- Usage in publication:
-
- Alonso Formation*
- Modifications:
-
- Named
- Dominant lithology:
-
- Tuff
- Volcanics
- AAPG geologic province:
-
- Caribbean region
Summary:
The Alonso Formation, herein named, is a sequence of brownish-red welded tuff, non-welded tuff, lava breccia, and volcanic breccia containing andesite lava fragments. Conformably overlies Tetuan Formation; top is not exposed. Although faulting prevents a positive correlation, similarity in rock type and stratigraphic position suggests a correlation with the Pozas Formation in the eastern part of the quadrangle. Maximum exposed thickness is 500 m. Age is Late Cretaceous (over Santonian to Campanian Tetuan Formation; fossils in Flor de Alba Limestone Lentil of the Pozas are Campanian and Maastrichtian).
Source: GNU records (USGS DDS-6; Reston GNULEX).
- Usage in publication:
-
- Alonso Formation*
- Modifications:
-
- Overview
- AAPG geologic province:
-
- Caribbean region
Summary:
The Alonso Formation occurs in central Puerto Rico and consists of welded and non-welded ash-flow tuff with minor interbeds of coarse tuff, laharic breccia, volcanic sandstone, and thin andesitic lava flows. Maximum estimated thickness is 2000 meters. The Alonso is of Late(?) Cretaceous age.
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 ([ ]).