Sedimentology and Depositional Environments of the Lower Atokan Spiro Sandstone in the Wilburton, Red Oak, and Kinta Fields, Arkoma Basin, Oklahoma

Abstract

The Lower Atokan Spiro Sandstone is located in the Arkoma Basin of Oklahoma. The Spiro is the main natural gas producing interval in the basin and therefore, has received much attention. Stratigraphic cross sections, isolith maps, cores, thin sections, and outcrops were used in the study to determine the depositional environments of the Spiro Sandstone. Multiple thrust sheets in the southern portion of the study area posed some difficulty in the preparation of maps and cross sections. In order to properly map the distribution of the Spiro interval the thrust sheets were restored to their previous stratigraphic position. This was accomplished by mapping individual thrust sheets and determining the approximate value of shortening. When the value of shortening was determined the thrust were pulled back and palinspastic maps of the Spiro interval were constructed. In the earliest Atokan a marine regression resulted in the formation of incised valleys on the shelf. These valleys were eroded into the Sub-Spiro Shale and locally into the Wapanucka Limestone; they provided a conduit for the transport of sediments from the north. During the lowstand small wavedominated deltas were forming at the mouth of the channels. Accompanying the progradation of the deltas sedimentation in the channels began to progress updip from the deltas. A subsequent, northward marine transgression resulted in the backstepping of the deltas and infilling of the incised valleys. With continued sediment influx and continuing northward marine transgression, the reworking of the deltas and the upper part of the incised channel fill sediments generated the Spiro Sheet Sand.