--> ABSTRACT: Application of Paleomagnetic Techniques for Dating Hydrocarbon Migration Events, by Douglas R. Elmore; #91030 (2010)

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Application of Paleomagnetic Techniques for Dating Hydrocarbon Migration Events

Douglas R. Elmore

Establishing a relationship between hydrocarbon migration and the precipitation of authigenic magnetite is important for the development of a method to date hydrocarbon migration using paleomagnetic techniques. Important evidence for the relationship comes from a study of light and dark-banded calcite speleothems that occur in Ordovician limestones in southern Oklahoma. The speleothems are Permian in age, based on interbedded fossils. The dark bands contain primary fluid inclusions filled with hydrocarbons that are not extensively biodegraded. They also possess over an order of magnitude stronger magnetization than light bands. Paleomagnetic and rock magnetic data indicate that the magnetization in the dark bands was acquired during the Early Permian and resides in magnet te. Spheres, interpreted to be authigenic magnetite, are also found in magnetic extracts from the dark calcite. The results from the light and dark bands suggest that chemical conditions created by the hydrocarbons caused precipitation of authigenic magnetite and acquisition of the associated chemical remanent magnetization.

The results from the speleothems indicate there is a genetic relationship between hydrocarbon migration and acquisition of a secondary magnetization. A study of hydrocarbon-impregnated dolomite in the Permian Phosphoria Formation, Wyoming, also illustrates how paleomagnetic analysis can be used to date a magnetization that may be related to hydrocarbon migration. The rocks contain a Cretaceous chemical remanent magnetism residing in authigenic magnetite. This magnetism may have been acquired when hydrocarbons migrated into the rock. The time of remanence acquisition is consistent with the previously proposed oil migration history for the Phosphoria.

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