Berwick Formation

Mica schist. In New Hampshire: Used as Berwick Formation of Merrimack Group. Consists of purple biotite-feldspar granofels or schist. Contains interbeds of calcsilicate granofels and minor metapelites. Includes Gove Member, mapped separately. Stratigraphic sequence with respect to Eliot Formation is uncertain. Age of all formations in Merrimack Group changed to Ordovician(?) to Silurian(?) based on isotopic age determinations of approx 440 and 420 Ma from detrital zircons from Berwick by J.N. Aleinikoff (oral commun., 1994) (Lyons and others, 1997).
State Massachusetts
Name Berwick Formation
Geologic age Silurian
Lithologic constituents
Major
Metamorphic > Schist > Mica-schist
Comments Part of Merrimack Belt (Silurian, Devonian and Pennsylvanian Rocks). Secondary unit description per MA010.
References
NGMDB product
Counties Essex - Middlesex