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Transgressive Recycling Produces Organic-Rich Carbonate Muds

Previous HitHaroldTop R. Wanless, Brigitte Vlaswinkel, and Kelly L. Jackson
University of Miami, Miami, FL

Typical carbonate muds in the coastal bays of south Florida contain 2-5% particulate organics. Carbonate muds formed in response to historical and Holocene transgressive recycling contain 20-30% organics.

Historical recycling is in response to a rapid sea level rise (25cm) that began about 1930. Organic-rich carbonates are rapidly filling lake and lagoon depressions in the coastal complex of Northwestern Florida Bay, Cape Sable, Mangrove Coast and 10,000 Islands as they are opening to increased sediment input. The organic component is composed of varying mixtures of algal/cyanobacterial, mangrove root peat, and freshwater marsh peat detritus depending on the particulate organic matter sources at a site. Algal/cyanobacterial organics are provided by mats growing on recycled deposits, from recycling older carbonate/organic muds, and from diatom blooms in response to higher nutrients in the transgressive water column. Mangrove organics are provided by both shore erosion of mangrove peats and post-hurricane decay of peats beneath collapsed mangrove forests. Freshwater peat organics are released by collapse and decay of freshwater marsh peats as a result of saline water intrusion. Organic composition in carbonate muds varies both regionally along the south Florida coastal complex and locally within coastal complex areas.

Rapid transgressive recycling of organic-rich carbonate sediment also occurred following a small rapid rise in sea level about 2,500-2,400 years before present. This sea-level-induced transgression triggered both a 100km-long rapidly shallowing carbonate mud tidal flat coastline and produced extensive channel- and lake-filling, organic-rich carbonate mud sequences.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005