Overlying the Pennsylvanian rocks is extensive unconsolidated material deposited by streams, glacial ice, wind, and slope wash. Stream-laid deposits occur as terraces or as alluvium along all major streams and their tributaries. Glacial drift, chiefly till and melt-water sediments, covers much of the mapped area, Because the till and melt-water sediments (glacial outwash) are poorly exposed, these deposits were not mapped separately. Eolian loess mantles many stream divides. Because the loess is generally thin and poorly exposed, it was included in mapping with either the glacial drift or the underlying Pennsylvanian rocks. About 10 feet of loess is exposed in a railroad cut just north of Tecumseh, where it overlies silts and gravels of Illinoian age (Davis and Carlson, 1952, p. 228). Colluvial deposits--principally clay, silt, and very fine sand--occur over much of the area; however, they are generally too thin to map and were included with the underlying bedrock or the glacial drift. In many valleys, colluvium has accumulated on stream terraces at the base of valley walls, and these deposits have markedly modified the terrace forms. No contact is evident between the colluval and terrace deposits, so the colluvium was included with the terrace matedal when mapped.
Chert gravel--In late Tertiary or early Pleistocene time, chert gravel derived from the west--primarily from the Wreford and Barneston Limestones of Early Permian age--was deposited in the valleys of the Kansas and Wakarusa Rivers. Subsequent erosion has left remnants of these deposits topographically isolated high above the present flood plains. During the Pleistocene Kansan Glaciation, ice overrode most deposits and incorporated the chert gravel in the till and glacial outwash. The few deposits remaining in eastern Shwwnee County and vicinity are too small to be indicated on the geologic map.
The deposit in an old gravel pit in the SW NE sec. 18, T. 11 S., R. 17 E., is composed of subangular to sub rounded granules and pebbles of light-gray and pale-yellowish-brown chert and light-yellowish-gray and dark-brown limestone in a matrix of moderately cemented light-yellowish-gray to medium-gray fine to medium quartz sand. A few limestone pebbles as much as 0.25 foot long also occur in the deposit. The best exposure of chert gravel is in an old pit in the NW NW sec. 7, T. 11 S., R. 16 E., where chert comprises over 98 percent of the deposit and no glacial erratics are present (Davis, 1951, table 3), Chert gravel is scatttered on the ridge in the south-central part of sec. 23, T. 13 S., R. 15 E., and on the interstream divide in the SE sec. 29, T. 13 S., R. 17 E, Looally, as in a roadcut in the SE cor, sec. 23, T. 13 S., R. 16 E., a thin layer of moderate-yellowish-brown subangular to subrounded chert gravel underlies the till.
In early Pleistocene time the main drainage in eastern Shawnee County and vicinity was to the east, virtually as it is at the present time, During part of the Kansan Glaciation, almost all the area was occupied by ice that caused major temporary changes in the drainage pattern. The Kansas River was dammed at St. George, Pottawatomie County (Mudge and Burton, 1959, p. 10), and from there was diverted. southeastward through a series of channels across northern Wabaunsee County and into the North Branch Wakarusa River in western Shawnee County. From there the water flowed by way of the Wakarusa River back into the Kansas River east of Lawrence.
The southern limit of the ice advance was at the Wakarusa River. Ice possibly did not override the east-facing escarpment formed by the Bern Limestone in the southwestern part of the area, for no glacial debris was found there. The ice front was established along a line extending from Shunganunga Creek, on the west side of the area, southeastward through Pauline and along Lynn Creek, to the north side of the Wakarusa River. A terminal moraine was deposited from Shunganunga Creek to near Pauline; elsewhere, melt water from the ice sheet laid down thick deposits of glacial outwash. After the withdrawal of the ice north of the Kansas River valley, the river resumed, in general, its previous course, and its major tributaries reoccupied their old valleys. Diversion channels are evident at several places where melt water from the retreating glacier spilled over stream divides or interfluves. Melt water flowed southward through a diversion channel in the E2 sec. 33, T. 9 S., R. 17 E., into the drainage basin of Rock Creek; a temporary channel, possibly through Meriden, may have connected Rock and Muddy Creeks. Certainly other diversion channels existed but have since been destroyed or so modified by erosion that they were not recognized.
The glacial drift ranges markedly in thickness in eastern Shawnee County and vicinity, It is thickest in the slopes north of the Kansas River. Test holes drilled in the SE sec. 9 and in the E2 sec. 10, T. 11 S., R. 15 E., penetrated 32-76 feet of stratified clay, sand, pebbles, and boulders. On the uplands south of the river, the drift (which is chiefly till) ranges from a very thin veneer to about 20 feet in thickness and probably averages less than 10 feet thick. A test hole drilled about 1 mile east of the area penetrated 48 feet of drift (O'Connor, 1960, p. 142), Near the Wakarusa River the glacial-outwash deposits are locally as much as 25 feet thick.
