Geology(The stratigraphic nomenclature used in this report is that of the State Geological Survey of Kansas and differs in some respects from that of the United States Geological Survey)
Unconsolidated deposits of Pleistocene age form the surficial material in most of Jefferson County (pl. 1). In the upland areas, the unconsolidated material is glacial drift mantled almost everywhere by eolian deposits. Alluvial deposits underlie the flood plains in the valleys and colluvium generally mantles the valley slopes. Bedrock of Pennsylvanian age crops out in sharp ridges and along bluffs and steep valley walls, especially in the western part of the county bordering the Delaware River valley and in the southern part of the county bordering the Kansas River valley. The Pennsylvanian rocks generally dip gently west-northwestward at about 15 feet per mile.
Pennsylvanian SystemThe Lawrence Formation of the Douglas Group is the oldest formation exposed; it crops out in the southeastern part of Jefferson County near the Kansas River valley. Rocks of the Shawnee Group overlie the Douglas Group (table 1) and are exposed in the southern, central, and eastern parts of the county. Rocks of the Wabaunsee Group overlie the rocks of the Shawnee Group and crop out in the central and western parts of the county. The Willard Shale of the Wabaunsee Group is the youngest formation of Pennsylvanian age that crops out in the county; it underlies glacial drift in the uplands in the northwestern part of the area. The stratigraphic relationship of the bedrock units is shown on the geologic section (pl. 1).
Bedrock SurfaceThe present configuration of the bedrock surface has resulted from subaerial erosion before Pleistocene time, erosion caused by the advance of continental glaciers into northeastern Kansas during Nebraskan and Kansan time, and development of Pleistocene interstadial and present drainage systems. The present drainage system generally has developed along courses coincident with those of a previous drainage system or systems. Present streams generally flow on the bedrock or on unconsolidated deposits just above the bedrock. Except in the upland area in the northeastern part of the county, the unconsolidated deposits generally are less than 50 feet thick.
Pleistocene SeriesContinental ice sheets advanced into northeastern Kansas during the Nebraskan and Kansan Stages of the Pleistocene Epoch. Nebraskan till has not been recognized in surface exposures in the county. However, a dense pebble-bearing clay overlying the bedrock that was penetrated by deep test holes in the vicinity of Nortonville may be Nebraskan till. The clay was either directly on the bedrock or above thin intervening glaciofluvial deposits of sand and gravel.
Kansan till overlies bedrock, or the till of possible Nebraskan age, everywhere in the upland part of the county. The Kansan till contains glacial erratics composed of principally pink quartzite, but pebbles and cobbles of igneous rock are common. Two or more zones of pebble-bearing clay interbedded with fine to medium glaciofluvial material were penetrated by test holes in the vicinity of Nortonville; these clays are also believed to be Kansan till. In areas where the till is thin and the topography reflects the bedrock surface, the bedrock formations are shown on the geologic map (pl. 1).
In the upland area in the north-central part of the county, the Kansan till is overlain by the "Nortonville clay." Frye and Leonard (1952, p. 81) suggest that this silty clay may have been "... deposited in slight initial depressions on the surface of the newly formed Kansan till plain as the Kansan ice front retreated..."
Loess underlies most of the upland areas in Jefferson County. It is principally of Wisconsinan age, but studies by James Thorp and others (unpublished material in the files of the State Geological Survey of Kansas) indicate that some of the loess is of Illinoisan age. The loess may be as much as 20 feet thick in the northern part of the county, but thins and becomes discontinuous southward. Where soils have developed on loess, the surface is virtually free of pebbles.
Terrace deposits are found principally in the Kansas and Delaware River valleys. The Newman terrace of late Wisconsinan age (Davis and Carlson, 1952) is a major topographic feature in the Kansas River valley. The material beneath the Newman terrace generally grades from clay and silt at the surface to coarse sand and gravel overlying the bedrock. These deposits generally increase in grain size and thickness with increasing distance from the valley wall. Dissected and weathered remnants of terrace deposits of Kansan, Illinoisan, and Wisconsinan age locally border the bluffs along the Kansas and Delaware River valleys.
Alluvium of Recent age is found in all the valleys. In the Kansas and Delaware River valleys, the material grades from clay and silt at the surface to coarse sand and gravel overlying the bedrock. In some areas, the material in abandoned meanders is clay. Alluvium in the smaller valleys generally is finer grained than in the two principal valleys.
Kansas Geological Survey, Jefferson County Geohydrology|
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Web version July 2002. Original publication date Dec. 1972.