Stratigraphic and Economic Significance of Mississippian Sequence at North Georgetown Canyon, Idaho

Abstract

Recognition of the Mississippian sequence exposed at North Georgetown Canyon, Idaho, as a facies belt largely different from those already known in ranges on the east and west adds significantly to knowledge of the Mississippian stratigraphy and petroleum geology in the Overthrust belt of Idaho, Wyoming, and Utah. In the newly recognized facies belt in the Aspen Range, the Madison Group is represented by the Lodgepole Limestone and Mission Canyon Limestone, but only the lower part of the latter is present. The greatly thinned Mission Canyon is the westernmost known occurrence of the formation. The overlying beds of middle Osagean to middle Chesterian age are a unique combination of deep-basin shallowing upward to peritidal lithofacies that are included in a new formation, the Aspen Range Formation. An organic-rich phosphatic member at the base of the Aspen Range Formation is a possible petroleum source rock. Also, westward thinning of the Mission Canyon Limestone into the Aspen Range and its absence farther west suggest a westward pinch-out that may provide stratigraphic traps for petroleum beneath a seal formed by the phosphatic member of the Aspen Range Formation.