The glacial drift is predominantly unstratified unsorted till but includes, particularly in the terminal area, deposits of stratified glacial outwash. Because the till and outwash are poorly exposed, they were not differentiated, and in many localities it was difficult to identify the glacial drift beneath the mantle of loess and soil. Consequently, the identification of glacial drift depended largely on the presence of erratics. The distribution of glacial drift shown on the geologic map (pl. 1) probably represents the minimum rather than the maximum extent, because many small areas covered by a thin veneer of drift probably were not mapped.
The till is composed principally of clay, but rock particles of silt, sand, granule, pebble, cobble, and boulder size are also abundant. Most of the till was derived from claystones and limestones that crop out in this part of Kansas, and only a small amount of the till is composed of rock fragments moved there from the northern part of the country, Most fragments of pebble size or larger are limestone, but some are igneous or metamorphic rock, chert, sandstone, ironstone, quartz, or shale, Most boulders are less than 2 feet long; the largest erratic measured--a conglomeratic quartzite--is 23 by 11 by 8 feet, and only part of it is exposed, Pink quartzite cobbles and boulders are conspicuous but make up only a small percentage of the coarse fraction of the till. The weathered till is light brown or pale reddish brown; no fresh till was observed.
The glacial outwash includes stratified clay, silt, sand, small gravel, and abundant random cobbles and boulders deposited by melt water from the Kansan ice sheet during its advance and retreat. The outwash deposited during the advance of the ice is classified as the Atchison Formation by the State Geological Survey of Kansas; deposits of the retreatal phase are included in the Grand Island and Sappa Formations. The composition of the outwash deposits is complex and variable, and seldom can the Atchison and Grand Island Formations be definitely separated on the basis of lithology in this part of Kansas. In fact, the Atchison is recognized with reasonable certainty only where it is overlain by Kansan till. The Sappa Formation, overlying the Grand Island, is made up chiefly of silt of glaciofluvial and glaciolacustrine origin. No attempt was made to differentiate the glacial outwash of the three formations in mapping.
The proglacial outwash, the Atchison Formation of the State Geological Survey of Kansas (Moore and others, 1951, p. 15), commonly consists of indistinctly crossbedded gravels interstratified with medium to coarse sand, Locally lenses of gravel are tightly cemented by calcite. In places the pebble-sized rock fragments are chiefly limestone and chert, although some are shale and sandstone; only a very small amount of glacial erratics is present (Davis and Carlson, 1952, p. 222). At other localities the Atchison contains a large percentage of glacial erratics and is indistinguishable from the Grand Island Formation. The similarity between the two formations is particularly evident in the terminal area of the ice sheet, near the Wakarusa River, Commonly, as in an old gravel pit in the SE NW sec. 16, T. 11 S., R. 16 E., as much as 15 feet of well-sorted yellowish-gray finely sandy silt overlies the gravel of the Atchison Formation and underlies Kansan till (Davis and Carlson, 1952, p. 221).
Most gravel deposits in the area consist of glacial outwash of the Grand Island Formation (Lugn, 1935, pp, 103-104). These deposits are particularly thick and abundant in the terminal area of the ice sheet near the Wakarusa River and along the north side of the Kansas River valley. The Grand Island is well exposed in an old gravel pit in a moraine in the SW SW sec. 11, T. 12 S., R. 15 E,; in a quarry in the SE sec. 10, T. 13 S., R. 16 E.; and in a pit in the SW NW sec. 24, T. 13 S., R. 16 E.
At many localities the glacial outwash of the Grand Island closely resembles till which is poorly bedded and from which much of the clay and silt has been removed. Locally till is interbedded with the outwash, Some exposures in the SW NW sec. 24, T. 13 S., R. 16 E., show indistinctly crossbedded moderately well cemented lenses of sand and gravel interbedded with beds of fine to coarse friable sand, In a quarry in the NE SE sec. 16, T. 11 S., R. 17 E., the outwash consists of a basal deposit about 3 feet thick of yellowish-brown very fine to medium very micaceous sand containing abundant subrounded pebbles of limestone, igneous rock, ironstone, and yellowish-brown chert. Overlying the sand is a layer of cobbles and small boulders of limestone, sandstone, and igneous rock, and, in turn, a zone 1.3 feet thick of light-gray silty to slightly sandy clay containing scattered limestone pebbles. The upper 22 feet of the outwash is interbedded sand and silt showing deltaic bedding. The sand is moderate yellowish brown and fine to medium grained; it is made up mainly of quartz but contains some feldspar and many pebbles of limestone, igneous rock, and ironstone. The silt, which is more abundant in the lower half, is light yellowish gray to olive gray and sandy, It contains scattered small pebbles and weathers light yellowish brown. Part of this deposit may be equivalent to the Sappa Formation.
North of the Kansas River valley, the outwash is not as thick, although several large deposits were observed. The outwash capping the ridge in the SE sec. 28, T. 9 S., R. 15 E., contains a high percentage of large boulders and may be partly morainal. The coarse sand and gravel of the deposit capping the ridge in E2 NE sec. 4, T. 10 S., R. 15 E., are partly cemented by calcite. Outwash also occurs along the stream in the W2 NW sec. 15, T. 10 S., R. 17 E.
