RI-28 Stratigraphy and Sedimentology of the Lower Proterozoic Virginia Formation, Northern Minnesota

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RI-28 Stratigraphy and Sedimentology of the Lower Proterozoic Virginia Formation, Northern Minnesota

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1983

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Minnesota Geological Survey

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Report

Abstract

The lower Proterozoic Virginia Formation, a thick sequence of argillite, siltstone, and graywacke, forms the top of the Animikie Group on the Mesabi range in northern Minnesota. It is overlain by thick Quaternary deposits, but is exposed locally where the underlying Biwabik Iron Formation has been mined. Drill cores available from four sites provide stratigraphic and sedimentologic data, and the 450 m of core from a site south of Biwabik and 342 m of core from south of Calumet are proposed as alternate reference sections to the original type locality. The Virginia Formation can be divided into two informal members--a lower argillaceous lithosome and an upper silty and sandy lithosome. The argillaceous lithosome thickens toward the west end of the Mesabi range where it also contains appreciable quanti ties of chert and a discrete unit of cherty, sideri tic iron-formation. The upper silty and sandy lithosome also consists predominantly of argillite, but is characterized by intercalated beds of siltstone and finegrained graywacke. Mineralogic and sedimentologic data indicate that the graywackes were derived largely from granitic and low-grade metasedimentary and metavolcanic rocks like those now exposed in the Archean greenstonegranite north of the Mesabi range, and that they were deposited by turbidity currents on a southward-dipping paleoslope into a basin south of the range. In detail, the sedimentologic attributes of the formation resemble "thickening- and coarsening-upward" turbidite sequences associated with the lower and mid-fan parts of a prograding submarine fan complex.

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Previously Published Citation

Lucente, M.E. and Morey, G.B., 1983, Stratigraphy and Sedimentology of the Lower Proterozoic Virginia Formation, Northern Minnesota, Minnesota: Minnesota Geological Survey Report of Investigations 28, 28 p.

Suggested citation

Lucente, M.E.; Morey, G.B.. (1983). RI-28 Stratigraphy and Sedimentology of the Lower Proterozoic Virginia Formation, Northern Minnesota. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/60721.

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