Current Research--Aber--page 13 of 15

Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 240, part 3
Chert Gravel and Neogene Drainage in East-central Kansas--page 13 of 15

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(INTERPRETATION OF ANCIENT DRAINAGES, continued)

Drainage Diversions

The ancestral drainage routes were altered through a series of stream captures. The ancestral Arkansas was diverted in two stages, first into the Walnut River, and later to the modern Arkansas River south of Wichita (Aber, 1992). The ancestral Verdigris was likewise captured in at least two locations, and portions were diverted into the modern Verdigris River in northeastern Greenwood County and the South Fork Cottonwood River in southern Chase County (fig. 13). The upper portion of the ancestral Neosho and parts of the upper ancestral Marais des Cygnes were also involved with stream captures and drainage shifts. The ages of these (and other) captures are unknown. Thus, it remains impossible to reconstruct the exact sequence and timing of various drainage diversions in eastern Kansas.

Fig. 13. Landsat multispectral scanner (MSS) image of central Flint Hills region in southern Chase, northwestern Greenwood, and northeastern Butler counties. Standard false-color composite, in which active vegetation appears pink and red. Vegetation is active within valleys, and Flint Hills uplands appear in green-orange colors in this autumn image from a drought year.

The abrupt change in direction of the upper North Branch Verdigris River is one of the most prominent drainage anomalies in Kansas. This anomaly is presumably a result of stream capture by the South Fork Cottonwood of the ancestral Verdigris. Note the alignment of headwaters for the North Branch Verdigris River and East Branch Fall River valleys. These two valleys are part of the Verdigris lineament trend at about 350° (Aber et al., 1997). Digital Landsat MSS data obtained from the EROS Data Center, U.S. Geological Survey.

Neotectonic Implications

During valley entrenchment, west-east rivers have migrated southward, and north-south streams have shifted eastward across nearly all parts of eastern Kansas. Valley asymmetry is highly systematic across a broad geographic region. This pattern is manifested both in the distribution of older upland gravel as well as by lower terraces and bedrock bluffs within modern valleys. These valley patterns are true for different hydrologic or geologic factors for individual rivers. Valley asymmetry is consistent regardless of direction or gradient of stream flow, valley width or depth, volume of discharge, channel bed or bank characteristics, or bedrock in the drainage basin. Only a few, local exceptions to the general pattern for valley asymmetry are known, such as the lower Walnut River and parts of the lower Fall and Verdigris rivers in the southernmost part of the study region.

This pattern of valley asymmetry has been noted before and several explanations considered (Aber, 1985), including Coriolis force, unequal input of sediment from tributary streams, and crustal tilting. Of these possibilities, it seems that slow, continuing crustal warping downward to the south and east toward the Gulf of Mexico is the only viable explanation on a regional basis (Aber, 1990). Local exceptions may result from differential movements in basement structures. However, crustal tilting and local structural movements remain impossible to verify through independent evidence. If such crustal tilting has occurred, it would have the effect of increasing gradients for streams that drain toward the south or southeast. Those streams, thus, would have an erosive advantage during dissection of the landscape. This may explain the predominance of drainage captures by streams flowing toward the south or southeast. It could also explain why northwest-trending valleys are so prominent in the modern landscape.

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Kansas Geological Survey
Web version March 18, 1998
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