Thaynes through Dinwoody Formation: Thaynes, Woodside, and Dinwoody Formations

Thaynes Formation: Gray and tan limestone with interbedded siltstone, shale, and tan sandstone. Locally with red shale tongues. Marine. Thickness as much as 290 m (950 ft). Woodside Formation: Maroon and red siltstone, dolomite, and shale. Tidal flat. Thickness as much as 250 m (820 ft). Dinwoody Formation (TRd): Interbedded green siltstone, shale, sandstone, and carbonate that grades eastward into red shale, siltstone, and anhydrite. Nearshore and restricted marine. Thickness as much as 330 m (1,083 ft).
State Montana
Name Thaynes through Dinwoody Formation: Thaynes, Woodside, and Dinwoody Formations
Geologic age Triassic
Lithologic constituents
Major
Sedimentary > Carbonate > Limestone (Bed)
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Mudstone > Shale (Bed)
Minor
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Carbonate > Dolostone (Bed)
Incidental
Sedimentary > Chemical > Evaporite > Anhydrite (Bed)
References

Vuke, S.M., Porter, K.W., Lonn, J.D., and Lopez, D.A., 2007, Geologic Map of Montana - Compact Disc: Montana Bureau of Mines and Geology: Geologic Map 62-C, 73 p., 2 sheets, scale 1:500,000. This map was digitized in 2012 as a result of a contract between the U.S. Geological Survey and the Montana Bureau of Mines and Geology.

NGMDB product
Counties Beaverhead - Madison