- Usage in publication:
-
- Algonkian period
- Modifications:
-
- Overview
- AAPG geologic province:
-
- Northern Rocky Mountain region
Summary:
The oldest rocks of the Lewis and Livingston Ranges belong to the Algonkian period (also called Algonkian series). Includes limestone, argillite, and quartzite 17,400 ft thick that are divided into five newly named formations: Altyn limestone (base), Appekunny argillite, Grinnell argillite, Siyeh limestone, Shepard quartzite, and Kintla argillite. These rocks are correlated with rocks in the Belt Mountains because fossil BELTINA DANAI found at foot of Appekunny Mountain in Appekunny is also present in Greyson shale of Belt Mountains and because large, cylindrical, concretionary masses in upper part of Siyeh are similar to those found in pre-Cambrian rocks north of Helena, MT. Intrusive diorite and extrusive diabase are associated with the Siyeh.
Source: GNU records (USGS DDS-6; Denver 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 ([ ]).