Illite in the Lower Paleozoic of the Illinois Basin: Origin, age, and polytype quantification

Illite was first named in 1937 in Illinois by Ralph Grim, one of the founders of clay mineralogy. Illite is the most abundant clay mineral on the earth's surface. However, we know very little about the origin of illite in Illinois. This dissertation focuses on two aspects of illite in the Lower Paleozoic of the Illinois Basin: (1) illite polytype quantification, which explains the anomalies of the distribution of illite and smectite in the Illinois Basin, and (2) the origin and age of diagenetic illite, which is used to link illitization to fluid migration.Illite polytype quantification allows the differentiation of diagenetic and detrital illite. In Paleozoic shales from the Illinois Basin three polytypes 1M\rm\sb{d}, 1M, and 2M\sb1 are observed. 1M\rm\sb{d} and 1M are of diagenetic origin and 2M\sb1 of detrital origin. All three polytypes were quantified by mixing single polytypes and comparing the experimental XRD traces with traces calculated using WILDFIRE$\copyright.$Illite polytype quantification of different size fractions combined with K/Ar dates allows the extrapolation to apparent ages of detrital and diagenetic end-members. The extrapolated age of the diagenetic end-members dates episodes of diagenesis. Results show that the Upper Ordovician Maquoketa Group shales contain diagenetic illite (dominantly 1M\rm\sb{d} with minor 1M) with an age of $\sim$360 Ma, that was not formed solely by burial diagenesis but mainly through either a hydrothermal or K-rich brine event. Ordovician and Cambrian shale partings and sandstones, older than the Maquoketa Group, contain diagenetic illite (1M\rm\sb{d} in shales and 1M in sandstones) having an age of 300 Ma. This late Paleozoic age falls within the span of the Alleghanian orogeny.The conclusion is that the diagenetic illite of the Maquoketa Group and that of the underlying formations formed from different precursors in different hydrologic systems. The diagenetic illite in the Maquoketa Group formed mainly during a hydrothermal or K-rich brine event ($\le$100\sp\circC) from smectite or kaolinite. During the Alleghanian orogeny the Maquoketa Group served as an aquitard to fluids ($\le$140\sp\circC) that precipitated the diagenetic illite in the older and more permeable sandstones and carbonates.U of I OnlyETDs are only available to UIUC Users without author permissio