Sedimentology of the Hannibal formation in Northeastern Missouri and Western Illinois
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thesis / dissertation description
"The Hannibal Formation (Kinderhookian) occurring in northeastern Missouri and western Illinois is a fine-grained, terrigenous, sedimentary unit which can be divided into an upper and a lower portion, based on lithology. The upper portion consists of alternating coarse and argillaceous, fine siltstone units, while the lower portion consists of a silty mudstone with an occasional thin siltstone unit. At the extreme western margin of the formation, near where the Hannibal almost pinches out, the formation consists entirely of a silty claystone. Extending southward along the study area, the coarse siltstone units of the upper Hannibal become thinner, and eventually pinch out completely. Results obtained from petrographic study, grain-size analysis, and sedimentary properties indicate an upward-coarsening sequence in most coarse siltstone units. These units consist of predominantly poorly sorted, angular, coarse and medium silt-size particles. Sand-size particles also occur in the Hannibal, but in very minor quantities.The Hannibal contains associated trace fossils which represent Seilacher's Cruziana and Zoophycus facies, indicating tranquil, shallow water, marine conditions.X-ray analysis indicates four clay mineral assemblages. Dioctahedral illite is the most prominant clay mineral, with disordered kaolinite occurring in substantial quantities. Iron and magnesium-rich chlorite and vermiculite also occur in the formation, but in relatively minor amounts.The Hannibal sediments were deposited in a restricted, shallow, tranquil sea from a northern source area. A low-lying drainage area, restricted marine circulation, and the possible existence of barrier islands explain the occurrence of predominantly silt and clay deposits, with only traces of sand-size particles. The study area is located in the distal portion of the formation, where the lower Hannibal mudstones represent pro-delta deposits, and the upper Hannibal siltstones represent delta front deposits"--Abstract, pages ii-iii.