Petrography and Diagenesis of Upper Smackover Formation (Oxfordian), Atlanta and Pine Tree Fields, Southwestern Arkansas: ABSTRACT

The upper Smackover Formation (Oxfordian) in Atlanta and Pine Tree fields is a regressive, shallowing-upward sequence that was deposited on the upper part of a carbonate ramp that sloped gently to the south. Low-relief salt anticlines active during upper Smackover deposition led to the localization of high-energy grainstones. In the study area, the upper Smackover is divided into the following rock types: (1) bioclast-oncoid-ooid grainstone, (2) sandy ooid grainstone, (3) sandy peloid-ooid grainstone, (4) sandy calcareous shale, and (5) well-sorted ooid grainstone. The 5 rock types represent deposition in subtidal to supratidal environments. The upper Smackover was affected by diagenesis in the marine-phreatic, freshwater-phreatic, freshwater-vadose, and late-burial diagenetic environments. Early cementation in the marine-phreatic and freshwater realm preserved primary interparticle porosity. Dissolution of unstable minerals in the freshwater realm created secondary porosity. Preservation of porosity during late-burial diagenesis was controlled by 2 sedimentologic factors: (1) presence of abundant detrital quartz, and (2) sorting. Porosity was also affected by late-burial cementation. Atlanta and Pine Tree fields are productive from the upper Smackover Formation and the Schuler Formation. In Atlanta field, the producing zone in the well-sorted ooid grainstone is a structural-stratigraphic trap. The producing zones in the bioclast-oncoid-ooid grainstone in both Atlanta and Pine Tree fields are structural traps. End_of_Article - Last_Page 455------------