Current Research--Aber--page 10 of 15

Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 240, part 3
Chert Gravel and Neogene Drainage in East-central Kansas--page 10 of 15

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(REGIONAL DISTRIBUTION OF UPLAND CHERT GRAVEL, continued)

Neosho Drainage Basin

Chert gravels occur in several portions and topographic positions within the Neosho River basin (figs. 2, 8). These are described beginning with upstream portions.

Kahola Creek valley. High-terrace gravels are preserved along the northern side of a small east-flowing tributary of the Neosho in the southeastern corner of Morris County. These gravels contain no exotic pebbles, and the creek is cutting bedrock bluffs on the southern valley side.

Middle Neosho River valley. Nearly continuous trend of chert gravel is present on high terraces and hilltops along the northeastern side of the valley in Lyon and Coffey counties. Gravel elevations range from 10 m to 50 m (33-160 ft) above the adjacent floodplain. These gravels contain occasional sandstone and petrified wood along with relatively common exotic pebbles.

Southwestern Coffey County. Broad upland distribution of chert gravel is found on high terraces and local divides west of the Neosho valley. Exotic pebbles are common.

Anderson and northwestern Allen counties. Chert gravel is preserved in the vicinity of the Missouri-Arkansas drainage divide in central Anderson County at elevations of 350-360 m (1,150-1,180 ft) (fig. 10). These gravels are remarkable for the high degree of chert-pebble roundness and for the abundance of exotic pebbles. The chert gravels extend on hilltops as a broad belt from the divide downward to the southwest. This gravel belt merges with the high-terrace trend along the northeastern side of the Neosho valley at an elevation of about 310-320 m (1,020-1,050 ft).

Fig. 10. Neosho chert gravel deposits. Digital elevation model for parts of Anderson, Coffey, Woodson, and Allen counties. Detailed distribution of upland chert gravel (Olpe soil) outlined in black; elevation classes shown by color coding. Model has 90 m (300 ft) resolution; derived and corrected from DEM-24K; UTM coordinate system. Digital elevation model obtained from the Kansas Geological Survey--DASC. Image processing by R. Byerley and N. Wilkins.

Lower Neosho River valley. Chert gravels occur along the western side of the valley in Woodson, Allen, and Neosho counties. High terraces are adjacent to and 10-20 m (33-66 ft) above the modern floodplain, whereas hilltop gravels form a discontinuous belt 30-40 m (100-130 ft) above and 6-8 km (3.7-5 mi) west of the valley. Exotic pebbles are found in both high-terrace and hilltop deposits.

Marais des Cygnes Drainage Basin

Well-defined belts of high-terrace and hilltop gravels are found along the northern margins of Marais des Cygnes River valley and tributaries in Osage and northeastern Lyon counties (figs. 2, 8). Gravel elevations range from 10 m to 40 m (33-130 ft) above adjacent floodplains. Exotic pebbles are not present in any gravels along the main Marais des Cygnes trend; however, a few exotics have been found in chert gravels on the Wakarusa-Marais des Cygnes divide in northwestern Osage County.

Verdigris Drainage Basin

Upland chert gravel is abundant in upper portions of the basin in southern Lyon and northeastern Greenwood counties (figs. 2, 8). Gravels are found north of the Verdigris valley and on the divide between the Verdigris and the Neosho and Cottonwood basins. Drainage-divide sites are as much as 80 m (260 ft) above and 6 km (3.7 mi) away from the Verdigris floodplain in northeastern Greenwood County. Exotic pebbles are common in these gravels.

In northeastern Greenwood County, the Verdigris River turns toward the south-southeast. Along most of this stretch, chert gravels bearing exotics are found west of the valley, and gravel occurs east of the valley in a few places. Near the junction with the Fall River, chert gravel caps the drainage divide between the two basins. Exotics are also found as isolated pebbles resting on bedrock terrain across north-central Greenwood County.

Fall Drainage Basin

Chert gravel deposits are preserved along much of the Fall River system (figs. 2, 8). Gravel elevations are highest in the headwaters of the Flint Hills at 440 m (1,440 ft), and lowest elevations are 250 m (820 ft) near the junction with the Verdigris River. For the most part, chert gravel is preserved on northern sides of the Fall River valley and its tributaries in Greenwood County. Downstream from Fall River Reservoir, gravel is found on both sides of the valley, and gravel is preserved south of the Fall River valley in southern Wilson County.

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Kansas Geological Survey
Web version March 18, 1998
http://www.kgs.ku.edu/Current/1997/aber/aber10.html
email:lbrosius@kgs.ku.edu