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) (similar to 10%) of the Southern High Plains of northwestern Texas and eastern New Mexi co. These deposits are concentrated in three west-east-trending belts of du nes (the Muleshoe, LeaYoakum, 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-Poakum and Monahans-Andrews du nes. 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 suppl y and an underlying surface that is relatively hard (Blackwater Draw Format ion, Pleistocene), and fence-row dunes, historic dunes formed along field b oundaries. These eolian deposits accumulated episodically in the late Pleis tocene and Holocene and provide clues to the history of regional drought an d aridity. The earliest phase of sedimentation occurred when sheet sands we re deposited between 11 000 and 8000 C-14 yr B.P., probably in several phas es, based on archaeological data, as a result of episodic drought beginning between 11000 and 10 000 yr B.P. Eolian deposits dating between 8000 and 3 000 yr B.P. are rare, although eolian sediment 8000-4500 C-14 yr B.P. is ub iquitous in the draws that cross the region, and paleoenvironmental indicat ors show that the region was subjected to aridity throughout middle Holocen e time. The middle Holocene de- posits most likely were remobilized in late Holocene time. Most of the deposits and landforms of the dune fields and s and sheets are late Holocene, dating before 4000 C-14 yr B.P. and mostly be fore 1500 C-14 yr B.P. The Muleshoe and Lea-Yoakum dunes and the Seminole s and sheet underwent substantial eastward expansion in late Holocene time. B uried soils and radiocarbon ages show that the eolian sand accumulated in s everal stages, probably in response to cyclic drought. The Muleshoe dunes a ccumulated after ca. 1300 cal yr B.P. (ca. 1400 C-14 yr B.P.), after ca. 75 0-670 cal yr B.P. (ca. 850-750 C-14 yr B.P.), just after ca. 500 cal yr B.P . (ca. 450 C-14 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 C-1 4 yr B.P.) and historically. The Seminole sand sheet was active ca. 430-330 cal yr B.P. (ca. 360 C-14 yr B.P.) and in the twentieth century. The Andre ws dunes were subjected to at least two phases of eolian sedimentation afte r ca. 2320 cal yr B.P. (ca. 2320 C-14 yr B.P.). Comparisons with eolian chr onologies from other regions on the Great Plains suggest that dune mobiliza tion was a regional phenomenon after ca. 2300 cal yr B.P. (ca. 2300 C-14 yr B.P.); after ca. 1500-1400 cal yr B.P. (ca. 1650-1550 C-14 yr B.P.), just after ca. 500 cal yr B.P. (ca. 800 C-14 yr B.P.); between 500 and 300 cal y r B.P. (ca. 450-300 C-14 yr B.P.); and in the nineteenth century. The clima tic fluctuations responsible for mobilizing the dunes probably were relativ ely minor, yet the landscape impacts were substantial, resulting in widespr ead wind erosion and dune construction.