STEPHENS, CECILE G., RYAN E. RUTHERFORD,
ALLYN S. POLSON, JR., MARINE D. COMMISSO, and ALLEN W. ARCHER
*, Department of Geology, Kansas State University, Manhattan, KS 66506-3201
Abstract: Conglomerates Associated With Pennsylvanian Incised Valley Fill Sequences Of Eastern Kansas
Significant localized occurrences of Pennsylvanian-age conglomerates occur within the U.S. Mid-Continent as portions of the basal facies developed at unconformities related to paleovalley formation. In eastern Kansas, large-scale incised valley-fills (IVFs) are well developed within the Douglas Group. During sea-level lowstands, a series of paleovalleys were eroded into pre-existing stratigraphic units. In northeastern Kansas, the incised valley-fill sequence developed within the largest of these paleovalleys includes the Tonganoxie Sandstone Member of the Stranger Formation. This paleovalley was incised as much as 40 m into carbonate and shale units of the Missourian Series.
Other paleovalley-forming episodes occurred during Douglas Group deposition. Within the upper part of Lawrence Shale, the Ireland Sandstone Member appears to form an IVF sequence similar in scale, although less well documented, to the paleovalleys of the Tonganoxie Member.
Both Tonganoxie and Ireland conglomerates are characterized as consisting of intrabasinal clasts that occur within a matrix of fine-grained, micaceous quartz-rich sandstone. The clasts include fragments of limestone, sideritic concretions, shale, and siltstone. Limestone clasts are subrounded to angular and commonly attain diameters of over 10 cm. These limestone clasts clearly indicate that the underlying bedrock was well lithified before it was erosionally incised.
AAPG Search and Discovery Article #90921©1999 AAPG Mid-Continent Section Meeting, Wichita, Kansas