Introduction

Bedrock stratigraphy of the Flint Hills region, east-central Kansas. The Admire Group is considered upper Pennsylvanian; the Council Grove and Chase groups are lower Permian (Baars et al. 1994). Chart adapted from Kansas Geological Survey (1997).

Stone line formed by the Crouse Limestone in the vicinity of the "cattle pens" exit on the Kansas Turnpike (I-35), southeastern Chase County. Photo date 9/95, © J.S. Aber.

The Florence Limestone forms the resistant cap along much of the escarpment. However, in eastern Chase County the Florence has been removed by erosion, and the Wreford Limestone forms the escarpment crest. Residual chert from the Florence and Wreford often drapes over underlying shale and limestone formations. The Chase Group is the surficial bedrock for most of Butler and western Chase counties west of the Flint Hills escarpment. Although the landscape is generally less rugged, intricate outcrop patterns have resulted from stream dissection, and outliers of resistant bedrock units form small hills--Figure 5.

6. Limestone: tan to gray, platy to massive, fossiliferous limestone, chalky limestone, or dolomitic limestone; cross bedding, oolites, and ripple marks common; locally cherty toward base with algal bed toward top; diverse fossils. Examples: Morrill, Funston, Schroyer, Fort Riley, Cresswell, Herington. Environment: offshore regressive sea to shallow, high-salinity, lagoon.

5. Shale: gray or green, fissile to platy, calcareous, fossiliferous shale or shaly limestone; diverse fossils including trilobites. Examples: Florena, Havensville. Environment: farthest offshore sea of maximum transgression.

4. Cherty limestone: tan or light gray, platy to massive, fossiliferous limestone or chalky limestone; scarce to abundant nodules or beds of chert; locally may display algal banding or cross bedding; diverse fossils including many echinoids and fusulinids. Examples: Neva, Cottonwood, Crouse, Threemile, Florence, Stovall. Environment: far offshore, shallow sea of near-maximum transgression.

Florence Limestone exposed along K-96 highway in southeastern Butler County. Light gray chert beds and nodules are conspicuous within the limestone. Scale pole marked in feet. Photo date 10/89, © J.S. Aber.

3. Shale: gray, tan or green, platy, fossiliferous, calcareous shale and shaly limestone; abundant brachiopod and mollusk fossils. Examples: upper Eskridge, upper Easly Creek, upper Speiser, upper Wymore, upper Gage. Environment: shallow, normal salinity, transgressive sea.

2. Limestone: one or more, thin, gray or tan, chalky or coquina, fossiliferous limestones; abundant brachiopods and mollusks. Examples: middle Eskridge, middle Speiser. Environment: shallow to estuarine, low-salinity sea.

Students examine the Eskridge Shale in the spillway at Lake Kahola, KS. The fall is formed by the "middle" limestone within the Eskridge Shale. Blocks of the Cottonwood Limestone rest on top of the fall. Photo date 10/81, © J.S. Aber.

1. Shale: platy, somewhat calcareous, maroon or red shale above green and black shale; generally few fossils, black shale has inarticulate brachiopods, maroon shale lacks marine fossils. Examples: lower Eskridge, lower Speiser, lower Wymore, lower Gage. Environment: lagoon or estuarine (green or black) to emergent (maroon) tidal flat or sabhka.

Students examine the red shale zone below the middle limestone bed in the Eskridge Shale in the spillway at Lake Kahola, KS. Photo date 10/89, © J.S. Aber.

The bedrock stratigraphy has remarkable lateral consistency--Figure 7; unit thickness varies little, and only a few noticeable facies changes are present. Slight thinning of bedrock strata occurs in the central portion of Butler County over the crest of the Nemaha Uplift. Many limestone units show evidence of deposition in very shallow water across this area. Typical sedimentary structures include cross bedding, ripple marks, oolites, and algal laminations. Such features are present in limestone units from the Cottonwood up through the Fort Riley. This region is part of what Imbrie et al. (1964) named the Greenwood Shoal of the early Permian sea.

	Cottonwood Limestone cross-laminated, algal facies indicative of shallow water of the Greenwood Shoal, eastern Butler County. Photo date 7/90, © J.S. Aber.
	Morrill Limestone ripple marks indicative of shallow water of the Greenwood Shoal, eastern Butler County. Photo date 7/89, © J.S. Aber.
	Ft. Riley Limestone cross-bedded, oolitic facies indicative of shallow water of the Greenwood Shoal, central Butler County. Photo date 7/90, © J.S. Aber.

Lower Permian cyclothems are similar to Upper Pennsylvanian cyclothems of eastern Kansas (Klein and Willard 1989); each cyclothem includes a triad of limestone-shale-limestone (units 4, 5 and 6) and represents mainly marine sedimentation. Lithologies of individual units within Lower Permian cyclothems differ considerably, however, from Upper Pennsylvanian cyclothems. Red beds, cherty limestone, dolomite, and evaporites (subsurface) are common in Lower Permian strata; whereas coal, sandstone, and black shale are scarce to absent. The lithologic differences between Upper Pennsylvanian and Lower Permian cyclothems are thought to reflect a combination of factors during early Permian time (Aber 1991).

