- Usage in publication:
-
- New Chicago Member*
- Modifications:
-
- Named
- Dominant lithology:
-
- Greenstone
- AAPG geologic province:
-
- Sierra Nevada province
Summary:
Named for town of New Chicago. Type locality: exposures in and near roadcut of HWY 49 sec 36 T7N R10E, Amador Co, CA. Adopted as uppermost member of Logtown Ridge Formation. Consists of volcanic-breccia greenstone with chiefly fine-grained clasts; forms thin, discontinuous, elongate bodies. Is 150 m thick. Conformably overlies Pokerville Member (new). Age is Late Jurassic (Callovian) and Middle(?) Jurassic (Oxfordian(?) and Kimmeridgian(?)) based on stratigraphic relations.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
-
- New Chicago Member*
- Modifications:
-
- Age modified
- AAPG geologic province:
-
- Sierra Nevada province
Summary:
Age changed based on Middle-Upper Jurassic boundary change based on top of Callovian-bottom of Oxfordian. Thus New Chicago Member is Middle Jurassic and Late(?) Jurassic 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 ([ ]).