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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 894

Last Page: 894

Title: Organic Geochemistry as a Geologic Tool: ABSTRACT

Author(s): Colin Barker

Article Type: Meeting abstract


Recent advances in techniques for analyzing organic matter, together with improved understanding of compositional changes with changing physical conditions, have led to the development of methods with considerable potential for providing insight into geologic processes. The physical character and chemical composition of organic matter change with temperature and can be used like a thermometer that is still reading its maximum value. As organic matter is extremely sensitive to past thermal effects, it responds at temperatures much lower than those needed to produce the mineral changes characteristic of the lowest grade of metamorphism. If values for geothermal gradient are known the actual depths of burial can be estimated from values for vitrinite reflectance and elementa composition. Faults or unconformities commonly show clearly in vitrinite reflectance plots and it is possible to use this information to calculate the displacement of the fault or the amount of overburden removed. Vitrinite reflectance and electron spin resonance have the potential for showing past geothermal gradients. The amount and type of organic matter in a rock are strongly influenced by the depositional environment. An obvious example is the presence of wood indicating input from terrestrial sources. A variety of characteristic organic compounds (biological markers) have potential as environmental indicators. The role of organic matter in controlling conditions, especially Eh, is well known but often poorly documented, while the significance of organic matter in complexing and tr nsporting trace elements in the subsurface is just starting to be investigated. Organic matter may also have an important role in recrystallization and diagenesis because of its adsorption on crystal surfaces. The wide range of compounds present in organic matter is controlled by depositional environment but subsequently modified by changes in temperature, pressure, Eh, and pH, and thus provide enormous potential for studying geologic processes.

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Copyright 1997 American Association of Petroleum Geologists