147 Recent Advances in Archaeological Geology (Posters)

Monday, 26 September 2016
9:00 AM - 6:30 PM
Exhibit Hall E/F

WHAT MAKES THE HOLE?—TOOL AND ORNAMENT CONSTRUCTION OF CODAKIA ORBICULARIS AND ITS ROLE IN RECYCLING OF THE ARCHAEOLOGICAL RECORD BY THE BLUE CRAB CARDISOMA GUANHUMI, SAN SALVADOR ISLAND, BAHAMAS

Paper number: 147-19
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The bivalve Codakia orbicularis (Linnaeus, 1758), Family Lucinidae and common name tiger lucine, is found throughout the Caribbean and Florida. C. orbicularis shells are found typically in Lucayan middens, with Lucayans being the indigenous inhabitants of the Caribbean. Of significance is the fact that the blue land crab, Cardisoma guanhumi, commonly recycles shells in the process of burrowing, thereby exporting C. orbicularis to the surface. Some of these shells are abraded in various areas, including the ventral, anterior and posterior margins, as well as in the umbo region. We measured 46 C. orbicularis shells from surface collections (N=29) and the 18 cm depth interval (N=17) from Pigeon Creek Dune 1 site, San Salvador, Bahamas (SS1 E29 S101 Plan view Grid #2 at 18 cm below the surface) examining the amount of abrasion in these four regions of the valve. Of the surface-collected materials that were recycled by C. guanhumi, 7% were abraded on the anterior margin, 17% on the posterior, 24% along the ventral margin and 10% within the umbo region. Ventral margin abrasion was most likely caused by Lucayans using shells as scrapers. Umbo abrasion was likely due to working the shell for bead or adornment purposes. In our sample, only 1 of 3 shells that were abraded in this way culminated in a complete hole. Of the other two, one was a failed attempt and broken and the other did not penetrate the valve. There was no correlation between valve size and abrasion area or frequency. Similarly, there was no difference in abrasion in shells of variable sizes collected from the surface and those found within the archaeological record. The fact that abraded shells occurred on the surface in areas adjacent to C. guanhumi burrows indicates significant recycling of shell material to the surface by these powerful burrowers. Thus, “crabturbation” has had a significant role in preservation of these archaeological sites, and other sites presently within the habitat of blue land crabs are vulnerable to similar disruption.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-286560

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