Flood Member of Blackleaf Formation

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).
State Montana
Name Flood Member of Blackleaf Formation
Geologic age Cretaceous
Lithologic constituents
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Mudstone > Shale (Bed)
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Clastic > Mudstone > Claystone > Bentonite (Bed)dark gray silty, bentonitic shale
Sedimentary > Chemical > Chert (Bed)
Sedimentary > Coal (Bed)

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 Cascade - Chouteau - Judith Basin