LATE QUATERNARY ENVIRONMENTAL CHANGE AND LUNETTE DUNE FORMATION AND EVOLUTION

Lunettes are isolated dunes that form along the downwind margins of some larger playas. They are relatively stable, depositional landforms that form from the accumulation of regional dust inputs and sediment deflated from associated upwind playas. Age data from High Plains lunettes indicate formation began as early as 250 kya, but most lunettes likely began forming in the late Pleistocene with episodic sedimentation throughout the Holocene.

The purpose of this research is to better understand mechanisms and timing of lunette formation and evolution on the Kansas High Plains. Objectives include: 1) reconstructing paleoenvironmental conditions throughout lunette development using a variety of proxy records; 2) interpreting geomorphic processes of lunette stratigraphy; and 3) establishing lunette chronology. To accomplish this, soil cores were collected to maximum depth possible from the windward slope of lunettes. Cores were described and analyzed for bulk density, spectral color, and magnetic susceptibility. Stable carbon isotope samples were collected in 1 – 10 cm intervals and analyzed to reconstruct past environmental conditions. Samples were collected from buried soils for radiocarbon analysis to provide age control.

Age data indicate that lunettes preserve lengthy records of environmental change, with most records extending >40 ka. Lunettes are dominated by several-meter-thick sequences of thin laminations composed of dark-light intercalated zones interpreted as incipient soil-sediment layers (i.e., A-C profiles). Stable carbon isotope and magnetic susceptibility data indicate repeated small-scale shifts in climate occurred throughout much of the late Pleistocene and into the early Holocene, with increased aridity throughout much of the Holocene. Geomorphic processes in the late Pleistocene regularly alternated between pedogenesis and deposition, while the early-to-middle Holocene was dominated by aeolian processes and the late Holocene by pedogenesis.