Cenozoic chronology of the Sierra Nevada, California.

Abstract

Potassium-argon dates on more than 50 whole-rock samples of volcanic extrusive and pyroclastic rocks of the Sierra Nevada are used with the stratigraphy to determine cenozoic and chronology regional correlation. Andesite pebbles from Wheatland Formation, which contains Eocene mollusks, give a composite date of 53.5 m.y. Dates of 19.9 to 33.2 m.y. on 18 early rhyoltic tuffs show a late Oligocene-early Miocene major period of rhyolitic volcanism; some rhyolite, however, gives dates of 4.7 m.y. The Mehrten Formation and andestic equivalents, including Table Mountain and other latites dated at 8.8 to 9.3 m.y. are middle Miocene-late Pliocene. Dates of 2.9 to 3.5 m.y. on basalts at elevations below Matthes' profile of the Pliocene San Joaquin River show that the Canyon stage of erosion was started by late Pliocene.

50 samples from this reference