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Helena limestone

Helena limestone: gray, unevenly laminated limestone, argillaceous and dolomitic; weathers light brown or yellow. Segregation structures and stromatolites are common. Distinguished only in general vicinity of Helena.
State Montana
Name Helena limestone
Geologic age Proterozoic | Mesoproterozoic
Primary rock type carbonate
Secondary rock type meta-conglomerate
Other rock types quartzite
Lithologic constituents
Sedimentary > Carbonate (Bed)Weakly metamophosed limestones and dolomites.
Metamorphic > Metasedimentary > Metaclastic > Metaconglomerate (Greenschist)Weakly metamorphosed conglomerates.
Metamorphic > Metasedimentary > Metaclastic > Quartzite (Greenschist)
Map references
Ross, P.R., Andrews, D.A., and Witkind, I.J., 1955, Geologic map of Montana: U.S. Geological Survey, 2 sheets, scale 1:500,000.
Unit references
Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1993, Geologic map of the Dillon 1o x 2o quadrangle, Idaho and Montana: U.S. Geological Survey Miscellaneous Investigations Series Map I-1803-H, scale 1:250,000.
Tysdal, R.G., Ludington, Steve, and McCafferty, A.E., 1996, Mineral and energy resource assessment of the Helena National Forest, west-central Montana: U.S. Geological Survey Open-File Report 96-683-A, 322 p., 6 plates.
Fox, J.E., 1993, Stratigraphic cross sections showing electric logs of Upper Cretaceous and older rocks, Powder River basin, southeastern Montana and northeastern Wyoming: U.S. Geological Survey Oil and Gas Investigations Chart OC-135 to OC-138,
Harrison, J.E., Whipple, J.W., and Lidke, D.J., 1998, Geologic map of the western part of the Cut Bank 1° x 2° quadrangle, northwestern Montana: U.S. Geological Survey Miscellaneous Geologic Investigations Series Map I-2593, scale 1:250,000.
McGill, G.E., and Sommers, D.A., 1967, Stratigraphy and correlation of the Precambrian Belt Supergroup of the southern Lewis and Clark Range, Montana: Geological Society of America Bulletin, v. 78, no. 3, p. 343-351.
Harrison, J.E., 1972, Precambrian Belt basin of northwestern United States--Its geometry, sedimentation and copper occurrences: Geological Society of America Bulletin, v. 83, no. 5, p. 1215-1240.
Whipple, J.W., Connor, J.J., Raup, O.B., and McGimsey, R.G., 1984, Preliminary report on the stratigraphy of the Belt Supergroup, Glacier National Park and adjacent Whitefish Range, Montana, in McBane, J.D., and Garrison, P.B., eds., Northwest Montana an
Earhart, R.L., Mudge, M.R., and Connor, J.J., 1984, Belt Supergroup lithofacies in the Northern Disturbed Belt, northwest Montana, in McBane, J.D., and Garrison, P.B., eds., Northwest Montana and adjacent Canada--Montana Geological Society 1984 Field Con
Counties Jefferson - Lewis and Clark - Powell