Slana Spur and Station Creek Formations and Tetelna Volcanics

Unit symbol: PIPt
Age range lower Permian to Middle Pennsylvanian (323.2 to 272.3 Ma)
Lithology: Sedimentary
Group name: Skolai and Mankomen Groups, undivided
Lower volcanic section chiefly submarine andesite and basalt flows, locally pillowed and brecciated; upper volcaniclastic section generally grades upward from coarse volcanic breccia to abundant volcanic graywacke and finally to volcanic lutite. No fossils are known in the type area. Age assignment is constrained by overlying Hasen Creek Formation (unit Peh) and stratigraphic and lithologic correlation with the Slana Spur Formation (Nokleberg and others, 1992a). As here mapped, includes units Pzt and IPt (Tetelna Volcanics) of Nokleberg and others (1992a). Unit Pzt of Nokleberg and others (1992a) consists of andesitic flows, mud and debris avalanches, and aquagene tuff interbedded with fine- to coarse-grained volcaniclastic rocks; this unit has yielded fragments of late Paleozoic bryozoans. The Tetelna Volcanics is similar, and consists chiefly of dark-green, dark-gray-green, and purplish-gray-green volcanic flows, locally graded mud and debris avalanches, and lapilli-pumice tuff interbedded with fine- to coarse-grained volcaniclastic rocks. In the Talkeetna Mountains quadrangle, Permian conodonts were collected from unit Pzv (Csejtey and others, 1978). Metamorphosed to lower greenschist facies. As here mapped, unit also includes greenstone of the Skolai Group in the Valdez quadrangle (Winkler and others, 1981) and early Permian(?) and Pennsylvanian andesitic volcanic rocks in the Healy quadrangle (Csejtey and others, 1992). Locally, may also include rocks that could be assigned to the Nikolai Greenstone (Trn) following more detailed mapping (J.M. Schmidt, written commun., 2007)

Source map information

Source map Csejtey, Bela, Jr., Nelson, W.H., Jones, D.L., Silberling, N.J., Dean, R.M., Morris, M.S., Lanphere, M.A., Smith, J.G., and Silberman, M.L., 1978, Reconnaissance geologic map and geochronology, Talkeetna Mountains quadrangle, northern part of Anchorage quadrangle, and southwest corner Healy quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-558-A, 60 p., 1 sheet, scale 1:250,000.
Symbol Pzv
Unit name Basaltic to andesitic metavolcanic rocks
Description Rocks of this unit form an interlayered heterogeneous, dominantly marine sequence over 5000 m thick. Primarily consists of metamorphosed flows and tuffs of basaltic and andesitic compositions. Mudstone, bioclastic marble, and dark-gray to black phyllite are subordinate.
Lithology Metamorphic

Correlated geologic units

Label Pzv
Description Slana Spur Formation, volcaniclastic rocks, Early Permian-Middle Penn. [equivalent to part of Station Creek Fm.]
Geologic age Pennsylvanian to Cisuralian
Geologic setting Extrusive
Lithology Form Importance
Mafic-volcanic < Volcanic < Igneous Volcaniclastic Indeterminate, major
Mafic-volcanic < Volcanic < Igneous Flow Indeterminate, major
Greenstone < Metaigneous < Metamorphic Indeterminate, major
Phyllite < Metaclastic < Metasedimentary < Metamorphic Zeolitic (prehnite-pumpellyite) Indeterminate, major
Conglomerate < Clastic < Sedimentary Bed Indeterminate, major
Marble < Metacarbonate < Metasedimentary < Metamorphic Zeolitic (prehnite-pumpellyite) Minor
Mudstone < Clastic < Sedimentary Bed Minor