BUTTS, SUSAN H., University of Idaho, Department of Geological Sciences, Moscow, ID

ABSTRACT: Paleontology and Paleoecology of the Arco Hills-Formation (Chesterian), South-Central Idaho

The purpose of this research is to determine the stratigraphy, biostratigraphy, paleoecology, sequence stratigraphy, and reservoir quality of the Upper Mississippian (Chesterian) Arco Hills Formation. The geographic range of the Arco Hills Formation is limited to the southern Lost River, Lemhi, and Beaverhead ranges, north of the Snake River Plain in south-central Idaho, but time equivalent units are found throughout southern Idaho, Montana, Utah, and Wyoming.

The Arco Hills Formation represents the final stage of deposition in the Late Paleozoic Antler-generated foreland basin. The unit has tempestites with abundant shell lags that have moldic porosity reservoir potential. It precedes cyclic coralalgalhydrozoan organic buildups, the equivalents of which are significant producers in the Paradox Basin.

The fauna of the Arco Hills Formation is well silicified and the unit has excellent exposure, which makes it ideal for paleontological analysis. Extraction of fossils by digestion of the matrix with muriatic acid yields near perfect whole fossils for systematic paleontological analysis. Sand left over from acidized carbonate samples will be examined in prepared thin sections to determine sediment source and transport direction of siliciclastic sediment.

Paleoecological analysis is based on faunal associations within individual beds and the relationship of organisms to sedimentation (including amount of siliciclastic input and nature of available substrate). Finally, with baseline data at hand, parasequences and larger scale cycles will be incorporated into a sequence stratigraphic framework.

AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid