Petrology, Stratigraphy and Sedimentation of the Middle Proterozoic Bayfield Group, Northwestern Wisconsin
1997-12
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Petrology, Stratigraphy and Sedimentation of the Middle Proterozoic Bayfield Group, Northwestern Wisconsin
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1997-12
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The Bayfield Group (Middle Proterozoic, Lake Superior region) is composed of three formations which are, from oldest to youngest, the feldspatholithic to lithofeldspathic Orienta Formation; the quartz-arenitic Devils Island Sandstone; and the feldspatholithic Chequamegon Formation. The average QFL percentages are 69/17 /14 for the Orienta Formation, 95/4/1 for the Devils Island Sandstone, and 79/14/7 for the Chequamegon Formation. The large amounts of quartz and appreciable feldspar suggest that the primary provenance was older Early Proterozoic and Archean rocks. Diagenetic action on the Bayfield Group is evidenced by authigenic quartz, hematite, kaolinite, zeolite, and minor amounts of potassium feldspar. The average pore space of the sandstones in the Bayfield Group decreases with depth. Dissolution of potassium feldspar is the major factor in the development of minor secondary porosity. Accessory minerals show that "normal" zircon is the most prevalent form found within the non-opaque, non-micaceous suite. The presence of "normal" zircons suggests that a potential provenance was Keweenawan volcanics; some residence time in previously deposited rift sediments (such as the Oronto Group) may have occurred. The minor amount of other zircon varieties support the framework grain analyses that older Early Proterozoic and Archean sources were shedding major amounts of sediment into the depositional basin. The Bayfield Group was deposited in a transgressive-regressive lacustrine to fluvial environnment in the waning stages of the Midcontinent Rift System. The Orienta and Chequamegon Formations represent fluvial environments of deposition while the Devils Island Sandstone was likely deposited in a nearshore lacustrine depositional environment. The paleocurrent trend for the Devils Island is toward the east and southeast while paleocurrent trends for the Orienta and Chequamegon Formations are toward the northeast. The exposed sections suggest that the near-shore environment was restricted in comparison to the fluvial systems that were transporting sediment towards the central rift valley.
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A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Kent Fred Adamson in partial fulfillment of the requirements for the degree of Master of Science, December 1997.
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Adamson, Kent Fred. (1997). Petrology, Stratigraphy and Sedimentation of the Middle Proterozoic Bayfield Group, Northwestern Wisconsin. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/212454.
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