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