Paleomagnetism of the Plio-Pleistocene Lousetown Formation, Virginia City, Nevada

The natural remanent magnetization of sixty-one lava flows from the Plio-Pleistocene Lousetown formation was measured. The field area extends from Virginia City, Nevada, to Truckee, California, on the eastern slope of the Sierra Nevada. Geomagnetic polarity epochs and stratigraphic controls are used to determine the general extrusion sequence. The flow-mean directions of magnetization separate into two distinct groups. Thiry-two flows at Lousetown Creek have a D ≃ 64°, I ≃ −67°, and the remainder of the flows have more usual normal and reverse polarity directions with D ≃ 20°, I ≃ +46° (north-seeking directions). Both sets of flows have directions of magnetization that are significantly different from an axial dipole field. It is concluded from the respective directions of magnetization that: (1) the first set of flows represents an intermediate direction of the geomagnetic field during a transition from reverse to normal polarity, and (2) the geomagnetic field deviated significantly from an axial dipole field within the late Pliocene.