Upper Cambrian and Lower Ordovician Rocks in Kansas
Authors: Keroher Raymond P. , Kirby Jewell J. 
Published: January 2025

This report deals with Upper Cambrian and pre-Simpson Lower Ordovician beds that lie below the surface in Kansas and crop out in the surrounding states. The investigation was begun as a project of the Kansas Geological Survey and was completed under the auspices of the United States Department of the Interior.
The delineation of recognizable lithologic units within the Upper Cambrian and Lower Ordovician rocks is based upon the examination of well cuttings and cores and of insoluble residues prepared from such samples. A short description of the method of sample examination is included. This method, in part a modification of methods in common use, permits graphic representation of observations in considerable detail, thereby facilitating the correlation of the beds represented.
Insoluble residues from representative wells throughout Kansas are described in detail. Six lithologic units, five of which are separated by unconformities, are differentiated on the basis of insoluble residues and are correlated with the equivalent units in Missouri. The Missouri equivalents of the six units, named in ascending order, are: Lamotte sandstone, Bonneterre dolomite, Eminence dolomite, undifferentiated Van Buren formation and Gasconade dolomite, Roubidoux formation, and undifferentiated Jefferson City and Cotter dolomites. The most nearly typical development of these units in Kansas is in the southeastern part of the state. Other stratigraphic units that have been recognized in Missouri may be present in the southern part of Kansas but have not been identified,
A zone of sandstone composed of coarse sand grains immediately overlies the Pre-Cambrian surface in Kansas. This zone, in part, is correlated with the Lamotte sandstone of Missouri. It is overlain by a dark-colored dolomite, the insoluble residues of which characteristically consist of fine, angular, glauconitic sand that grades upward into fine sandy shale and dolocastic shale. This zone is correlated with the Bonneterre dolomite of Missouri. Next in upward order is a zone of light-colored dolomite that contains an abundance of quartzose chert; this overlies the Bonneterre dolomite throughout most of Kansas and is correlated with the Eminence dolomite of Missouri. Overlying the Eminence is a zone of dolomite characterized by a high percentage of insoluble material in which white and blue chert predominate. This zone, which is correlated with the Van Buren formation and the Gasconade dolomite of Missouri, is not differentiated in Kansas. A thin, sandy dolomite at the base is correlated with the Gunter sandstone member of the Van Buren of Missouri. A light-colored coarsely crystalline sandy dolomite which contains interbedded sandstones and which overlies the Gasconade dolomite and older beds is correlated with the Roubidoux formation. The uppermost recognized zone consists of dolomites of various textures and colors, characterized by a high percentage of chert, some of which is oölitic, and interbedded sandstones. This part of the section is correlated with the Jefferson City and Cotter dolomites of Missouri but is not differentiated in Kansas.
Rocks of Early Ordovician age, including the Powell dolomite and the Smithville limestone which overlie the Cotter dolomite in Missouri and Arkansas, were not identified in Kansas. If present in Kansas, they are included in the undifferentiated Cotter- Jefferson City sequence.
The relations of the subsurface zones in Kansas reveal that there were four major cycles of deposition in Late Cambrian and Early Ordovician time, each of which was followed by deformation and erosion that resulted in uncomfortable relationships between the zones. The record indicates (1) unconformable deposition of Lamotte sandstone on the pre-Cambrian surface, followed by conformable deposition of Bonneterre dolomite and possibly the Davis formation and Derby and Doe Run dolomites; (2) unconformable deposition of the Eminence dolomite on the eroded Bonneterre surface; (3) unconformable deposition of the Van Buren formation and Gasconade dolomite on the beveled surface of pre-Van Buren rocks; (4) unconformable widespread deposition of the Roubidoux on the eroded surface of pre-Roubidoux rocks, followed by deposition of Jefferson City and Cotter dolomites, and probably the Powell dolomite and Smithville limestone; (5) the conformable deposition of St. Peter sandstone or the Simpson formation on the beveled surface of rocks ranging in age from Cotter to Pre-Cambrian.
After St. Peter time, deformation of major importance followed by erosion several times modified the original thickness and distribution of the younger rocks of the pre-St. Peter sequence. In this discussion, the effects of post-St. Peter deformation and erosion have been disregarded except insofar as they may have affected the interpretation of pre-St. Peter events.
At the beginning of Cambrian sedimentation in Kansas the central part of the state is believed to have been relatively high. The Lamotte sandstone, followed by the Bonneterre dolomite overlapping onto the granite, was deposited on the eastern and western flanks of this area. Lithologic differences suggest that the beds on the east flank are marginal deposits of the Ozark basin, whereas those on the west flank are eastward extensions of Sawatch and Deadwood deposition. Whether separate basins actually existed at this time or whether the two types of lithology represent facies changes has not been determined.
Resumption of sedimentation resulted in the spreading of Eminence deposits conformably over the Potosi dolomite, which was restricted to the deeper parts of the basin in Missouri, and over the beveled edges of the Bonneterre dolomite in Kansas. It has not been ascertained whether the Eminence dolomite covered the central uplift area. Beds occupying the stratigraphic position of the Eminence dolomite in the eastern part of the state are slightly different from those of the same apparent stratigraphic position in the western part. This difference may or may not be due to a facies change.
The Van Buren formation, including its basal Gunter sandstone member, and the undifferentiated overlying Gasconade dolomite, which seem to have been restricted to eastern and southeastern Kansas, overlap the beveled edges of the older beds onto the Pre-Cambrian rocks exposed at the pre-Gunter surface in south-central Kansas.
After Gasconade deposition, deformation was renewed and erosion of the uplifted areas exposed, in places, rocks ranging in age from Pre-Cambrian to Gasconade. The Roubidoux formation was deposited widely upon this surface. It is present everywhere in the subsurface of Kansas except in local areas where it has been removed by post-Cotter erosion. Minor unconformities occur between the Roubidoux dolomite and the Jefferson City-Cotter sequence, and within the sequence.
Preceding St. Peter deposition, the region was tilted along a line parallel to the northern margin of Kansas. All the Jefferson City and Cotter deposits and part or all of the Roubidoux deposits were stripped from a wide area in the northern part of the state. The Cotter dolomite is now present only in the southern part of the state.