MULTIPLE GLACIAL TILLS IN AN EXPOSURE ALONG THE LOWER ELKHORN RIVER, NEBRASKA

It was once thought that there were only two glacial sequences in the area around Elkhorn, Nebraska. However, it is now known that the simple, two-fold “Kansan” and “Nebraskan” sequence division is invalid. Several pre-Illinoisan glacial sequences that deposited glacial till occurred in this region.

While studying an outcrop along the Elkhorn River, four separate tills were identified. A stratigraphic section was developed, and the structural relationships between the tills were studied. The bottom most till (~4m) is dark olive color with a massive habit. In two distinct areas of the exposure a layer (~4m) of fluvial outwash exists directly above the lowest till. The next till (~15m) is a mustard yellow color with high clay content and significant weathering. The two uppermost tills (both ~3m) are mustard yellow colored and well jointed, with the topmost till abruptly truncating the lower. Evidence suggests that lodgement till, flow till, and melt out till all exist within this one outcrop.

Within the exposure are also two distinct features which may allow for determining the age of the tills. Between the two uppermost tills, a zone of alteration may exist. Also, within the associated fluvial deposits, there are unique snail shells which may be indicative of the time of deposition.

Future analyses planned include X-ray diffraction to determine clay mineralogy to pinpoint source material. An analysis of clay weathering will also be undertaken.