- Usage in publication:
-
- Norwood Member*
- Modifications:
-
- Named
- Age modified
- Dominant lithology:
-
- Shale
- Limestone
- AAPG geologic province:
-
- Michigan basin
Summary:
Age of the Antrim Shale in the Michigan basin is changed to Late Devonian only based on conodonts, and is divided into four members, from base to top: Norwood, Paxton, Lachine, and upper members. The name Norwood Member formalizes the poorly defined "Norwood shale" of Ehlers (1938), which is retained because of long-standing usage. Norwood is the lowest 8 m of the Antrim, consisting of black fissile pyritic shale with thin fossiliferous limestone beds, calcareous concretions, and greenish-gray bioturbated shale. Conformably overlies the Squaw Bay Limestone [See Below]; conformably underlies the Paxton Member of the Antrim. Age is Late Devonian (early Frasnian) based on conodonts.
[NOTE: The Squaw Bay Limestone is in the process of being renamed, in accordance with the Department of the Interior's Secretarial Order 3404, issued on November 19, 2021, formally identifying the term “squaw” as derogatory.]
Source: GNU records (USGS DDS-6; Reston 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 ([ ]).