A # 24 000 YEAR PERIOD CLIMATE SIGNAL IN 1.7-2.0 MILLION YEAR OLD DEATH VALLEY STRATA

Abstract

Continental records of Plio-Pleistocene climatic fluctuations are often confined to fragmentary, localized basins, and not easily dated. One exception is the Confidence Hills of Southern Death Valley. In this study, we present a detailed description of a Plio-Pleistocene section of interfingering alluvial fan and saltpan sediments from the Confidence Hills, southern Death Valley. This well exposed section accumulated with an average deposition rate of # 25 cm/1000 yr with no bioturbation, permitting more precise paleomagnetic dating than in oceanic records [1]. We interpret the sequence of facies changes in the Olduvai Normal Polarity Zone of the Confidence Hills to represent alternations between wetter and drier regional climatic regimes. The frequency of this variation (# 24 000 yr) appears to correspond to the Milankovitch precessional cycle (23 000 yr). We believe this section records a Milankovitch-driven climatic variation in the Death Valley basin annual precipitation about 1.7-2.0 Ma. This is the first report of the precessional cycle in continental sediments of this age in the United States.