Abstract: Chemical Remagnetization and Diagenesis of Clays; Implications for Dating Hydrocarbon Migration

The purpose of this study is to continue testing for a connection between clay diagenesis and chemical remagnetization. Current theories about the origin of authigenic magnetite (e.g., orogenic fluid hypothesis) can not explain the pervasive nature of many chemical remanent magnetizations (CRM). Since diagenesis of smectite to illite closely parallels that of organic matter, the proposed relationship might provide a means for dating hydrocarbon generation and migration.

The first year of funding supported by AAPG led to preliminary paleomagnetic results from Jurassic/ Cretaceous limestones in SE France. A primary magnetization is identified only at one location in the Vocontian Trough in SE-France where little diagenetic alteration of the clay minerals occurred. A pervasive remagnetization is present at all other locations which are characterized by alteration of the clays. In younger units with abundant smectite, the remagnetization is either unstable or poorly defined. These results are consistent with the creation of a magnetization during burial diagenesis of smectite.

Additional sampling is needed to examine consistency of the proposed relationship and to constrain the timing and origin of the magnetization with various field tests (e.g., fold tests). Strontium isotope ratios will determine the potential importance of orogenic fluids. X-ray diffraction work will provide additional information on the origin of the magnetization. This research could lead to the development of a method to date hydrocarbon generation and expulsion which would be useful in hydrocarbon exploration strategies. 

AAPG Search and Discovery Article #90940©1997 AAPG Foundation Grants-in-Aid