• Increasing aridity of the climate.
  
• Decreasing supply of clastic sediment.
  
• Decreasing amplitude of transgressive/regressive cycles.

	Red and maroon colored strata of the Gage Shale, central Butler County. The small fold is likely the result of collapse following subsurface solution of evaporites. The red beds represent an arid, terrestrial sedimentary environment, Photo date 1/91, © J.S. Aber.
	Herington Limestone, northwestern Butler County. This rock is dolomitic, chalky limestone with numerous quartz concretions. It indicates arid conditions of shallow marine sedimentation. Photo date 6/90, © J.S. Aber.

Many explanations for Pennsylvanian and Permian cyclothems of the midcontinent have been proposed. These explanations generally fall into three categories--crustal movements, glacio-eustatic sea-level changes, and delta-lobe shifting. The Lower Permian cyclothems of the Flint Hills do not contain features associated with deltaic sedimentation (i.e. channel sandstone), and the remarkable lateral consistency of units argues against significant local crustal movements during the early Permian (Moore 1964). The most reasonable explanation for repeated marine transgressions and regressions is glacioeustasy related to glaciation in Gondwana (Aber 1991).

Fold structures--anticlines and synclines--are present in surficial bedrock in many parts of Butler and Chase counties--Figure 8 and Table 1 (below). In most cases, anticlines and synclines occur in closely matched pairs, but this is not true in all situations. Basement control of structures in surficial bedrock of the midcontinent was recognized long ago by Fath (1921, p. 149), who stated that these structures are "in large part the surface expression of deep-seated readjustments along ancient faults or lines of weakness present in the pre-Cambrian basement rocks of the region."

Table 1. Surficial anticlines and synclines of Butler County, Kansas. See Fig. 8 for locations.

Structure	Associated Oil Field or River
1. Blankinship Anticline	Blankinship, Young.
2. Beaumont Anticline	Ferrel, Ferrel South, Shinn, Shinn NE, Wehrman.
3. Grouse Syncline	Grouse Creek.
4. Latham Syncline	none.
5. Brant Anticline	Brant-Sensenbaugh.
6. Eagle Syncline	Eagle Creek.
7. Cole Syncline	Cole Creek.
8. Burns Dome	oil field.
9. DeGraff Anticline	none.
10. Walnut Syncline	Walnut River and West Branch Walnut River.
11. Dunkle Syncline	unnamed stream.
12. El Dorado Anticline	El Dorado.
13. Hammond-Fowler Syncline	none.
14. Pierce Anticline	Pierce.
15. Shumway Anticline	El Dorado.
16. Augusta North Anticline	Augusta North.
17. Augusta Syncline	Walnut River.
18. Augusta South Anticline	Augusta.
19. Gordon Syncline	none.
20. Douglass Anticline	oil field.
21. Salter Syncline	none.
22. Rose Hill Anticline	oil field.
23. Seltzer Syncline	Seltzer Spring.

Surficial folds of Butler County are located above major uplifts in the basement surface. Folds in the western portion of the county are associated with the Nemaha Uplift, which is bounded on its eastern side by the buried Humboldt Fault--Figure 8. The basement surface is offset by several 100 feet to more than 1000 feet (300 m) along the fault zone (Bickford et al. 1979). Local culminations on the Nemaha Uplift correspond to the Burns, El Dorado, and Augusta-Douglass regions of surficial folding. Surficial folds in the southeastern portion of Butler County are located above a more subtle uplift in the basement surface.

Joints are ubiquitous in bedrock of the Flint Hills. Joint measurements show that at most sites two sets of joints are present--Figure 9. Some sites have three joint sets, a few sites have only one set of visible joints. The two dominant joint sets (1 and 2) are complementary (around 90° angle) and are found at most sites. Joint set 1 is widely present throughout eastern Kansas, at nearly all sites. It parallels the Fredonia tectonic zone and the Silver City-Rose Dome tectonic zone, which trend about 50° (Berendsen and Blair 1991). Joints sets 2 and 3 are related to well-known basement structures. Joint set 2 is parallel to numerous northwest-trending basement faults found throughout eastern Kansas--the Neosho and Fall River trends. Joint set 3 corresponds to the buried Humboldt Fault zone.

	Joints in Ft. Riley Limestone at the Augusta city lake, Butler County. This joint set trends 325°. Photo date 11/90, © J.S. Aber.
	Thrust fault exposed in roadcut along U.S. highway 54 west of Augusta, Kansas. The band of shale marks the thrust within the Ft. Riley Limestone. Scale pole marked in feet. Photo date 2/91, © J.S. Aber.

Faults are relatively rare in surficial rocks of Chase and Butler counties. Both normal and thrust faults are present in a few localities in association with anticlines. This pattern suggests that faulting occurred in connection with layer-parallel folding of brittle rocks--Figure 10. For example, a thrust fault is exposed along U.S. highway 54-77 on the western flank of the Augusta North anticline (see fig. 8). The fault cuts through the Ft. Riley Formation, which here strikes/dips 160°/10°SW. The thrust fault strikes/dips 170°/20°SW and has an estimated throw of 20 feet. This site displays the greatest amount of structural disturbance seen at the surface anywhere in Butler County.