USING SEQUENCE STRATIGRAPHY TO FIND CONCENTRATIONS OF ORDOVICIAN CONODONTS IN DEEP-WATER SILICICLASTIC ROCKS

Conodonts from deep water siliciclastic bedding plane surfaces are well known, but finding conodonts on these surfaces is a 'needle in a haystack' problem. Sequence stratigraphic models suggest that when sea level is high, siliciclastic material may be choked in newly created accommodation space, resulting in less sediment being transported to deep water environments. This, in turn, results in deposition of a greater amount of biogenic material relative to siliciclastic detritus. This model explains high concentrations of conodonts on certain bedding surfaces in Lower (Floian) and Upper Ordovician (Sandbian and Katian) deposits at Trail Creek, Idaho and Black Knob Ridge, Oklahoma, USA, respectively. The Floian portion of the Phi Kappa Formation, exposed along Trail Creek Road in central Idaho, preserves a graptolite fauna from the Didymograptus bifidus - Isograptus victoriae zones.  This section also contains a low diversity, high abundance conodont fauna dominated by Periodon flabellum, Oepikodus sp,, O. communis and uncommon elements of Protopanderodus, Paroistodus proteus? and Drepanodus arcuatus?.  The Sandbian portion exposed at Little Fall Creek in central Idaho, and the Athens Shale from Pratt Ferry, Alabama, USA contain  Hustedograptus teretiusculus and Nemagraptus gracilis zone faunas, respectively. They also preserve a low diversity, high abundance conodont fauna dominated by Periodon aculeatus?,  Pygodus anserinus, and  Drepanodus?. The Katian deposits at Black Knob Ridge preserves a Climacograptus bicornis - Diplacathograptus caudatus graptolite zone fauna. This section also preserves a low diversity, high abundance conodont fauna dominated by Periodon grandis, Scabardella, Amorphognathus tvaerensis, with lower abundances of Icriodella superba?, Drepanoistodus suberectus, Protopanderodus liripipus, and Oistodus. Amorphognathus superbus? occurs near the base of the Diplacanthograptus caudatus Zone. At each locality, intervals interpreted as sea-level highstands contain biostratigraphically significant conodonts that are part of the deepwater community. This approach to finding conodonts in deep water settings should improve the resolution between conodont and graptolite zonations.