J. Russ et al., ORIGIN OF THE WHEWELLITE-RICH ROCK CRUST IN THE LOWER PECOS REGION OFSOUTHWEST TEXAS AND ITS SIGNIFICANCE TO PALEOCLIMATE RECONSTRUCTIONS, Quaternary research, 46(1), 1996, pp. 27-36
A calcium oxalate (whewellite)-rich crust occurs on exposed limestone
surfaces in dry rock and open air shelters in the Lower Pecos region o
f southwest Texas, The crust, which also contains gypsum and clay, for
med over silica-rich limestone during the Holocene. SEM and optical ph
otomicrographs reveal similarities between whewellite microstructures
and the lichen Aspicilia calcarea. This desert lichen is known to prod
uce calcium oxalate, and has been found in several sites in the region
, The ubiquity of the whewellite-rich crust in the Lower Pecos shelter
s suggests that the lichen flourished in the past, Since A. calcarea i
s a desert species, the virulence of the organism likely peaked during
xeric climate episodes then waned during mesic periods. Thus, radioca
rbon ages of whewellite would correspond to dry climate periods experi
enced in the region, while periods with few or no C-14 data would indi
cate wet climate episodes, A preliminary paleoclimate reconstruction b
ased on fourteen AMS C-14 dates indicates the Lower Pecos experienced
dry to wet climate fluctuations during the late Holocene, This reconst
ruction generally agrees with other models established for Texas. (C)
1996 University of Washington.