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Magnetic Mineralogy and Diagenesis of the Middle Ordovician Everton Formation, Northern Arkansas

SPROWL, D. R., and M. R. FARR, University of Kansas, Lawrence, KS

Three remanent directions can be isolated in rocks from the Everton Formation: a relatively low-intensity, primary remanence, carried by apparently detrital magnetite; a higher intensity, secondary remanence of Late Pennsylvanian age, carried by apparently authigenic magnetite; and a recent direction carried as a CRM (chemical remanent magnetization) by authigenic goethite, and as a VRM (viscous remanent magnetization) by magnetite. Hematite is present in some samples, but does not appear to carry a significant remanent signal.

The primary component is mostly recoverable from sandy dolomite and dolomitic sandstone that contain a relatively high concentration of accessory detrital minerals. The Late Pennsylvanian overprint is dominant in the lower half of the Everton Formation. Intensity of overprinting is laterally consistent and peaks in intensity correlate approximately with bounding silstone/shale that may have acted to restrict the upward migration of parent fluids responsible for authigenic magnetite.

Correlation between lithologic character and magnetic mineralogy permits segregation of the remanent components independent of magnetic directions.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)