develop more comprehensive and predictive analogs for spatial heterogeneity in ancient tidally dominated oolitic shoals.