Abstract

A sample of Upper Block underclay (middle Pennsylvanian) was taken near Brazil, Indiana, and its void ratio was determined in the laboratory. By dispersing, resedimenting, and reconsolidating the underclay in the laboratory, it was possible to estimate the stress cycle required to consolidate the underclay to its present void ratio. The maximum-stress value determined from the estimated stress cycle was translated into a thickness value of overlying, subaqueous sediments. Results of this initial study permit the estimate that the underclay was once buried under at least 4,300 ft. of subaqueous sediments, and that at least 3,700 ft. of Pennsylvanian or post-Pennsylvanian sediments have been eroded in this region of the Illinois basin. The depth-of-burial estimate is considered to be a minimum one because the systematic increase in void ratio (bed thickness) toward the surface of the reconstructed sediment column has not been taken into account.

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