Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 241,
Distribution of the Bandera Shale of the Marmaton Group, Middle Pennsylvanian of Southeastern Kansas--page 8 of 9
Outcrop observations coupled with subsurface analysis indicate that sediments of the Bandera Shale in southeastern Kansas were deposited as a siliciclastic complex that prograded onto the Midcontinent seaway shelf during a sea-level lowstand. A generalized, podlike geometry suggests that initial deposition may have been fluvial influenced. Funnel-shaped well-log characteristics of thicker sandstones observed on gamma-ray and neutron logs, combined with the sedimentary characteristics observed in outcrops, indicate marine influence not only along the margins of the Bandera complex, but also within the siliciclastic wedge. Rhythmic stratification within sandstone beds that are interbedded with shale resemble tidal features described elsewhere and suggest that tidally influenced environments were present, perhaps where tidal cells were amplified along a morphologically irregular shoreline. Bioturbated sandstone units interbedded with clay shale record high-energy storm events that influenced sand distribution along wedge margins.
We postulate that the siliciclastic sediments of the Bandera Shale were initially deposited by fluvially influenced siliciclastic wedges or deltas that prograded westward during a period of sea-level lowstand. These sediments were probably generated as low base levels caused channels to incise into underlying strata east of the present-day outcrop belt, in areas that have either been removed by later periods of erosion or are covered by later Pennsylvanian and Pleistocene strata. Subsequent marine transgression reworked these siliciclastics into coast-parallel sand bars that were shaped by currents generated by storm wave and tidal events.
We thank Philip H. Heckel and Allan P. Bennison, with whom we had valuable discussions about stratigraphic relations and the locations of key Bandera outcrops. Well logs were provided by the Kansas Geological Survey. We would also like to thank Alan W. Archer, Anthony W. Walton, and Allan P. Bennison for thoughtful and thorough critical reviews that were of great importance in revising this manuscript for publication.
Kansas Geological Survey
Web version October 15, 1998