Eolian landscape evolution and soil formation in the Chaco dune field, southern Colorado Plateau, New Mexico

Abstract

Eolian deposits of the Chaco dune field cover a broad expanse of the southeastern Colorado Plateau in New Mexico and comprise a large part of the late Quaternary sedimentary record in this region. The primary eolian landforms include sand sheets, parabolic and modified parabolic dunes, barchan-barchanoid dune complexes, and ridge dunes. Many of the eolian landforms in the Chaco dune field have remained stable over a sufficiently long time to permit soil development. Weakly to moderately developed calcic soils, which formed in eolian deposits of mid-Holocene and latest Pleistocene age, possess clay-enriched, weak argillic B horizons. These soils have been buried progressively by younger eolian sediments, forming regionally correlative bounding surfaces over the Chaco dune field and recording relict latest Pleistocene and middle Holocene eolian landscapes. Soil-geomorphic relations and radiocarbon-dated material within the eolian deposits have been useful in (1) delineating three regionally correlative soil-stratigraphic units and their associated landforms and (2) studying the types and rates of landscape evolution and climatic changes within this portion of the Colorado Plateau. The most significant period of eolian landform construction is inferred to have occurred during the latest Pleistocene glacial-to-interglacial climatic change, forming widespread sand sheets and modified parabolic dunes. Eolian deposition during the middle and late Holocene were dramatically influenced by the presence of previously developed latest Pleistocene to early Holocene (buried) soils which may have enhanced sand-sheet and parabolic-dune development due to the binding effect of the soils. Middle Holocene eolian deposition may be related primarily to neoglacial climatic changes which enhanced ground-surface moisture and promoted sand-sheet and parabolic-dune formation. The youngest period of wolian deposition occurred after 1.5 ka and resulted in the formation of the most diverse suite of eolian landforms and deposition of volumetrically more eolian sediments than the mid-Holocene event. In contrast to earlier interpretations, the classic mid-holocene or “altithermal event” apparently did not play a major role in the formation of eolian landscapes in the Chaco dune field.