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Regional subsurface and lithofacies mapping has revealed that epeirogenic movement, particularly involving subtle, periodic reactivation of preexisting structural weaknesses has affected sedimentation through time in the Mid-Continent. Similarly, regional outcrop studies have provided many examples where paleostructures have influenced sedimentation. Detailed measurements of the earth's gravity and magnetic field intensity, remote sensing, and geomorphologic analysis also have identified surface and subsurface features which can be used to infer discontinuities in the composition and structure of basement rocks. Faults, folds, and possible fracture systems have propagated up through the sedimentary section, are expressed in the topography of the present land surface, and ontrol stream and river drainage patterns. Structural elements, large and small, appear to have influenced regional and local sedimentation, erosion, and diagenetic patterns through long periods of time, as suggested by the geologic record in Kansas.
In some situations, bathymetric and topographic highs related to preexisting structural elements have affected markedly the distribution of petroleum reservoir-quality carbonates and sandstones from the Cambrian through the Cretaceous. A review of four, vertically stacked carbonate-dominated cyclothems from the Upper Pennsylvanian Kansas City Group in central and western Kansas reveals an evolving display of time and location dependent features caused by the combined effects of epeirogenic and recurrent structural movement, sedimentologic controls such as clastic influx, and eustatic changes in sea level. Favorable reservoir facies trends of the carbonates and early freshwater diagenetic patterns can be explained, in part, by variations in the configuration of the Pennsylvania epeiric shelf.
In addition to trap formation, subtle structural development also may affect indirectly the reservoir distribution by influencing markedly the processes of sedimentation and diagenesis. Inasmuch as the subtle expression of deep structure usually can be detected in shallow and surface records, it follows that remote sensing and geomorphologic analysis can assist conventional geophysics and subsurface geology in the development of new energy and mineral prospects.
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