Miospores and organic-walled microphytoplankton of Devonian-Carboniferous boundary beds (Bakken formation), southern Saskatchewan: a systematic and stratigraphic appraisal

Diverse and well preserved palynofloras occur in cores of the marine Bakken Formation from five wells in the Williston Basin, southern Saskatchewan. Miospores and acritarchs are abundant; prasinophyte phycomata are less common. Thirty-seven species of miospores, 21 of acritarchs, and seven of prasinophytes are illustrated herein, and most of them are described. Three miospore combinations are new � Diaphanospora angusta? (Hacquebard), Grandispora saurota (Higgs, Clayton, and Keegan), and Knoxisporites concentricus (Byvsheva) � as is one name, Vallatisporites drybrookensis. Retispora lepidophyta (Kedo) Playford, 1976 and Gorgonisphaeridium winslowiae Staplin, Jansonius, and Pocock, 1965 are the most consistently occurring species of miospores and acritarchs, respectively. Both are stratigraphically important. On marine faunal (primarily conodont) evidence, the lower member of the Bakken Formation has been assigned to the Late Devonian (Famennian) Lower and Middle Palmatolepis gracilis expansa zones, and the upper member has been considered Early Carboniferous (Tournaisian), not younger than the Lower Siphonodella crenulata Zone. The Devonian�Carboniferous boundary has been inferred to lie within the conodont-depauperate middle member. The acritarch�prasinophyte evidence from this study connotes a late Famennian to possibly early Tournaisian age for the three members of the Bakken Formation. The miospore results show that the upper beds of the lower member are not older than late Famennian (Strunian, Vallatisporites pusillites�Retispora lepidophyta Assemblage Zone), and the middle member is not older than mid-Strunian. The middle and upper members, which contain R. lepidophyta throughout, would be entirely late Famennian, following the conventional concept of that species as an indicator of latest Devonian age. However, the upper member may be all or in part Tournaisian, according to associated conodonts from the PCP et al. Flat Lake DD2�14 well. If so, R. lepidophyta in it either is reworked (our preferred interpretation), or represents the first definitive in situ Carboniferous record of that globally distributed species.