Blackleaf Formation through Ellis Group: Blackleaf, Kootenai, Mount Pablo, Morrison, Swift, Rierdon, and Sawtooth Formations

Blackleaf Formation (Kbl) - Bootlegger Member (Kbb): Dark gray shale interbedded with sandstone, siltstone, and bentonite beds. Marine. Thickness as much as 100 m (328 ft). Vaughn Member (Kbv): Black carbonaceous shale, light gray, greenish to pinkish bentonitic to tuffaceous siltstone and porcellanite, tuffaceous, arkosic sandstone, thin coal; conglomerate beds in western Montana. Fluvial and coastal delta plain. Thickness as much as 200 m (656 ft). Taft Hill Member (Kbt): Black shale, gray bentonitic siltstone, and glauconitic sandstone. Marine. Thickness as much as 180 m (590 ft). Flood Member (Kblf): Upper part: medium gray, cliff-forming fine- to medium-grained chert-rich, quartzose sandstone, middle part medium to dark gray shale or gray siltstone; lower part: yellowish brown, gray, or olive gray fine-grained sandstone and siltstone with carbonaceous laminae and thin films of coal and dark gray silty, bentonitic shale. Sandstone beds thin eastward. Quartzose basal sandstone in southwestern Montana. Nearshore marine, tidal flat, and lagoon. Thickness as much as 230 m (755 ft). Kootenai Formation (Kk, Kku, Kkm, Kkl): Red, maroon, and olive gray mudstone, tan or gray siltstone, calcareous concretions, limestone beds, and several prominent sandstone beds that include the Greybull Member (top of the formation in south-central Montana) and the Sunburst Member (middle to lower part of the formation in northwest-central Montana), both dominantly quartzose sandstone. Basal Cutbank or Pryor Conglomerate. Alluvial plain with local marine influence in the north. Thickness as much as 335 m (1,099 ft). Mount Pablo Formation: Reddish gray and grayish green mudstone and dark gray shale interbedded with gray limestone and sandstone. Gray basal conglomerate or conglomeratic sandstone. Alluvial plain. Thickness as much as 30 m (98 ft). Morrison Formation (Jm): Green, gray, or red mudstone and marlstone with subordinate limestone and sandstone beds. Upper part Neocomian age in central Montana and contains carbonaceous black shale and coal. Fluvial, paludal, and lacustrine. Thickness as much as 180 m (590 ft). Ellis Group (Je) - Swift Formation (Jsw): Orangish brown, glauconitic, flaggy-bedded, commonly fossiliferous, fine-grained sandstone or sandy coquina with subordinate dark gray shale interbeds; chert pebbles common. In west-central and northwestern Montana, a dark gray, noncalcareous, micaceous shale forms the lower part of the formation, commonly with a basal chert-pebble conglomerate or conglomeratic sandstone as much as 3 m (10 ft) thick. Shallow marine. Thickness as much as 70 m (230 ft). Rierdon Formation (Jr): Gray, locally fossiliferous limestone that may contain floating grains of quartz sand, interbedded with greenish gray limy shale. Lagoonal and marine shelf. Thickness as much as 105 m (344 ft). Sawtooth Formation: Western Montana: dark gray, platy to shaly, dense limestone with local basal conglomerate. Central Montana: upper calcareous siltstone, middle dark gray shale with thin limestone interbeds, and lower fine-grained sandstone. Three local members Bowes, Firemoon, and Tampico, in descending order. Bowes Member: dark gray to medium gray, calcareous mudstone, limestone, and quartzose sandstone. Firemoon Member: dark to medium gray, limestone and calcareous mudstone. Tampico Member: very light gray, well-sorted quartz sandstone and siltstone, and chert-pebble conglomerate. Shallow marine. Thickness as much as 205 m (673 ft).
State Montana
Name Blackleaf Formation through Ellis Group: Blackleaf, Kootenai, Mount Pablo, Morrison, Swift, Rierdon, and Sawtooth Formations
Geologic age Cretaceous and Jurassic
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Shale (Bed, Carbonaceous)
Sedimentary > Clastic > Siltstone (Bed, Tuffaceous, Calcareous)
Sedimentary > Clastic > Sandstone (Tuffaceous, Arkosic, Glauconitic)
Minor
Sedimentary > Carbonate > Limestone (Bed)
Sedimentary > Coal (Bed)
Sedimentary > Clastic > Conglomerate (Bed)
Sedimentary > Clastic > Mixed-clastic > Conglomerate-sandstone (Bed)
Sedimentary > Clastic > Mudstone > Claystone > Bentonite (Bed)
Sedimentary > Carbonate > Marlstone (Bed)
Sedimentary > Clastic > Mudstone > Shale > Black-shale (Bed, Carbonaceous)
Sedimentary > Clastic > Mudstone (Bed, Calcareous)
Incidental
Sedimentary > Clastic > Mixed-clastic > Siltstone-mudstone (Bed)silty shale
Sedimentary > Carbonate > Limestone > Coquina (Bed)sandy coquina
Sedimentary > Chemical > Chert (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 Lewis and Clark - Pondera - Teton