Description of the Late Holocene South-east Saline Everglades, Florida palustrine depositional environment with comparisons to other Holocene environments

Abstract

A transgressive palustrine depositional model is described for the South-east Saline Everglades, Florida. The origin, development and termination of freshwater carbonate mud (marl) deposition along the very low gradient Late Pleistocene carbonate ramp are responses to changing rates of rising sea level during the Late Holocene. The onset of the Late Holocene is defined by a decrease in the rate of sea-level rise from between 2 and 3 to <1 mm year⁻¹. Freshwater marl deposition began with this decrease ca 3165 ± 187 year BP, in a shallow (<0.3 m deep), ephemeral wetland that developed landward of a fringing mangrove forest and is maintained by seasonal Everglades water delivery. Sedimentation kept pace with sea-level rise forming a 1.2 m thick wedge shaped, landward thinning deposit. The rate of global sea-level rise began to accelerate ca 1900, the Anthropocene Marine Transgression, and presently the regional rate is 9.4 mm year⁻¹. Saltwater encroachment rates >80 m year⁻¹ are driven by sea-level rise. Saltwater encroachment resulted in retreat and transformation of coastal communities and their biogenic facies, resulting in a decrease in freshwater wetlands and marl production. Inundation ponding, mangrove overstep and the beginning of submergence are the responses to the accelerating rate of sea-level rise, however, small scale topographic and tidal ingress differences create considerable variability between Biscayne Bay and Florida Bay coastal basins. The freshwater marl producing habitat will probably be lost within 55 years, and submergence within the next century at the present rate of sea-level rise. The unique South-east Saline Everglades depositional environment is compared to other Holocene palustrine depositional environments.