Zarth, Randee Jo2025-02-282025-02-281977-06https://hdl.handle.net/11299/270149A thesis submitted to the faculty of the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Master of Science. There is no page #21 or page #60 in the physical document (a black-and-white photocopy of the original) this file was scanned from.Study of late Wisconsin glacial deposits of the Wrenshall and Frogner quadrangles, southwest of Duluth, suggests a revised model for the late- and post-glacial history of the area. Two major sedimentary environments are distinguished: (1) an ice-disintegration environment and (2) a glaciolacustrine environment associated with Glacial Lake Duluth. Sediments produced by ice-disintegration are stratified, moderately to poorly sorted sand and gravel with clasts predominately of Precambrian sandstone, volcanics, granite, and slate; and minor bodies of laminated silt and clay. Topographically, these sediments comprise a wide belt of kettles, kames, and disintegration ridges, that are dissected locally by meltwater channels and tunnel valleys, some of which contain eskers. The lacustrine environment contains the following units: (1) thick, horizontally-bedded sand, (2) cross-bedded sand, (3) laminated silt and clay, (4) massive clay, and (5) massive and stratified dropstone deposits. In the nearshore environment are found moderately sorted and well rounded sand (0.25 mm) with lag boulders and gravel at the shoreline. At 300 to 309 min elevation the sand grades rather abruptly to massive clay. The nearshore facies overlies the offshore facies (silt and clay) indicating progradation of Glacial Lake Duluth. The highest strandline features occur at elevations near 330 m. They are expressed primarily as beach scarps and other well developed shoreline features such as several spits, an offshore bar, and a delta. A prominent linear, northeast trending scarp between 300 and 309 m, previously considered to be a strandline, is here interpreted to be the depositional front of a coarse grained shelf deposited into Glacial Lake Duluth as it stood near its highest stage (330 m). This indicates that what previously had been considered to be two stages, Glacial Lake Nemadji and Glacial Lake Duluth, is actually a single stage, that of Glacial Lake Duluth. The following late- and early-postglacial history is indicated: (1) Ice from the last advance of the Superior Lobe stagnated at the margin of the Lake Superior basin, resulting in the development of an ice-disintegration complex and stratified glacial deposits. (2) Meltwater from the disintegrating ice and the retreating Superior Lobe, along with other sources, was ponded in front of the retreating ice. A lake level rise to 330 m is indicated by a transgressive sequence of sediments. (3) The lake stabilized as Glacial Lake Duluth long enough to develop strong beach features. Sediment supplied at this stage appears to have been derived mainly from the ice-disintegration complex and the Superior Lobe (as ice-rafted sediment). (4) Progradation of the shallow water facies over the deep water facies was the result of sediment laden streams, meltwater and other runoff entering the lake. (5) The lack of a regressive facies indicates a rapid drop in lake level as a lower outlet was uncovered.en-USUniversity of Minnesota DuluthPlan As (thesis-based master's degrees)Master of ScienceMaster of Science in GeologyDepartment of Earth and Environmental SciencesThesis or Dissertation