Sedimentary Petrology and Provenance of the Teddy Creek Group SW Montana

The TCG consists of a basal pebble-conglomerate with distinctive black chert clasts overlain by sandstones interlayered with white-purple volcanic ash. All lithologies have experience an episode of post-deposition silicification. Petrographic analysis reveals sandstones are compositionally mature with high abundances of quartz and minor amounts of feldspar and muscovite or biotite mica. Most grains and lithic clasts are subrounded; however monocrystalline quartz grains are subangular. The TCG also preserve crossbedded laminations indicating a fluvial depositional environment as well as fragments of petrified wood. In contrast, the Renova Formation consists mainly of tuffaceous sandstones containing abundant muscovite and biotite micas. The presence of the micas is attributed to the unroofing of the Idaho batholith. However, the general lack of micas, especially biotite, in the TCG suggests a different source than that of the Renova Formation.