ABSTRACT

Atoka Formation (Lower Pennsylvanian, Atokan Series) sandstones along the western margin of the Arkoma Basin show distinct north-south petrologic differences. To the north, in the shallower parts of the basin, Atoka sandstones chiefly are very fine to fine-grained, very well to well-sorted quartzarenites. They were derived from pre-existing sedimentary terranes and mostly represent offshore bar deposits that accumulated on a southward dipping shelf. Dissolution of early calcite cement was an important diagenetic process because it generated zones of high porosity (35%) and permeability (1,425 md) in the rocks.

In contrast, Atoka sandstones to the south in the deeper parts of the basin chiefly are fine-grained, moderately well to moderately sorted sublitharenites and subarkoses. They were derived from sedimentary and metamorphic terranes and probably represent offshore bar deposits that accumulated near the outer shelf margin. Moreover, early calcite cement is lacking in these sandstones and porosity and permeability are considerably reduced by compaction, pressure solution, and clay authigenesis.