Tatnic Hill Formation (CTOta;0)

Tatnic Hill Formation

Medium- to dark-gray, medium-grained gneiss or schist composed of quartz, andesine, biotite, garnet, and sillimanite, locally kyanite, muscovite, or K-feldspar, interlayered with locally mappable units and thinner layers of rusty-weathering graphitic pyrrhotitic two-mica schist, amphibolite, and calc-silicate rock.

State	Connecticut
Name	Tatnic Hill Formation
Geologic age	Upper? and Middle Ordovician
Lithologic constituents	Major Metamorphic > SchistMedium- to dark-gray, medium-grained gneiss or schist composed of quartz, andesine, biotite, garnet, and sillimanite, locally kyanite, muscovite, or K-feldspar, interlayered with locally mappable units and thinner layers of rusty-weathering graphitic pyrrhotitic two-mica schist. Metamorphic > GneissMedium- to dark-gray, medium-grained gneiss or schist composed of quartz, andesine, biotite, garnet, and sillimanite, locally kyanite, muscovite, or K-feldspar. Incidental Metamorphic > Metasedimentary > Calc-silicate-rock Metamorphic > Amphibolite
Comments	Part of Eastern Uplands; Iapetus (Oceanic) Terrane - Merrimack Synclinorium; Brimfield Schist and equivalent formations (includes Tatnic Hill Formation) (Upper? and Middle Ordovician). The age of the Putnam Group, including its Tatnic Hill Formation, is considered to be Late Proterozoic(?) based on the 730 my age of the Fishbrook Gneiss in MA and the 440 my age of the Hedgehog Hill gneiss intruded into the upper part of the younger Brimfield Group (Pease, 1989) per CT013.
References	Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000. Pease, M.H., Jr., 1989, Correlation of the Oakdale Formation and Paxton Group of central Massachusetts with strata in northeastern Connecticut: U.S. Geological Survey Bulletin, 1796, 26 p. https://pubs.er.usgs.gov/publication/b1796
NGMDB product	NGMDB product page for 54245
Counties	Middlesex - New London - Tolland - Windham

Tatnic Hill Formation

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

Pease, M.H., Jr., 1989, Correlation of the Oakdale Formation and Paxton Group of central Massachusetts with strata in northeastern Connecticut: U.S. Geological Survey Bulletin, 1796, 26 p.