The thermal alteration of organic matter in buried sediments can be understood and modeled using the rate laws and the Arrhenius equation. However, modeling organic reactions at geologic temperatures and heating rates requires accurate activation energies and frequency factors. Although the mechanisms of kerogen degradation are complex and poorly known, appropriate kinetic parameters that fit both laboratory and geologic data can be derived from both open- and closed-system laboratory pyrolysis experiments. Algorithms that treat organic maturation as a set of parallel first-order reactions having a range of activation energies are widely used for nonisothermal data. This relatively simple approach is certainly not an accurate account of organic maturation, but it appears to give reasonable kinetic parameters for extrapolating to geologic conditions. While questions persist about the validity of extrapolating laboratory-derived kinetics to geologic temperatures and heating rates using the Arrhenius law, the problem can only be addressed empirically by testing the fit of the laboratory data with geologic observations.
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Geochemistry of Organic Matter in Sediments and Sedimentary Rocks
As both researchers and educators, the authors have faced the difficult task of lecturing on the subject of organic geochemistry to an audience that is genuinely interested in but unable to keep pace with this rapidly advancing field. The technical jargon makes it difficult to become engaged with the topic of geochemistry without a major investment in background readings. This volume was written specifically for the graduate student or professional geoscientist needing a brief but reasonably comprehensive review of the potential applications of organic geochemical data to geological studies. This volume is divided into three sections. Section I, organic matter is viewed as a highly reactive constituent of soil, water column and sediment. Section II, the focus is on the molecular constituents of geological materials and their ability to record the history of changes in organic matter ranging from its biological formation, through sediment deposition and compaction, to its modification under the thermal stress of diagenesis and maturation. Section III, changes in the composition of organic matter in buried sediments are discussed in terms of chemical kinetics.