PENNSYLVANIAN CONODONT BIOSTRATIGRAPHY OF THE SNAKY CANYON FORMATION, EAST-CENTRAL IDAHO

Early (Morrowan) to Late (Missourian) Pennsylvanian conodonts from the Snaky Canyon Formation in east-central Idaho establish biostratigraphic dating of more-or-less continuously deposited foreland basin sequences. Within a siliciclastically influenced carbonate dominated succession, fifteen consecutive conodont biozones are defined and traceable along a 90 km. east to west transect in Idaho's Basin and Range Province. These biozones were deposited along a eustatically and tectonically influenced continental platform recording deep subtidal to nearshore, peritidal eolian, siliciclastic influenced deposition. Conodont faunas within the biostratigraphic interval are dominated (95%) by species of Adetognathus, Rhachistognathus, Declinognathodus, Idiognathodus, Idiognathoides, Neognathodus, and Streptognathodus. The 15 conodont biozones are the 1) Rh. primus biozone – lower Morrowan, 2) D. noduliferous biozone – Morrowan, 3) Id. sinuatus biozone – Morrowan, 4) I. sinuosus biozone – Morrowan, 5) St. suberectus biozone – upper Morrowan, 6) D. marginodosus/Id. sulcatus parvus biozone – lower Atokan, 7) Neo. atokaensis biozone – Atokan, 8) I. incurvus biozone – Atokan, 9) Neo. bothrops biozone – upper Atokan - lower Desmoinesian, 10) Neo. asymmetricus biozone – Desmoinesian, 11) I. obliquus biozone – Desmoinesian, 12) I. expansus biozone – Desmoinesian, 13) I. magnificus biozone – upper Des-moinesian - lower Missourian, 14) I. sp. “X” biozone – Missourian, and 15) Swadelina nodocarinatabiozone – Missourian.

These defined biozones redefine stratigraphic positioning of rock units and provide a framework for correlation. The Bloom Member of the Snaky Canyon Formation was deposited from the basal Morrowan to the earliest Missourian and the Gallagher Peak Sandstone Member was time transgressive from west (Desmoinesian) to east (Missourian). Conodonts from the lower Juniper Gulch Member indicate a Morrowan to Atokan age, making the member correlative with the Bloom Member. Palaeoaplysina buildups initially occur in the middle Desmoinesian. Tectonic and eustatic controls greatly influenced deposition during the early Atokan (eustatic), late Atokan (tectonic), and middle Desmoinesian (mixed). Cyclicity is of 4^th order (parasequence) scale that comprises at least three 3^rd order sequences.