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Abstract

Tripolitic chert development in the southern Ozark region is associated with a third-order, transgressive-regressive cycle comprising St. Joe transgressive packstones, succeeded by lower Boone calcisiltites, with black, penecontemporaneous, nodular chert deposited during maximum flooding, overlain by basal upper Boone calcisiltites deposited during highstand. The onset of regression produced upper Boone packstones and grainstones with white-gray, later diagenetic chert reflecting groundwater replacement along bedding planes. Tripolitic chert is a product of the highstand calcisiltites at the base of the upper Boone Formation of Arkansas, and its equivalent, the Elsey Formation of southern Missouri. This tripolitic chert appears to reflect a hydrothermal event likely occurring after the emplacement processes of both Boone cherts that had ended by Chesterian time. After hydrothermal silicification, the interval experienced groundwater removal of most of the remaining carbonate leaving open porosity characteristic of tripolitic chert. A second hydrothermal event precipitated terminated and doubly terminated quartz crystals as well as quartz druse in the cavities produced by the earlier carbonate leaching from the tripolitic chert. Timing of the hydrothermal events is not clear, but they may reflect lateral secretion produced by the Ouachita Orogeny in the late Pennsylvanian.

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