Helderberg Group (geology)
| Helderberg Group | |
|---|---|
| Stratigraphic range: Lochkovian-Emsian ~ | |
| Type | Group |
| Sub-units |
|
| Underlies | |
| Overlies | |
| Lithology | |
| Primary | Limestone |
| Other | Dolomite, Chert |
| Location | |
| Region | |
| Country | United States |
| Type section | |
| Named for | Helderberg Escarpment |
| Named by | Conrad, T.A. 1839 |
The Helderberg Group is a geologic group that outcrops in the State New York, Pennsylvania, Maryland, New Jersey, and West Virginia. It also is present subsurface in Ohio and the Canadian provinces of Ontario and Nova Scotia. It preserves fossils dating back to the Early Devonian and Late Silurian period. The name was coined by T.A. Conrad (1839) in the New York State Geological Survey Annual Report, named for the Helderberg Escarpment or Helderberg Mountains.
The upper portion of the Helderberg, or the Kalkberg Formation is host to the Bald Hill ash bed, dated to 417.6 million years ago.
The Helderberg is composed chiefly of limestone and dolomite.
In Maryland and southern Pennsylvania, the Helderberg is divided into three formations. These are the New Creek Limestone, the Corriganville Limestone, and the Mandata Shale. The total thickness is about 60 feet (18 m). The formations weather easily and are poorly exposed except in cuts and quarries.