The Helderberg Group is a

geologic group In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into superg ...

that outcrops in the States of 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 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 ...

dating back to the

Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the Pr ...

and

Late Silurian The Silurian ( ) is a geologic period and system spanning 23.5 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 third and shortest period of t ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

. The name was coined by T.A. Conrad (1839) in the ''New York State Geological Survey Annual Report,'' named for the

Helderberg Escarpment The Helderberg Escarpment, also known as the Helderberg Mountains, is an escarpment in eastern New York (state), New York, United States, roughly west of the city of Albany, New York, Albany. The escarpment is the northeastern extremity of th ...

or Helderberg Mountains. The upper portion of the Helderberg, or the

Kalkberg Formation The Helderberg Group is a geologic group that outcrops in the States of 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 fo ...

is host to the Bald Hill ash bed, dated to 417.6 million years ago. The Helderberg is composed chiefly of

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

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 . The formations weather easily and are poorly exposed except in cuts and quarries.

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 Administrative divisions of New York#Town, town to the south east of Syracuse, New York, Syracuse in Onondaga County, New York, United States. As of the 2020 Census, the population was 33,712, making it the third largest suburb in Sy ...

. The Manlius is composed of

grainstone Under the Dunham classification (Dunham, 1962) system of limestones, a grainstone is defined as a grain-supported carbonate rock that contains less than 1% mud-grade material. This definition has recently been clarified as ''a carbonate-dominated ...

, calcareous mudstone and

bindstone Bindstone is a special type of carbonate rock in the Dunham classification. The term did not appear in the original Dunham classification from 1962 and was introduced by Embry and Klovan 1971 in the modified Dunham classification. Description Em ...

. The Manlius is 419 - 411 Ma. The Thacher Member of the Manlius extends along eastern New York and down into parts of northern New Jersey. It is characterised as a "ribbon rock", meaning 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 thick. It makes up the upper part of the Manlius in New York State and makes up the entirety of the Manlius in northeastern New Jersey. Moving southwest, it become more

argillaceous Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay mineral ...

and

arenaceous Arenite (from the Latin ''arena'', "sand") is a sedimentary clastic rock with sand grain size between 0.0625 mm (0.00245 in) and 2 mm (0.08 in) and containing less than 15% matrix. The related adjective is ''arenaceous''. The e ...

as it grades into Depue Limestone. The Thacher contains fossils of stromatoporoids,

crinoids Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...

rugose corals The Rugosa or rugose corals are an extinct class of solitary and colonial corals that were abundant in Middle Ordovician to Late Permian seas. Solitary rugosans (e.g., '' Caninia'', '' Lophophyllidium'', '' Neozaphrentis'', '' Streptelasma ...

, tabulate corals, tranchiopods, tentaculitids, and

ostracodes Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant) have been identified,Brandão, S.N.; Antonietto, L.S; Nery, D.G.; Santos, S.G.; Karano ...

References

* {{Devonian footer, state=expanded Devonian Pennsylvania Silurian New York Devonian West Virginia Silurian West Virginia Limestone groups of the United States Dolomite groups Chert groups Geologic groups of New York (state) Geologic groups of Pennsylvania Geologic groups of West Virginia Geologic groups of Maryland Geologic groups of Ohio