Eastward from the Flint Hills, chert gravel deposits attain higher relative positions in the local topography. This trend culminates in Anderson County, where chert gravel is preserved on the Missouri-Arkansas drainage divide, up to 75 m (250 ft) above adjacent floodplains. Frye (1955) concluded that these highest gravels mark an early river system that crossed in an easterly direction what is now a major drainage divide and joined with streams in the Ozark region of Missouri. In an earlier paper, I used the name Old Osage River to refer to this supposed through-drainage route to the east (Aber, 1985).
The ages of the chert gravel deposits can be estimated only on the basis of topographic positions above modern floodplains and degree of soil development. The deposits consist of insoluble siliceous minerals; all soluble components have been removed by prolonged weathering. Thus, appropriate fossils or materials suitable for dating are not preserved. Most geologists have agreed upon Neogene (Miocene or Pliocene) age for upland chert gravels, and these gravels are classified as Tertiary on state and county geologic maps (Aber, 1993). Frye (1955) considered that the oldest chert gravels date from the early Tertiary (Paleogene). I previously designated upland chert gravels within the Walnut drainage basin as the Leon Gravel, a lithostratigraphic unit of formation rank (Aber, 1992). However, similar chert gravel deposits in other basins have not received any formal stratigraphic recognition.
Exotic pebbles of quartzite were noted in upland chert gravels by some early investigators (see Mudge, 1875; Wooster, 1934), who thought the exotics had been washed into the region by glacial meltwater. Some later geologists, however, overlooked the existence of exotic pebbles or discounted their importance. Frye and Leonard (1952, p. 181-184), for example, stated that ". . . the late Tertiary sediments in the eastern one-fourth of Kansas are entirely attributable to the Permian and Pennsylvanian rocks eastward from and including the Herington Limestone." They concluded that "some time during the Tertiary the Flint Hills became a major drainage divide separating two strongly contrasting depositional provinces" (Frye and Leonard, 1952, p. 184). This interpretation was repeated in other reconstructions of Kansas drainage development. Seevers and Jungmann (1963) suggested, in contrast, that Neogene drainage from central Kansas did cross the Flint Hills and transported quartzose materials derived from Cretaceous source strata into eastern Kansas.
Kansas Geological Survey
Web version March 18, 1998