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The east-to-west oriented Arkoma Basin is a peripheral foreland basin or depositional trough that developed during the Carboniferous Period. This formation covers an aerial extent of approximately 33,800 square miles and spans from west-central Arkansas into southeastern Oklahoma (McGilvery, Manger, and Zachry, 2016; Perry, 1995). The Atoka Formation, deposited during the early Pennsylvanian, is the largest Paleozoic formation by aerial extent in the state of Arkansas and is located within and comprises the bulk of Arkoma Basin sediments (McFarland, 2004; Nance, 2018). This formation has been informally divided into three divisions, the lower, middle, and upper, based on their stratigraphic response to differing tectonic processes. A tectonostratigraphic interpretation was made for each division of the Atoka Formation using high resolution cross sections; correlated using well log, seismic, and surface data. Five condensed regional transects were constructed that aided in the development of a cross section "grid" meant to represent the deep marine to shallow marine depositional hinge lines. Each of the three Atoka divisions have a different dominant depositional force. The Lower Atoka deposition was dominated by eustasy, and with sediment supply from the start of Arkoma Basin tectonics, the middle division was dominated by tectonic subsidence and the upper was dominated by sediment supply. The transition between the Atoka divisions and the magnitude of migration between each deep marine hinge line indicates the progradation of the Upper Atoka depositional cycles occurred more rapidly than the retrogradation of the Middle Atoka. The maximum flooding of the formation occurred within the Middle Atoka's uppermost informal member, the Morris Member. The Lower Atoka was deposited on an extensive tectonically stable structural platform, which is supported by no lithostratigraphic transition to deep marine deposits within this project's study area. The deep marine deposition is characterized by shales encapsulating tumultuously distributed and isolated sandstone complexes. These sandstone complexes are not correlated to the shallow marine sandstones by anything but a condensed geologic timeline.
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The Arkoma Basin is a Carboniferous peripheral foreland basin creating a structural depression covering an approximate area of 33,800 miles2 that extends through east-central Oklahoma and west-central Arkansas. The entire basin fill includes Pre-Mississippian carbonate shelf deposits, Mississippian marine carbonates and black shales, and Pennsylvanian mixed carbonated/clastic and shore zone/deltaic deposits. The Lower Atoka formation (Pennsylvanian) occurs in outcrop along the southern Boston Mountain Plateau in northern Arkansas and extends into the subsurface of the Arkoma Basin over an area of 2,300 miles2. The Lower Atoka ranges from 600 to 1500 feet in thickness and represents a cyclic succession of stacked shelf to shore zone/deltaic deposits recording a single 3rd order (1-10 m.y.) Vail/Exxon depositional sequence. It was deposited across a broad, tectonically stable platform along the southern margin of Laurasia just before its collision with the Gondwana and the formation of Pangea at the end of the Paleozoic. Tectonic influences meant that it was not a 100% stable platform during the Lower Atoka deposition. This affected the deposition of all the sequences in the Lower Atoka. Topographic relief on preceding deposition also helped create areas of accommodation space filled by offset, compensation bedding. Finally, subsidence on a passive margin has been argued to be up to almost 4 km. This helps explain the "long distance" shoreline shifts and cyclicity in the current time of deposition. This means that these 4th to 5th order cycles (10's to 100's k.y.) may reflect glacio eustacy and sediment supply and can be correlated across the entire area or a very large area. In addition, there appears to be a tectonic over print that influences onlap edges that define northern limits and areas of bypass and nondeposition.