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The transitional Mississippian-Pennsylvanian Springer Formation, exposed in the Ardmore basin of southern Oklahoma, consists of coarsening-upward progradational sequences that were deposited in the southern Oklahoma aulacogen. The unit is divided into three sandy members: the Rod Club, Overbrook and Lake Ardmore, which are separated by shale intervals. Each of the sandy members consists of one or more of the coarsening-upward sequences. A typical sequence includes from the base upward, dark gray shale with abundant siderite concretions, rhythmically interbedded siltstones and shales, interbedded burrowed sandstones and shales, and abundantly burrowed sandstones. The latter contain wood impressions, ripple cross-laminations, and occasional festoon cross-stratification. In ddition, one of the sequences contains a thin, discontinuous marine limestone. These sequences represent the transition from an offshore/prodelta setting to a distributary mouth bar/lower shoreface setting.
One of the sequences in the Rod Club contains an additional lithofacies at its base which consists of interbedded shales and green-gray sandstones. Sedimentary features of the sandstones include: massive nongraded bedding, large lutite casts, ripple and dish laminations, flute casts, and numerous soft sediment microfaults. The general characteristics of the sandstones suggest deposition by sediment gravity flows. This lithofacies represents deposition in a slope setting, with the sandstones derived from the proximal delta/shoreface.
Offsets on microfaults in the lower Rod Club occur on two different scales. Small scale microfaults have displacements of a few millimeters. Offset on the larger microfaults (up to 5 cm, 2 in.) is expressed on both the upper and lower surfaces of a sandstone bed. There are no fault zones within the beds which suggest the faults are synsedimentary and represent deposition on an unstable slope. The microfaults are consistently oriented approximately 90° to the flute casts, and most are downthrown in the direction of transport. Paleoslope data from the flute casts and microfaults indicate the sandstones were transported southeastward along the axis of the Ardmore-Anadarko basin during deposition of the Springer.
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