Deerfield Basalt (MAJdb;0)

State	Massachusetts
Name	Deerfield Basalt
Geologic age	Lower Jurassic
Original map label	Jdb
Comments	Part of Mesozoic Basins (Jurassic and Triassic Rocks); Sedimentary and Volcanic Rocks of Deerfield and Northfield Basins. Secondary unit description per MA003 as reported in USGS Geologic Names lexicon (ref. MA024): The Deerfield Diabase is here redefined as Deerfield Basalt of the Newark Supergroup to reflect its extrusive origin, shown by pillows and pillow breccias at the base, and by vesicular pahoehoe flows at the top. The Triassic-Jurassic boundary is arbitrarily drawn at the base of the Deerfield in clastic rocks of the Sugarloaf Formation (Robinson and Luttrell, 1985).
Primary rock type	tholeiite
Secondary rock type
Other rock types
Lithologic constituents	Major Igneous > Volcanic > Mafic-volcanic > Basalt (Flow, pillows)Well-jointed quartz tholeiite, locally vesicular and locally pillowed near base.
Map references	Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.
Unit references	Zen, E-An (ed.), Goldsmith, R. (comp.), Ratcliffe, N.M. (comp.), Robinson, P. (comp.), Stanley, R.S. (comp.), Hatch, N.L., Jr., Shride, A.F., Weed, E.G.A., Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000. Robinson, Peter and Luttrell, G.W., 1985, Revision of some stratigraphic names in central Massachusetts, IN Stratigraphic notes, 1984: U.S. Geological Survey Bulletin, 1605-A, p. A71-A78. [http://pubs.er.usgs.gov/publication/b1605A] USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Franklin