The Helderberg Group is a
geologic group
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...
that outcrops in the State New York, Pennsylvania, Maryland, New Jersey, and West Virginia. It also is present subsurface in Ohio and the Canadian Providence of Ontario It preserves
fossils
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
dating back to the
Early Devonian and
Late Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...
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 Dolomite may refer to:
*Dolomite (mineral), a carbonate mineral
*Dolomite (rock), also known as dolostone, a sedimentary carbonate rock
*Dolomite, Alabama, United States, an unincorporated community
*Dolomite, California, United States, an unincor ...
.
Stratigraphy
Manlius Limestone
The Manlius Limestone was first noted by Vanuxem (1840, p. 372) as a "waterlime" (hydraulic limestone) near
Manlius, New York
Manlius is a town in Onondaga County, east of the city of Syracuse, New York, United States. The population was 33,712 at the 2020 census, making it the third largest suburb in metropolitan Syracuse. In 2005, the town was ranked 98th on CNN's ...
. The Manlius is composed of
limestone,
grainstone,
calcareous mudstone and
bindstone. The Manlius is 419 - 411 Ma.
The Thacher Member member of the Manlius along eastern New York and down into parts of northern New Jersey. It is characterised as a "ribbon rock", meaning that it contains very thin layers of alternating limestone and
argillaceous rock. The color of the Thacher is dark blueish-black. The limestone is fine to medium grained. It averages 51 feet thick. It makes up the upper part of the Manlius in New York and makes up the entirety of the Manlius in northeastern New Jersey. Moving southwest it become more
argillaceous and
arenaceous, as it grades into the Depue Limestone.
The Thacher contains fossils of
stromatoporoids,
crinoids,
rugose corals
The rugosa, also called the tetracorallia or horn coral, are an extinct order of solitary and colonial corals that were abundant in Middle Ordovician to Late Permian seas.
Solitary rugosans (e.g., '' Caninia'', '' Lophophyllidium'', '' Neoza ...
,
tabulate corals
Tabulata, commonly known as tabulate corals, are an order of extinct forms of coral. They are almost always colonial, forming colonies of individual hexagonal cells known as corallites defined by a skeleton of calcite, similar in appearance to ...
,
tranchiopods,
tentaculitids, and
ostracodes
Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typical ...
.
References
*
{{NewYork-geologic-formation-stub
Devonian Pennsylvania
Silurian New York
Devonian West Virginia
Silurian West Virginia