Abstracts: Magnetic Stratigraphy of the Eocene-Oligocene Lincoln Creek Formation, Porter Bluffs, Washington

ARMENTROUT, JOHN M., DONALD R. PROTHERO and CHRISTOPHER D. JAQUETTE

The Lincoln Creek Formation at Porter Bluffs, Washington, contains an important sequence of late Eocene-Oligocene strata containing foraminifera and molluscs, and is the type section of the Echinophoria fax molluscan zone of Armentrout (1973, 1975). Under thermal and alternating field demagnetization, and stable magnetic component was obtained which passes a reversal test, and shows little tectonic rotation or translation (given the large error estimates). Magnetic stratigraphy shows that the Porter Bluffs section consists of three unconformity-bounded packages. The lowest contains the upper E. dalli zone, which correlates with late Eocene Chron C13r (about 34 to 34.5 Ma). The second, which consists of most of the type E. fax zone, apparently correlates with early Oligocene Chrons C13n and early Chron C12r (33.7-32.7 Ma). The third, which includes part of the E. rex zone, correlates with early Oligocene Chron C12n (30.5-30.8 Ma). Apparently unconformities removed strata representing the lower E. fax zone and the Eocene-Oligocene boundary (33.5-34.0 Ma), and also the lower E rex zone (30.9-32.9 Ma).

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California