Ordovician Shin Brook Formation

Ordovician Shin Brook Formation
State Maine
Name Ordovician Shin Brook Formation
Geologic age Ordovician
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanic > RhyoliteW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith U - Rhyolitic volcanic rocks
Minor
Sedimentary > Clastic > ConglomerateW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith U - Rhyolitic volcanic rocks
Sedimentary > Clastic > SiltstoneW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith U - Rhyolitic volcanic rocks
Incidental
Igneous > Volcanic (Volcaniclastic-volcanic breccia)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith U - Rhyolitic volcanic rocks
Comments Munsungun Lake Formation is part of the late Middle Ordovician to early Late Ordovician volcanogenic tract in northern Maine. Rocks are largely felsic volcanic tuffs, agglomerates and flows. Subsidiary lithologies include sandstone, siliceous shale, and chert. Extensively intruded by diabase sills in the study area. Regionally extensive, cropping out in a belt over 60 km in length and 5 km in width. Total thickness is estimated to be 1500 m in the westernmost portion of the outcrop belt. Unconformably overlies the Lower Ordovician Chase Brook Formation and conformably overlies the Bluffer Pond Formation in the Munsungun Lake area where chert was extensively quarried by early humans for tool making. Elsewhere conformably underlies the Blind Brook Formation. The Middle Ordovician Munsungun Lake was deformed during the Devonian Acadian Orogeny. (ME067) Unit description from USGS GEOLEX website (ME078). W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith T - Rhyolitic volcanic rocks
References
NGMDB product
Counties Aroostook - Penobscot