A surficial-geologic map was constructed from field work, laboratory analysis, airphotos, and topographic maps. The study area is located in Lake County in northeastern Minnesota. Parts of the Isabella Quadrangle lie within the Toimi Drumlin Area, Border Lakes, Area, and the North Shore Highland. Bedrock in the surrounding areas is composed of Duluth Complex plutonic rocks, the North Shore Volcanic Group, Superior syncline elastics, and Vermilion District intrusive and metamorphic rocks. Surficial materials were distinguished as to genesis and provenance. Two distinct provenance groups were identified: Brown-colored drift incorportating rock fragments from the Superior syncline, North Shore Volcanic Group, and part of the Duluth Complex; Gray-colored drift incorporating rock fragments almost entirely from the Duluth Complex with minor Vermilion District input. Surficial materials were divided into genetic units a.s follows: Till, Ice-Marginal Gravels, Other Ice-Contact Deposits, Proglacial Outwash, Lag Acumulations, Loess, and Peat Deposits. The most prominent landforms are the merging Highland and Vermilion Moraines composed primarily of brown and gray ice-marginal gravels. Additional minor brown-till end moraines are situated in front of the Highland Moraine, and are superposed on a gray-till ground moraine that represents the northeast corner of the Toimi Drumlin Area. These minor moraines are in turn partially buried by the Vermilion Moraine. The area behind the Vermilion Moraine is characterized by extensive outwash complexes, a long esker system, and a series of parallel ridges composed of gray till. Lakes have formed in outwash-plain depressions that resulted from wastage or stagnantice blocks. The non-organic surficial material.s in the area were deposited during the St. Croix (ca.>20,500 yr B.P.) and Automba (ca.>16,000 yr B. P.) pha.se of the late Wisconsin. Conterminous Rainy and Superior Lobes emanating from the Rainy Lake area and Superior Lowland deposited the materials composing the Toimi Drumlin Area during the St. Croix phase. During the Automba phase the Superior Lobe advanced laterally out of the Superior Lowland in the southeast while the Rainy Lobe flowed southwestward into the study area. The ice masses met near the town of Isabella, producing interlobate terminal moraines. A sub lobe of the Superior Lobe extended beyond the Highland Moraine, producing the minor brown-till end moraines. As this sublobe receded, part of the Rainy Lobe extended into the vacated area, forming a sharp bend in the Vermilion Moraine. This extension is described as an ephemeral, thinned, frozen-base ice mass that sheared off sections of the substrate into thrust-block ridges. The extension stagnated and disintegrated rapidly as the Rainy Lobe receded, forming extensive ice-contact and outwash deposits. Loess was winnowed from exposed brown-drift outwash plains and deposited as a thin, discontinuous blanket over the entire region. Extensive wetlands formed in poorly-drained depressions and other lowlying areas.
A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Albert Louis Friedman in partial fulfillment of the requirements for the degree of Master of Science, March 1981. Plates I-II referenced in the thesis are also attached to this record.
Friedman, Albert Louis.
Surficial Geology of the Isabella Quadrangle, Northeastern Minnesota.
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.