A paleomagnetic study of basalt flows from the Absaroka Mountains, Wyoming

Abstract

A paleomagnetic study of 34 flows from the Absaroka Volcanic Supergroup (Eocene) in northwestern Wyoming showed that 23 of these flows have normal polarity, 7 have reversed polarity, and 4 are anomalously magnetized. Two of the anomalously magnetized flows occur between normally and reversely magnetized flows and may have been extruded during a field reversal; the other two are probably contaminated with a stable lightning-induced remanence. The magnetic component of the flows is a titanomagnetite in the range 25–40 mol % ulvospinel which has in some cases been oxidized at low temperature to a cation deficient spinel. The pattern of polarities of the flows, which were sampled at four separate locations, provides an excellent basis for refining the correlation between the flows in this area. The pattern also suggests that the 34 flows were extruded over a period of time less than (and perhaps much less than) one million years in length. Nineteen flows satisfied sampling and stability criteria and were used to determine a new Eocene pole position for North America at 83.5°N, 177.4°E with an α95 of 10.1°. Paleosecular variation of the magnetic pole during this part of the Eocene was about 17°.