1996-03 Origin of Whewellite-Rich Rock Crust in the Lower Pecos Region of Southwest Texas and its Significance to Paleoclimate Reconstructions
1999-14 Fourier Transform Raman Spectrographic Studies Of Prehistoric Rock Paintings from Big Bend
1999-17 Nature of a Whewellite-Rich Rock Crust Associated with Pictographs in Southwest Texas
Variations in global climate appear to have become more complex during the middle and late Holocene (O’Brien et al., 1995), which increases the difficulty of resolving the mechanisms of short-term (decadal/centennial scale) climate fluctuations and predicting near-future climate changes due to anthropogenic greenhouse gas emissions. To discriminate between potential mechanisms of short-term climate fluctuations (Rind and Overpeck, 1993) superimposed on modifications due to orbital variations will require high-resolution (decadal/centennial scale) paleoclimate data from various physiographic sections. Most continental paleoclimate records are based on fossil pollen, glacial advances and retreats, tree-line migrations, tree-rings, ice-core variations, and lake level changes which have provided a consistent centennial-scale Holocene climate record for northern latitudes (Williams and Wigley, 1983). However, these proxies are generally unavailable in arid and semiarid regions, so data for paleoclimate modeling for areas such as the southwestern United States rely primarily on assemblages in pack rat middens, augmented with pollen data from archaeological sites and the occasional bog (e.g., Thompson et al., 1993). New sources of paleoclimate information are required to test and supplement existing data for many arid/semi-arid regions.
We present a new strategy for obtaining paleoclimate information using residues from past lichen activity on rock surfaces as a climate proxy. Many lichens occur only within specific environments; thus, evidence of past production of lichen with specific environmental requirements,
coupled with radiocarbon dates of biogenic residues, could possibly provide high resolution paleoclimate information. Our study focuses on calcium
oxalate produced by epilithic lichen that flourished episodically in southwestern Texas. We report here a paleoclimate reconstruction for the middle and late Holocene based on the temporal distribution of this biogenic residue, and compare these results with previous paleoclimate records from the region.