USGS Visual Identifier
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Geologic Unit: Portland

Portland Formation of the Newark Supergroup (CT*,MA*)
Portland Arkose of the Newark Supergroup (CT*)

Jurassic, Early*
Sinemurian, late
Toarcian, early
Jurassic, Middle(?)
Geologic Province:
New England province*
Hartford basin*
Pomperaug basin*

Areal Extent:

Type Locality:
Exposures in the Portland "brownstone" quarries near Middletown, Middlesex Co., CT (Krynine, 1950).

Unit Name History:
Named Portland Arkose of Newark Group (Krynine, 1950).
Overview (Schnabel, 1960).
Extended into MA (Hartshorn and Koteff, 1967).
Age modified (Cornet, 1977).
Redefined as Portland Formation (Leo and others, 1977).
MA State Geol. Map usage (Zen and others, 1983).
Assigned to Newark Supergroup; Age modified (Robinson and Luttrell, 1985).
CT State Geol. Map usage (Rodgers, 1985).

Note: If you need more information, please contact Nancy Stamm (
Asterisks (*) indicate usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" implies that a name has been abandoned or that it has fallen into disuse. Former usage and, if known, replacement name given in parentheses ().

Slashes (/) indicate unit name usage violates the 1983 North American Stratigraphic Code. This violation may be explained within brackets ([ ]).

U.S. Department of the Interior, U.S. Geological Survey, Reston, VA, USA
Database project personnel
Last modified: 15-Jan-2013