Kansas Geological Survey, Bulletin 187, pt. 1, originally published in 1967

Age of Mississippian Rocks in a Core from Northwestern Kansas

by Edwin D. Goebel

Originally published in 1967 as part of "Short Papers on Research in 1966," Kansas Geological Survey Bulletin 187, part 1, p. 15-16. This is, in general, the original text as published. The information has not been updated.

Abstract

Conodonts recovered from a core from extreme northwestern Kansas indicate an age of late Osagian and late early Meramecian for Mississippian rocks from 5,265 to 5,365 feet. Parts of the Taphrognathus varians-Apatognathus? Assemblage Zone and the Gnathodus texanus-Taphrognathus Assemblage Zone are recognized from this interval.

Eighty conodont specimens representing eight genera, three species, and several unnamed representatives of four additional genera were recovered from the J. O. Farmer No. 1 Wagner well (C SW SW sec. 5, T. 2 S., R. 40 W., Cheyenne County, Kansas). The core was taken for the Continental Oil Company. The well, drilled from an elevation of 3,523 feet above sea level, was cored from 5,148 to 5,365 feet across the Pennsylvanian-Mississippian boundary. Scouting information placed the top of the Mississippian at 5,264 feet, and the top of Cambro-Ordovician (Arbuckle) rocks at 5,470 feet.

Part of the core from 5,264 feet to 5,365 feet (carbonate and chert-carbonate rocks) was slabbed and half of the core was dissolved in dilute acetic acid. The distribution and abundance of conodonts recovered from this core were plotted (Table 1).

Table 1--Distribution and abundance of conodonts recovered from the J. O. Farmer No. 1 Wagner core (sec. 5, T. 2 S., R. 40 W.) Cheyenne County, Kansas. Numbers indicate identifiable specimens recovered. Dashed line indicates interval of high chert content in core.

The conodonts indicate that these rocks in extreme northwestern Kansas are of late Osagian and late early Meramecian age. Parts of the Taphrognathus varians-Apatognathus? Assemblage Zone and the Gnathodus texanus-Taphrognathus Assemblage Zone, both of the Valmeyeran of Illinois (Collinson et al., 1962), are recognized in this Kansas conodont fauna.

Taphrognathus sp. and Gnathodus sp. are the most abundant conodonts in the fauna followed by Neoprioniodus tulensis. Few gnathodid conodonts were recovered above 5,300 feet and Taphrognathus is common from 5,266 to 5,300 feet. Below 5,300 feet Gnathodus dominates the conodont fauna and Taphrognathus is absent.

According to Collinson et al. (1962), the base of the Taphrognathus varians-Apatognathus? Assemblage Zone of the type locality in the Upper Mississippi River valley, which includes the Warsaw Limestone, the Salem Limestone, and the lower part of the St. Louis Limestone, is marked by the oldest occurrence of Apatognathus? and the common occurrence of Taphrognathus varians. The upper boundary of the zone is marked by the youngest regular occurrence of Taphrognathus sp., the oldest occurrence of abundant Apatognathus?, and the oldest common occurrence of Cavusgnathus sp. Collinson et al. (1962) state that the Gnathodus texanus-Taphrognathus Assemblage Zone coincides with the boundaries of the Keokuk Limestone.

Rexroad and Collinson (1965) demonstrated a similarity between the Keokuk fauna and the Warsaw-Salem fauna in species present, but dissimilarity in proportions of species present. Gnathodus texanus dominated Rexroad and Collinson's Keokuk collection, making up 78 percent of the fauna, and Taphrognathus constituted only 7 percent of the fauna. In the Warsaw Gnathodus represented 44 percent of the specimens and Taphrognathus 20 percent of the specimens. In the Salem Gnathodus represented 3 percent and Taphrognathus 58 percent of the specimens. Thompson and Goebel (1963) and Thompson (1965) reported a distribution of Meramecian conodonts in the Warsaw and Salem rocks of Kansas similar to the distribution found at the type localities.

Unidentifiable fragments of conodonts were recovered from the core interval ranging from 5,305 to 5,335 feet. Study of this part of the core, which is transitional from a dominance of Gnathodus to a dominance of Taphrognathus, yielded few specimens. This interval is composed of cherty dolomite and dolomitic chert and the residues make up 60-80 percent of the rock by weight. The Osagian-Meramecian boundary falls at the top of this interval. However, some scouting data indicate that the youngest Mississippian rocks in the Wagner core are the Warsaw Limestone (Meramecian) starting at 5,267 feet. The top of the Osagian rocks was designated at 5,320, and the top of Kinderhookian rocks at 5,368 feet.

The conodont fauna from 5,340 to 5,365 feet indicates late Osagian age only. The fauna in the upper part of the core studied, from 5,265 to 5,300 feet, indicates late early Meramecian age.

References

Collinson, Charles, Scott, A. J., and Rexroad, C. B., 1962, Six charts showing biostratigraphic zones and correlations based on conodonts from the Devonian and Mississippian rocks of the Upper Mississippi Valley: Illinois State Geol. Survey, Circ. 328, p. 1-32.

Rexroad, C. B., and Collinson, Charles, 1965, Conodonts from the Keokuk, Warsaw, and Salem Formations: Illinois State Geol. Survey, Circ. 388, p. 1-26.

Thompson, T. L., 1965, Conodonts from the Meramecian Stage (Upper Mississippian) of Kansas: Unpublished Ph.D. thesis, Dept. Geol., Univ. Iowa.

Thompson, T. L., and Goebel, E. D., 1963, Preliminary report on conodonts of the Meramecian Stage (Upper Mississippian) from the subsurface of western Kansas: Kansas Geol. Survey, Bull. 165, pt. 1, p. 1-16.

Kansas Geological Survey, Short Papers on Research in 1966
Placed on web July 25, 2011; originally published in Feb. 1967.
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