Analysis of Facies Sequences and Paleoenvironmental Interpretation of Kyrock Sandstone (Pennsylvanian), Edmonson County, Kentucky

John S. Goin, Jr.

The Kyrock sandstone member of the Caseyville Formation consists of a sequence of interlayered conglomerate and distinctly cross-bedded coarse-grained sandstone. The Kyrock sandstone is dominated by conglomerate near its base, but it is a fining-upward sequence.

In this study, the Kyrock sandstone is interpreted as a product of braided-stream deposition. The change from conglomerate-dominated to sandstone-dominated in vertical section is attributed to a transition from medial to distal braided-stream environments.

Facies transitions were recognized in 21 measured sections in the Kyrock sandstone and classified according to the fluvial facies models of A. D. Miall. Markov chain analysis and cryptologic statistical techniques were used to determine significant facies relationships. These analyses indicate that the sequence is noncyclic with borderline rhythmic-nonrhythmic facies ordering. Therefore, the fluvial environment probably consisted of braided streams throughout the sequence. Comparison of facies relationships with braided-stream sequence models also indicates that the sequence was deposited by a braided stream. The lower part of the sequence closely resembles Miall's Donjek model, which typifies a distal braided stream. This transition from medial to distal probably resulted from a rise in base level in response to the Early Pennsylvanian sea encroaching on the Illinois basin.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.