A Pennsylvanian paleomagnetic pole from the mineralized Late Cambrian Bonneterre Formation, southeast Missouri

Abstract

One hundred eighty‐eight oriented samples of the Late Cambrian Bonneterre carbonates of southeastern Missouri were taken from Viburnum Trend mines and local surface outcrops. Initial natural remanent magnetization directions have south‐southeasterly declinations and downward inclinations. Progressive demagnetizations using thermal and AF techniques give two directions: one is a viscous present‐day field direction, and the other is of reversed polarity, with south–southeasterly declinations and very shallow inclinations. The resulting paleopole, at 43°N, 126°E, is located near the Pennsylvanian to Early Permian segment of the North American apparent polar wander path. A negative conglomerate test supports this assignment for the magnetization age. Magnetic extracts from the mineralized as well as unmineralized zones of the Bonneterre contain spherical crystal aggregates of pure magnetite of late diagenetic origin. The secondary magnetization resides in the magnetite spheroids, and we infer that the spheroids formed prior to sulfide mineralization.