REGIONAL GLACIATION OF
KANSAS AND NEBRASKA
James S. Aber
|Introduction||Glaciation of Kansas|
|Ice-lobe dynamics||Age of glaciation|
|Digital elevation model for central Great Plains, including parts of Kansas, Nebraska, Missouri and Iowa. The Kansas valley marks the southernmost extent of glaciation in the plains region. DEM derived from TOPO30 database; image processing by J.S. Aber.|
Kansas and Nebraska are an environmental transition zone with generally warm, dry, grassland conditions to the south and west, and cool, moist, forest conditions to the north and east. Plant, animal and human populations have migrated through the region as environmental conditions shifted back and forth.
The Quaternary stratigraphy of Kansas and Nebraska was traditionally interpreted in line with four major Pleistocene glaciations--see Fig. 17-1. Each glacial cycle could be recognized by till, outwash, or coarse-grained deposits in non-glacial river valleys. Interglacial stages were identified from buried soils, fossil beds, or fine-grained river deposits. Regional stratigraphy was correlated by reference to the Pearlette volcanic ash, a supposedly unique ash found just above Kansan till.
This simple stratigraphy began to fall apart in the 1960s and 70s with discovery of multiple tills in eastern Nebraska and adjacent states. Volcanic ash beds were also demonstrated to be multiple ashes of greatly different ages--see Table 17-1. Fission-track dating of volcanic ashes and paleomagnetism of tills proved the great age of older glaciations and led to considerable confusion in stratigraphic terminology.
|Pearlette||0.6||Lava Creek Tuff, Yellowstone|
|Hartford||0.75||Mount Jackson Rhyolite, Yellowstone|
|Mount Claire||0.8||Bishop Tuff, Long Valley caldera, California|
|Coleridge||1.2||Mesa Falls Tuff, Yellowstone|
|Borchers||2.0||Huckleberry Ridge Tuff, Yellowstone|
* Age is approximate date in millions of years before present. Hartford, Coleridge,
and Borchers ashes were previously confused with Pearlette ash in many places.
|Independence Park beside the Missouri River at Atchison, Kansas. The Lewis and Clark expedition camped at a nearby creek on July 4, 1804. They named it "Independence Creek" and this name is applied to the glaciation of Kansas (Aber 1991). Photo date 6/85; © by J.S. Aber. See space-age Lewis and Clark bicentennial atlas.|
It is safe to say that few if any original glacial landforms are preserved in northeastern Kansas. The upper 10 m of glacial deposits are so altered by weathering that their initial composition and texture cannot be determined with certainty. In many places, glacial deposits are covered with younger loess or alluvium. In spite of these handicaps, a reasonably good understanding of glaciation has been developed.
|Wyeth Bluff on the east side of the Missouri valley at St. Joseph, Missouri. Thick loess overlies alluvial sediment in this exposure. Such deposits conceal older glacial sediment across much of northeastern Kansas and northwestern Missouri. Photo date 6/85; © by J.S. Aber.|
Features created by glacial erosion, deformation and deposition, as well as by melt-water rivers and lakes are found throughout northeastern Kansas--see Fig. 17-4. Two major ice advances took place during the Independence glaciation, as demonstrated at the stratotype. Each of the major phases included lesser glacier advances and retreats with accompanying damming of lakes and catastrophic flooding. The early Independence ice sheet advanced as far south as northern Leavenworth County and as far west as Nemaha County. It deposited a dark gray, stony, wood-bearing, clayey till.
|Large erratic boulder of Sioux Quartzite north of Topeka, Kansas. William Boltz, a well-known rockhound and collector of glacial erratics, stands next to the giant erratic. Photo date 8/86; courtesy of Wm. Boltz.|
|Closeup view of conglomeratic texture of Sioux Quartzite boulder. Sioux Quartzite varies considerably in texture and color; conglomerate is one of the more distinctive types.|
|Bedrock deformed by ice pushing, west of Topeka, Kansas. Upper limestone blocks are tilted and shoved over the undeformed limestone beds in lower part of exposure. Glacial sediment is present between and below the tilted blocks. The deformed blocks are part of a large, thin mass of transported bedrock. Scale pole marked in feet. Photo date 10/89; © by J.S. Aber.|
|Large exposure of glacial till (gray) and overlying glaciolacustrine sediment (tan) in gravel pit near Wathena, Kansas. Brad Hedstrom works on a safety rope in the till unit. The till rests on preglacial alluvium visible to lower right. Photo date 6/85; © by J.S. Aber.|
|Overview of outwash sand and gravel that underlie the Menoken terrace within the Kansas River valley at Topeka. This coarse gravel was deposited when the valley carried melt-water runoff from both the ice sheet and non-glaciated regions to the west and north. Height of exposure about 10 m. Photo date 8/86; © by J.S. Aber.|
|Closeup view of coarse, cemented cobble gravel from base of Menoken terrace fill. Hat for scale. Photo date 8/86; © by J.S. Aber.|
The early Independence ice advance overran a forest as it entered the region. Pieces of wood are common in till wherever the organic material has not been destroyed by weathering. The wood is identified as spruce (Hedstrom 1986), most likely white spruce which makes up the boreal forest of central Canada today. Although much wood is present, no bark, needles, or cones have yet been found. This suggests that ice advanced over remnants of a forest that had already died from deteriorating climate as the ice approached.
