- Usage in publication:
-
- Step Conglomerate*
- Modifications:
-
- Named
- Biostratigraphic dating
- Dominant lithology:
-
- Conglomerate
- Sandstone
- Limestone
- AAPG geologic province:
-
- Alaska East-Central region
Summary:
Named for Step Mountains, east-central AK. Type section designated in Step Mountains, northwest of Nation River, 2.5 mi northeast of bench mark 3977 (Nat), from NW/4 sec.20 T8N R31E (lower contact) to SE/4 sec.28 (upper contact), Charley River C-1 and B-1 quads. Exposed over wide area between Yukon, Black, and Little Black Rivers. Unit is chert-pebble conglomerate that grades upward into light-gray sandstone with bioclastic limestone beds in lower part. Is approximately 2000 ft thick. Unconformably overlies Ford Lake Shale (new) or locally, unnamed rocks of Paleozoic and probable Precambrian age; unconformably underlies Glenn Shale (new) or, locally Biederman Argillite (new). Occurrence of limestone and similarity of faunas indicate Step Conglomerate and Tahkandit Limestone are lateral facies. Fossils from Step Conglomerate (listed in table) identified by R.E. Grant indicate Permian age.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
-
- Step Conglomerate*
- Modifications:
-
- Age modified
- AAPG geologic province:
-
- Alaska East-Central region
Summary:
Correlation chart shows that Tahkandit Formation and Step Conglomerate (lateral equivalent) are Early Permian age. List of fossils collected from Tahkandit Formation included in report.
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 ([ ]).