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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.
Arkoma basin is a prolific natural gas basin. The defining feature of this basin is the Atoka Formation that was deposited in the early-middle Pennsylvanian. The Atoka is held equivalent to the tectonic and structural evolution of the basin. This study focuses on one of the many gas fields in the Arkoma Basin in Arkansas to assess the stratigraphic and structural evolution that the strata in this particular field display. Aetna Gas Field extends from T. 8N. R. 27 W to T. 9 N, R. 27 W and T. 8 N, R. 26 W to 8N, R. 27. Geographically, Aetna field covers parts of Franklin, Johnson and Logan counties. It is one of the pioneer gas fields in the Arkoma Basin. First discovery of gas in Aetna Field was made in March 1928. The first three producing wells were completed in the upper Carpenter and middle Alma sands of the middle Atoka Formation. An analysis of structures and stratigraphy of the gas field through well log correlations reveal a combination trap for the gas. Using IHS Petra, stratigraphic correlations were performed on 49 wells in 10 cross sections. The wells selected were sorted by several criteria. Gamma ray logs were given priority. Stratigraphic tops were determined for correlation purposes. The stratigraphic tops were picked and correlated. The middle Atoka Formation was addressed exclusively for the purpose of this study. Structural analysis indicates an arch-and-trough setting that led to gas accumulation in this field. The stratigraphic analysis confirms a thickening to the south following the general southern thickening trend of Atoka Formation in the Arkoma Basin.
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.
The Arkoma Basin of Arkansas and Oklahoma formed in the Ouachita foreland during the late Mississippian and Pennsylvanian periods (about 290- to 330 million years ago). The basin developed in response to convergent tectonic boundaries that closed obliquely from west to east associated with Ouachita orogenic event. The Backbone anticline in the northern Arkoma Basin is a prominent product of this convergence, and represents the first major component of this study. The structure is asymmetric with beds on the southern limb dipping steeply to the south. It is also expressed topographically as a prominent ridge that trends eastward from the Oklahoma-Arkansas border approximately 30 miles. The ridge is bounded on the northern side by a steeply dipping normal fault with most of the sedimentary exposure occupying a position on the southern hanging wall of the structure. Strata involved in the structure are sandstone and shale units from the middle and upper part of the Atoka Formation. A recent road cut in southern Sebastian County, Arkansas exposes a complete and continuous section of more than 600 feet in thickness through an upper Atoka sandstone unit along the Backbone anticline. A subsurface stratigraphic study of the middle of the Backbone anticline was also conducted. Several normal and some reverse faults were noted from cross-sections of the subsurface using IHS PETRARTM software program. The upper 5400 feet of the Atoka Formation includes intervals from the middle and upper part of the formation. This interval extending from the Casey Sand to the Upper Alma Formation was examined by means of three cross-sections prepared from wire line logs to determine the role of faulting in the sedimentary section