Increased Periplatform Sedimentation Produces Large Deep-Water Coral Mounds from the Leeward Side of Great Bahama Bank
The modern ocean floors contain abundant azooxanthellate, scleractinian deep-water corals that either grow as isolated corals or form large mound structures through coral growth and sediment entrapment. These modern mounds vary widely in size, orientation and density, indicating that their growth pattern adjusts to local environmental conditions. To better understand the controlling parameters for deep-water coral mound growth, we conducted high-resolution mapping and submersible surveys on five coral mound fields in the Straits of Florida. Multibeam data revealed that coral mounds vary in their size and spatial density across the Straits, with the highest mounds (up to 120 m) located on the toe-of-slope of Great Bahama Bank (GBB). Sediment analyses reveal that varied sediment inputs across the Straits underpin the differences in coral mound height.
Sediment analyses document that GBB mounds consist mostly of nonskeletal-peloidal grains, while the relative percentage of pelagic grains is highest away from the Bahamas bank. In addition, the percentage of aragonite in matrix sediments is positively correlated with proximity to the slope of GBB, while the percentage of low-Mg Calcite is positively correlated with distal position from the GBB slope. Both, the high aragonite and peloid content are likely banktop-derived since other aragonitic fragments that could contribute to aragonite x-ray diffraction peaks (e.g., pteropods) were relatively low in abundance (< 4%) at all sites. The greater aragonite content and abundance of peloidal grains in matrix sediments at the GBB sites indicates that proximal large mounds receive an increased amount of platform-derived sediments compared to the smaller mounds within the axis of the Florida Straits and along the Miami Terrace. Therefore, increased periplatform sedimentation is interpreted to be the reason for the greater mound heights along GBB. Consequently leeward locations of ancient carbonate platforms may be optimal areas for the development of large mound structures.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009