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Depositional Environments of Wood Siding Formation and Onaga Shale (Pennsylvanian-Permian), Northeast Kansas

Curtis G. Bisby

The eastern Kansas sedimentary deposits of the Wood Siding Formation and the Onaga Shale are recognized as products of Late Pennsylvanian-Early Permian cyclic sedimentation. Reconstruction of depositional events associated with the units is important in understanding cyclic sedimentation in the Mid-Continent.

In Kansas, the Wood Siding Formation-Onaga Shale outcrop belt trends nearly parallel to the Nemaha anticline in an approximately northeast-southwest direction. Detailed field studies of 26 stratigraphic sections (nine measured and described in detail) in the northeastern part of this belt provide the basis for interpretation of the depositional environments of the two formations. Results of this study indicate that variations in water depth/distance from shore, controlled by late Paleozoic structural features and eustatic sea level changes, were the major factors controlling sedimentation.

On the basis of lithologic and paleontologic characteristics, four fifth-order transgressive-regressive (T-R) units, with periodicities of 300,000 to 500,000 years, have been identified within the Wood Siding Formation and the Onaga Shale. At least five sixth-order T-R units, with periodicities of 50,000 to 130,000 years or less, have also been identified within the two formations. The boundaries between sixth-order T-R units are represented by thin, laterally persistent marine units or by climate change surfaces.

Paleogeographic reconstructions, based on the correlation of sixth-order T-R units, provide strong evidence for a northeast-southwest-trending shoreline during Wood Siding-Onaga time. The most marine sedimentary rocks are in the southern part of the study area and contain a diverse marine fossil assemblage. Channel facies with pyritized and coalified plant fossils are more common in the northern part of the outcrop belt and suggest marshy to swampy depositional conditions.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.