Origin and Characteristics of Devonian-mississippian Novaculitic Chert in Oklahoma
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Limited research has been performed since 1980 on the origin of novaculitic chert in the Arkansas Novaculite in the Ouachita Orogen of southeastern Oklahoma and in the Woodford Shale in the Oklahoma Shelf. Further research needs to be performed that applies emerging analytical technology and geologic concepts in order to formulate a more modern set of paleoenvironmental interpretations and to identify characteristics unique to each depositional setting. This study employed outcrop, core, thin section and SEM/EDS analysis to characterize and interpret the chert from megascopic to nanoscopic scales. Based on the high abundance of siliceous microfossils and the phosphatic nature of the chert, it is proposed that it formed from a biogenic silica source in a region influenced by marine upwelling and high organic productivity, which led to the development of an oxygen minimum zone. There is great similarity between the structures, sedimentation, and fabric on all scales in Woodford chert and the Arkansas Novaculite. The chert was deposited in a broad range of shelf, slope and basinal environments. On the Oklahoma Shelf the novaculitic chert was deposited atop a major Cambrian-Devonian carbonate bank. In the Ouachita Embayment, by contrast, similar chert was deposited in an oceanic setting above a succession including Cambrian-Silurian turbidite fan deposits that were likely deposited on the continental rise. Thicker bedding, a lower proportion of terrigenous sediment, and an absence of phosphate suggests that novaculite in the Broken Bow uplift was deposited in a distal setting where upwelling was less intense. Novaculitic chert within the Woodford Shale is an important component of unconventional reservoirs in the southern Midcontinent, from not only the standpoint of brittleness, but also in terms of organic content and hydrocarbon storage potential. Similarity between Woodford chert and the Arkansas Novaculite suggests that the hydrocarbon potential of novaculitic chert in the southern Midcontinent is underexplored.
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