Magnetostratigraphy and Tectonic Rotation of the Eocene-Oligocene Makah and Hoko River Formations, Northwest Washington, USA

Abstract

The Eocene-Oligocene Makah Formation and subjacent middle Eocene Hoko River Formation of the northwestern Olympic Peninsula, Washington, yield mollusks, crustaceans, foraminifera, and early neocete whales; their age has never been precisely established. We sampled several sections; most samples showed a stable single-component remanence held largely in magnetite and passed a Class I reversal test. The upper Refugian (late Eocene) and lower Zemorrian (early Oligocene) rocks at Baada Point correlate with Chron C13r (33.7-34.7 Ma) and Chron C12r (30-33 Ma). The Ozette Highway section of the Makah Formation spanned the early Refugian to late Refugian, with a sequence that correlates with Chrons C15r-C13r (33.7-35.3 Ma), and a long reversed early Zemorrian section that correlates with Chron C12r (30-33 Ma). The type section of the Hoko River Formation correlates with Chron C18r (40.0-41.2 Ma). The area sampled shows about 45• of post-Oligocene counterclockwise tectonic rotation, consistent with results obtained from the Eocene-Oligocene rocks in the region.

A new Early Oligocene toothed ‘baleen’ whale (Mysticeti: Aetiocetidae) from western North America: one of the oldest and the smallest

“…Nevertheless, magnetostratigraphic data place a large portion of the Makah Formation, including some of the Refugian horizons and the Jansen Creek Member, into a single reverse polarity zone. Given the presence of Refugian foramina in its lower portion, and assuming that there are no major gaps, the most likely correlation of this magnetozone is with Chron C12r, implying an age of approximately 33.2–31.0 Ma, or Early Oligocene [ 23 , 24 ].…”

Mass occurrence of echinoids in an Oligocene hydrocarbon-seep limestone from the Olympic Peninsula, Washington State, USA

“…The limestone studied herein, derived from the Jansen Creek Member of the Makah Formation, was collected on a beach terrace c. 1 km east of the mouth of the Bullman Creek (48.3466°N, 124.5204°W), Clallam County, Washington. The Makah Formation includes strata that range in age from the late Eocene (late Narizian, c. 36 Ma) to the early Oligocene (Zemorrian, c. 30 Ma; Snavely et al 1980;Prothero et al 2009). The Jansen Creek Member is an olistostrome (Snavely et al 1980;Niem et al 1989), c. 10 km long and 200 m thick, composed of uppermost Eocene and lowermost Oligocene fossiliferous sandstones (both deep-and shallow-water marine) and other clastics including shallow water conglomerate that slid off a shelf in the area that is now Vancouver Island (Snavely et al 1993) and into the deep Tofino Basin.…”

“…1980; Prothero et al . 2009). The Jansen Creek Member is an olistostrome (Snavely et al 1980; Niem et al .…”