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The AAPG/Datapages Combined Publications Database

Earth Science Bulletin (WGA)


Earth Science Bulletin
Vol. 17 (1984), No. 1. (Annual), Pages 1-48

Measured Sections, Magnetic Polarity and Biostratigraphy of the Eocene Wiggins, Tepee Trail and Aycross Formations Within the Southeastern Absaroka Range, Wyoming

Kent A. Sundell, Peter N. Shive, Jeffrey G. Eaton


The Absaroka volcanic sequence of northwestern Wyoming contains a wealth of stratigraphic data which may be used for local, regional and world-wide correlations during the Eocene. A composite measured section containing 1,693 meters (5,557 feet) of middle Eocene volcaniclastic rocks from the Aycross, Tepee Trail and Wiggins Formations within the southeastern Absaroka volcanic sequence is presented herein. The volcanic rocks are composed predominantly of volcanic siltstones, sandstones, conglomerates and breccias, with lesser amounts of volcanic claystones, bentonite and primary tuff. In general the entire volcanic sequence coarsens upward with siltstones dominant in the Aycross Formation, sandstones in the Tepee Trail Formation and conglomerates in the Wiggins Formation.

Magnetic polarity, vertebrate fossil, invertebrate fossil, plant fossil and radioisotopic age data occur within the measured section. The magnetic polarity zonation forms excellent markers, traceable throughout the complex volcanic sequence and tentatively correlated with anomalies 20, 21 and 22 of the marine magnetic anomaly timescale. The vertebrate fossils indicate a change from the Bridgerian to the Uintan land mammal age within the lower Tepee Trail. The basal portion of the Wiggins Formation is time-transgressive, decreasing in age from the northwest to the southeast. This form of detailed stratigraphic research should benefit ongoing oil exploration within the volcanic terrane and also lead to refinements within and correlation between the magnetic polarity, biostratigraphic and radioisotopic timescales.

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