This study has made possible the zonation of two major upper Smackover reservoirs productive at Walker Creek field, Lafayette and Columbia Counties, Arkansas, and a reconstruction of the depositional environments that were present contemporaneously throughout this area.

Petrographic examination of etched core plugs, petrographic-microscope studies of thin sections, core descriptions, and consultation with authors of published papers permitted a grouping of upper Smackover carbonate rocks into facies more or less environmentally controlled and similar to those already established in the literature. Minor changes in petrographic groupings were necessitated by the additional data and the numerous core descriptions incorporated in this paper; otherwise, the facies groupings of W. F. Bishop generally have been followed.

Distribution of nonskeletal particles in the sea which existed during deposition of the upper Smackover in this area resembled in many aspects that at the present northeastern tip of Yucatan.

The presence of discrete sandstone bodies and their carbonate equivalents permitted lithologic markers to be correlated throughout this area of predominantly carbonate deposition, resulting in a unique interpretation of depositional environments. Major zonations of oolite bars have been confirmed by pressure data, and dense dark limestones useful as a diagnostic facies appear to have environmental significance. Certain diagnostic phenomena disclosed in thin-section analysis indicate possible eolianite lithification in the vadose or phreatic zone.

The Walker Creek field produces from a structurally controlled stratigraphic trap containing nearly 100 million bbl of oil in place plus 100 Bcf of recoverable gas.