Shadygrove Formation

Pure, light-colored limestone, stromatolitic in part; abundant pinkish limestone and cream-colored chert.
State Pennsylvania
Name Shadygrove Formation
Geologic age Cambrian
Lithologic constituents
Sedimentary > Carbonate > Limestone (Bed)pure, light-colored limestone, stromatolitic in part; abundant pinkish limestone
Sedimentary > Chemical > Chert (Bed)
Comments Secondary unit description from USGS Geologic Names lexicon (ref. PA003): Named for Shadygrove, Franklin Co., PA. Type section is in a farm field, 0.6 mile south and slightly east of Shadygrove on State Highway 16. Shadygrove used to be the upper part of the Conococheague Formation. This paper raises the Conococheague to group rank and divides it into a lower Zullinger Formation and an upper Shadygrove Formation. Shadygrove is composed of light blue-gray micritic limestone with pinkish cast, light gray weathering micritic algal limestone with muddy gray dolomite laminae and beds, light blue to gray mechanical limestone with grayish buff to yellow-orange seams and laminae of dolomite. Thickness is approximately 650 feet. The contact with the underlying Zullinger is gradational within an interval of thick beds of light colored to pink limestone interbedded with typical limestone and dolomite of Zullinger Formation. Shadygrove underlies the Stoufferstown Formation. Age is considered Late Cambrian based on Trempealeauan trilobites, but it is speculated that the Cambrian-Ordovician boundary may lie as much as 300 feet below the top of the Shadygrove.

Berg, T.M., Edmunds, W.E., Geyer, A.R., and others, compilers, 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey, 4th ser., Map 1, 2nd ed., 3 sheets, scale 1:250,000.

Pennsylvania Bureau of Topographic and Geologic Survey, Department of Conservation and Natural Resources, Miles, C.E., and Whitfield, T.G., compilers, 2001, Bedrock Geology of Pennsylvania, edition: 1.0, digital map, scale 1:250,000.

USGS Geologic Names lexicon found at:

NGMDB product
Counties Cumberland - Franklin - Fulton