Extensive deposits of pale-yellowish-brown to pale-red clayey to sandy silt and very fine sand are present in the Kansas River valley, particularly on the north side. The silt is massive and contains many granules and pebbles. It is more than 40 feet thick in places and extends northward beyond the valley as much as 1 mile. These deposits, which are in the Sappa Formation (Condra, Reed, and Gordon, 1941, p. 12, 22), couId not be accurately delineated, for they are generally concealed by soil and loess; consequently, they were not mapped separately from the glacial drift, Good exposures of the Sappa occur along the north side of Soldier Creek in the SW sec. 12, T. 11 S., R. 15 E.; in an old gravel pit in the SE NW sec. 16, T. 11 S., R. 16 E.; and along Whetstone Creek in the NE sec. 32, T. 11 S., R. 11 E.
Buck Creek(?) Terrace Deposits
Small remnants of terrace deposits of post-Kansan age occur at several localities in the Wakarusa River valley; they consist mainly of reddish-brown clayey silt with scattered pebbles and lie about 5-10 feet above adjacent terrace deposits of Wisconsin age. These topographically higher deposits are questionably correlated with the Buck Creek terrace deposits of Illinoian age in the Kansas River valley east of the mapped area (Davis and Carlson, 1952, p. 213). In a railroad cut just north of Tecumseh, an unmapped deposit correlated with the Buck Creek terrace includes, from its base upward, at least 12 feet of gravel, 10 feet of silt, and a well-developed soil profile of the Sangamon Interglaciation (Davis and Carlson, 1952, p. 228). This Buck Creek deposit is overlain by about 10 foot of loess of more recent age.The largest renmants of the Buck Creek(?) terrace are in the Wakarusa River valley upstream from Wakarusa. The terrace, at the common corner of secs. 26, 21, 34, and 35, T. 13 S., R. 15 E., probably overlies beds of the upper part of the Topeka Limestone. The small deposit east of Richland, in the SW NE sec. 21, T. 13 S., R. 11 E., rests on the Plattsmouth Limestone Member of the Oread Limestone, Remnants of Buck Creek(?) terrace deposits are probably more widespread in the area than is shown by the geologic map, but they are partly concealed by loess or colluvium and were not recognized.
Newman Terrace Deposits
Extensive alluvial deposits of Wisconsin age occupy much of the bottom land in the Kansas River and Wakarusa River valleys and in the valleys of the major tributaries. In the Kansas River valley the deposits underlie a flat poorly drained terrace surface--the Newman--which is 20-40 feet above the river. The width of the terrace ranges from less than 100 feet, near Tecumseh, to about 1.75, miles, at the east edge of the area. The Newman is best preserved on the north side of the Kansas river, Together, the Newman terrace and the alluvium form the flood plain of the Kansas River; however, only severe floods inundate the terrace, and the high points remain above flood level.
On the basis of test borings, Davis and Carlson (1952, p. 229) reported that the Newman terrace deposits in the Kansas River valley are locally almost 90 feet thick. The lower part of the deposits consists of coarse sand, gravel, and numerous cobbles, but these materials grade upward to clay, silt, and fine sand in the upper 40 feet. The sediments in the upper part are similar to those now being transported by the Kansas River (Davis and Carlson, 1952, p. 229). Newman terrace deposits form most of the flood plain of the Wakarusa River and the flood plains of major creeks in the area, Ordinary floods cover these deposits. The Wakarusa River has incised 20-25 feet below the level of the flood plain on the Newman deposits. The thickness and composition of the Newman terrace deposits along the Wakarusa River within the mapped area are not known; however, about 5.5 miles to the east, the deposits are about 65 feet thick and consist mainly of silty and sandy clay that is underlain by 1-3 feet of medium sand and very coarse gravel composed of chert, limestone, sandstone, and quartz (O'Connor, 1960, p. 143-144).
The belt of alluvium along the Kansas River ranges in width from about 0.75 mile to more than 2.5 miles and, together with the Newman terrace, forms the flood plain of the river. The alluvial surface is irregular and marked by meander scars that in places contain small ponds. A scarp marks the contact between the alluvium and the Newman terrace. At the surface the alluvium consists of coarse silt and fine sand that grade downward to fine to coarse gravel; fine silt and clay are confined to meander scars (Davis and Carlson, 1952, p. 230). The belt of alluvium along the narrow channel of the Wakarusa River is less than 150 feet wide; hence, it was not mapped separately from the Newman terrace deposits. The alluvium along the major tributaries of the Kansas River is generally narrow, and the scarp separating it from the Newman terrace deposits is commonly less than 5 feet high and in many places is obscure. Near the mouths of the creeks, the alluvium grades to that in the Kansas River valley, but upstream along some creeks it merges with the Newman terrace surfare.
Kansas Geological Survey, Geology
Placed on web October 2005; originally published 1967.
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