ABSTRACT

This triangular, 1,000-square mile, bimodally windy, sub-tropical lagoon is a honeycomb of closely spaced, interconnecting, sub-oval, pan-shaped basins individually upwards of 10 miles long and 12 feet deep. It lies north-south between multiple mangrove swamp belts along the Everglades shoreline and the emergent barrier reef of the Florida Keys and east-west between Biscayne Bay and a zone of broad, marly, sandy and shelly shoals facing the Gulf of Mexico, north of Vaca Key.

Basin walls of Holocene marl (mostly shelly calcareous silt converting above to mangrove peat) made stable by alternations of mangrove swamp bands and marine grasses form a honeycomb pattern throughout the lagoon. Walls rise to 2.5 feet and basin floors are as deep as 11-12 feet msl. Bottoms are muddy or floored by shell concentrate. Near the Keys are bottom exposures of the underlying hard Pleistocene Miami limestone.

Basin areas and depths increase irregularly southward (a) from tiny oriented, oval fresh-water marsh-ponds of the Everglades border (b) by multiple mergings and irregular loss of separating walls (c) to form large, nearly smooth-sided bays along the barrier reef with its "keys" cut by tidal inlets. The honeycomb pattern of the geographic map appears below water as a more intricate though fragmentary basin-in-basin structure.

Alignments of basins (a) trending roughly north-south between nearly continuous mangrove belts which mark former rill-valleys of the Everglades marsh (b) cross northeast-southwest alignments separated by walls which seem to have been reinforced by shoreline storm-debris ramparts.

Aqueous erosion of a contemporaneously gradually thickening marl-and-peat formation is indicated by (a) sub-oval basin form (b) maintaining a rough width/depth relation (c) in a windy region (Price 1947), while (d) sediment accumulating (e) in step with rising sea level (f) produced Scholl's (1964) dated regional stratigraphy of the last 5,000 to 4,000 years.

The basin-in-basin honeycomb is the result of conflict between (a) aqueous erosion in saline basins, and (b) the strong sediment-potential of tropical paralic vegetation, while (c) the erosion continued during the slow transgression of an 8-mile-wide fresh/salt contact zone like that of today which passed across a rock basin at first lightly carpeted with Everglades marsh. Thus, salt-denuded rilly-valley lows developed oriented lakes, which were drowned to form tidal bays. Shoaling of ponds, with mangrove occupation, alternates today with deflation and flushing-out of wave-eroded marl. Total volumes of walls and water are now roughly equal.

Patches of a similar basin honeycomb occur along 270 miles of the north-eastern Cuban lagoon behind its emergent barrier reef. Pleistocene examples occur in Florida and Cuba. Drowned oriented Carolina "bay" lakes along a Chesapeake Bay shore have failed to develop a similar honeycomb pattern.

No process of accumulation adequate by itself to form such honeycombs is known. The genetic process was the drowning and embayment of oriented lakes formed in drowned marsh rills.