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ABSTRACT

The Devonian-Mississippian Chattanooga (Woodford) Shale and equivalent formations are widely distributed in North America. Deposited under generally anoxic conditions during the Kaskaskian marine transgression, they are known to be important petroleum source rocks in many intracratonic basins of the Midcontinent.

The formation can be divided into several members, including the basal Misener Sandstone, and informally designated lower, middle, and upper shale members. The middle shale member is the most radioactive part of the formation, although the radioactivity of all three members decreases to the north. Isopach maps of the shale members in northwestern Oklahoma and Kansas show that the middle shale member has the greatest areal extent and thickness, indicating that it was deposited when the Kaskaskia I transgression was at its maximum. Total organic carbon content of the three shale members decreases to the north, but the middle shale member is the most organic-rich part of the formation and has the greatest component of hydrogen-rich type I and II organic matter, making it the part of the Chattanooga (Woodford) Shale likely to be the best petroleum source rock where the formation is thermally mature.

The shale members of the Chattanooga (Woodford) Shale represent a third-order depositional sequence that is bounded below and above by unconformities. The distribution and organic geochemistry of the shale members suggest that the lower, middle, and upper shale members are the transgressive and early and late highstand systems tracts of the sequence.

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