The Cloquet quadrangle is bisected by the St. Louis River, a major stream that flows into the western end of Lake Superior. Precambrian rocks are extensively exposed in the river valley where overlying Pleistocene glacial deposits have been eroded. The Precambrian rocks are dominated by the Thomson Formation, which consists of interbedded slates, slaty graywackes, and graywackes. Small-scale cross-bedding, graded bedding, flute casts, load casts, clastic dikes, and other primary and penecontemporaneous structures are common, as are calcareous and siliceous concretions. The formation probably was deposited in a relatively deep-water basin, in part by turbidity currents. It has only one conspicuous marker bed, the Otter Creek unit, so the stratigraphic thickness across the intricate folds of the region is difficult to determine, but it probably is about 20,000 feet. Normal and reverse faults with displacements of a few tens of feet are common, as are steeply dipping conjugate joints of northwest and northeast trends. Cleavage is well developed in slaty units. The Thomson Formation is correlated with the Animikie Group. Abundant microgabbro dikes were intruded during subsidence of the Lake Superior syncline. The Pleistocene glacial history was marked by three phases of advance and retreat of the Superior Lobe, preceded by a phase of the Rainy Lobe. Drumlins, moraines, outwash plains, eskers, lake plains, and diversion channels constitute distinctive landforms. During final withdrawal of the Superior Lobe from the area, the St. Louis River, which carried the outflow from Glacial Lake Upham, was diverted to form prominent erosional channels leading to the St. Croix River at progressively lower elevations, until it finally flowed into the proglacial Lake Nemadji, whose outlet formed a final channel in the sequence.
Wright, H.E. Jr; Mattson, L.A.; Thomas, J.A..
Geologic Map Series 3. Geology of the Cloquet Quadrangle Carlton County, Minnesota.
Minnesota Geological Survey.
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.
Showing items related by title, author, creator and subject.
Jirsa, Mark A.; Boerboom, Terrence J.; Chandler, V.W.; Mossler, John H.; Runkel, Anthony C.; Setterholm, Dale R. (Minnesota Geological Survey, 2011)
This map is a new construct that incorporates existing geologic maps where prior mappers had adequate ground control, and new interpretations based on drill hole, geophysical, and unpublished data where they did not. The ...
Johnston, Lisa R; Thorleifson, Harvey (Geoscience Information Society, 2012)
The Minnesota Geological Survey (MGS) hosts information systems containing data sets that are valuable historic and scientific resources for the state. Several options are being pursued to curate, preserve, describe, and ...