ANOMALOUS ELLIPTICAL RIDGE IN SOUTHWESTERN FLORIDA: POSSIBLE CAROLINA BAY MORPHOLOGY

The geomorphic relief of southern Florida is generally very subdued with variations measured in meters over several kilometers; but a pronounced and unique anomaly exists along the southwestern coast. An elliptical ridge that surrounds Barfield Bay (3.0 km in a NNW direction and 2.0 km in an ENE direction; located at 81^o 41’ W. and 25^o 55’ N.) on the eastern side of Marco Island has elevations typically 8 meters above the adjacent and relatively flat regional land surface where elevations are at or below 2 meters above sea level (asl). A common misconception is that this ridge is solely the product of Late Archaic Native American mound construction. Archeological studies (Russo, 1991) have shown that the ridge has been accentuated in discrete locations by 3 to 5 meters of anthropogenic shell debris (predominately Crassostrea, Ostrea, and Mercenaria). On the southwest side of the ridge at Caxambus, anthropogenic debris has raised the ridge from its natural surface of 13 meters (asl) to a total elevation of 16 meters (asl). The bulk of the ridge is composed of massive, well-sorted, fine-grained quartz sand that lacks internal laminations and is sparsely bioturbated only by plant roots extending from the surface. The elliptical ridge is likely an aeolian feature, once encircling a central depression completely in the past, but now breached and modified by active tidal currents. The original shape and orientation of the feature suggest that it is a distant outlier to the vast population of Carolina Bays that first appears northward in northernmost Florida and southern Georgia.