2015:348 - Carrowdough, Sligo

The Carrowdough shell midden geoarchaeological project was a collaboration between the lead investigator Katherine Napora of the University of Georgia, Dr James Bonsall of IT Sligo and Earthsound Archaeological Geophysics, and Stuart Rathbone. Funding was provided by a Young Explorer Grant from The National Geographic Society and the work was undertaken with the assistance of a large number of student volunteers from IT Sligo. Fieldwork took place on 6 and 7 June 2015. The Carrowdough site is listed in the Sligo SMR (SL013-032) where it is described as “an extensive roughly rectangular area (c.400m by 200m) of exposed midden material… mainly periwinkle, oyster and some limpet… also contains fire-cracked stone and animal bone. Within the area [there are] no less than seven areas of concentrated midden material centered on areas of charcoal-rich sand that may represent hearths.” A number of middens in this area of Sligo Bay have been investigated through small-scale excavation, including this site, and a confusing mixture of Neolithic, Bronze Age, early medieval and post-medieval dates have been forthcoming. The goal of this project was to investigate changes in human-marine interactions over time through the employment of geophysical and zoorchaeological techniques.

During field work it became apparent that rather than a single extremely large midden the site consisted of around a dozen small middens that have eroded to create a very large but extremely thin spread of shells within which the still intact areas of the small middens can be identified as particularly dense concentrations of shell.

Geophysical work was conducted under Detection License Number 15R0053. Selected transects of Ground Penetrating Radar (GPR) established the overall response across the area. Two particular concentrations of midden materials were assessed by a detailed (0.25m x 0.05m) GPR survey. Selected areas were also assessed by electromagnetic, magnetic susceptibility and earth resistance survey. The magnetic susceptibility survey was able to distinguish between intact middens, eroded shell spreads and potential areas of burning. The magnetometer survey failed to identify a known and prominent midden spread, despite the presence of some burnt horizons visible in section. The earth resistance survey has suggested the presence of some high conductivity features which may be related to the middens.

Ten cores were obtained from the site using a bucket auger (0.2m Intervals) at locations that either appeared to be intact areas of midden or where the geophysical survey indicated potentially interesting subsurface features. For the shell-rich locations, coring continued until 3 sterile levels were encountered, while for the locations targeted for their subsurface potential, coring continued until the depth of the subsurface feature was surpassed or the maximum auger depth of 1m was reached. The material from these core sections, which consisted almost entirely of mollusc shells, was subsequently shipped to the U.S. under a license to export archaeological material for zooarchaeological analysis, which is currently ongoing. Separate samples from core locations and from a hearth associated with one of the intact middens were obtained for the purposes of obtaining radiocarbon dates.

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