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Stratigraphy of the Carlile Shale (Upper Cretaceous) in Kansas

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1. The Fairport Member is a mappable stratigraphic entity of wide geographic extent that differs from the rest of the Kansas Carlile in lithologic, sedimentological, and paleontological characters. Although the Fairport is treated as a member of the Carlile in this report, in my opinion the Fairport is more appropriately ranked as a formation.

2. The Blue Hill and Codell Members are related genetically, through both vertical and lateral lithologic gradation, and together are a mappable stratigraphic unit. I suggest return to the original definition of the term "Blue Hill Shale" and elevation of the unit to formational rank.

3. Although the Fairport and Blue Hill consist mainly of monotonous successions of chalky strata and concretionary gray shale, respectively, numerous marker beds provide a framework useful for understanding the lithostratigraphic and biostratigraphic relationships and differential sedimentation in the formation. The framework provided by the marker beds will aid future investigators in more detailed studies of the Carlile.

4. The contact between the Greenhorn Limestone and Carlile Shale is conformable and gradational, hence arbitrary, and is time parallel throughout the west-central Kansas area. The Fairport-Blue Hill contact is usually sharp but conformable, and at least in west-central Kansas, nearly time parallel. The Blue Hill-Codell contact is gradational laterally and vertically. Where the Codell is thickest, the upper sandy beds of the Blue Hill are thinnest. The Niobrara Chalk rests on the Codell or Blue Hill with regional diastem in the Kansas outcrop area.

5. Carbonate sediments of the Fairport Member were generated chiefly within the sedimentary basin and most were composed originally of microcrystalline calcite ooze, fossils, and calcareous fecal pellets of an unknown eater of coccolithophores. In chalky limestone and marly chalk much of the ooze has been recrystallized to microsparry calcite. Coarse spar is common inside foraminifers and as cement in lenses of calcarenite. Terrigenous detritus, mostly clay, is more abundant toward the top of the Fairport Member and reflects change in depositional environment toward that of Blue Hill sedimentation.

6. Blue Hill and Codell sediments are composed chiefly of quartz-dominant terrigenous detritus and resulted from erosion of Paleozoic and Precambrian terrains that were exposed to the east and northeast of the west-central Kansas area. Upward coarsening of grain size in the Blue Hill-Codell sequence indicates that the regressive shore of the Western Interior sea was approaching the west-central Kansas area.

7. The Carlile Shale of Kansas contains distinctive faunas that can be traced widely beyond the region where the names Fairport, Blue Hill, and Codell are applicable. Westward into western Colorado and Utah, and southwestward into western New Mexico, the Carlile faunas are recognized in the Mancos Shale. Zonal index species of the Fairport, Blue Hill, and Codell have been identified in the middle part of the Frontier Formation of southern Wyoming. Two of the zones can likewise be traced northwestward into the Colorado Shale of Montana. The Arcadia Park Formation of the Eagle Ford Group of Texas is at least partly equivalent to the Carlile Shale of Kansas. Fossils in the Assiniboine Member of the Favel Formation of Manitoba and Saskatchewan suggest at least partial correlation with the Fairport Member of Kansas. Seemingly, at least part of the Morden Member of the Vermilion River Formation of Manitoba is correlative with the Blue Hill, because the Morden is lithologically similar to the Blue Hill and conformably overlies the Assiniboine, or Fairport equivalent. Thus, the Carlile of Kansas can be correlated with all contiguous or formerly contiguous strata to the south, southwest, west, northwest, and north.

Collignoniceras marks the Carlile fauna as Turonian in age, and C. woollgari is characteristic of the zone of Terebratulina lata of the English Middle Chalk and of the middle part of the Turonian of continental western Europe. Inoceramus labiatus, which is characteristic of the lower part of the European Turonian, occurs in the Rhynchonella cuvieri and T. lata zones of the English Middle Chalk. Specimens of I. labiatus from the zone of T. lata are broader than those from the zone of R. cuvieri. The broad I. labiatus is transitional to I. latus. I. latus is characteristic of the Holaster planus zone of the English Middle Chalk. In Kansas the forms of I. labiatus transitional to I. latus lie in the lower few feet of the Fairport; therefore, one can infer equivalence of these strata to the zone of T. lata. I. latus ranges upward through the rest of the Fairport Member and through the Blue Hill Member of the Carlile. These strata can probably be correlated with at least the lower part of the H. planus zone of the Middle Chalk. Local limestone at the top of the Codell in Hamilton County is judged to be of early late Turonian age and is correlative with some part of the H. planus zone of the English Middle Chalk in which species of Prionocyclus are common. Because C. woollgari is found throughout the Fairport of Kansas, including the lower part of the range of I. latus, its stratigraphic distribution is seemingly greater than in England, where C. woollgari is restricted to the T. lata zone, as pointed out above.

8. The Fairport sediments accumulated slowly in clear water of normal salinity, far from shore, and mostly below the depth of normal wave activity. Lenses of calcarenite and overturned specimens of Inoceramus cuvieri attest to sporadic, severe wave agitation of the bottom sediments. Blue Hill and Codell sediments were laid down more rapidly than the Fairport, in turbid waters of normal or nearly normal salinity, closer to shore than the Fairport, and mostly below the depth of normal turbulence. Local gently cross laminated sandstone and siltstone, a few lenses of pelecypod valves, a fish-tooth conglomerate, and a few clay pebbles are evidence of occasional current or wave activity. Ripple marks at a single locality indicate that the water was very shallow locally.

9. The Carlile Shale of Kansas is mostly the regressional part of a sequence of strata deposited during the first cycle of Late Cretaceous sedimentation in the Western Interior region. The cycle comprises seven phases, the first and the last being sandstone, chalky strata representing the phase of maximum transgression. Lowermost Fairport beds are identical to those of the upper part of the Greenhorn and were deposited during maximum transgression of the sea. Higher Fairport strata reflect the beginning of widespread regression. Increased turbidity during Blue Hill deposition brought carbonate sedimentation to a close and caused virtual disappearance of the epizoal benthos. Continued regression brought a flood of coarse silt and fine sand to the Kansas area as upper beds of the Blue Hill and the Codell were laid down.

10. The diastem that separates Carlile from Niobrara strata resulted from a prolonged interval of nondeposition, probably accompanied by at least some sublevation. The second Late Cretaceous sedimentary cycle had reached the phase of maximum transgression before sediments again began to accumulate on the sea floor.

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Kansas Geological Survey, Geology
Placed on web March 11, 2010; originally published May 1962.
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