Cantwell Formation, volcanic rocks subunit

Unit symbol: Tpcv
Age range Tertiary, Paleocene (66 to 56 Ma)
Lithology: Igneous - Volcanic
Group name: Volcanic rocks, undivided
Intercalated, moderately deformed sequence of andesite, altered basalt, rhyolite, and dacite flows, felsic pyroclastic rocks and minor sandstone and carbonaceous mudstone largely in the Healy quadrangle (Csejtey and others, 1992). K/Ar ages are typically Paleocene, although some are as young as Eocene. The Teklanika formation of Gilbert and others (1976) is sometimes used in the literature as a synonym for this unit. Gilbert and others (1976) pointed out the significant difference in age of the volcanic rocks of this unit relative to the underlying sedimentary rocks of the Cantwell Formation. Also includes unit Tv of Nokleberg and others (1992a) in the Mount Hayes quadrangle, which consists chiefly of ash-flow tuff, breccia, agglomerate, flows, dikes, sills, and minor volcanic sandstone, conglomerate, and fossiliferous limestone. Nokleberg and others (1992a, b) assigned their unit Tv an Eocene age on the basis of a K/Ar whole-rock age determination of 49.0 Ma (Age has been recalculated using constants of Steiger and Jager (1977) as 50.3±1.6) Ma) on a rhyodacite tuff. In the Healy quadrangle, ages range between 64.6±3.4 and 44.0 Ma, with the majority of the ages greater than 55 Ma

Source map information

Source map Csejtey, Bela, Jr., Mullen, M.W., Cox, D.P., and Stricker, G.D., 1992, Geology and geochronology of the Healy quadrangle, south-central Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-1961, 63 p., 2 sheets, scale 1:250,000.
Symbol Tcv
Unit name Cantwell Formation -- volcanic rocks subunit
Description Intercalated, moderately deformed sequence of andesite, generally zeolitized basalt, rhyolite and dacite flows, dominantly felsic pyroclastic rocks, a few interbeds of sandstone and carbonaceous mudstone, and a few small bodies of related subvolcanic intrusive rocks.
Lithology Igneous

Correlated geologic units

Label Tcv
Description Cantwell Formation, volcanic rocks subunit
Geologic age Paleocene
Geologic setting Extrusive
Lithology Form Importance
Felsic-volcanic < Volcanic < Igneous Pyroclastic Indeterminate, major
Andesite < Mafic-volcanic < Volcanic < Igneous Flow Indeterminate, major
Dacite < Felsic-volcanic < Volcanic < Igneous Flow Minor
Rhyolite < Felsic-volcanic < Volcanic < Igneous Flow Minor
Mudstone < Clastic < Sedimentary Carbonaceous Incidental
Sandstone < Clastic < Sedimentary Bed Incidental