Merrimack Group, Berwick Formation, Unnamed member

Contains more calc-silicate (15 percent) than does the remainder of the formation (5 percent).
State New Hampshire
Name Merrimack Group, Berwick Formation, Unnamed member
Geologic age Ordovician? - Silurian?
Lithologic constituents
Major
Metamorphic > Schist
Metamorphic > Granoblastic > Granofelspurple biotite-quartz-feldspar granofels, interbeds of calc-silicate granofels (Contains more calc-silicate (15 percent) than does the remainder of the formation (5 percent)).
Minor
Metamorphic > Metasedimentary > Calc-silicate-rock
Comments Part of the Nashoba-Casco-Miramichi Terrane (Merrimack Trough). Secondary unit description from USGS Geologic Names lexicon (ref. NH047): 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). Onway tholeiite dike (point within formation) = 177 K/Ar, whole rock per NH042.
References
NGMDB product
Counties Hillsborough - Rockingham