Abstract

Possible sources of sedimentary magnetic anomalies include:

  • Detrital magnetite deposited in sediments that have a nearby source in igneous terrain; magnetization is induced and sometimes detrital or depositional remanent magnetism.

  • Diagenetic magnetic minerals (such as magnetite, pyrrhotite, greigite, and maghemite) that may be related to chemical changes of the sediments from microseepage of hydrocarbon reservoirs; magnetization is induced and sometimes chemical remanent magnetism.

  • Diamagnetism of salt and anhydrite, responsible for negative anomalies over salt structures.

  • Fault mineralization due to upward-migrating hydrothermal fluids along fractures and fault planes, which may or may not be related to hydrocarbons.

  • Combustion metamorphism (CM) of carbonaceous pyrite-rich and organic-rich sediments, producing strong magnetization as a result of exothermic oxidation of pyrite to magnetite, as well as thermal remanence acquisition. The organic material in the rocks is consumed as fuel, but host rock remains after combustion. The phenomenon can be related to source rock outcrops or seepage.

  • Clinkers (burned coal seams and lignite beds) is a special case of CM; however, host rock is consumed after combustion. Clinkers are diagenetic sources of strong magnetic anomalies over sedimentary rocks.

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