- Usage in publication:
-
- Retreat group*
- Modifications:
-
- Named
- Dominant lithology:
-
- Schist
- Graywacke
- Marble
- Slate
- AAPG geologic province:
-
- Alaska Southeastern region
Summary:
Named for rocks that underlie western part of Mansfield Peninsula from Point Retreat to south boundary of Juneau (B-3) quad, southeastern AK. Consists of interlayered sericite, schist, greenschist, slate, graywacke, and marble. Individual beds are 0.5 to more than 100 ft thick. Total thickness is at least 6000 ft before allowance is made for repetition by folding. Is in contact with Barlow Cove formation (new) along bedding plane fault. Age is given as Late Triassic(?) to Early Cretaceous(?) [based on correlation with other units in Admiralty Island area.]
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
-
- Retreat Group*
- Modifications:
-
- Age modified
- AAPG geologic province:
-
- Alaska Southeastern region
Summary:
Retreat Group is mapped in northern part of area from Pybus Bay to Point Retreat, and Gambier Bay Formation is mapped in southern part. Two units are same in lithology, state of metamorphism, structure, and stratigraphic position; they are considered correlative and probably equivalent. On basis of fossils of Devonian (probably Middle? Devonian) age found in Gambier Bay Formation, age of Retreat Group is considered to be Middle(?) Devonian.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
-
- Retreat Group*
- Modifications:
-
- Age modified
- AAPG geologic province:
-
- Alaska Southeastern region
Summary:
Age of the Retreat Group is Late Triassic based on fossils.
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 ([ ]).