Shelton Member [of Trap Falls Formation]

White, light-gray, or buff, fine- to medium-grained, generally well foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and garnet (in tiny almost ubiquitous grains), also commonly minor biotite; generally interlayered with mica schist, biotite gneiss, and calc-silicate rock. Thought to be metavolcanic equivalent of unit Og. Shelton Member of Trap Falls Formation (Rodgers, 1985) is here referred to as Shelton muscovite granite. On the basis of field and laboratory studies, Ansonia, Beardsley, Pumpkin Ground, and Shelton gneisses, previously considered stratigraphic units, are reinterpreted as plutonic. Shelton is a foliated, medium-grained, garnet-bearing muscovite leucogranite with a conspicuous white color and abundant garnets. Age of crystallization determined from U-Pb garnet analysis is 380+/-3 Ma (Middle Devonian). Southeast margin of the Shelton is in contact with the Trap Falls Formation (Sevigny and Hanson, 1993).
State Connecticut
Name Shelton Member [of Trap Falls Formation]
Geologic age Middle or Lower Ordovician
Lithologic constituents
Major
Metamorphic > GneissWhite, light-gray, or buff, fine- to medium-grained, generally well foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and garnet (in tiny almost ubiquitous grains), also commonly minor biotite. Generally interlayered with biotite gneiss.
Minor
Metamorphic > Schist > Mica-schistgenerally interlayered with mica schist
Incidental
Metamorphic > Metasedimentary > Calc-silicate-rockgenerally interlayered with calc-silicate rock
Comments Part of Central Lowlands; Iapetus (Oceanic) Terrane - Connecticut Valley Synclinorium; Hartland Belt. Part of Hawley Formation and equivalent formations (includes Trap Falls and Cobble Mountain Formations) (Middle Ordovician). Secondary unit description per CT007.
References

Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.

Sevigny, J.H. and Hanson, G.N., 1993, Orogenic evolution of the New England Appalachians of southwestern Connecticut: Geological Society of America Bulletin, v. 105, no. 12, p. 1591-1605.

NGMDB product
Counties Fairfield