Date of Award
Master of Science (MS)
Michael E. Nelson
The Fort Hays Limestone is upper Cretaceous (Coniacian) in age and occurs in a wide area across the middle United States. It is recognized in the filed primarily by its thick, massive bedding and the small amounts of interbedded shale. It is resistant to erosion and forms prominent outcrops, especially where it capes hills or forms valley walls. The Fort Hays Limestone covers approximately 350 square miles in Ellis County, Kansas. The thickness varies from a few feet to over 90 feet with an average thickness of 50 feet. The beds are dipping gently northward at approximately 2-4 degrees. The beds of limestone are massive, varying from 6” to 6’ in thickness and are interbedded with shaly limestone. Various structures occur in the Fort Hays Limestone. These include joints and faults due to stresses of regional structural movement. Small scale faulting is common in the Fort Hays Limestone. Most faults are normal high angle with displacements of a few inches to several feet. Slumping is also common with displacement of 50 feet or more. The Fort Hays Limestone is a fine-grained bio-micrite composed or coccoliths, or on compounds, shell fragments, rock fragments and other trace mineral in a calcite matrix. The calcium carbonate content of the limestone varies from 82.5%-98.5%, the average content being 94.5%. The highest percentage of insoluble residue is contained in the lowest bed decreasing abruptly upwards. The insoluble residues include: quartz, feldspar, magnetite or limonite, biotite, collophane, chalcedony, pyrite, hematite, leucoxene, and rock fragments rarely occur above the lowest bed. Geographic distribution of insoluble residues indicates a source of the residues to the northwest of Ellis County. The residue changes from rock fragments in the west to weathered feldspar to limonite along the eastern margins. There have been 37 species of microfossils, 10 species of macrofossils, and 13 trace fossils described from the Fort Hays Limestone in Ellis County. Most of the fossils consist of inceramid pelecypods but race fossils including worm burrows are also extensive. The fauna is indicative of a shallow marine environment. The Fort Hays was deposited in a shallow sea probably from 50-200 feet deep with periodic lowering of the sea or raising of the land as shown by shell disruption due to wave action and by scour zones. The bottom, however, probably remained a soft slurry-like mud as shown by extensive worm burrows and turbidity flows. Slow deposition of the limey mud can be inferred due to several generations of worm burrows in the limestone.
Copyright 1974 Robert H. Drees
Drees, Robert H., "The Geology of the Fort Hays Limestone in Ellis County, Kansas" (1974). Master's Theses. 1502.