This facies is best exposed at the northeast Foster section in Bates County, Missouri (figs. In addition, total clay content is generally less than 30% of rock samples. The clays in this facies are characterized by 1) illites with low crystallinity values, 2) kaolinite percentages ranging from 15% to 55%, and 3) mixed-layered clays accounting for 20-60% of clays. 12 for exact location from Aden, 1982.Īden's (1982) "shoreline-coastal facies" include coal beds with underlying seatrocks, as well as relatively high percentages of siltstone and sandstone units. Dashed line in right-hand column is placed at illite-crystallinity value = 1.2. I, illite C, chlorite K, kaolinite and M, mixed-layer clays. Dots show relative abundances of eurytopic fossils (productid brachiopods plus ostracodes). Sample points and numbers are shown by arrows. In the units immediately below thin sandstone bodies, illite-crystallinity values drop and mixed-layer clay-mineral percentages increase upward, perhaps indicating short-lived increases in sedimentation rates (Aden, 1982).įigure 45-Compositional variations in mudrock portions of Banzet formation at Neosho River Park section, Labette County, Kansas. These characteristics are best observed in the Neosho River Park section (fig. The "prodeltaic mud facies" of Aden (1982) is characterized by 1) high illite-crystallinity values, 2) mud percentages of 75% or greater, 3) kaolinite percentages less than 10%, and 4) mixed-layer clay percentages of less than 20%. Considering the clay components of these facies, it can be seen that the clay mineralogies vary as one moves vertically within measured surface sections and laterally along the outcrop belt and into the subsurface. 44).įigure 44-Ternary diagram showing composition of sandstone units in Banzet formation sampled from entire study area see appendix B for data summary.īy combining clay-mineral variation with paleontologic considerations, Aden (1982) recognized three distinct mudrock facies, which he interpreted to be related to depositional settings. Likewise, sandstone bodies tend to be medium-grained lithic arenites in northeastern Kansas (Leavenworth County cores) and become more quartzose and finer grained to the south and west (fig. In general, mudrocks become clayier southwestward from northeastern Kansas as kaolinite-rich silty shales give way to illite-rich clay shales, as determined by Aden (1982) using x-ray diffraction analyses. The outcrop samples, collected from western Missouri through southeastern Kansas and into northeastern Oklahoma, show some of these variations. The petrographic characteristics of sandstone and shale units vary between core samples collected in northeastern Kansas and those of southeastern Kansas and northeastern Oklahoma. Next Page-Paleontology, Depositional Environments
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