Stromatolites in Modern Reef Settings: Key Insights from the Exuma Cays, Bahamas

Miriam S. Andres¹, Pamela Reid², and James E. Eckman^3
1Earth Science R&D, Chevron Energy Technology Company, San Ramon, CA
²RSMAS-MGG, University of Miami, Miami, FL
³Office of Naval Research, Arlington, VA

Stromatolites, layered deposits of calcium carbonate, once dominated Precambrian oceans and, although declining since that time, they continue to be important episodic reef builders throughout the Phanerozoic. The warm Bahamian shallows currently exhibit a rich and diverse range of stromatolites, best developed within fringing windward reefs and tidal channels.

Although abundant, the literature sparsely addresses the controlling factors and lacks process-orientated thinking to understand stromatolite nucleation and evolution of modern systems and their ancient counterparts. Bahamian stromatolites thus offer the unique opportunity to identify, characterize and quantify some of the physical environmental controlling factors.

A multi-year environmental monitoring program captured hydrodynamic and sedimentation regimes, wind patterns complemented by detailed mapping of stromatolite locations, substrate and sediment burial events in a fringing reef in the Exuma Cays.

Irrespective of setting, Exuma stromatolites form on hardened substrate. Space between substrate and sea-level defines available accommodation space. Within the fringing reef, stromatolites prefer areas with comparatively reduced wave energy; moreover they grow tallest in the wave-restricted back reef lagoon. Overall wave speeds, however, need to be high enough to maintain rigorous sediment suspension and bed-load transport. Suspended sediment is important as it provides grains for trapping and binding and thus stromatolite accretion. Conversely, the height of the burying sediment package governs stromatolite height as they cannot outgrow their sources. Furthermore, frequent sediment burial removes epilithic algae, and maintains a prokaryotic dominance.

In summary, the physical environmental boundary conditions in the fringing reef help to define and constrain the acceptable habitat space of stromatolites.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas