Merriam, Daniel F., Kansas Geological Survey, University of Kansas, Lawrence, KS 66047, dan_merriam@kgs.ku.edu and Förster, Andrea, GeoForschungsZentrum Potsdam, Telegrafenberg A17, D-14473 Potsdam, Germany, for@gfz-potsdam.de
'Plains-type folds'are structural features formed in the thin sedimentary package overlying a shallow, cratonic,crystalline basement. The local anticlines are subtle blocks. They are small in areal extent (less than 1km2) and their definition increases with depth, which is either the result of: (1) differential compaction of the sediments (usually shale units); (2) nondeposition of sediment; or (3) a combination. The development of the anticlines be continuous but intermitted movement of basement blocks in the Late Paleozoic is substantiated by the alignment of the traces of anticlinal axes to the known basement faults.
The recurrent movement, which reflects adjustment to external stresses, is revealed by computing the structural interval gradient, which expresses the change in thickness of stratigraphic units over the crest of the fold. By plotting the structural interval gradient for diffferent stratigraphic units of individual anticlines on different fault blocks, it is possible to determine the timing of movement of the blocks assuming thinning of sediments over the structure reflect time of structural adjustment. The shale units in the Permo-Pennsylvanian, because of their compactibilty, best reflect the times of differential movement. The structural interval gradient for numerous structures in the Cherokee, Forest City, and Salina Basins and on the Nemaha Anticline of the Midcomtinent (USA) were determined and compared for location and timing of the adjustments. A similar variability in movement of local structure is shown in these regional geological areas.
Kansas Geological Survey
Updated April 17, 1997
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