Late Quaternary sedimentology and geochronology of small playas on the Southern High Plains, Texas and New Mexico, U.S.A.

Playas are small, circular basins forming a ubiquitous component of the southern High Plains landscape. They are filled with carbonaceous mud deposited since the terminal Pleistocene. The stratigraphy and geochronology of 30 playas was investigated to better understand the paleoenvironmental record of basin filling. At the base of the fill in some playas is a well sorted eolian sand dated between ~ 13,000 and ~ 11,000 14C yr BP. The beginning of mud deposition, representing aggradation of eolian dust on a moist, vegetated playa floor was largely between ~ 12,000 and ~ 10,500 14C yr BP. Playa filling slowed ~ 9000 to ~ 4000 14C yr BP, probably due to dry conditions, increased ~ 4000 to ~ 2000 14C yr BP, then slowed again. Eolian sand and loam, likely representing regional aridity, accumulated in some basins episodically just prior to ~ 10,700 14C yr BP, between ~ 8600 and ~ 4700 14C yr BP, and at ~ 1300 14C yr BP. Stable C isotopes from one basin indicate that the playa was inundated only seasonally throughout the record beginning ~ 11,500 14C yr BP. The phytolith record in that basin indicates an abrupt shift toward cooling ~ 11,400 to ~ 11,200 14C yr BP and then increasing importance of xeric-adapted C4 grasses through the Holocene.