Stable carbon and oxygen isotopes in Quaternary soil carbonates as indicators of ecogeomorphic changes in the northern Chihuahuan Desert, USA

Stable carbon and oxygen isotopes in soil carbonates provide an additional technique for investigating Quaternary ecogeomorphic changes in arid and semiarid regions. This study presents delta(13)C and delta(18)O values in surface and buried soils in a Basin and Range region of southern New Mexico and west Texas. Three landform categories were investigated for their isotopic content: (1) middle piedmont slopes; (2) a lower piedmont slope and adjacent playa depressions; and (3) an intermontane basin floor. Soils of the middle piedmont slopes had greatest delta(13)C variability, ranging from -0.6 parts per thousand in buried soils to similar to 11.1 parts per thousand (PDB) in surface soils. Soils of the basin floor had greatest variability in delta(18)O values, ranging from -0.6 parts per thousand to -7.6 parts per thousand(PDB). Fossil pollen patterns roughly paralleled delta(13)C shifts, With Cheno-Am pollen exhibiting greatest changes. Both isotope and pollen data across stratigraphic discontinuities suggest that a conversion from C-4 grasses to C-3 desert shrubs accompanied Holocene erosion. (C) 1998 Elsevier Science B.V.