New Mexico Geological Society Annual Spring Meeting — Abstracts

Eolian sand sheets of the Chihuahua Desert commonly exhibit buried paleosols. These buried soils have been viewed as evidence for a punctuated response to climate change characterized by erosion-sedimentation; followed by landscape stability and soil formation during the Late Quaternary. However, a recent chronology of sand sheets, using optically stimulated luminescence (OSL), has challenged this view for sand sheet formation. This has invoked debate about eolian sedimentation and whether it was slow and continuous or punctuated since the Last Ice Age to the middle Holocene Altithermal. In order to improve our understanding of eolian sedimentation, we tested both hypotheses using radiocarbon and OSL dating techniques to evaluate a ~2.5-meter section of eolian paleosols in southern New Mexico. These dates and soil stratigraphy indicate that eolian sedimentation occurred until ~42 ka when a sedimentation hiatus occurred. This permitted the formation of a “Btk” horizon during the last Ice Age. Eolian sedimentation resumed sometime before~12 ka during the onset of warmer conditions of the Bølling–Allerød. The second break in sedimentation occurred when the water table rebounded during the Younger Dryas Chronozone. This event hydrologically altered the eolian sand and permitted the formation of a mottled “Bg” paleowetland horizon. Water table conditions fluctuated for ~3.7 ka and dropped immediately during the early Holocene no later than ~8.3 ka. This surface was exposed for ~3 ka. Eolian sedimentation resumed sometime around ~5.3 ka during the onset of Antevs’ mid-Holocene Altithermal. The third break in sedimentation occurred by ~4.5 ka with the start of slightly wetter conditions during late Holocene. This permitted the formation of a “Bk” horizon. Our results do not support the “Slow and Continuous Hypothesis”, but instead finds evidence that eolian sedimentation was punctuated and was followed by three periods of landscape stability and soil formation since the last Glacial Maximum to the middle Holocene Altithermal.