Eramosa
Encyclopedia
The Eramosa is a Silurian
stratigraphic unit exposed along the Niagara Escarpment Niagara Escarpment
in Ontario and western New York State. In the late nineteenth century it was an important source of building stone in Hamilton, Ancaster and Waterdown , and in the late twentieth century quarries in a similar unit, also called the Eramosa, near Wiarton in the Bruce Peninsula, became an important source of dimension stone at a time when most of the other resources of similar stone were depleted. Work in these quarries led to the discovery of exceptionally well preserved fossils (the Eramosa lagerstätte
). On the east Mountain at Hamilton, a well developed cave system was discovered in the Eramosa and has now been designated as the Eramosa Karst Conservation Area .
The exceptionally preserved biota are present in a stratum of rock about 8 m thick, which extends for around 16 km in the South Bruce Peninsula, Ontario
.
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
stratigraphic unit exposed along the Niagara Escarpment Niagara Escarpment
Niagara Escarpment
The Niagara Escarpment is a long escarpment, or cuesta, in the United States and Canada that runs westward from New York State, through Ontario, Michigan, Wisconsin and Illinois...
in Ontario and western New York State. In the late nineteenth century it was an important source of building stone in Hamilton, Ancaster and Waterdown , and in the late twentieth century quarries in a similar unit, also called the Eramosa, near Wiarton in the Bruce Peninsula, became an important source of dimension stone at a time when most of the other resources of similar stone were depleted. Work in these quarries led to the discovery of exceptionally well preserved fossils (the Eramosa lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....
). On the east Mountain at Hamilton, a well developed cave system was discovered in the Eramosa and has now been designated as the Eramosa Karst Conservation Area .
Stratigraphy
The term was first used for a stratigraphic unit by Williams (1915) who named the Eramosa Member (of the Lockport Formation) for the bituminous dolomites exposed below the Guelph Formation along the Eramosa River, northeast of Guelph, Ontario. No detailed description of the type section has ever been published, and the status of the unit has been subject to many different interpretations. Until recently, the Eramosa in Ontario was regarded as the highest Member of the Lockport Formation , with gradational contacts with the Goat Island Member (below) and the Guelph Formation (above). In 1995, the US Geological Survey proposed a revised stratigraphy based on studies in the Niagara region. It extended the Lockport to Group status and included, from base to top, the Gasport, Goat Island, Eramosa, and Guelph as Formations within the Lockport Group. In a “reference section” in the Niagara River Gorge, the Eramosa was divided into six “units” recognized throughout the Niagara region, but a shaly lower unit previously named for the Hamilton area (the Vinemount Member) was transferred to the Goat Island Formation. Brunton (2009) has proposed a revision for Ontario which restores the Vinemount Member to the Eramosa and recognizes two other members.Age
The exact age and correlation of the Eramosa are still uncertain. Conodonts at first indicated that the Eramosa age was Ludlovian (c.420 Ma), but recent studies of both conodonts and the Eramosa lagerstätte suggest an earlier, late Wenlockian (c.425 Ma) age.Paleoenvironment
The rocks forming the Eramosa are mostly dolomites, but the composition varies from almost pure, grey-weathering, fine grained dolomite (at Ancaster) to shaly, bituminous, brown-weathing, bioturbated dolomites. Fossils are common at some localities, scarce at others, and chert is generally a minor component. The most characteristic feature is bituminous shaly interbeds. Probably the Eramosa was deposited in several related environments, most likely including shallow, restricted (and poorly oxygenated) marine waters. Among the fossils, perhaps the most spectacular are the eurypterids, an extinct form of scorpions. Some species lived in fresh or brackish water, but Silurian examples were marine.The exceptionally preserved biota are present in a stratum of rock about 8 m thick, which extends for around 16 km in the South Bruce Peninsula, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
.