Odom, J. Edgar
M.S. (Master of Science)
Department of Geology
The Franconia Formation is an Upper Cambrian glauconitic, feldspathic sandstone which crops out in southeastern Minnesota and southwestern Wisconsin. Seventy thin sections representing various stratigraphic positions and geographic locations in the outcrop area were studied. The chemistry of the feldspar in 14 samples was studied using electron probe microanalysis. Modal analyses of the thin sections show that quartz, K-feldspar, glauconite, dolomite, and a silt-clay matrix account for the major part of the total volume of the rock. The relative proportions of these constituents vary considerably throughout the stratigraphic range and geographic distribution of the Franconia. K-feldspar is very abundant throughout the formation except in the Woodhill Member, which generally contains less than one percent K-feldspar. Samples from the Tomah Member, however, average 40 percent K-feldspar. Many samples from the Birkmose and Reno Members contain 20 percent K-feldspar. The K-feldspar consists of detrital cores of microcline surrounded by authigenic overgrowths of very pure K-feldspar. The overgrowths are untwinned but exhibit zoning in some instances. They have a definite optical relationship to the cores. Determination of the cross-cutting relationships between the various mineral constituents reveals that authigenesis of the K-feldspar occurred during the compaction of the sediment. The presence of authigenesis early in the diagenetic history of the sediment, along with the geographic and stratigraphic position of the Franconia Formation, agree with the conditions required for feldspar authigenesis according to Swett's (1968) hypothesis.
Kramer, David J., "Authigenic and detrital K-feldspars in the franconia formation" (1970). Graduate Research Theses & Dissertations. 1588.
Northern Illinois University
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