--> ABSTRACT: Petrographic and Magnetic Characteristics of Hydrocarbon-Saturated Red Beds: Implications for Diagenesis and Hydrocarbon Exploration, by B. Kilgore, R. McCollum, and R. Douglas Elmore; #91030 (2010)
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Petrographic and Previous HitMagneticNext Hit Characteristics of Hydrocarbon-Saturated Red Beds: Implications for Diagenesis and Hydrocarbon Exploration

B. Kilgore, R. McCollum, R. Douglas Elmore

To test the hypothesis that there is a relationship between hydrocarbons and authigenic Previous HitmagneticNext Hit minerals, both hydrocarbon-saturated and unaltered samples of the Triassic Chugwater Formation were examined using petrographic, rock Previous HitmagneticNext Hit, and paleomagnetic techniques. Samples were collected from the crest of Red Dome in Montana where the Chugwater is saturated with hydrocarbons and bleached around fractures. The fractures, which formed during Laramide deformation, provided conduits for oil migration. The magnetization in the unaltered red beds resides in hematite. The magnetization in the oil saturated sandstones, however, resides in magnetite, although the Previous HitmagneticNext Hit intensity is at least an order of magnitude less than that observed in the red beds. The bleached samples possess intermediate Previous HitmagneticNext Hit characteristics and contain abundant authigenic specular hematite. Although a Previous HitmagneticNext Hit direction could not be isolated from the hydrocarbon-saturated sandstones, the bleached samples contain an early Tertiary magnetization that resides in authigeneic hematite.

The Previous HitmagneticTop found in the hydrocarbon-saturated sandstones is probably a combination of detrital and authigenic magnetite. The chemical conditions created by the hydrocarbons caused the removal of the hematite, which uncovered the detrital magnetite, and may also have caused precipitation of some authigenic magnetite. The magnetization in the bleached sandstones was probably acquired when iron removed from the red beds precipitated as specular hematite. This magnetization constrains the timing of oil migration and bleaching.

The results of this study, particularly the intensity differences between the unaltered and hydrocarbon-saturated red beds, also have important implications for aeromagnetic hydrocarbon exploration.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.