Nebraska in relation to the problems of Pleistocene stratigraphy

Abstract

Introduction. CONTENTS. Glacial and fluviatile Pleistocene materials in Nebraska. Age of the Loveland loess. Pleistocene classiflcation. Correlation with Europe. Glacial or interglacial. Glacial or interglacial loess. Duration of the glacial advances. Post-Loveland pre-Peorian erosion. Geomorphology of the Great Plains and Pleistocene history. Sources of loess materials. River valleys and loess deposition. Dust storms. The "Oitell'/l,s" zone. The problem of animal survival. Aftonian (?) fauna. Antiquity of varved sediments. Conclusions. ABSTRACT. Nebraska is so peculiarly situated with respect to Pleistocene deposits of glacial, fluviatile, and eolian origin that it holds the key to the solution of many important problems of the stratigraphy of that period. A brief outline of the Pleistocene geology of Nebraska with several illustrations is followed by a statement of and brief discussion of several of these problems. The main problems touched upon are: age of the Loveland loess, Pleistocene classification, correlation with Europe, the need for a better understanding of what is meant by "glacial" and "interglacial," the problem of glacial and interglacial loess, the duration of the glacial advances, post-Loveland pre-Peorian erosion, the geomorphology of the Great Plains as an aid in understanding Pleistocene history, sources of loess materials, the relation of river valleys to the origin and deposition of the loess, the significance of the lesson of the dust storms, the "Oitellus" zone and the antiquity of Man, problem of animal survival and Pleistocene faunal succession, what constitutes the Aftonian fauna, and the problems of varved sediments. Pleistocene geology still is in the "experimental" stage.

Geologic studies of the Platte River, south-central Nebraska and adjacent areas — Geologic maps, subsurface study, and geologic history

“…The current Platte River is confi ned by valley walls composed of the late Wisconsin Peoria Loess and older units both upstream and downstream from Kearney, indicating that the river has occupied its current valley at least since the late Wisconsin. Lugn (1935Lugn ( , 1939b, Stevenson (1972), and Bentall (1982) outlined a chronology of stream capture of the lower Platte region from its mouth to about Kearney. Progressive capture of tributaries of the Elkhorn and Loup Rivers (fi g. 1) eventually diverted the Platte into its present course downstream from Kearney.…”

Isotopic evidence for the diversity of late Quaternary loess in Nebraska: Glaciogenic and nonglaciogenic sources

“…Alternatively, it has been suggested that paleowinds were primarily from the west or northwest, but that the Platte River was situated farther to the north during the last glacial period (Winspear and Pye, 1995). Other workers (Lugn, 1939(Lugn, , 1968Condra et al, 1950;Reed, 1968;Wright, 1970;Mason, 2001;Mason et al, 2003;Miao et al, 2005;Jacobs and Mason, 2007) have suggested that the Nebraska Sand Hills or other nearby dune fi elds have played a role in the origin of loess in Nebraska.…”

“…Possible non-glacial candidates for the source(s) of Nebraska loess are widespread Tertiary tephra-rich epiclastic sedimentary rocks, for example the White River Group, that crop out in the north-central Great Plains (Condra et al, 1950) or the silt facies of an eolian sand sheet of Pliocene age that occurs beneath the Nebraska Sand Hills (Swinehart et al, 1994b). Another possible source for Peoria Loess is the Nebraska Sand Hills, although early workers were not very specifi c as to how this dune fi eld played a role in the origin of loess origins (Lugn, 1939(Lugn, , 1968Condra et al, 1950;Reed, 1968;Wright, 1970). Mason (2001) has emphasized that the importance of the Nebraska Sand Hills for loess genesis was mainly as a "surface of transport," with the ultimate source of the particles from farther upwind.…”

Origin and paleoclimatic significance of late Quaternary loess in Nebraska: Evidence from stratigraphy, chronology, sedimentology, and geochemistry

“…The Nebraska Sand Hills and smaller, nearby dune fi elds have long been hypothesized to have played an important role for loess origins in Nebraska and Kansas (Lugn, 1939(Lugn, , 1968Condra et al, 1947;Reed, 1968;Wright, 1970;Mason et al, 1999Mason et al, , 2003aMason, 2001;Miao et al, 2005Miao et al, , 2007Jacobs and Mason, 2007).…”

“…As mentioned above, Peoria Loess in the Great Plains has no clear link to outwash of the Laurentide ice sheet, except possibly in that part of Nebraska adjacent to the Missouri River. Previous workers proposed a variety of sources for loess in the Great Plains, including Platte River alluvium (including glacial outwash from the Rocky Mountains); glacial outwash from the Missouri River; sediments from the Tertiary Ogallala, Arikaree, and White River Groups; and sediment from the Nebraska Sand Hills or other dune fi elds (Lugn, 1939(Lugn, , 1968Bryan, 1945;Condra et al, 1947;Swineford and Frye, 1951;Reed, 1968;Wright, 1970;Flint, 1971;Smalley, 1995;Winspear and Pye, 1995;Aleinikoff et al, 1999;Muhs et al, 1999).…”