Hammer Creek Formation

The Hammer Creek Formation is a mapped bedrock unit consisting primarily of conglomerate, coarse sandstone, and shale.

Hammer Creek Formation Stratigraphic range: Late Triassic
Type	Sedimentary
Unit of	Newark Supergroup
Overlies	New Oxford Formation
Thickness	9400 to 12200 feet[1]
Lithology
Primary	Sandstone, conglomerate
Other	Shale
Location
Extent	Pennsylvania
Type section
Named for	Hammer Creek
Named by	J. D. Glaeser, 1963[2]

The Hammer Creek Formation was originally mapped as part of the Gettysburg Formation in Adams County, Pennsylvania in 1929.[3] J. D. Glaeser renamed part of the Gettysburg to the Hammer Creek in 1963,[2] to "avoid extending either the Gettysburg Formation from the west or the Brunswick Formation from the east to include rocks typical of neither unit."

A major groundwater resources study of the Hammer Creek Formation and other formations of the Newark Supergroup in Pennsylvania was published by Charles R. Wood in 1980.[1]

Depositional Environment

The Hammer Creek Formation and other formations of the Newark Supergroup were deposited in the Newark Basin, just one of many Triassic rift basins existing on the east coast of North and South America, which formed as plate tectonics pulled apart Pangaea into the continents we see today.

Stratigraphy

The Hammer Creek Formation is conformably underlain by the New Oxford Formation, which is the basal unit of the Newark Supergroup in south-central Pennsylvania. The Hammer Creek is mapped from the southern borders of Dauphin and Lebanon Counties to the northeast to the Schuylkill River. A laterally equivalent rock unit called the Brunswick Formation is mapped on the east side of the river and into New Jersey.[4]

Notable exposures

The type section is along Hammer Creek, Richland quadrangle, Lebanon County, Pennsylvania.[2]

Age

Relative age dating of the Hammer Creek Formation places it in the Late Triassic period.

References

1. Wood, C. R., 1980, Groundwater resources of the Gettysburg and Hammer Creek Formations, southeastern Pennsylvania: Pennsylvania Geological Survey, 4th ser., Water Resource Report 49, 87 p. (web release).
2. Glaeser, J.D., 1963, Lithostratigraphic nomenclature of the Triassic Newark-Gettysburg basin: Pennsylvania Academy of Science Proceedings, v. 37, p. 179-188.
3. Stose, G.W., and Bascom, Florence, 1929, Description of the Fairfield and Gettysburg quadrangles (Pennsylvania): U.S. Geological Survey Geologic Atlas of the United States, Fairfield-Gettysburg folio, no. 225, 22 p.
4. Van Houten, F.B., 1980, Late Triassic part of Newark Supergroup, Delaware River section, west-central New Jersey, IN Manspeizer, Warren, ed., Field studies of New Jersey geology and guide to field trips: New York State Geological Association Guidebook, 52nd Annual Meeting, Newark, NJ, no. 52, p. 264-275.