Magnetostratigraphy of Plio-Pleistocene Lake Sediments in the Confidence Hills of southern Death Valley, California

Abstract

Over 200 meters of continuous playa and lacustrine sediments and volcanic ashes are exposed in the Confidence Hills of southern Death Valley. Oriented samples from two stream canyons which cut through the sediments possess stable characteristic components of Natural Remanent Magnetization (NRM). Progressive demagnetization experiments yield several normal and reversed polarity zones which are stratigraphically distinct, and the characteristic components pass the reversal test. The presence of the Huckleberry Ridge volcanic ash (c.a. 2 Ma) in one of the reversed polarity zones provides a dated stratigraphic marker for correlation of the magnetostratigraphy to the magnetic polarity timescale. The correlation indicates that deposition began before the Reunion magnetic event (2.14-2.15 Ma) in the early Matuyama reversed chron (late Pliocene), and continued through the Olduvai normal subchron (c.a., 1.79 Ma) into the early Pleistocene. Deposition rates for the portion of the formation studied average about 26 cm/ky. Despite the close proximity of the sequence to strands of the Death Valley Fault, no net vertical-axis tectonic rotation could be detected.