2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 6
Presentation Time: 3:00 PM

Oxygen and Carbon Isotope Compositions of Land Snail Shells from ~8ka B.P. Archeological Sites in Interior Algeria

FABER, Meredith1, YAPP, Crayton J.1 and LUBELL, David2, (1)Roy M. Huffington Department of Earth Sciences, Southern Methodist University, PO Box 750395, Dallas, TX 75275, (2)Department of Anthropology, University of Waterloo, Waterloo, ON N2L 3G1, Canada, mfaber@smu.edu

Well-preserved aragonitic shells from Early Holocene land snail species ranging in age from ~7300 to 9600 (14C years) were collected from the archeological sites Aïn Misteheyia (AM) and Kef Zoura D (KZD) in northeastern Algeria in the 1970s. Measured d18O values of Helix melanostoma shells ranged from -3.3‰ to 0.0‰ (PDB) at AM and -3.1‰ to -0.6‰ at KZD. At AM, the d18O values of Hygromiidae sp. shells ranged from -2.0‰ to 0.7‰ and, at intervals of abrupt, persistent change in d18O, exhibited an approximately antithetical relationship with the d18O variation of Helix. d13C values ranged from -9.9‰ to -5.8‰ (PDB) and from -10.8‰ to -8.7‰ for Helix at AM and KZD, respectively. Similar values were obtained for Hygromiidae at AM (-9.1‰ to -6.6‰). The d13C data indicate a diet of predominantly C3 organic matter for both snail species. The average d18O values (-5.0‰) of winter precipitation from an Algerian IAEA site were combined with a published oxygen isotope flux balance model to calculate expected values of snail shell d18O as a function of relative humidity and temperature. Comparison of model-predicted shell d18O values with measured values for both species suggests that the ranges in the measured values of d18O could reflect fluctuations in winter relative humidity of as much as 10%. The possible effect of relative humidity on the observed d18O values of snail shells suggests that microenvironmental, seasonal and/or physiological factors may have played a role during the times in which the d18O of Helix and Hygromiidae vary antithetically at the AM site. One of these times may temporally correspond to an abrupt decrease in d18O observed ~8.2ka B.P. in the Greenland ice cores. d18O indications of a North African ~8ka climatic perturbation may have implications for the development of human cultures in the area.