CLIMATE VARIABILITY INFERRED FROM AEOLIAN SEDIMENTS, BURIED SOILS AND PLAYA LAKE DEPOSITS FOR THE PAST 500 KA FOR THE MONAHANS DUNE FIELD, WEST TEXAS, USA

The Monahans dune field is the largest of eolian systems associated with the Pecos River in the southern-most, driest area of the Great Plains. Questions remain on the origin of this and other dune fields and response to past and future climate changes. This dune field attains heights of >50 m of the surrounding sand sheet with a perched and unconfined water table and reflects significant hydrologic variability in the Late Pleistocene. Stratigraphic analyses and sixty-one optically stimulated luminescence (OSL) ages from seven Geoprobe cores and one section from the Monahans reveal a ~550 ka old aeolian sedimentary record with seven carbonate/argillic paleosols and a playa-lake margin deposit. Quartz-grain OSL ages by two protocols, single aliquot regeneration and thermal transfer yield congruent ages between 50 and 250 ka, with the oldest ages of ca. 550 ka, potentially minima. This chronostratigraphic analysis and finite-mixture modeling of the OSL-age distribution identify four aeolian depositional periods (ADP) at 545 to 475, 300 to 260, 70 to 45, and post 16 ka and possibly two additional ADPs 460 to 420 ka and 350 to 320 ka. Playa lake deposits identified west of the Monahans and correlative to carbonate-rich paleosols indicate that wetter conditions prevailed during interglacial MIS 7, 235 to 195 ka. Another wetter period, 25 to 16 ka, with the formation of Lake King perched between the Pecos and Rio Grande Valley is correlative with pedogenically-modified < 2 m-thick aeolian sand. This chronostratigraphic study underscores that there may be multiple climatic states, during glacials and interglacials, associated with wetter conditions. In turn, the thickest, preserved aeolian deposits are associated with transitional climate periods, often contemporaneous with stadials, when the Laurentide ice sheet was <80% of the last glacial maximum volume, with precipitation-bearing zonal circulation shifted northward and weakened meridional moisture flux.