LATE DEVONIAN ORGANIC-RICH WOODFORD SHALE DEPOSITS AND THE FRASNIAN/FAMENNIAN (F/F) AND DEVONIAN-CARBONIFEROUS (D/C) GLOBAL ANOXIC EVENTS

The Woodford Shale was accumulated in the Late Devonian – Early Mississippian time when anoxic global events have been described for the Frasnian/Famennian (F/F) boundary (Lower and Upper Kellwasser events), and the Devonian / Carboniferous boundary (Hangenberg event). This work shows a compilation of d¹³C stable isotopes, organic geochemistry, biomarkers, palynology, thin sections, SEM-EDX and X-ray fluorescence element compositional analysis from Woodford Shale rocks cored by the Wyche-1 well, Lawrence Uplift, Pontotoc Co., Oklahoma. The core was subdivided into Welden Shale and Lower, Middle and Upper Woodford intervals, where nine (9) lithofacies were defined. A series of positive isotopic Carbon excursion were correlated with the Kellwasser and Hangenberg events, thanks to the temporal restrictions supported by a detailed conodont zonation reported from adjacent localities.

The stratigraphic relationship between the organic rich Woodford Shale deposits with the positive d¹³C isotopic excursions, the anoxic (euxinic) shallow seawater conditions interpreted by biomarker (C40 Carotenoids and Aryl-Isoprenoids) compounds help to support the idea that the organic-rich middle Woodford Shale deposits was related with the F/F anoxic and faunal crises. Moreover, molybdenum/TOC ratios show changes in the paleo-redox and deep-water circulation conditions from more restricted circulations in the Lower/Middle Woodford Shale toward more open marine deep-water circulation during the accumulation of the Upper Woodford Shale. The titanium (Ti) concentrations relative to aluminum (Al) reflect a possible coastline progradation in agreement with a higher content of pollen and spores respect to the marine palynomorphs (i.e. tasmanites and acritarchs).