Twenty-five AMS radiocarbon ages of calcium oxalate-rich rock crust samples from 14 sites in southwestern Texas suggests that oxalate was produced episodically during the middle and late Holocene. The occurrence of oxalate is correlated with periods of aridity, whereas gaps in the record of oxalate deposition are interpreted to coincide with more mesic intervals. The results of this study demonstrate the potential for obtaining paleoclimate data from biogenic residues on rock surfaces. Lithobiont communities are common in desert regions (Staley et al., 1982), and the distribution of these communities is dependent on environmental conditions (Danin, 1986, 1993). Knowledge of past activity of lichen or microbes with specific climate requirements, coupled with radiocarbon ages of metabolic byproducts, could provide a new source of paleoclimate information.
We thank J. Labadie, E. Brotherton, N. Chavez, D. Ing and J. Skiles for help with “eld work; R. Modarres, C. Christophi and G. Goodfriend for the statistical analysis; R. Palma and R. Cox for helpful discussions; and J. Southon for the AMS dating. Support for this research was provided by a Cottrell Science Award of Research Corporation, a grant from the National Center for Preservation Technology and Training, and an Arkansas State University Faculty Grant. We further acknowledge the donors of The Petroleum Research Fund, administered by the ACS, for partial support of this research.