Paper No. 4
Presentation Time: 9:00 AM
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,
. 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.
biozone – Missourian, and 15) Swadelina nodocarinata
biozone – 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 4th order (parasequence) scale that comprises at least three 3rd order sequences.