Mancos Shale

The Mancos Shale or Mancos Group is an Late Cre-taceous (Upper Cretaceous) geologic formation of theWestern United States.The Mancos Shale was first described by Cross and Pur-ington in 1899[1] and was named for exposures near thetown of Mancos, Colorado.

1 Geology

It is dominated by mudrock that accumulated in off-shore and marine environments of the Cretaceous NorthAmerican Inland Sea. The Mancos was deposited duringthe Cenomanian through Campanian ages, approximatelyfrom 95 Ma to 80 Ma.Stratigraphically the Mancos Shale fills the interval be-tween the Dakota Group and the Mesaverde FormationGroup.[2]

The Mancos Shale rests conformably on the Dakota andin its upper part grades into and intertongues with theMesaverde Group. The shale tongues typically have sharpbasal contacts and gradational upper contacts.

2 Occurrences

The Mancos occurs in the Basin and Range Province, theColorado Plateau Province, and the San Juan MountainsProvince.

2.1 Structural basins

It also occurs in the following structural basin:[3]

2.2 Subunits

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

3 See also

• List of fossiliferous stratigraphic units in Arizona

• List of fossiliferous stratigraphic units in Colorado

• List of fossiliferous stratigraphic units in New Mex-ico

• List of fossiliferous stratigraphic units in Utah

• List of fossiliferous stratigraphic units in Wyoming

4 References[1] Cross, W. and Purington, C. W. (1899) “Description of

the Telluride quadrangle, Colorado”United States Geolog-ical Survey Atlas, Folio 57

[2] Weimer, R. J. (1960) “Upper Cretaceous Stratigra-phy, Rocky Mountain Area” American Association ofPetroleum Geologists Bulletin 44: pp. 1-20

[3] “Colorado River Basin Stratigraphy: Mancos Shale”United States Geological Survey

[4] New Mexico Geological Association.edu: “SURFACEand SUBSURFACE STRATIGRAPHY of the BURROCANYON FORMATION, DAKOTA SANDSTONE,and INTERTONGUED MANCOS SHALE of theCHAMA BASIN, NEW MEXICO”; 2005.

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2 5 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

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