|Wood buried in till, near Wathena, Kansas. Such wood fragments are common within the lower gray till of the Independence Formation, northeastern Kansas. Similar wood-bearing tills are found in north-central Missouri and eastern Nebraska. Photo date 10/89; © by J.S. Aber|
|Scanning electron micrograph (SEM) of wood recovered from till. An annual growth ring is visible in center position; the large opening is a resin canal. This wood structure is typical of spruce (Picea). Scale bar is 100 µm in length. SEM by Brad Hedstrom (1986).|
The early Independence glaciation came from the northeast as shown by striations, till fabrics, and ice-pushed structures. During its advance, it blocked the eastern outlet of the major pre-glacial valley in the region. This valley became the site of a large proglacial lake, Lake Atchison, in which thick glaciolacustrine sediment was deposited. The lake must have risen rapidly, as it received melt-water drainage from the ice sheet as well as run-off diverted from all the northern Great Plains and Rocky Mountains.
The lake eventually overflowed its drainage divide north of Manhattan and north of Kansas City; spillway valleys were quickly eroded through soft shale and limestone bedrock. The resulting catastrophic floods cut the present lower Big Blue, Kansas, and Missouri River valleys. Once established, this route continued as the principal drainage for northeastern Kansas. The early Independence glaciation underwent multiple local advances, perhaps as a result of surging into Lake Atchison.
|Stream bank exposure on White Clay Creek, near Atchison, Kansas. This section serves as the stratotype for the Independence Fm. Photo date 10/87; © by J.S. Aber|
|Overview of exposed sediments in the Independence Fm. stratotype. Lower gray till, middle tan sand, and upper brown till. The lower till is deformed into a large diapir where the people are working. The lower till was deposited by ice advances from the northeast, whereas the upper till was laid down by ice movement from the northwest. The intervening sand is glaciolacustrine sediment from glacial Lake Atchison. Photo date 10/87; © by J.S. Aber|
|Closeup view of large diapir of lower gray till that intrudes into middle sand of section. Upper brown till is visible to top right. Scale pole marked in feet. Photo date 6/81; © by J.S. Aber|
The late Independence advance next moved into the region from the northwest. This glaciation overspread all the area covered by the earlier advance and reached much farther south. Brown, stony, clay-rich till was deposited along with associated stratified drift. Nearly all glacial deposits and erratics visible at the surface in northeastern Kansas are related to this glaciation. The late Independence glaciation reached a maximum limit west of the Big Blue and south of the Kansas valleys. Its maximum limit was controlled by the positions of resistant bedrock escarpments. Between these bedrock obstacles, small ice lobes spread southward over intervening lower areas.
The late Independence ice sheet locally crossed and blocked parts of the Blue, Kansas and Missouri spillway system. This created proglacial lakes in the vicinity of Manhattan, Topeka, and elsewhere. Few traces of the actual lakes remain today, although glaciolacustrine sediment is preserved at many sites. Catastrophic flooding from these lakes has left a prominent record, however. Several smaller valleys, such as Mill Creek and Wakarusa River valleys, that parallel the Kansas valley were eroded as spillway routes during floods. Conspicuous boulder beds along the glacial border zone in Wabaunsee, Shawnee, and Douglas Counties were deposited by these floods.
|Glaciolacustrine sediment in northern Wabaunsee County, Kansas. The exposure and surrounding hills are underlain by thick stratified fine sand and silt, which were deposited in an ice-dammed lake within the Kansas valley. Photo date 10/89; © by J.S. Aber|
|Section in glaciolacustrine sediment exposed in Hamm quarry east of Topeka, Kansas. Sediment consists of fine sand and silt that were deformed by slumping and/or flowing into a recumbent fold. This deltaic sediment was deposited in the Kansas valley when the valley was blocked by ice farther to the east. Height of section about 3 m. Photo date 8/86; © by J.S. Aber|
|Kansas River, northeastern Kansas. NASA space-shuttle photo, STS47-105-21, 70 mm format, 9/92. Low-oblique view toward north showing Kansas River, Milford Reservoir (left) and Tuttle Creek Reservoir (top center). Tuttle Creek Reservoir is dammed in the lower Big Blue valley, which formed as a melt-water spillway, when glacial Lake Atchison overflowed from the north. NASA Johnson Space Center, Imagery Services.|
|Landsat thematic mapper (TM) image of Kansas City vicinity, 3/83. Standard false-color composite in which active vegetation appears bright red and pink. Junction of the Kansas and Missouri valleys marks the southernmost extent of the ice sheet in this vicinity. The Kansas valley and Missouri valley (east of K.C.) were ice-marginal drainage routes. The Missouri valley northwest of Kansas City formed as a melt-water spillway, when glacial Lake Atchison overflowed from the north. Image obtained from NASA Goddard Space Flight Center, Maryland.|
|Glacial boulder bed in eastern Wabaunsee County, Kansas. Most of the boulders scattered across the field are varieties of Sioux Quartzite. A few granites and other crystalline erratics are also present. The boulders rest directly on bedrock. Such boulder beds are common along the glacial border zone south of the Kansas River valley. Photo date 10/80; © by J.S. Aber|
|Glacial striations and shallow grooves beautifully preserved on surface of lichen-covered quartzite boulder, Wabaunsee County. Pen for scale. Photo date 4/96; © by J.S. Aber|
|Fragment of rotten granite within boulder bed, Wabaunsee County. After half a million years of exposure at the surface, even granite has decayed, along with most other softer sedimentary and crystalline rock types. Only quartzite, chert, and other pure-silica rocks have survived prolonged weathering. This explains why quartzite is the most common erratic seen at the surface in northeastern Kansas. Photo date 4/96; © by J.S. Aber|
The dynamic structure of the Independence ice sheet may be reconstructed by
reference to directional indicators and comparison to the younger
Laurentide Ice Sheet, about which much more is known. The Late Wisconsin
glaciation of the northern Great Plains consisted of two large ice lobes
that followed bedrock troughs either side of the Coteau des Prairies
upland--see Fig. 17-5. Drainage diversions related to these lobes
are in three positions.
