Extensive Bahamian Submarine Hardgrounds Are Foundations for Microbiolites and Patch Reefs

Robert N. Ginsburg and Noah Planavsky
Marine Geology and Geophysics, University of Miami, Miami, FL

Submarine hardgrounds of non-skeletal sands cemented with fibrous aragonite are widespread on Great Bahama Bank in depths < 20 m. Where they develop on mobile tidal sand bars they can provide the necessarily hard or firm foundations for domal and columnar micrbiolites up to 2 m. tall. In addition, hardground pavements, tens of meters in extent, fragment spontaneously to produce rounded cobble-size interclastic breccias. Elsewhere on the open Bank veneered with sands, discontinuous and friable hardgrounds are the foundations for coralline patch reefs in normally barren mid-bank locations.

The prevalence of Bahamian submarine hardgrounds in non-skeletal sands and their scarcity in skeletal sands, if confirmed by fossil examples, would be an initial guide to predict areas where microbiolites or patch reefs may occur. Additionally these hardgrounds that are often of low permeability could compartmentalize reservoirs and aquifers.

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