| Abstract: | Stable reversed remanence carried by pseudo-single-domain magnetite shows systematic direction changes in three thick ( 70m) Eocene basalt flows from the Absaroka Mountains of Wyoming. Three cores were collected at each of 24 sites in the lower flow, 26 sites in the middle flow, and nine sites in the upper flow. Cores in the two lower flows were oriented by sun compass and in the upper flow with a magnetic compass. Although remanent directions do not change smoothly through the entire thickness of the flows, portions of the record indicate that the field direction was changing as rapidly as 0.5° per year during remanence acquisition. Rough paleointensity estimates suggest that this behavior occurred while the field was in a stable reversed state rather than during a transitional period. Paleomagnetic studies of flows should avoid sampling the upper parts, because the declination record may be distorted by rotations of portions of the crust. |
