Lower Mississippian Chert Development, Southern Midcontinent Region

Journal of the Arkansas Academy of Science Volume 70 Article 12 2016 Lower Mississippian Chert Development, Southern Midcontinent Region J. M. Cains University of Arkansas, Fayetteville, A. Potra University of Arkansas, Fayetteville E. D. Pollock University of Arkansas, Fayetteville Follow this and additional works at: http://scholarworks.uark.edu/jaas Part of the Geology Commons, and the Hydrology Commons Recommended Citation Cains, J. M.; Potra, A.; and Pollock, E. D. (2016) "Lower Mississippian Chert Development, Southern Midcontinent Region," Journal of the Arkansas Academy of Science: Vol. 70 , Article 12. Available at: http://scholarworks.uark.edu/jaas/vol70/iss1/12 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact , . Journal of the Arkansas Academy of Science, Vol. 70 [2016], Art. 12 Lower Mississippian Chert Development, Southern Midcontinent Region J.M. Cains*, A. Potra, and E.D. Pollock Department of Geosciences, University of Arkansas, Fayetteville, AR 72701 *Correspondence: Running title: Lower Mississippian Chert Development, Southern Midcontinent Region Abstract Introduction The Lower Mississippian Boone Formation is a chert-bearing, fossiliferous limestone typically 100115m. thick forming the Springfield Plateau across the tri-state region of northwestern Arkansas, southwestern Missouri, and northeastern Oklahoma. The Boone represents the maximum flooding, highstand, and regressive intervals of a single, third order transgressive-regressive carbonate cycle bounded by regional unconformities. Two types of chert occur in this formation, and provide the basis for subdivision of the Boone into informal lower and upper members in northern Arkansas. The lower Boone represents early Osagean maximum flooding conditions and consists of calcisiltites with interbedded dark, nodular chert. This chert exhibits compaction phenomena and shrinkage fractures, indicating a penecontemporaneous origin from reorganization of silica immediately below the sediment water interface prior to lithification of the carbonate sediments (Manger et al. 1988a). The upper Boone represents late Osagean highstand and regression and consists primarily of carbonate grainstones and packstones (Shelby 1986). This interval contains white, later diagenetic chert, interpreted as a groundwater phenomenon in which silica has replaced lithified carbonate along its bedding planes, replicating the fabric of the limestone (Manger and Shelby 2000). This later diagenetic chert replacement favors the finer grained intervals and replicates the fabric of the limestone being replaced. Previous studies have shown that the penecontemporaneous chert typically comprises 4050% of the lower Boone interval, while the later diagenetic chert contribution to the upper Boone ranges from 30-95% (Liner 1979). Understanding chert development is unsettled, and has been the subject of debate, primarily involving the source of the silica producing the chert, and the mode of formation of the chert-bearing intervals. Geochemical analyses suggest a volcanic rather than biogenic source for the silica in the Boone Formation. The Lower Mississippian Boone Formation is a succession of chert-bearing limestones deposited on a carbonate platform called the Burlington Shelf (Lane 1978). This succession in northern Arkansas reflects production of carbonates within effective wave base and subsequent transportation and deposition of excess sediment down ramp. There are two types of chert development in the Boone Formation that can be easily identified in outcrop and hand sample— penecontemporaneous and later diagenetic chert. Historically, Boone chert development has been attributed to a biogenic source (Hesse 1990). This study suggests that the primary silica source for the chert is more likely volcanogenic. Geologic Setting The geology of the southern midcontinent is dominated by the Ozark Dome, a broad, asymmetrical cratonic uplift (Manger et al. 1988b). A sedimentary section of Cambrian through Pennsylvanian units dips radially away from the Precambrian core (Manger et al. 1988b). Northeastern Oklahoma and northern Arkansas make up the south and west flanks of the dome, where beds are regionally dipping less than one degree (Chinn and Konig 1973). A series of major en echelon normal faults trends northeast-southwest, and are downthrown on the southeast (Manger et al. 1988b). Three broad plateau surfaces are developed away from the center of the Ozark Dome, and include the Salem, Springfield, and Boston Mountains Plateaus. The Salem Plateau consists of Ordovician rocks, primarily limestones, dolomites, and orthoquartzitic sandstones exposed across much of southern Missouri and adjacent northern Arkansas. The Springfield Plateau comprises a thin and sporadic Silurian and Devonian section, succeeded by a thick, pervasive Lower Mississippian section at its top. The Boston Mountains Plateau includes Upper Mississippian through Middle Pennsylvanian strata (Manger et al. 1988b). Journal of the Arkansas Academy of Science, Vol. 70, 2016 59 Published by Arkansas Academy of Science, 2016 59 Journal of the Arkansas Academy of Science, Vol. 70 [2016], Art. 12 J.M. Cains, A. Potra, and E.D. Pollock Lithostratigraphy Differences in lithostratigra lithostratigraphic phic nomenclature exist within the tri tri-state state area of northwestern Arkansas, northeastern Oklahoma, and southwestern Missouri. The term Boone is the oldest valid designation for the chert bearing limestone in the southern midcontinent, chert-bearing the name being credit credited ed to J.C. Branner in 1891 for Boone County, Arkansas. Arkansas is the only state to formally use the name Boone, whereas the equivalent chert bearing carbonate interval in Missouri is divided chert-bearing into three formations (ascending order): Reeds Spring, Elsey, and Burlington Burlington--Keokuk Keokuk (Manger and Thompson 1982). In Oklahoma, this interval is designated the Reeds Spring and overlying Keokuk Formation (Huffman 1958). Recently proposed revisions in Oklahoma promote use of the names Reeds Spring and overlying Bentonvi Bentonville lle Formation, presumably separated by an unconformity (Mazzullo et al al. 2013). The Boone Formation in northern Arkansas is subdivided informally into lower and upper members primarily based on chert content, but the transition from lower to upper Boone is also marked by a change to coarser coarser-graine (...truncated)