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

uplift the organic matter in the Woodford Shale is composed of immature, type II marine kerogen (Figure 8). Furthermore, these data show that photic zone euxinia increased upward from the lower Wood- ford into the middle Woodford and that a deep, persistent chemocline likely typified the upper Woodford deposition (Connock et al., 2018). Petrified Log Discovery During our reconnaissance work for an up- coming field trip, we came across a most remarkable find, a 34ft (10m) long log of petrified wood that is more than 3ft (1m) wide (Figure 9). The full length could not

be determined because the east end of the log is buried. Petrification has exquisitely preserved some of the primary fabric of the log including bark (which appears to be coalified) (Figures 10a, 10b), vascular tissue (Figure 10c), and differential com - paction in the encasing siliceous mudrock (Figure 10d). We believe that this log was rafted offshore and sank into the euxenic water bottom to be preserved. Most pre-Pennsylvanian petrified wood in Oklahoma has come from the Wood- ford Shale and is the Progymnosperm Archaeopteris, genus Callixylon (Sune- son, 2010). Until properly identified by a paleobotanist, we consider the quarry

log as petrified Callixylon. Callixylon is one of the oldest “true” petrified woods and probably formed Earth’s first forests of vascular plants. Petrified wood in the Woodford occurs throughout the areal extent of the Woodford but is not a fre- quent occurrence. It is interesting that the pyrolysis data from the Wyche Quarry (modified vanKrevelen diagram, Figure 8) yields a classic algal source rock from the Woodford Shale with little indication of having Type-3 terrestrial kerogen from humic, woody debris. Biomarker data (poly-aromatic hydrocarbons) around the Frasnian-Famennian boundary from the Woodford Shale and other Devonian sec- tions globally show an influx of pyrogenic

Figure 7 - North wall of the active Wyche Quarry. The vertical fractures are part of the regional EW fracture set.

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