Key Findings - University of Kansas
Assessing the internal depositional motif of Pennsylvanian aged strata (upper Cherokee through Shawnee groups) in eastern KansasStephan C. Oborny and Franek Hasiuk Kansas Geological Survey, University of Kansas, Lawrence, KS ------------------------------------------------------------------------------------------------------------Key Findings Data suggest that a forebulge-backbulge setting existed in eastern KansasPennsylvanian strata were observed to have thickened to the east-southeast towards a depo-center in MissouriFacies belts were observed to trend southwest-to-northeast. Previous interpretations suggested these facies belts ran approximately west-to-east.Data suggest that the Ozark Uplift did not exist as a regional high until after deposition of Pennsylvanian strata------------------------------------------------------------------------------------------------------------SignificanceThe data presented here are components of the first phase of an on-going regional investigation of Paleozoic strata in eastern Kansas. The overarching goal is to improve our understanding of the distribution and genesis of economically viable resources in the region; in particular, sources of fine and coarse aggregates, hydrocarbons, coal, and rare earth elements. Many of these resources are either sourced from, or known to exist within, Paleozoic strata in eastern Kansas. These strata have undergone extensive study for well over a century and as such we have a general understanding of structural provinces and the correlative nature of strata between them. Unfortunately, our regional understanding of stratigraphy within the basins and arches of eastern Kansas remains heavily reliant upon studies that 1) focused on correlating individual lithostratigraphic groups or 2) had insufficient data, therein requiring a great deal of geological inference (e.g., 3-10 data points per county). Due to the increased accessibility of subsurface data over the last few decades, we are now able to increase the resolution of these previous studies by at least two orders of magnitude in many cases (e.g., > 300 data points per county). ResultsHere, we provide an interlocking web of subsurface geophysical correlations traversing 29 counties in the basins and arches region of eastern Kansas and western-most Missouri (Figure 1). These correlations span from the upper Cherokee through middle Shawnee Groups and provide a detailed assessment of the internal architecture of these units (i.e., down to the member). As such, these correlations represent the first dataset of their kind in eastern Kansas and permit a more detailed analyses of facies belts and regional structure. These analyses have revealed the existence of a previously unobserved forebulge-backbulge setting in eastern Kansas that developed during deposition of the Pleasanton Group and persisted throughout a majority of the Pennsylvanian (Figure 2). This feature is a distal component of the Arkoma Basin to the southeast and this study’s correlations demonstrate that facies belts throughout the studied interval trended southwest-to-northeast and that a depocenter existed in southwestern Missouri. These findings run antithetical to previous interpretations in which the basin depocenter was to the south and facies belts ran approximately west-to-east. Additionally, these findings require further assessment of the Ozark Uplift in southwestern Missouri, as current interpretations place the uplift of the Ozarks prior to the deposition of these strata, while this study’s interpretation is that the Ozark Uplift did not exist as a regional high until after deposition of Pennsylvanian strata.Figure SEQ Figure \* ARABIC1: A) Late Pennsylvanian (~303 Ma) paleogeographic map, modified from Blakey. B) Regional Map of study area. C) Map of study area with transects and datapoints.Figure 2: Comparison of depositional architecture within transects D (top transect) and E (bottom transect). ................
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