Stratigraphy and geochronology of upper Quaternary eolian sand on the Southern High Plains of Texas and New Mexico, United States
Eolian sand in dune fields and sand sheets cover >10 000 km 2 (∼10%) of the Southern High Plains of northwestern Texas and eastern New Mexico. These deposits are concentrated in three west-east–trending belts of dunes (the Muleshoe, Lea-Yoakum, and Andrews dune fields, from north to south) that appear to be eastern extensions of the Mescalero-Monahans dune system in the Pecos River valley, and in the Seminole sand sheet, a discontinuous accumulation of sheet sands between the Lea-Yoakum and Monahans-Andrews dunes. The most common landforms are parabolic dunes associated with blowouts, coppice dunes, and sand sheets, all typical of sandy, vegetated, semiarid landscapes, barchan dunes, in keeping with a relatively limited sand supply and an underlying surface that is relatively hard (Blackwater Draw Formation, Pleistocene), and fence-row dunes, historic dunes formed along field boundaries. These eolian deposits accumulated episodically in the late Pleistocene and Holocene and provide clues to the history of regional drought and aridity. The earliest phase of sedimentation occurred when sheet sands were deposited between 11 000 and 8000 14 C yr B.P., probably in several phases, based on archaeological data, as a result of episodic drought beginning between 11 000 and 10 000 yr B.P. Eolian deposits dating between 8000 and 3000 yr B.P. are rare, although eolian sediment 8000–4500 14 C yr B.P. is ubiquitous in the draws that cross the region, and paleoenvironmental indicators show that the region was subjected to aridity throughout middle Holocene time. The middle Holocene deposits most likely were remobilized in late Holocene time. Most of the deposits and landforms of the dune fields and sand sheets are late Holocene, dating before 4000 14 C yr B.P. and mostly before 1500 14 C yr B.P. The Muleshoe and Lea-Yoakum dunes and the Seminole sand sheet underwent substantial eastward expansion in late Holocene time. Buried soils and radiocarbon ages show that the eolian sand accumulated in several stages, probably in response to cyclic drought. The Muleshoe dunes accumulated after ca. 1300 cal yr B.P. (ca. 1400 14 C yr B.P.), after ca. 750–670 cal yr B.P. (ca. 850–750 14 C yr B.P.), just after ca. 500 cal yr B.P. (ca. 450 14 C yr B.P.), and during the nineteenth and twentieth centuries. The Lea-Yoakum dunes were active after ca. 3400 cal yr B.P. (ca. 3200 14 C yr B.P.) and historically. The Seminole sand sheet was active ca. 430–330 cal yr B.P. (ca. 360 14 C yr B.P.) and in the twentieth century. The Andrews dunes were subjected to at least two phases of eolian sedimentation after ca. 2320 cal yr B.P. (ca. 2320 14 C yr B.P.). Comparisons with eolian chronologies from other regions on the Great Plains suggest that dune mobilization was a regional phenomenon after ca. 2300 cal yr B.P. (ca. 2300 14 C yr B.P.); after ca. 1500–1400 cal yr B.P. (ca. 1650–1550 14 C yr B.P.); after ca. 700 cal yr B.P. (ca. 800 14 C yr B.P.); between 500 and 300 cal yr B.P. (ca. 450–300 14 C yr B.P.); and in the nineteenth century. The climatic fluctuations responsible for mobilizing the dunes probably were relatively minor, yet the landscape impacts were substantial, resulting in widespread wind erosion and dune construction.