progradation have caused peninsulas to migrate westward across leeside subtidal 
deposits. Most of the offshore islands in northeastern Florida Bay have a wedge of 
paralic or marsh sediment at the base of their windward margin. Supratidal muds 
directly overlie this basal wedge along portions of the windward side of some islands. 
This sequence is identical to that of the coastal levees, and these portions of islands are 
interpreted as parts of former coastal levees. On the windward margins of other 
islands, the basal paralic swamp and marsh sediment wedge is overlain by subtidal 
sediments, which become thicker to the west, and are capped by supratidal muds which 
thin to the west. This indicates that the windward margins of islands, like the 
peninsulas, have eroded and the islands are migrating (prograding) westward. It was 
concluded that the position of early shorelines was defined by pre-existing drainage 
patterns produced by mangrove-bordered rills, along which swamp and marsh 
sediments accumulated. As the area flooded, these deposits persisted and evolved into 
thin, northwest-southeast trending mangrove peninsulas. Subtidal sediments 
accumulated adjacent to leeward shores, while windward shores eroded. With sea level 
rise and transgression, sections of the shoreline levees and peninsulas were breached, 
forming islands. These early islands continued to accrete leeward muds and erode their 
windward margins, resulting in the westward migration of islands from their point of 
inception. 
1989 0 
Davies, T. D., and A. D. Cohen (1989) Composition and significance of the peat deposits of 
Florida Bay. Symp. on Florida Bay: A Subtropical Lagoon. Miami, FL. June, 1987. Bull. Mar. 
Sci. . 44(1 ):387-98. 
[DATE OF SAMPLING PRIOR TO 1980 BUT UNKNOWN.] Late Holocene vegetation and 
geologic history of Florida Bay is elucidated by analysis of the petrographic/botanical 
compositions of its surface and subsurface peat deposits. Over 600 sites were 
investigated, of which 134 were found to contain some peat. Cores were obtained in 
Ninemile Bank, Spy Key - Panhandle Key Bank, Joe Kemp Key, Cluett Key, Jim Foot 
Key, Samphire Key, Man-of-War Key, Shell Key, Panhandle Key, Spy Key, Russell Key, 
Eagle Key, Crane Key and Pigeon Key. Most of these peat deposits were overlain by 
marine carbonate-rich marls. A representative selection of these peat deposits was 
sampled and analyzed using piston coring and microtome-sectioning procedures. Peat 
types representing 12 different depositional environments were identified. Three of 
these represent marine, mangrove-dominated settings (Rhizophora Peat, Rhizophora- 
Avicennia Peat, and Avicennia Peat); two are transitional settings (Rhizophora 
Transitional Peat and Conocarpus Transitional Peat); and seven represent freshwater 
settings ( Uariscus [Cladium] Peat, Acrostichum Peat, Acrostichum-Mariscus Peat, 
Mariscus-Nymphaea Peat, Mariscus-Cephalanthus Peat, Cephalanthus Peat, and 
Myrica-Persea-Salix Peat). The properties used in defining each peat type and in 
reconstructing its environment of deposition were the abundances and types of: (1) 
identifiable plant fragments, (2) plant decomposition products, (3) animal remains 
(such as sponge spicules, radiolaria, foraminifera, shejl fragments, and insect parts), 
and (4) mineral components (such as carbonates and pyrite). The identification of the 
freshwater peat types at all sites analyzed is especially significant because these types 
represent depositional settings that do not occur in Florida Bay today but are presently 
forming on the mainland in the Everglades. The evidence thus supports the hypothesis 
that the peat deposits of Florida Bay represent erosional remnants of a more extensive 
area of freshwater Everglades-type peat that occupied portions of this region before it 
was converted to Florida Bay by a transgressing sea. [This study was also presented 
in: Cohen, A. D., and T. D. Davis (1989) Petrographic/botanical composition and 
significance of the peat deposits of Florida Bay. Symp. on Florida Bay: A Subtropical 
Lagoon. Miami, FL. June, 1987. Bull. Mar. Sci. . 44(1 ):515-6. Abstract only.] 
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