Date of this Version
In field studies of the late Tertiary Ash Hollow Formation of the Ogallala Group in western Nebraska the alluvial deposits are composed of large volumes of sand and gravel up to large cobbles. Because the current understanding of the climate of the region at the time of deposition does not provide for a source for deposits of this character, a scanning electron microscopic study of the surface features on the quartz sand grains from these sediments was undertaken. Nine samples, collected from locations in Banner, Morrill and Keith Counties, were examined to see if they had one or more of 22 surface features. The results were compared with models for glacial, glacio-fluvial and fluvial sand compiled from the work of others. Preliminary results indicate that two of the samples correspond well with the glacial model, five others correspond with the glacio-fluvial model and none corresponds well with the fluvial model. These results indicate the need to look further for corroborating evidence of a glacial source for at least part of the Ash Hollow Formation and to consider the implications for a partial glacial history of the mountain sediment source regions in the late Tertiary.