Robert L. Brenner, Department of Geology, University of Iowa, Iowa City, IA 52242-1379
John P. Pope, Department of Geology, University of Iowa, Iowa City, IA 52242-1379
Exposures of the Bandera Shale in Bourbon County, Kansas, consist of interbedded shale and calcite-cemented, fine-grained sandstone. Sandstone beds, ranging from 3 cm to 20 cm (1.2-7.9 in) in thickness, are, in places, rhythmically laminated with organic-rich and organic-poor lamina forming 2-mm (0.8-in)-thick couplets. Many sandstone bedding surfaces in the lower and middle portion of the Bandera Shale are bioturbated with horizontal feeding trails and some vertical burrows that suggest marine environments. Thicker sandstone units are either trough cross-bedded, with sets up to 1.5 m (4.9 ft) thick, or amalgamated ripple cross-laminated and flaser-laminated.
Outcrop observations coupled with subsurface analysis indicated that Bandera Shale in southeastern Kansas was deposited as a siliciclastic complex that prograded westward during a sea-level lowstand. Siliciclastic sediments may have been deposited in a clastic wedge or deltaic complex, but sedimentary characteristics observed in outcrops record marine influence at least along the margins of the complex. Rhythmic stratification within sandstone beds that are interbedded with shale resemble tidal features described elsewhere in the Pennsylvanian of North America and suggest that embayments were present where tidal cells were amplified along a morphologically irregular shoreline. Bioturbated sandstone units, interbedded with clay shale, record high-energy events that influenced sand distribution.
Kansas Geological Survey
Web version June 24, 1998