Mancos Shale

The Mancos Shale or Mancos Group is an Upper Cretaceous geologic formation of the Western United States dominated by mudrock that accumulated in offshore and marine environments of the Cretaceous North American Inland Sea. The Mancos was deposited during the Cenomanian through Campanian ages, approximately from 95 Ma to 80 Ma. The Mancos Shale was first described by Cross and Purington in 1899^[1] and was named for exposures near the town of Mancos, Colorado. Stratigraphically the Mancos Shale fills the interval between the Dakota Group and the Mesa Verde Group.^[2]

The Mancos Shale rests conformably on the Dakota and in its upper part grades into and intertongues with the Mesaverde Group. The shale tongues typically have sharp basal contacts and gradational upper contacts.

Occurrences

The Mancos occurs in the Basin and Range Province, the Colorado Plateau Province and the San Juan Mountains Province, as well as in the following basins:^[3]

Black Mesa Basin Estancia Basin Green River Basin

Orogrande Basin Paradox Basin Piceance Basin

San Juan Basin Uintah Basin

Subunits

The Mancos occurs with the following subunit names (listed alphabetically):^[3]

Anchor Mine Tongue (CO,UT), Aspen Member (UT,WY), Black Butte Tongue (WY), Blue Gate Member (UT), Bridge Creek Limestone Member (NM), Buck Tongue (CO,UT), Bull Point Sandstone Member (UT), Carlile Member (NM), Clay Mesa Tongue (NM), Cooper Arroyo Sandstone Member (NM), Emery Sandstone Member (UT), D-Cross Tongue (NM), Devils Grave Sandstone [Member] (CO), El Vado Sandstone Member (NM), Ferron Sandstone Member (CO,UT),

Fort Hays Limestone Member (CO), Fort Hays Limestone Member (CO), Frontier Formation (CO,UT), Garley Canyon Sandstone Member (UT), Graneros Member (CO,NM), Greenhorn Limestone Member (NM), Hartland Shale Beds (NM), Hopi Sandy Member (AZ), Horsehead Tongue (NM), Hunt Creek Sandstone [Member] (CO), Juana Lopez Member (CO,NM), Loyd Sandstone Member (CO), Masuk Member (UT) or Masuk Tongue (UT), Meeker Sandstone Member (CO), Morapos Sandstone Member (CO),

Mowry Member (UT) or Mowry Shale (CO,UT), Mulatto Tongue (NM), Muley Canyon Sandstone Member (UT), Niobrara Member (CO,NM), Pescado Tongue (AZ,NM), Rangely Tongue (CO,UT), Rio Salado Tongue (NM), Sanastee Sandstone Member (NM), Satan Tongue (NM), Semilla Sandstone Member (NM), Tocito Sandstone Lentil (CO,NM), Tununk Member (UT), Whitewater Arroyo Tongue (NM), Wildcat Canyon Sandstone Member (UT), Wind Rock Tongue (AZ).

References

1. ^ Cross, W. and Purington, C. W. (1899) "Description of the Telluride quadrangle, Colorado" United States Geological Survey Atlas, Folio 57
2. ^ Weimer, R. J. (1960) "Upper Cretaceous Stratigraphy, Rocky Mountain Area" American Association of Petroleum Geologists Bulletin 44: pp. 1-20
3. ^ ^{a b} "Colorado River Basin Stratigraphy: Mancos Shale" United States Geological Survey