Stable isotopes and soil-geomorphology as indicators of Holocene climate change, northern Chihuahuan Desert

Coeval delta(13)C Shifts recorded in buried soils at both piedmont slope and basin floor sites in the northern Chihuahuan Desert indicate a major shift from C(4) grasses to C(3) desert-scrub between 7 and 9 ka. The age assignments are based on stratigraphic correlations to charcoal dates and carbon-14 dates of carbonate. This shift is synchronous with a period of cooling in the North Atlantic that: may have triggered a period of drought in the south-western United States. Coinciding with this vegetation change, geomorphic evidence in Rio Grande, piedmont, and basin floor eolian environments indicates a major period of erosion. Subsequent gradual enrichment of pedogenic carbonate delta(13)C values in younger deposits suggests that C(4) grasses rebounded in the late Holocene (approximately 4 ka), which is consistent with other evidence of increased moisture regionally. A period of less severe aridity at approximately 2.2 ka is indicated by erosion and subsequent deposition along the alluvial fans and within the basin, and correlates with depleted pedogenic carbonate delta(13)C values suggesting a decrease in C(4) grasses. Isotope and packrat midden records should be used together to infer past environmental conditions at different elevations. (C) 1999 Academic Press.