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

Neolithic, Copper Age and modern land snail shells from the Los Castillejos archeological site (37 degrees 20'N), SE Iberian Peninsula, were analyzed for C-13/C-12 and O-18/O-16 ratios to estimate the paleoenvironmental conditions during shell deposition. Modern and ancient delta C-13 values ranged from -9.2 parts per thousand to 7.77 parts per thousand and from -13.67 parts per thousand to 5.77 parts per thousand, respectively, and they differed among taxa. delta C-13 values were similar for Neolithic (delta C-13 = -8.1 +/- 2.37.), Copper Age (delta C-13 = -8.4 +/- 0.6%) and modern (delta C-13 = -8.4 +/- 0.5 parts per thousand) herbivorous Cernuella specimens. Alternatively, fossil shells of the herbivorous Ferussacia folliculum (delta C-13 = -9.9 +/- 1.2 parts per thousand) and the omnivorous Rumina decollata (delta C-13 = -11 +/- 1.2 parts per thousand) showed substantially lower delta C-13 values than modern specimens, which may suggest lower water stress during the early to mid Holocene than today. The delta O-18 values from modern specimens ranged from to -1.1 parts per thousand to 0.6 parts per thousand while the delta O-18 values from fossil specimens ranged from -6.7 parts per thousand to +0 parts per thousand and they differed among species. Cernuella exhibited shell delta O-18 values that increased from the Neolithic (delta O-18 = -2.3 +/- 1.8 parts per thousand) and Copper Age (delta O-18 = -1.7 +/- 0.6 parts per thousand) to the present (delta O-18 = -0.3 +/- 0.5 parts per thousand. The delta O-18 values of fossil shells of F. folliculum (delta O-18 = -3.7 +/- 1.0 parts per thousand) and R. decollata (delta O-18 = -4.0 +/- 1.67 parts per thousand) were also lower than modern shells. Calculations of a published snail-flux balance mixing model for delta O-18 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 similar to 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. (C) 2011 Elsevier Ltd and INQUA. All rights reserved.