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Investigations have established that within basins that experience continuous sedimentation, maturation profiles are linear when vitrinite reflectance values are plotted on a logarithmic scale. Not unusual, however, are nonlinear profiles where discontinuities and/or reversals are present. Common geologic interpretations of discontinuities in such profiles include unconformities, faults, and intrusions. Faults and intrusions usually can be confirmed by paleontology, logging, and seismic techniques, and will not be considered further. Although unconformities can commonly be recognized by such techniques, their magnitude in terms of eroded section is usually difficult to measure or interpret. Time-temperature modeling presents an approach to quantifying the amount of erosio at unconformities.
Frequently, the estimate of the amount of erosion at an unconformity is determined using the graphical technique developed by Dow. However, modeling suggests that this graphical approach would be valid only when the vitrinite reflectance discontinuity is located at or near the surface, with no significant reburial after its development. Our models show that with reburial and time, the discontinuity in vitrinite reflectance values would diminish. The result is an apparent decrease in the estimate of eroded section as reburial continues.
Many nonlinear vitrinite reflectance profiles cannot be accurately modeled. This may result from the lack of sufficient data to correctly interpret the geology, stratigraphy, and/or thermal history of the basin being examined.
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