|Big Sioux River flowing over Sioux Quartzite ledges at Sioux Falls, SD. This river was diverted between the Des Moines and James ice lobes during the last glaciation. The river flows north to south overall along the center of the Prairie Coteau upland in an interlobate position. Photo date 7/96; © by J.S. Aber|
The Independence ice sheet was thicker and completely covered the Coteau des Prairies, but the Sioux Quartzite ridge was still sufficient to split ice flow in two lobes--Minnesota and Dakota. The lobes were confluent southward into Nebraska and Iowa, but evidently separated farther south. The Minnesota lobe was apparently first to reach Kansas from the northeast; it deposited the lower till, dammed Lake Atchison, and caused flooding that eroded the Blue, Kansas and Missouri spillway valleys. The Dakota lobe entered Kansas later from the northwest; it laid down the upper till and caused catastrophic flooding along the glacial border zone. Kansas City is located at a reentrant in the maximum ice margin, which might mark an interlobate boundary between the Dakota and Minnesota lobes. The genesis of the Missouri River valley in eastern Nebraska is problematic. It is clearly the result of glacial diversions, as it cuts across preglacial drainages; different portions may have formed in lobe-axis, interlobate, and/or lobe-marginal settings (Aber 1982).
|Vertical section of exposed glacial and preglacial sediments, near Wathena, Kansas. From the top down: glaciolacustrine sand (tan), lower Independence till (gray), sand and gravel preglacial alluvium (brown). Scale pole marked in feet. The Wathena local fauna was recovered from the alluvium and is estimated to be one million years old. Photo date 6/85; © by J.S. Aber|
|Closeup view of basal preglacial gravel. Chert derived from the Flint Hills and a few quartzite pebbles of High Plains/Rocky Mts. origin. Such preglacial chert gravels are common across eastern Kansas south of the region of glaciation. Photo date 10/89; © by J.S. Aber|
|Volcanic ash bed (light gray) exposed in alluvium near Desoto, Kansas. The alluvium is preserved within the Kansas River valley and is assumed to postdate glaciation of the region. This ash has been identified as the Lava Creek ash, about 600,000 years old (Geil 1987). Photo date 8/86; © by J.S. Aber|
Lower Independence till displays two paleomagnetic patterns in both surface and subsurface samples: (1) normal polarity where no structural disturbance is present, and (2) mixed polarity in structurally disturbed settings. No till with primary reversed polarity has been found in Kansas. Normal till polarity restricts the age of the Independence Fm. to the range 620,000 to 780,000 years ago (Aber 1991; Colgan 1998). The paleomagnetic data also indicate that older (reversed) Nebraskan till is not present in Kansas.
This age range is consistent with cosmogenic dating of exposed Sioux Quartzite bedrock in southwestern Minnesota. This region is located at the southern end of the Coteau des Prairies upland, which was presumably the confluence between the Minnesota and Dakota ice lobes. The bedrock surface has been exposed since 575±57 thousand years ago. This means that no younger glaciation has advanced over the southern Prairie Coteau upland.
The Independence Fm. is thought to correlate with the type A2 and A3 tills of Nebraska and western Iowa--see Fig. 17-3. Upper and lower tills of the Independence Fm. likely are equivalent to the upper and lower tills of the McCredie Fm. across northern Missouri (Guccione 1983). This age range corresponds to oxygen-isotope stages 16-18. Stage 16 is suitably one of the largest glacial stages in the oxygen-isotope record. The Independence Fm. represents one of the greatest Pleistocene glaciations with a regionally preserved record on land.
|Cedar Bluffs section on the Platte River near Fremont, Nebraska. Three tills are exposed, from the bottom up: lower gray till, middle brown till, and upper yellow-brown till. The tills are capped by a strongly developed paleosol (red), which is overlain by loess at section top. The lowest gray till is thought to match with the lower Independence till, and the middle till may correlate with the upper Independence till of northeastern Kansas. Photo date 7/85; © by J.S. Aber|
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