ASA Digital Art’s theory, not a published finding: over immense spans of time, material was weathered, eroded and carried by rivers and currents, then redeposited in the marine sediments that became South Florida’s bedrock. This is untested.
The published geology is clear about the rock itself. The U.S. Geological Survey’s State Geologic Map Compilation describes the Miami Limestone as occurring at or near the surface in southeastern Florida from Palm Beach County to Miami-Dade and Monroe Counties, forming the Atlantic Coastal Ridge and extending beneath the Everglades[1]. It has an oolitic facies and a bryozoan facies, contains mollusks, bryozoans and corals, and forms much of the Biscayne Aquifer[1]. To the north it grades into the Anastasia Formation[1].
Stratigraphically, the Miami Limestone is among the most complex formations in Florida’s Cenozoic record. A 1993 Geological Society of America abstract by R. A. Johnson describes it overlying and grading into the upper Pleistocene Fort Thompson Formation to the west, the Anastasia Formation to the north and east, and the Key Largo Limestone to the southeast, while resting unconformably on the Pliocene Tamiami Formation[2]. In most places it either forms the land surface or lies beneath thin, discontinuous surficial sediments[2]. The abstract is a conference summary rather than a peer-reviewed paper, and is cited with that caution.
These units are upper Pleistocene[2,1], and the Pleistocene began about 2.58 million years ago[3]. South Florida’s bedrock is therefore geologically very young, while carbonado’s published ages exceed 2.6 billion years[4].
Florida’s rocks are rich in fossils. The Florida Museum of Natural History’s invertebrate collections document the state’s fossil record[5], and fossil shark teeth, including megalodon, are found in Florida[6,7]. Megalodon lived from about 20 million to about 3 million years ago, with new estimates placing its extinction about 2.6 million years ago[6].
Any link between that young, fossil-rich stone and carbonado is our hypothesis alone. Carbonado is published as known only from Brazil and the Central African Republic[4].