THE CAROLINA BAYS

Age



The age of the Carolina Bays is constrained by a variety of dating techniques as predating the end of the Pleistocene by ten of thousands to over a hundred thousand years. The techniques, which demonstrate a pre-terminal Pleistocene age for the Carolina Bays, are radiocarbon dating, Optically Stimulated Luminescence (OSL) dating, and palynology.

Radiocarbon dates: As illustrated in Figure 3 of Heinrich (2005), numerous radiocarbon dates have been collected from the sediments, which fill the basins, of Carolina Bays. The majority of these samples, from which these dates were obtained, were collected from cores of undisturbed sediments that filled Carolina Bays in North and South Carolina.

These cores were collected to reconstruct region paleoenvironemtal records using pollen, diatoms, and other fossils found in the distinctly and conformably layered sediments that fill the Carolina Bays (Brooks et al. 2001, Frey, 1953, Frey 1955, Gaiser et al. 2001, Watts 1980, Whitehead 1981). Additional radocarbon dates have been obtained from organic matter collected from the undisturbed sediments filling Carolina Bays by Blilet and Burney (1957). Kaczorowski (1977), Mixon and Pilkey (1976), and Thom (1970).

Many radiocarbon dates, which were obtained from organic matter preserved within undisturbed sediments, which fill Carolina Bays, are greater than 14,000 BP radiocarbon in age. The finite radiocarbon dates range in age from 440 ± 50 to 27,700 ±2,600 BP radiocarbon in age (Whitehead 1981, Gaiser et al. 2001).

Some samples are so old that they contained insufficient radiocarbon for dating, which results in "greater than dates". For example, samples from sediments filling Carolina Bays have been dated at greater than 38,000 to 49,550 BP radiocarbon years (Frey 1955, Brooks et al. 2001).

In case of Carolina Bays where multiple radiocarbon dates have been determined from a single core, radiocarbon dates are consistent in terms of their stratigraphic position within a core and accumulation rates calculated from them with only the occasional exception. Given the nature of radiocarbon dating, such discordant dates occasionally occur even in undisturbed deposits, when multiple samples were dated.

The occasional discordant date by themselves are meaningless as an indicator of disturbance, contrary to the arguments of Firestone (2006). The intact internal stratigraphy of the bay sediments, their paleosols, and their pollen zones, i.e. as observed by Brook et al. (2001) in case of Big Bay, refutes such arguments.

As discussed by Gaiser et al. (2001), radiocarbon dates reported from any Carolina Bay are all minimum dates for their formation. Because only organic matter can be dated by radiocarbon dating, the reported radiocarbon dates only represents times during which organic matter of some type accumulated in Carolina Bays and was later preserved.

At other times, datable organic matter would either not have been preserved as sediment accumulated within them or older organic matter destroyed when they dried out completely. During glacial periods when sea level was 130 meters (400 feet) below present, the water table would have been below the bottom of the vast majority of the bays. At such times, any organic matter would have been destroyed by oxidization and weathering of the lake bottom. Also, at that time eolian processes would have eroded any existing sediments filling the bottom of many bays removing any older lake sediments and the pollen, and datable organic matter. As a result, it is highly unlikely that organic matter dating to the exact age of any Carolina Bay would have been preserved except in the deepest of them. Thus, the oldest radiocarbon date from a Carolina Bay only indicates when the water table rose high enough for a permanent lake or swamp to exist within it.

 (Gaiser et al. 2001).