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Mineral Resources > Online Spatial Data > Geology > by state > Montana Geology

Geologic units in Carter county, Montana

Hell Creek formation (Phanerozoic | Mesozoic Cenozoic | Cretaceous-Late Tertiary | Paleocene) at surface, covers 19 % of this area

Hell Creek formation: somber-gray sandstone and greenish shaly clay and mudstone containing dinosaur bones; a few thin lignite and subbituminous coal beds.

Lithology: sandstone; mudstone; coal

Pierre shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 38 % of this area

Pierre shale: dark-gray clay shale with calcareous and ferruginous concretions and sandy members.

Lithology: shale; sandstone; bentonite

Niobrara formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 4 % of this area

Niobrara formation: chiefly calcareous shale with limestone concretions; many thin bentonite beds locally.

Lithology: shale; bentonite

Lance Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area

LANCE FORMATION north Wyoming--Thick-bedded buff sandstone and drab to green shale; thin conglomerate lenses; south and northeast Wyoming--Brown and gray sandstone and shale; thin coal and carbonaceous shale beds.

Lithology: sandstone; shale; conglomerate; coal

Arikaree formation (Phanerozoic | Cenozoic | Tertiary) at surface, covers 2 % of this area

Arikaree formation: gray sandstone with layers of concretions; contains volcanic ash and, locally, channels filled with conglomerate; known only in southeastern Montana.

Lithology: sandstone; tuff; conglomerate

Pierre Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area

Blue-gray to dark-gray, fissile to blocky shale with persistent beds of bentonite, black organic shale, or light-brown chalky shale. Contains minor sandstone, conglomerate, and abundant carbonate and ferruginous concretions. Thickness 1,000-2,700 ft (305-823 m).

Lithology: shale; clay or mud; sandstone; conglomerate

Terrace Deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers < 0.1 % of this area

Clay to boulder-size clasts deposited as pediments, paleochannels, and terrace fills of former flood plains. Thickness up to 75 ft (23m).

Lithology: clay or mud; silt; sand; gravel

Pierre Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area

PIERRE SHALE (AGE 72 TO 78 Ma)--Dark-gray concretionary marine shale; contains several bentonite beds.

Lithology: shale; mixed clastic/volcanic

Fox Hill sandstone (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 4 % of this area

Fox Hills sandstone: Typically shaly sandstone grading upward into massive brownish sandstone with white sandstone of the Colgate member locally at top.

Lithology: sandstone; mudstone

Greenhorn Formation and Belle Fourche and Mowry Shale (Phanerozoic | Mesozoic | Cretaceous-Early) at surface, covers < 0.1 % of this area

GREENHORN FORMATION AND BELLE FOURCHE AND MOWRY (Kmr) SHALE. GREENHORN FORMATION--Light-colored limestone, marl, and limy sandstone interbedded with gray concretionary shale. BELLE FOURCHE SHALE--Black soft bentonitic concretionary shale. MOWRY SHALE (AGE 94 TO 98 Ma)--Silvery-gray hard siliceous shale containing abundant fish scales and bentonite beds.

Lithology: mixed clastic/carbonate; fine-grained mixed clastic; mixed clastic/volcanic

Ludlow Formation (Phanerozoic | Cenozoic | Tertiary | Paleocene ) at surface, covers < 0.1 % of this area

White, tan, yellow, and gray, cross-bedded, fine- to medium-grained,silty sandstone interbedded with locally bentonitic, gray siltstone, claystone, and sandy to silty claystone. Characterized by uranium-bearing lignite beds and "clinker" beds fromed by burning coalseams. Thickness up to 420 ft (128 m).

Lithology: sandstone; siltstone; claystone

Greenhorn formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 0.6 % of this area

Greenhorn formation: mainly light-gray marl and calcareous shale.

Lithology: mudstone; limestone; bentonite

Alluvium (Phanerozoic | Cenozoic | Quaternary) at surface, covers < 0.1 % of this area

Clay to boulder-size clasts with locally abundant organic material. Thickness up to 75 ft (23m).

Lithology: clay or mud; silt; sand; gravel

Carlile shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 1 % of this area

Carlile shale: dark-gray shale with calcareous and ferruginous concretions; middle part commonly sandy

Lithology: shale

Alluvium and Colluvium (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers < 0.1 % of this area

ALLUVIUM AND COLLUVIUM--Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.

Lithology: alluvium; colluvium

Fox Hills Sandstone (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area

FOX HILLS SANDSTONE--Light-colored sandstone and gray sandy shale containing marine fossils.

Lithology: sandstone; shale

Belle Fourche shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 1 % of this area

Belle Fourche shale: dark blue-gray siliceous shale with many calcareous and ferruginous concretions and intercalated thin layers of bentonite.

Lithology: shale; bentonite; sandstone

Fort Union formation (Phanerozoic | Cenozoic | Tertiary Cretaceous-Late | Paleocene) at surface, covers 23 % of this area

Fort Union formation: Clay shale, siltstone, and sandstone; local lenses of impure limestone, and numerous lignitic beds; contains Tertiary plant and animal fossils but no dinosaurs; base generally placed at the lowest of the succession of lignite beds within it; includes the Tongue River member, Lebo shale member, and Tullock member.

Lithology: shale; siltstone; sandstone; coal; limestone

Mowry shale (Phanerozoic | Mesozoic | Cretaceous-Early) at surface, covers 0.2 % of this area

Mowry shale: chiefly light-gray silicified shale and claystone with minor amounts of sandy shale and sandstone; contains some thick beds of bentonite.

Lithology: fine-grained mixed clastic; bentonite

Alluvium (Phanerozoic | Cenozoic | Quaternary) at surface, covers 8 % of this area

Alluvium: mainly valley fill consisting of silt, sand, and gravel; includes some terrace deposits and glacial drift of Pleistocene age in some areas; locally includes hot spring tufa. The older part of the alluvium, where present, is probably of Pliocene age.

Lithology: alluvium; glacial drift; carbonate

Niobrara Formation and Carlile Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area

NIOBRARA FORMATION (Kn) AND CARLILE SHALE (Kcl). NIOBRARA FORMATION (AGE ABOUT 83 Ma)--Light-colored limestone and gray to yellow speckled limy shale. CARLILE SHALE--Dark-gray sandy shale; Sage Breaks Member at top; Turner Sandy Member in middle.

Lithology: shale; fine-grained mixed clastic; limestone

White River formation (Phanerozoic | Cenozoic | Tertiary) at surface, covers 0.1 % of this area

White River formation: Light-colored clay with minor beds of sandstone and local beds of nodular limestone.

Lithology: claystone; sandstone; limestone