Evidence of Late-Holocene floods in the central Great Plains
- Univ. of Northern Iowa, Cedar Falls, IA (United States). Dept. of Geography
From southwestern Kansas to northeastern Nebraska alluvial studies are revealing stratigraphic and morphological evidence of two brief periods of large-magnitude floods in the central Great Plains during the past 2,500 years. Evidence for these floods consists of deeply-scoured paleochannels, coarse-textured point-bar deposits overlying fine-grained deposits, soils on former floodplains that are buried by alluvium, and fluvial terraces. Wood and bone collagen in several deeply-scoured paleochannels date to about 2,300--2,000 yr B.P. Modest incision and floodplain reconstruction at this time is evident from both maps of fluvial landforms and C-14-dated stratigraphic sections in both large and small basins. Sediments near the base and top of inset gully fills in both trenched and untrenched tributary valleys to Great Plains rivers date to about 2,000 yr B.P. A second episode of large floods in the central Great Plains occurred about 1,300--850 yr B.P. Throughout most valleys a buried soil that developed in alluvium occurs from 50 cm to 1.0 m below terraces. Recently, stratified point-bar deposits beneath a low terrace in a small (9.6 km[sup 2]) basin in east-central Nebraska were exposed and studied. Crossbedded, gravelly sand strata alternative with massive, dark, silty strata. The C-14-dated section indicates that multiple floods occurred between 1,250 and 850 yr B.P. Such widespread evidence of flooding about 2,300--2,000 yr B.P. and again 1,250--850 yr B.P. attests to regional, and probably, global climate changes at these times. Discontinuities in the alluvial record have previously been recognized at 2,000 and 1,200 yr B.P. Furthermore, a discontinuity in the pollen record at 850 yr B.P. has long been recognized.
- OSTI ID:
- 5689121
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
USA
FLOODS
GEOLOGIC HISTORY
CARBON 14
CLIMATIC CHANGE
GEOMORPHOLOGY
ISOTOPE DATING
PALEOCLIMATOLOGY
QUATERNARY PERIOD
STRATIGRAPHY
AGE ESTIMATION
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBON ISOTOPES
CENOZOIC ERA
DEVELOPED COUNTRIES
DISASTERS
EVEN-EVEN NUCLEI
GEOLOGIC AGES
GEOLOGY
ISOTOPES
LIGHT NUCLEI
NORTH AMERICA
NUCLEI
PALEONTOLOGY
RADIOISOTOPES
YEARS LIVING RADIOISOTOPES
580000* - Geosciences