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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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Dipmeter techniques recently developed to solve Mid-Continent stratigraphic problems use short-correlation-interval dip computations and a statistical approach to interpretation. These techniques extend dipmeter interpretation methods first introduced in Tertiary formations along the Gulf Coast.
Paleozoic sandstones, as in the Pennsylvanian section of the Anadarko basin, commonly were deposited on surfaces of low dip and low topographic relief. Lithologic unit boundaries usually are nearly parallel, providing little information with which to predict the direction of improved sandstone development. In these nearly parallel bed, cross-stratification anomalies produce most of the dips computed.
To detect cross-bedding and describe its orientation within thin sedimentary units, correlation intervals must be short, yielding computed dips for every few feet of hole. Correlations are influenced by many factors, including the attitude of the underlying surface at the time of deposition and subsequent tilting. Many of the dips computed were caused by current-bedding, and indicate the direction of structure transport.
Random variations in sedimentation tend to cause confusion if the data are studied only superficially. To emphasize trends and minimize random events, statistical methods are used. Azimuth-Frequency diagrams and Modified Schmidt plots reveal the direction of sediment transport, the direction of interval thickening, and present structural dip. These methods produce greater accuracy and confidence in orienting and extrapolating sandstone isopachous contours.
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