Evolution of the Magnetic Properties of Sediments Associated with Hydrocarbon Microseepage

Abstract

It has been clear for some time that bacteria are a major factor in controlling the chemical environment in which sediments are deposited. Redox changes, due to these organisms, can alter mineral stabilities during and after deposition. The iron containing minerals in sediments and, therefore, the magnetic properties of sediments are very susceptible to such redox changes. For example, sulfate reducing bacteria will reduce Fe{sup +3} to Fe{sup +2}, thus destabilizing minerals like hematite or magnetite and facilitating the nucleation of iron sulfide and iron carbonate minerals. In the process, magnetite may totally disappear, resulting in large changes in the magnetic properties of affected sediments. Hydrocarbon microseeps can provide optimum environments for sulfate reducing bacteria, but environmental conditions near seeps vary radically from place to place, depending on local variations in volatiles, water, sediment permeability, and other factors. The authors will present a regolith hydrocarbon microseepage model that includes those factors controlling the development of the iron containing minerals that they feel may be important in influencing the magnetic properties of affected sediments, the minerals likely to be affected, how these minerals vary as the redox setting changes, and some resulting magnetic effects.