A NUMERICAL AND STATISTICAL STUDY OF THE PENNSYLVANIAN GEOLOGY OF SULLIVAN COUNTY, INDIANA

SCOT CRAWFORD ADAMS, Purdue University

Abstract

In a numerical subsurface investigation of the Pennsylvanian age sediments of Sullivan County, Indiana, two alternating types of sediments were defined--"low energy" and clastic. The "low energy" sediments consist of thin, semicontinuous layers of coal, limestone, underclay, and black shale. These four facies evidence restricted sediment transportation over a wide area. The clastic sediment type is comprised of thicker, detrital sands, siltstones, and shales. Thirteen facies maps of the vertical sequence of electric log resistivities demonstrate a high degree of vertical and lateral variability. Map examination of clastic interval thickness, of sand trends, and of facies distributions indicates that constructive clastic depositional settings can be separated into two general environmental end members: (1) "shallow water" and (2) "deeper water" deposits. The "shallow water" milieu is characterized by sand richness, a high degree of lateral discontinuity, and a relatively high percentage of fluvial fining upward sequences. Dendritic fluvial or distributary sandstone channels tend to occur within thicker intervals on clastic interval thickness maps. Depositional environments are highly complex, interfingered, gradational, and in one case so localized as to be nearly unmappable with existing data. The "deeper water" milieu is represented by clay richness, a dominance of coarsening upward prodelta sequences, and greater lateral continuity. Deposition of fining upward channel facies occurred later over shaley areas within the thinnest prodelta sequences. One example of a sand enriched prodelta longshore shoaling is inferred from a strike parallel feature. Three examples of destructive fluvial channels, characterized by anomalous thicknesses and abrupt facies transitions, are located. County wide dip predominantly controls coal and limestone structures. Structural maps, interval thickness maps, interval thickness histograms, cummulative probability graphs of sequences of interval thicknesses indicate that three types of differential compaction are responsible for local concordant draping of coal seams. The Mississippian-Pennsylvanian unconformity has a local relief of about 300 feet and is partially responsible for sediment thickness variations below the Seelyville Coal. The relative percentage of Pennsylvanian sand below the Seelyville Coal is responsible for coal elevation departures of up to 50 feet. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI

Degree

Ph.D.

Subject Area

Geology

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