Magnetic stratigraphy of the upper Miocene (Hemphillian) Rattlesnake Formation, central Oregon
Prothero DR, Hoffman JM, Foss SE. 2006. Magnetic stratigraphy of the upper Miocene (Hemphillian) Rattlesnake Formation, central Oregon. PaleoBios. 26(1):31-35
The Rattlesnake Formation near Picture Gorge in the John Day region of central Oregon consists of about 120 meters of siltstones and conglomerates punctuated by several tuff beds. This formation is well known for its early Hemphillian mammals, and it was originally part of the Wood Committee's (1941) concept of the Hemphillian. Paleomagnetic samples were collected from the type section of the Rattlesnake Formation between Rattlesnake and Cottonwood Creeks 2 kilometers south of Picture Gorge. Samples were demagnetized with both alternating field and thermal demagnetization, and yielded a stable remanence held mainly in magnetite. After cleaning, the normal and reversed directions passed a reversal test, so the remanence is interpreted to be primary. Almost the entire section is reversed in polarity except for the basal 10 meters and a single site near the top of the section. Based on 40Ar/39Ar dates of either 7.2 Ma or 7.05 ± 0.01 Ma on the Rattlesnake Ash Flow Tuff near the top of the section, we correlate the section with magnetic Chrons C3Bn to C3Br2n (6.9–7.3 Ma), or late early Hemphillian in age (Hh2 of Tedford et al. 2004).
- Type
- Journal Article
- Authors
- Prothero, Donald; Hoffman, Jonathan; Foss, Scott
- Units
- NRSS