This stop is the emergency spillway of the Tuttle Creek Reservoir.  This site is under the jurisdiction of the U.S. Army Corps of Engineers and collection of in-situ geological samples is by permit only. During the midwest floods of 1993, water was released over this spillway at rates as high as 60,000 cfs.  This water flow extensively eroded the spillway, and resulted in fresh, unweathered exposures.  These exposures provided an unprecedented opportunity to examine bedding plane  surfaces and paleosol profiles over broad areas.  Much of the upper part of the spillway has been subsequently covered, but good exposures remain along the spillway walls.  The spillway exposes the stratigraphic interval from near the base of the Hughes Creek Mbr. of the Foraker Limestone, to the top of the Neva Limestone Mbr. of the Grenola Limestone.  A detailed description of this interval is available from the Kansas Survey (Miller, 1994).  

Figure 16. Exposure of the Bennet Shale Member and the Howe Limestone Member of the Red Eagle Limestone at the Tuttle Creek Spillway. The black Bennet Shale contains abundant orbiculid inarticulate brachiopods and shark teeth. The base of the Bennet and top of the Glenrock Limestone Member marks the base of the Permian.

    The spillway provides an excellent exposure of the newly-recognized Pennsylvanian-Permian boundary (Fig. 16). Recent conodont work (Ritter, 1995) has placed the boundary at the top of the Glenrock Limestone Member of the Red Eagle Limestone. The stratigraphic sequence of conodont species in Kansas was found to be the same as that across the type boundary in Russia. This boundary placement was subsequently confirmed by the decision of the International Subcommission on Permian Stratigraphy to formally propose the first occurrence of the "isolated-nodular" morphotype of Streptognathus "wabaunsensis" as the base of the Permian System . The Virgilian/ Wolfcampian boundary of the midcontinent section is thus now precisely defined as the top of the Glenrock.

    Underlying the Red Eagle Limestone is the Johnson Shale. This yellowish gray mudstone interval is noteworthy in that it displays an excellent example of a natric paleosol profile (Fig. 17). As mentioned above, these paleosols are characterized by a distinctive pedogenic structure called columnar peds. Natric horizons are suggestive of highly evaporitic environments and are commonly associated with coastal settings. This interpretation is supported by the presence of replaced evaporitic nodules, tepee structures and a low-diversity restricted mollusk fauna in the underlying units. A detailed description of the Johnson Shale paleosol profile can be found in McCahon and Miller (1997).

Figure 17. Johnson Shale displaying the characteristic columnar ped structure of natric, or sodium-influenced, soil formation.

    At the base of the Roca Shale, on the top surface of the underlying Howe Limestone Member of the Red Eagle, a surface covered by algal stromatolites (Fig. 18) was exposed following the ’93 flood. Although this bedding plane exposure of stromatolites has subsequently been destroyed, stromatolites can still be found on the cut sides of the spillway. The ’93 flood also formed exceptional three-dimensional exposures of the paleosol profiles of the overlying Roca Shale. The lower red-and-green variegated profiles contained extensive pedogenic carbonate in the form of both nodules and rhizocretions (carbonate precipitated around roots) (Fig. 19). The upper greenish-gray paleosol displayed the characteristic undulatory pseudoanticlines or gilgai of modern Vertisols (Fig. 20). These bowl-shaped undulatory surfaces were complete with clay-coated and slickensided surfaces. Detailed descriptions of these Roca paleosols are given in Miller and others (1996).

Figure 18. Stromatolite-covered surface at the top of the Howe Limestone Member. Desiccation cracks are common the shales that immediately overlie this stromatolitic layer.

Figure 19. Lower Roca Shale calcic paleosol profile displaying the abundant caliche nodules and calcareous rhizocretions characteristic of semi-arid climates.

Figure 20. Exceptional exposures of vertic paleosols in the upper part of the Roca Shale. The upper image shows the undulatory surfaces, called gilgae, typical of Vertisols. The lower image illustrates the striated and clay-coated slickensides formed by the repeated expansion and contraction of the soil in monsoonal climates.


    Roadcuts on Seth Childs Blvd. north of Manhattan provide good exposures of the Matfield Shale and the terrace-capping Florence Limestone.

    The Wymore Shale Mbr. at the base of the Matfield displays very well-developed polygenetic paleosols. This unit again illustrates the repeated pattern of red and green variegated calcic paleosols being overlain by greenish-gray vertic profiles (Fig. 21).

    The Blue Springs Shale Mbr. at the top of the Matfield consists largely of a stacked series of paleosol profiles giving a "barber pole" appearance to the outcrop (Fig. 22). These paleosols have well-developed pedogenic structures in their lower parts but are capped by massive rooted siltstone layers. As discussed above, the silts in these paleosols may have had an eolian origin, accumulated during drier climates phases near the end of paleosol formation.

Figure 21. The Wymore Shale showing the transition from mottled and calcium carbonate-rich paleosols at the base and greenish gray vertic paleosols at the top.

Figure 22. Exposure of Blue Spring Shale on Seth Childs Blvd showing gray shales at base and stacked paleosols at the top overlain by the Florence Limestone. The photo below shows the stacked paleosols with caps of rooted siltstone of possible eolian origin.


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