Geography & Earth Sciences Publications

Subterranean Transport and Deposition of Quartz by Ants in Sandy Sites Relevant to Age Overestimation in Optical Luminescence Dating

W. Jack Rink et al. — Tue, 18 Dec 2012 13:51:27 PST

An artifical layered sandy site was created using a combination of native sand and colored sand (3 parts native uncolored quartz, 1 part colored quartz) in Apalachicola National Forest near Tallahassee, Florida. Twelve layers of sand, each 1 by 1 m in horizontal extent by 10 cm in thickness were emplaced to a depth of 2 meters followed by implantation at the surface of a Florida harvester ant (Pogonomymrex badius) colony (the lower two layers were 50 cm thick). The colony excavated a nest, and after 7 months, the sand layers were excavated to the base to test the hypothesis that sand grains were moved upward within the ant nest without reaching the surface. The ants penetrated 11 of the 12 colored layers reaching a depth of 130 cm. Thirty nine sticky-acetate peels of ant chamber floors were collected and colored sand grains were counted under a microscope. More than 16,000 grains were identified in layers that did not originally host them. Of these, more than 80% were unambiguously moved upward. This means that possibly as many as 54,000 upwardly mobile grains were present (ratio of 3:1 uncolored to colored). In relation to optical luminescence (OSL) dating, this means that grains that would not have been optically zeroed by transport to the surface (defined here as subterranean-transported) were present in abundance, and that if the site was ancient, there would have been found many grains that were older than the layers they presently reside in, even if only one colony of harvester ants had disturbed the layers. This is in addition to the fact that backfilling of chambers and tunnels may contribute even more significantly to the presence of a subterranean-transported component of an OSL sample.

We conclude that ants can significantly affect the age distributions in sandy archaeological sites. Multiple examples of such disturbances have been documented in the literature. Most relevant to our results are recent studies of the OSL chronology of Pre-Clovis-age and Palaeoindian age archaeological sites in sandy environments in North America that may have been compromised by ant bioturbation of quartz sand grains. Here we have examined in detail the potential effects of one episode of ant nest-building on the age overestimation of affected sediments. From this we found that as few as 12 episodes of bioturbation involving backfilling of chambers in the same volume of sand could lead to the presence of 1 contaminant grain per 50 grains of sample.

The Wakulla Springs Lodge Site (8WA329): 2008 Excavations and New OSL Dating Evidence

W. Jack Rink et al. — Tue, 11 Dec 2012 13:40:05 PST

The Wakulla Springs Lodge site (8WA329), located in north Florida's panhandle (Figure 1), has been known for many years as one of the state's early sites. Recent reassessment of research conducted by the Florida Bureau of Archaeological Research in the mid-1990s suggests that this site was occupied well before the Clovis people who were initially thought to have been the first Americans. This report summarizes the results of field investigations carried out in 2008 at the Wakulla Springs Lodge site as well as the ensuing research.

Geoarchaeological Investigations and OSL Dating Evidence in an Archaic and Paleoindian Context at the Helen Blazes Site (8BR27), Brevard County, Florida

W. J. Rink et al. — Mon, 10 Dec 2012 13:31:14 PST

The excavation of the Helen Blazes site (8BR27) between 1949 and 1951 by William Edwards was remarkable for its time, but the assemblage of Archaic and Paleoindian artifacts yielded no materials that could be scientifically dated. This article reports on new excavations at Helen Blazes that were designed to incorporate optically stimulated luminescence (OSL) dating of quartz sand grains and sedimentological studies of the sediment aimed at a better understanding of the depositional context. The new excavations yielded lithic materials with typologies consistent with those found by Edwards (1954). Samples for sedimentological study were analyzed to better understand the depositional context of cultural materials by means of geoarchaeological analysis of site deposits. The OSL ages ranging from about 5,400 to 12,000 years before present are in line with expectation for Archaic to Paleoindian period contexts. However, the sedimentological and geoarchaeological interpretation together with the fine detail of the OSL results suggest that the cultural material at the site was buried by bioturbation and internal reorganization of the deposits rather than normal geological sedimentation following occupation.