--> Abstract: The Origin of the Magnetic Susceptibility Signal and the Timing of Burial Diagenesis the Woodford Shale, Oklahoma, by Grant Heard, Mike Aufill, S. Johari Pannalal, Donald Walker, R. Douglas Elmore, Anna M. Cruse, and Stanely Paxton; #90078 (2008)
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The Origin of the Magnetic Susceptibility Signal and the Timing of Burial Diagenesis the Woodford Shale, Oklahoma

Grant Heard1, Mike Aufill1, S. Johari Pannalal1, Donald Walker1, R. Douglas Elmore1, Anna M. Cruse2, and Stanely Paxton3
1ConocoPhillips School of Geology and Geophysics, University of Oklahoma, Norman, OK
2School of Geology, Oklahoma State University, Stillwater, OK
3United States Geological Survey, Oklahoma City, OK

The Upper Devonian-Mississippian Woodford Shale is a prolific petroleum source rock of the southern mid-continent of the United States and has also attracted interest as a shale gas reservoir. In this study geochemical, paleomagnetic, and rock magnetic results are used to investigate the origin of the magnetic susceptibility (MS) signal and to date diagenetic events in the Woodford Shale in the Arbuckle Mountains, Oklahoma. The MS in the Woodford shows considerable variability vertically with fissile shales having the highest values and siliceous intervals the lowest values. Geochemical results suggest that much of the iron in the unit is authigenic in origin. Preliminary paleomagnetic results from thin carbonate lenses within the Woodford Shale indicate they contain a Previous HitmagnetizationNext Hit with southeasterly declinations and shallow to moderate downward inclinations. Analysis of demagnetization characteristics and rock magnetic data indicates that the Previous HitmagnetizationNext Hit resides in magnetite. This Previous HitmagnetizationNext Hit was acquired in the late Paleozoic although the timing relative to deformation is still under investigation. It is interpreted as a chemical remanent Previous HitmagnetizationTop (CRM) in authigenic magnetite acquired during burial diagenetic processes such as maturation of organic matter and/or clay diagenesis. Although this authigenic magnetite may contribute to the MS signal in some intervals, the vertical variability in MS values is more likely controlled by paramagnetic minerals such as pyrite and clays. The relative contribution of pyrite, clays, and authigenic magnetite to the MS signal is under investigation.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas