Magnetostratigraphy, paleomagnetism, and remanence acquisition in the Triassic chugwater formation of Wyoming

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Abstract
The magnetic reversal sequence determined at five sections of the Chugwater Formation can be correlated over a distance of more than 200 km. A detailed study of 203 cores constituting a grid of samples taken from a normal to reverse transition zone at the Red Grade section shows that the transition is characterized by a fairly smooth 180° direction change accompanied by an intensity decrease in about 80 cm of section. The transition occurs in the same way in all vertical columns within the grid and in other columns at the same stratigraphic level up to 80 m from the grid and appears identical to the transition reported by Herrero‐Bervera and Helsley at the same lithologic horizon about 1 km from the grid. Thermal and chemical demagnetization of grid samples removes a secondary remanence in the general direction of the earth's present magnetic field and does not reveal the presence of normal and reverse components in the same sample. The transition appears to have been magnetized during a reversal of the earth's field. Samples probably became magnetized in a few hundred years or less while they were close to the deposition surface. Paleomagnetic pole positions for all five sites are very closely clustered, and there appears to be no consistent long‐term polar wander from bottom, to top in the sections. The mean pole position (46.6°N, 113.5°E; α95 = 1.88°) is significantly different from pole positions for the Early Triassic Moenkopi Formation from the Colorado Plateau, suggesting that post‐Triassic rotation has occurred between the plateau and the basement uplifts of Wyoming.