- Usage in publication:
-
- Unibon Shaleâ€
- Modifications:
-
- Abandoned
Summary:
Rocks named the Unibon Shale by Semmes (1919) in the extreme east-central part of the Ciales quadrangle, and eastward into the Corozal quadrangle, are here redefined as the Carreras Siltstone and the name Unibon is abandoned. Consist of fine-grained, thin- to medium-bedded light-colored bands or laminae of mixed reworked ash and epiclastic particles. Is in fault contact with the informal basalt tuff member of the Pozas Formation in the Ciales quadrangle and grades downward into thick arkosic conglomerate in the Corozal quadrangle. Unconformably underlies the San Sebastian Formation. Thickness ranges from several hundred to more than 1,000 m. Age is either Late Cretaceous (Maastrichtian) or early Tertiary (Paleocene or younger) based on meager fossil evidence.
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 ([ ]).