Beekmantown Group

Includes, in descending order, the Pinesburg Station (Ops), Rockdale Run (Orr), and Stonehenge (Os) Formations.
State Pennsylvania
Name Beekmantown Group
Geologic age Ordovician
Lithologic constituents
Sedimentary > Carbonate > Limestone (Bed)
Sedimentary > Carbonate > Dolostone (Bed)Ops and Orr
Sedimentary > Chemical > Chert (Bed)Orr
Comments Secondary unit description from USGS Geologic Names lexicon (ref. PA003): [Pinesburg Station ] Named Pinesburg Station dolomite for Pinesburg Station, Washington, Co., MD. Unit is a succession of dolomites overlying the Rockdale Run formation and underlying the Row Park limestone. Formation averages about 450 feet thick and the top of the Pinesburg Station is placed at the base of the lowest limestone bed in the overlying Row Park. The lack of fossils in this unit makes it difficult to date, however, correlation to sections in PA suggest that the Lower-Middle Ordovician boundary is near the top of the Pinesburg Station dolomite and is therefore tentatively placed at the top of the formation. [Rockdale Run Formation] Named Rockdale Run formation of the Beekmantown group for Rockdale Run, near Hicksville, Washington Co., MD. Consists of interbedded limestones and dolomites overlying the Stonehenge limestone. The lower two-thirds of the formation is predominantly limestone, while dolomite dominates the upper third. The top of the Rockdale Run is placed at the top of the highest limestone bed beneath the Pinesburg Station dolomite. The formation averages about 2450 feet thick. A number of faunal zones may be useful for local and regional correlation including the LECANOPIRA zone (200-560 feet above base), the ARCHAEOSCYPHIA zone (560-790 feet above base), the DIPARELASMA zone (790-1420 feet above base), and the SYNTROPHOPSIS-CLELANDOCERAS zone (1650-2070 feet above base). The formation is considered of Early Ordovician age. [Stonehenge Formation] Named for the community of Stonehenge, just east of Chambersburg, Franklin Co., PA. Consists of a lower dark to light gray limestone with sandy laminae less developed than overlying beds and an upper fine-grained light to dark gray limestone containing contorted laminae of sandy matter that stand in relief or fall to sandy shale on weathering and thick beds of "edgewise" conglomerate. 485 feet thick. Overlies Conococheague limestone; underlies remainder of Beekmantown limestone. Report contains measured section of Beekmantown limestone. Considered of Ordovician age.

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:

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Counties Adams