Abstract Sedimentary facies deposited in channel and interchannel positions within an actively prograding, river-dominated delta are illustrated at two localities near the Arkansas-Oklahoma border south of Fort Smith, Arkansas. Locality 1 (94°17—20"W.; 35°11'41—N.; Greenwood, Arkansas, Quadrangle) is a distinctive, terraced roadcut on U.S. 71, approximately 12 mi (20 km) south of Fort Smith (Fig. 1). The Hartshorne Sandstone dips steeply north (nearly vertical) along the north limb of the Washburn anticline (Fig. 2). Locality 2 (94°31—20W.; 35°10—30"N.; Spiro, Oklahoma, Quadrangle) is a roadcut on old Oklahoma 112, approximately 8 mi (12 km) west of Hackett, Arkansas (Fig. 1). The Hartshorne Sandstone dips 15° southward along the southern limb of the Backbone anticline (Fig. 2).

Abstract Shale gas is produced from the Woodford, Caney, and Fayetteville shales (Devonian and/or Mississippian), and coal-bed gas is produced from the Hartshorne and McAlester coal beds in the Arkoma basin of Oklahoma and Arkansas. The U.S. Geological Survey is currently assessing the technically recoverable hydrocarbon resources of the Arkoma basin and for assessment purposes has divided the continuous shale gas (unconventional) resources into three total petroleum systems together with their associated assessment units (AUs). Each of the gas shale AUs contains 2.5 % or more total organic carbon, is thermally mature with respect to gas generation over much of its area within the basin, and may be accessed by the drill at depths less than 14,000 feet. In addition, the Woodford, Caney, and Fayetteville Shale Gas AUs underlie relatively large areas that have not been tested adequately by the drill. Coal-bed gas is currently being produced from the Hartshorne and McAlester coal beds in the Arkoma basin, and for assessment purposes they have been grouped together into one total petroleum system and one AU. Much of the area where the coal beds are relatively shallow in the northern part of the AU has been drilled. However, the area underlain by coal in the southern part of the basin, which is deeper and more structurally deformed, remains largely unexplored for coalbed methane.

Abstract The Arkansas basin in eastern Oklahoma, as in central Arkansas, is a westerly trending topographic and structural trough wherein enormous thicknesses of Paleozoic rocks have been preserved, at least 20,000 feet in the deeper parts. Within this region there are many long, narrow anticlines of major magnitude, generally faulted, and many faults not associated with anticlinal folds. This region extends south from the northern and western limits of the outcrop of the Hartshorne sandstone to the Choctaw fault. Within it are several gas-producing structures, a few of major importance. Production is mostly from the Hartshorne sandstone (basal Allegheny) of Pennsylvanian age, but there are also gas-bearing sandstones higher in the Allegheny succession of rocks and lower in the Atoka and Wapanucka formations of the Pottsville subdivision. There are not less than 30 gas-bearing zones within the region. The gas-bearing sandstone reservoirs are commonly lenticular, and the producing areas do not necessarily conform with the structural form of the folds. The most important gas-producing locality, at this time, is the Kinta-Quinton-Featherston district in Haskell and Pittsburg counties. It consists of gas-producing areas scattered along the axis of a west-southwest pitching anticline, faulted on the north flank. Gas only has been produced within the confines of the region. Some attribute this phenomenon to the degree of metamorphism shown by the carbon ratio of coals, others to conditions of sedimentation prevailing prior to consolidation of the sediments.