PROVENANCE OF EARLY MISSISSIPPIAN BAKKEN CLASTICS BASED ON DETRITAL ZIRCON AND DETRITAL CONODONTS

The middle sandstone member of the Bakken Formation (MBM) is a widespread silty sandstone sheet that accumulated in shallow marine settings across the Williston Basin during the latest Devonian- early Mississippian. Sediment sourcing for such widespread sandstone sheets is typically associated with major sediment-dispersal systems. In the case of MBM, neither provenance nor sediment dispersal systems have been identified. This study aims to (1) constrain the provenance of MBM clastic deposits and to (2) understand the sediment dispersal system of these deposits, using an approach that combines detrital zircon U-Pb geochronology and reworked conodonts recognized by colour alteration index (CAI) and preservational variations. Detrital zircon U-Pb analysis and reworked conodonts from three MBM samples indicate sediment transport from local basement as well as thrust-belt sources to the north and northeast. Four detrital zircon age populations include: (1) early Paleozoic to late Neoproterozoic 370- 700 Ma grains that were shed from the Franklinian and Caledonian orogens, (2) Mesoproterozoic 850- 1500 Ma grains derived from the Grenville orogeny, (3) Paleoproterozoic 1600- 2100 Ma grains similar to Yavapai-Mazatzal provinces, and (4) early Paleoproterozoic to late Archean grains 2400-2900 Ma that were shed from the Canadian Shield to the east. Population 1 is accompanied by reworked conodonts of Chirognathidae and Protopanderodontidae suggesting M-U Ordovician sources (445- 470 Ma) and other elements may be as young as L-M Devonian (385- 420 Ma). These conodonts have much higher CAI values compared to in-situ specimens indicating that they may have been buried to depths in excess of 3 km prior to uplift and exhumation. Our findings suggest derivation of at least 30% of Bakken clastics from northern sources exhumed during the middle Devonian Franklinian orogeny. This interpretation suggests sediment transportation most likely by long-shore drift. Outlining sediment provenance and dispersal systems has implications for rock property distribution and prediction and reservoir facies modeling in the Bakken Formation.