Holocene paleoenvironment (∼7200–4000 cal BP) of the Los Castillejos archaeological site (SE Spain) inferred from the stable isotopes of land snail shells

Abstract

Neolithic, Copper Age and modern land snail shells from the Los Castillejos archeological site (37°20′N), SE Iberian Peninsula, were analyzed for 13C/ 12C and 18O/ 16O ratios to estimate the paleoenvironmental conditions during shell deposition. Modern and ancient δ 13C values ranged from −9.2‰ to −7.7‰ and from −13.6‰ to −5.7‰, respectively, and they differed among taxa. δ 13C values were similar for Neolithic (δ 13C = −8.1 ± 2.3‰), Copper Age (δ 13C = −8.4 ± 0.6‰) and modern (δ 13C = −8.4 ± 0.5‰) herbivorous Cernuella specimens. Alternatively, fossil shells of the herbivorous Ferussacia folliculum (δ 13C = −9.9 ± 1.2‰) and the omnivorous Rumina decollata (δ 13C = −11 ± 1.2‰) showed substantially lower δ 13C values than modern specimens, which may suggest lower water stress during the early to mid Holocene than today. The δ 18O values from modern specimens ranged from −1.1‰ to +0.6‰ while the δ 18O values from fossil specimens ranged from −6.7‰ to +0‰ and they differed among species. Cernuella exhibited shell δ 18O values that increased from the Neolithic (δ 18O = −2.3 ± 1.8‰) and Copper Age (δ 18O = −1.7 ± 0.6‰) to the present (δ 18O = −0.3 ± 0.5‰). The δ 18O values of fossil shells of F. folliculum (δ 18O = −3.7 ± 1.0‰) and R. decollata (δ 18O = −4.0 ± 1.6‰) were also lower than modern shells. Calculations of a published snail-flux balance mixing model for δ 18O values indicate that early to mid Holocene shells precipitated during times when relative humidity was greater than today. The SE Iberian Peninsula was noticeably wetter ∼7200 cal BP, and experienced drier conditions thereafter. The results are consistent with other regional paleoclimatic proxies and reinforce the potential use of land snail shells as paleoenvironmental archives.