- Usage in publication:
-
- Chisana Formation*
- Modifications:
-
- Biostratigraphic dating
- AAPG geologic province:
-
- Alaska Southern region
Summary:
Age of formation shown on summary of fossil occurrences and stratigraphic nomenclature as Early Cretaceous (Hauterivian to Barremian) age.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
-
- Chisana Formation*
- Modifications:
-
- Named
- Biostratigraphic dating
- Dominant lithology:
-
- Volcanics
- Volcaniclastics
- Argillite
- Graywacke
- Conglomerate
- AAPG geologic province:
-
- Alaska Southern region
Summary:
Named for nearby settlement of Chisana in Nabesna A-3 quad. Type section designated as exposures of lower part in valley of Bonanza Creek, secs.25,35 and 36, T4N R19E, and exposures of upper part in valley of Toby Creek secs.28,33, and 34, T4N R20E, Nabesna A-2 quad, AK. Composed of marine and subaerial volcanic and volcaniclastic rocks. Color is maroon and dark-green or gray-green. Lower part of formation contains dark gray argillite, thin bedded graywacke, pebble to cobble conglomerate and tuffaceous mudstone. Thickness is greater than 10,000 ft. Gradationally overlies Jurassic and Cretaceous (Valanginian) mudstones. Unconformably underlies Cretaceous(?) sedimentary rocks. Is intruded by middle Cretaceous granodiorite. Age is Early Cretaceous based on biostratigraphic dating of a fragment of ammonite SHASTICRIOCERAS of Barremian age.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).
Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).