Step Conglomerate

Unit symbol: Pstc
Age range lower Permian (298.9 to 272.3 Ma)
Lithology: Sedimentary
Group name: Step Conglomerate
Chert-pebble conglomerate that grades upward to light-gray, very fine-grained chert arenite and contains minor bioclastic limestone in lower part of unit (Brabb, 1969; Clough and others, 1995). Conglomerate is clast-supported and chert clasts are subangular to rounded, medium-gray, dark-gray, and black. Clasts include fossil debris (coral, crinoid, brachiopod, pelecypod, and bryozoan) and organic imprints to 8 cm long (Clough and others, 1995). Unit is facies equivalent of Tahkandit Limestone. Western and northern exposures are nonfossiliferous and generally of uncertain age. Thickness about 600 m. Unit originally named and described by Brabb (1969)

Source map information

Source map Brabb, E.E., and Churkin, Michael, Jr., 1969, Geologic map of the Charley River quadrangle, east-central Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-573, 1 sheet, scale 1:250,000.
Symbol Ps
Unit name Step Conglomerate
Description Chert-pebble conglomerate and chert arenite. Minor siltstone, bioclastic limestone, and quartz arenite. Has Tahkandit fauna in Step Mountains area. Nonfossiliferous and uncertain age in western and northern part of quadrangle except for single Permian fauna from sandstone near Takoma Bluff. Thickness and about 2,000 feet. Names and described by Brabb (1969)
Lithology Sedimentary

Correlated geologic units

Label Psc
Description Step Conglomerate, Permian, chert and quartzite clast pebble- and cobble conglomerate
Geologic age Cisuralian
Geologic setting Sedimentary, continental
Lithology Form Importance
Conglomerate < Clastic < Sedimentary Bed Major
Quartzose-sandstone < Sandstone < Clastic < Sedimentary Bed Minor