Paleomagnetic Dating of Alteration Associated with Fluid Flow Events in Carboniferous Carbonates, Northern Rockies

Matthew S. Zechmeister¹, Vanessa J. O'Brien³, Shanmugam J. Pannalal¹, Richard D. Elmore¹, Eric C. Ferre², and Mark A. Evans^4
1The School of Geology and Geophysics, The University of Oklahoma, Norman, OK
²Geology Department, Southern Illinois University Carbondale, Carbondale, IL
³Noble Energy, Houston, TX
⁴Department of Physics and Earth Science, Central Connecticut State University, New Britain, CT

Determining the timing of diagenetic events relative to orogenic events is crucial for understanding the interaction between thin skinned tectonics and diagenesis. Several models have been proposed for fluid flow events that could result in diagenetic alteration during deformation. Paleomagnetic analysis of secondary chemical remanent magnetizations (CRMs) can provide information on the timing of diagenetic events which can be used to test these models. We are currently investigating the timing of CRM acquisition in Carboniferous carbonates in the fold and thrust belts in NW Montana and SW Alberta. We are focusing on determining the timing of remagnetization relative to deformation and the diagenetic origin of the CRM. Paleomagnetic analysis of folds with various geometries along the eastern margin of the Northern Rockies, show that a characteristic remanent magnetization (ChRM), interpreted to be a CRM, is Late Jurassic to Tertiary in age and is contained in magnetite. However the stage of folding at the time of acquisition varies with fold geometry. In a fault bend fold the ChRM is pretilting and in multiple fault propagation folds the ChRM is syntilting. Whether the syntilting magnetization is actually a reorganized pretilting magnetization, rather than a magnetization acquired during the fluid flow event is still under investigation. Petrographic observations indicate that the rocks contain degraded hydrocarbons as well as liquid and methane filled fluid inclusions. Geochemical (87Sr /86Sr) data indicate that the rocks have been altered by fluids with a radiogenic signature and fluid inclusion results provide evidence for saline brines. These results suggest that the CRM process could be the result of either hydrocarbons and/or evolved basinal fluids.

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