Paleoenvironment of the Folsom archaeological site, New Mexico, USA, approximately 10,500 14C yr BP as inferred from the stable isotope composition of fossil land snail shells

Well-preserved aragonitic land snail shells (Vallonia) from late Pleistocene Eolian sediment in the Folsom archaeological site in New Mexico exhibit an overall decrease of delta(18)O(PDB) from maximum values of +2.7parts per thousand (more positive than modem) to younger samples with lower average values of about -3.6parts per thousand (within the modern range). The age of the samples (approximately 10,500 C-14 yr B.P.) Suggests that the decrease in delta(18)O may manifest climatic changes associated with the Younger Dryas. Some combination of increased relative humidity and cooler temperatures with decreased delta(18)O of precipitation during the times of snail activity can explain the decrease in shell delta(18)O. A well-known Paleoindian bison kill Occurred at the Folsom site during this inferred environmental transition. Average delta(13)C values of the aragonite shells of the fossil Vallonia range from -7.3 to -6.0parts per thousand among different archaeological levels and are not as negative as modern values. This suggests that the proportion of C-4 vegetation at the Folsom site approximately 10,500 C-14 yr B.P. was greater than at present; a result which is consistent with other evidence for higher proportions of C-4 plants in the region at that time. (C) 2004 University of Washington. All rights reserved.