Guidebook—Geology of Northeastern Kansas
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Stop 1 to Stop 2
The first part of the route between Stop 1 and Stop 2 (see map), heading north on the South Lawrence Trafficway, is in the gently rolling upland formed on the Oread Limestone (see stratigraphic section). As the road goes under U.S. 40, it cuts through a ridge capped by the next younger limestone formation, the Lecompton Limestone. The slopes of this ridge are formed on the Kanwaka Shale, the rock unit that lies between the Oread and Lecompton Limestones. Just before the road reaches the turnpike (I-70), the Oread surfaces again east of the trafficway. In this area, the Oread is about 80 feet lower in elevation than it is 5 miles to the east at the crest of Mount Oread. This reflects the slight regional dip to the west of rocks in this part of Kansas.
The next leg of the route, heading west on the Kansas Turnpike (I-70), climbs onto a gently dipping plateau formed on the Lecompton Limestone. These gently dipping plateaus are known as cuestas, a Spanish word that means slope. Proceeding west to Topeka, the turnpike climbs onto cuestas formed by a series of successively younger limestones--namely, the Deek Creek Limestone, the Topeka Limestone, and the Howard Limestone (see stratigraphic section).
In south Topeka, the route continues west on I-470 and passes Burnett Mound, part of a prominent escarpment marking the east margin of a cuesta formed on the Bern Limestone, the next younger limestone formation. As the route continues west on 21st Street, it crests a ridge supported by the Emporia Limestone. The route then heads south and west on Kansas Highway 4, passing by prominent outcrops of the Tarkio Member of the Zeandale Limestone (see stratigraphic section).
Sandstone deposits at Echo Cliffs.
Stop 2--Echo Cliff
Echo Cliff, which stands about 75 feet above the stream, is an excellent example of ancient river-channel deposits. Cycles of submergence and emergence, caused by changes in sea level, occurred many times during the Pennsylvanian here in the Midcontinent. When sea level fell, streams cut deep channels into previously deposited layers of limestone and shale. As channels meandered across the landscape, sand-, silt-, and clay-sized sediments were deposited, removed, and redeposited again and again, much as they are in a modern river like the Kansas River. Evidence indicates that channel cutting occurred in a freshwater environment when the ground was above sea level, and in most cases, the channels filled with nonmarine sandstones and shales. Some channel filling, however, may have taken place in a transitional setting, where marine and nonmarine environments met and tides affected sediment deposition. Much of the material filling the channel probably came from the uplands to the north and northwest.
The channel deposits at Echo Cliff probably represent two separate channels (see diagram below). The first river channel, which developed about the same time the Plumb Shale was being deposited, cut down into rocks below the Plumb Shale. Later, a second river channel started in the Towle Shale and cut into the older Plumb Shale channel. A prominent layer of conglomerate (a rock composed of pebbles and rock fragments that have been naturally cemented together) can be seen about two-thirds of the way up from the base of the cliff; this marks the base of the Towle Shale channel (see diagram below).
Channel deposits exposed at Echo Cliff (cg = conglomerate, ss = sandstone, ls = limestone, sh = shale).
Plumb Shale Channel
About 48 feet of the Plumb Shale channel is exposed at Echo Cliff. The Plumb channel fill is alternating layers of very fine grained micaceous (containing flakes of the mineral mica) sandstone, and micaceous siltstone and claystone. The entire deposit exhibits large-scale crossbedding. Crossbedding is a series of thin, inclined layers in a large bed of rock (usually sandstone) that is inclined at a distinct angle to the typically horizontal bedding surface. Formed by currents of water or wind, crossbedding is found in dune, stream channel, or delta deposits. The direction in which the beds are inclined usually indicates the direction the current of water or air was flowing at the time of deposition. In this case, the crossbedding was formed by water. Some sandstone crossbeds fill small channels cut into more massive beds. Carbonized leaf and wood fragments are common on bedding planes, giving the outcrop a streaked or banded appearance. Limonite (iron oxide) nodules are abundant, and the entire outcrop is stained with iron oxide. Calcium carbonate, iron oxide, and locally, barite cement the sand grains together.
Normally, the Plumb Shale is about 10 feet thick, but where deep channels develop, it can be up to 105 feet thick. The Plumb Shale channel at Echo Cliff trends east to southeast and is probably not more than 1.5 miles wide.
Towle Shale Channel
The Plumb Shale channel is separated from the overlying Towle Shale channel by a limestone conglomerate. The conglomerate commonly forms a prominent ledge and breaks into large slabs. This conglomerate is 2-3 feet thick and consists of angular to subrounded fragments of local limestone and shale. Many of the limestone fragments are from the Brownville Limestone and Grayhorse Limestone Members of the Wood Siding Formation; this is evidence the channel is younger than these units. In other words, sometime when the Towle was being deposited, channel downcutting eroded through the limestone layers in the Brownville and Grayhorse, and fragments of these limestones were broken off and carried downstream to be deposited within the conglomerate at a level lower than where they initially occurred. This dates the Towle channel as younger than the Brownville. It also shows the channel cannot be the same age as the Plumb because the Brownville and Grayhorse, which occur above the Plumb, hadn't been deposited when the Plumb channel was active.
At Echo Cliff, the conglomerate is overlain by about 23 feet of very fine-grained micaceous sandstone that is interbedded with sandy siltstone. The Towle channel trends west to southwest. The channel is less than a mile wide and is about 85 feet deep. Normally, the Towle is only 10-20 feet thick in Wabaunsee County.
The channel sandstone in the Towle Shale Member is informally called the Indian Cave sandstone, referring to sandstone bluffs, locally called the "Indian Caves," on the Missouri River in southeast Nebraska where this unit was first described.
At this location we are very close to the Flint Hills. The eastern boundary of the Flint Hills can be defined by rocks deposited during the Permian Period (about 290 million years ago), which are slightly younger than the Pennsylvanian rocks at Echo Cliff. The Pennsylvanian and Permian rocks were deposited under similar conditions--that is, in shallow seas that fluctuated in depth. Because the rocks left behind by the Permian seas are similar to those deposited during the Pennsylvanian (alternating beds of limestone and shale), geologists have a difficult time deciding where the Pennsylvanian ends and the Permian begins. At one time, the boundary was placed at the base of the conglomerate in the Towle Shale, so that everything above would have been considered Permian and everything below Pennsylvanian. In 1994, however, the Pennsylvanian-Permian boundary was moved, based on fossil evidence, much higher up in the geologic rock section. This means that all the rocks at Echo Cliff are now considered Pennsylvanian, and you don't encounter Permian rocks (and thus the edge of the Flint Hills) until you go several miles west of here.
Directions to Stop 2
From Dover (a small town about 10 miles southwest of Topeka on Kansas Highway 4), drive 1.5 miles west on Kansas Highway 4. Turn south (left) and follow the gravel road one mile. Just before crossing the bridge over Mission Creek, turn east (left) into the Echo Cliff picnic area.
This guidebook is also available in print form as Kansas Geological Survey, Open-file Report 2000-55, from KGS Publications Sales office, 785-864-3965.
Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey. Text by Jim McCauley, Liz Brosius, Rex Buchanan, and Bob Sawin, Kansas Geological Survey.
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