Abstract: New Age Constraint on the Kern River Formation

NEGRINI, ROB, California State University, Bakersfield, Bakersfield, CA; DONALD MILLER, Aera Energy LLC, Bakersfield, CA; MICHAEL MCGUIRE, Saudi Aramco, Saudi Arabia; CYNTHIA HUGGINS, Texaco Exploration and Production Inc., Bakersfield, CA; MICHAEL MINNER, Texaco Exploration and Production Inc., Bakersfield, CA; B. HACKER, University of California, Santa Barbara, CA; A. SARNA-WOJCICKI; C. MEYER; R. FLECK, U.S. Geological Survey; STEPHEN REID, Occidental of Elk Hills, Inc., Tupman, CA

The upper Tertiary Kern River Formation is an important continental deposit in the eastern San Joaquin Valley near the basin margin with the southern Sierra Nevada. Although detailed stratigraphic correlation has been completed to support the production of more than 1 billion barrels of oil at the Kern River Field, the age of the Kern River Formation and its relation to basin formation and uplift of the Sierra Nevada remain poorly understood.

Previously identified Hemphillian vertebrate fossils near the base of the formation correlate with an 8.2 Ma tuff. The upper age of the Kern River Formation was previously based on the geochemical correlation of a volcanic ash layer in the middle of this formation with the Bishop tuff. Here we report a new radiometric age date of 6.12 + 0.05 Ma for the volcanic ash that was previously correlated with the 760 + 2 Ka Pleistocene Bishop Tuff. This age is a direct 40Ar/39Ar determination for sanidine crystals extracted from a core sample of the volcanic ash. We also revise geochemical correlation in light of new data on 6.0 + 0.2 Ma volcanic tuffs from the Volcanic Hills and the Silver Peak Range in westernmost Nevada.

Both lines of evidence indicate the uppermost known age constraint on the Kern River Formation is 6.1 Ma, which is nearly an order-of-magnitude older than previously interpreted. The age control implies that the productive portion of the Kern River Formation at the Kern River field is time correlative with the upper Monterey Formation and Etchegoin Formation.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California