A NEW SPECTRAL GAMMA-RAY PROFILE OF UPPER DEVONIAN/LOWER MISSISSIPPIAN WOODFORD SHALE ON THE SOUTH FLANK OF THE ARBUCKLE ANTICLINE, ARBUCKLE MOUNTAINS, OKLAHOMA (Invited Presentation)
This new profile contains gamma-ray patterns observed at an outcrop section located about four kilometers to the west. Notably, a major SGR “marker” with about 100 ppm of uranium is present in both locations. In the greater southern Arbuckle Mountains area, this SGR marker occurs at the top of the informal middle member of the Woodford Shale and is used to subdivide the mudstone on a sub-regional basis.
Historically, identifying the contact between the Woodford Shale and the overlying Sycamore Limestone using geophysical well logs or cuttings has been problematic (e.g., the contact may be abrupt or gradational). The contact in the Springer quarry is clearly gradational with intercalated beds of Woodford Shale lithofacies and poorly lithified gray-green mudstone characteristic of the overlying Sycamore Limestone. The gray-green mudstone is clay-rich and ductile in comparison to the siliceous and brittle Woodford Shale. The first occurrence of gray-green mudstone in the quarry is about four meters from the top of the exposure. Above this first occurrence, the gray-green mudstone changes back to Woodford Shale lithofacies. The gray-green mudstone interval contains the highest concentration of potassium and thorium observed in the SGR profile.