An Enigmatic Carbonate Layer in Everglades Tree Island Peats



Recent archaeological excavations on the heads (i.e., the most elevated and upstream parts) of several large Everglades fixed tree islands may reshape what is understood about the age and formation of these landforms, and about the role of humans in the early Everglades wetland, between 3500 and 1000 B.C. Tree islands are patches of high ground, dry enough to support trees, that rise about 1 meter above the surrounding wetland, and those islands termed “fixed” are the large teardrop-shaped islands thought to have formed over localized high points in the underlying bedrock (Figures 1a and 1b). A hard, cemented carbonate layer perched in the sediments of two tree islands in the southern Everglades was discovered by U.S. National Park Service archaeologists, and penetration of it with a concrete saw revealed that beneath the layer are unconsolidated sediments containing archaeological artifacts dating back to late-Archaic times (3000–1000 B.C.) [Schwadron, 2006].