Skip to Main Content

Lower Cretaceous strata of Kansas are divisible into two unconformity-bound stratigraphic sequences that are overlain by a third sequence of Upper Cretaceous age. The sequences were deposited on the eastern shelf of the Western Interior foreland basin and are equivalent to sequences defined by Weimer (1984) in the center of the basin in Colorado. The bounding unconformities are present throughout the outcrop belt of central Kansas, and are contiguous with the ones at the bases of the Plainview Formation, J Sandstone, and D Sandstone, respectively, of the Denver basin.

A basal Cretaceous sequence consisting of the Lytle Formation of Colorado (informally “Cheyenne Sandstone” of southern Colorado) is restricted to extreme northwest Kansas and is not detailed in this study. The lower sequence of Kansas onlaps this basal Cretaceous sequence and progressively oversteps it to the east. This sequences also onlaps and oversteps Jurassic and Permian strata from west to east. Internally it consists of landward-stepping progradational events of fluvial and nearshore siliciclastics succeeded by open-marine shale. Included in the sequence are the Cheyenne Sandstone (formal) of Kansas (fluvial), the Longford Member of the Kiowa Formation (nearshore), and the Kiowa Formation (marine). Strata deposited during a relative sea-level fall at the top of the sequence are present in Colorado but were mostly removed by erosion in Kansas prior to deposition of the second sequence.

The second sequence comprises strata between the unconformity at the top of the Kiowa Formation to the unconformity within the middle of the Dakota Formation of Kansas. It also is composed of landward-stepping progradational events of fluvial and nearshore siliciclastics succeeded by marine shale. Fluvial deposits dominate the sequence in central Kansas, and merge through facies transitions with nearshore and marine strata in western Kansas and eastern Colorado. Included in the sequence are the lower half of the Dakota Formation (fluvial), J Sandstone (fluvial and nearshore), and Huntsman Shale (marine). Strata deposited during a relative sea-level fall at the top of the sequence are present in the subsurface of western Kansas but were removed by erosion prior to deposition of the upper half of the Dakota Formation.

The unconformity at the top of the second sequence is the onlap surface and basal bounding unconformity of a third sequence that extends upsection to an unconformity at the Codell Sandstone. As in the two underlying sequences, basal strata of this sequence (D Sandstone) occur in landward-stepping progradational events. This unconformity is distinguished in central Kansas outcrops at the base of a laterally continuous conglomeratic sandstone that represents a seaward shift in facies from meandering to braided stream deposits. The lower unconformity of this sequence is reported as Upper Cretaceous age in eastern Colorado. Therefore the upper one-half of the Dakota Formation in Kansas, including all of the Janssen Clay Member and the upper part of the Terra Cotta Clay Member, is Upper Cretaceous.

You do not currently have access to this chapter.

Figures & Tables

Contents

References

Related

Citing Books via

Related Book Content
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal