Radiocarbon Ecology of the Land Snail Helix Melanostoma in Northeastern Libya

Abstract

Terrestrial gastropods are problematical for radiocarbon because they tend to incorporate carbon from ancient sources as a result of their dietary behaviour. The radiocarbon ecology of the pulmonate land snail, Helix melanostoma in Cyrenaica, north eastern Libya, was investigated as part of a wider study on the potential of using terrestrial mollusc shell for radiocarbon dating of archaeological deposits. H. melanostoma was selected out of the species available in the region as it has the most predictable radiocarbon ecology and also had a ubiquitous presence within the local archaeology. The ecological observations indicate that H. melanostoma has a very homogenous radiocarbon ecology with consistent variations in F 14 C across sample sites controlled by availability of dietary vegetation. The majority of dated specimens from non-urbanized sample locations have only a small old carbon effect, weighted mean of 476 ± 48 14 C yrs, with between~1-9% of dietary F 14 C from non-organic carbonate sources. Observed instabilities in the radiocarbon ecology can all be attributed to the results of intense human activity not present before the Roman Period. Therefore, H. melanostoma and species with similar ecological behaviour are suitable for 14 C dating of archaeological and geological deposits with the use of a suitable offset.

Aminochronology and time averaging of Quaternary land snail assemblages from colluvial deposits in the Madeira Archipelago, Portugal

“…Accordingly, the results support our hypothesis of real multimillennial age mixing of shells within colluvial deposits from The Desertas Islands. The scale of age mixing documented here was not significantly impacted by potential dead carbon intake by the snails (e.g., Hill et al, 2017), because the studied islands are poor in carbonate sediments and recently dead (modern) shells yielded 14 C ages younger than ~300 years that could potentially be explained by a post-bomb effect after the 1950s (Quarta et al, 2007). Even if snails’ carbonate intake is possible, the effects of carbonate ingestion (<300 years) cannot explain the large degree of age mixing within colluvial sediments (>6 ka).…”

“…Only small patches of colluvial silty-clay sediments with minor content of biogenic eolian carbonates (Goodfriend et al, 1996) can be found scattered around these two islands. Due to the lack of extensive carbonate-rich sediments and limestone throughout the Desertas Islands, the potential incorporation of dead carbon into snail shells (Pigati et al, 2004, 2010; Quarta et al, 2007; Hill et al, 2017) is likely limited in the study area.…”

“…A. nitidiuscula (sensu lato) is ideal for geochronologic and paleoclimatic studies, as it is endemic to the Madeiran Archipelago, abundant, and ubiquitous throughout the Holocene and late Pleistocene (Cook et al, 1990). Moreover, A. nitidiuscula is a small and thin species (shell width ≤12 mm), which is preferable, considering that small snails appear to require less calcium input and are therefore less likely to display contamination from recycled carbonate (Ellis et al, 1996; Pigati et al, 2004, 2010) as has been sometimes observed in larger land snail species living in carbonate-rich areas (e.g., Yanes et al, 2007; Hill et al, 2017). This inferred relationship between land snail shell size and recycling of carbonate is still being examined but was taken into consideration when selecting Actinella over larger and similarly abundant land snail species in this locality.…”

Supplemental Material: A 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa

“…(*) Terrestrial snails may incorporate carbon from ancient sources as a result of their dietary behaviour thus providing older radiocarbon ages (Hill et al, 2017).…”

Seasonal records of palaeoenvironmental change and resource use from archaeological assemblages

“…Biogenic carbonates also offer the additional advantage that they can be directly dated using methods such as radiocarbon (e.g. Magnani et al 2007;Butler et al 2009a;Reimer 2015;Bosch et al 2015b;Hill et al 2017), U-Th series (e.g. Magnani et al 2007;Rowe et al 2015), or amino acid racemisation (e.g.…”