Shale Shaker Vol 72, No 4 July-August 2021

An IntactThirty Four Foot Long Petrified Log in theWoodford Shale, Oklahoma: AQuestion of Preserving Geological Heritage, cont. Oil and Gas Exploration

1998). The Woodford shale also preserves the record of Late Devonian and Devoni- an-Carboniferous mass extinction events that are regarded as one of the five largest Phanerozoic mass extinction events (Raup and Sepkowski, 1982). For these reasons, the Woodford Shale can arguably be con- sidered as the most important stratigraphic unit in Oklahoma. Local Geology The Lawrence Uplift is a modest sized horst block about 30 miles northeast of the Arbuckle Mountains (Figure 1b). The Ahloso and Stonewall faults are the re- spective northern and southern boundaries (Figure 1a). The Lawrence Uplift is a rela- tively flat lying block. The surface geol - ogy is dominated by the Woodford Shale rimmed by the underlying Hunton Group

carbonates. The low dips result in poorer exposures of less complete stratigraphic section than in the more studied roadcut outcrops of the Arbuckle anticline. The early work of Huddle and Hass (1965) relied on outcrop along creeks. However, currently the best exposures are the nu- merous shale pits and quarries that pro- vide road fill material (Figure 2). Huddle and Haas (1965) studied the Woodford Shale at 5 locations on the Lawrence Uplift (Figure 2). Each section is incomplete and relatively thin (C-1ft, D-1.6ft, E-22ft, F -no thickness given, G- 21.6ft). Augmenting the work of Huddle and Hass (1965) with some additional sec- tions Over (1990) constructed a composite stratigraphic column on the Lawrence Up- lift and established regional correlations based on conodont biostratigraphy and

lithology (Figure 3). Our cursory obser- vation at five quarries and previous de - scriptions (Over, 1990, 1992; Huddle and Hass, 1965) suggest that there is less bed- ded chert and a higher proportion of silty beds (Figure 4) in the uplift compared to exposures further south. At most of the shale pits operators merely scrapped off the Woodford from the top down resulting in good exposures of bed tops and fracture patterns (Figure 5) but limited vertical in- formation (Figure 6). The most complete section of Woodford on the Lawrence Uplift is a 120ft long behind-the-face core taken at the Wyche Quarry which has recently reopened to provide riprap for the expansion on State Highway 3 (Figure 7). Bulk geochemi- cal and biomarker data from the Wyche Quarry core show that on the Lawrence Figure 2 - Lawrence Uplift locations of Hass and Huddle sections (red circles) and Woodford shale pits and quarries (green circles).

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