Earth and Atmospheric Sciences, Department of
Date of this Version
1985
Citation
Institute for Tertiary-Quaternary Studies-TER-QUA Symposium Series, 1 (1985): 111-117
Abstract
Most of the stream courses of eastern Nebraska came into existence during the recession of an ice margin. Their patterns include many drainage anomalies that suggest both the manner and the times of ice disappearance. Rivers coming from the west flow down the regional slope of the High Plains. Along and east of the "Kansan" glacial border most streams are subparallel, trend S300 _40 0 E, and probablY mark pauses of an actively retreating ice margin. Logan Creek, an underfit stream, flows S4SoE from Hartington to the Thurston/Burt c<;mnty line, then directly southward to the Elkhorn. East of Logan Creek and above the bend, South Blackbird, Omaha, and Cow creeks flow parallel to Logal Creek then bend abruptly back northward to the Missouri. The Bow creeks in Cedar and Knox counties describe a series of arcs that surely mark successive retreatal positions of an ice lobe that crossed the Missouri trench around Yankton, South Dakota. Bazile Creek in the Santee Sioux Reservation flows northward to the Missouri, but the gravel and sand along it indicate a southeastward flow for the currents that deposited them. These sediments can be traced into the North Fork of the Elkhorn, thence to the Platte Valley near Fremont. These drainage lines define the lobate margins of the ice through the J ames and Red River lowlands. The degree of dissection and alteration of the associated tills suggests the relative lengths of time since the ice melted from them. The compact and weathered tills in east-central Nebraska are oldest (classical Kansan); the softer, less weathered tills near the Missouri are younger (Illinoian?); Wisconsinan ice may have blocked the Missouri River near Yankton and shunted it to the Elkhorn, but left little till on the south side of the Missouri.