The Chazy Reef Formation is a mid-

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

limestone deposit in northeastern

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. It consists of some of the oldest

reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...

systems built by a community of organisms rather than the deposit of a limited range of similar organisms, such as

Stromatolite Stromatolites ( ) or stromatoliths () are layered Sedimentary rock, sedimentary formation of rocks, formations (microbialite) that are created mainly by Photosynthesis, photosynthetic microorganisms such as cyanobacteria, sulfate-reducing micr ...

mounds deposited by ancient cyanobacteria. The reef structure was formed largely by cryptostome and trepostome

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

, some of the oldest known bryozoans, but

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

s made an early appearance, and stromatoporoids. The formation is named for the small town of Chazy, New York, where the reef was noted by James Hall in ''Palaeontology of New York'' (vol. I, 1847) and the fossils first studied by the Canadian paleontologist Elkanah Billings (1858, 1859). The reef extends from

Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...

Quebec Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...

and

Newfoundland Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the population ...

, but its most easily studied outcropping is at Goodsell Ridge, Isle La Motte, the northernmost island in

Lake Champlain Lake Champlain ( ; , ) is a natural freshwater lake in North America. It mostly lies between the U.S. states of New York (state), New York and Vermont, but also extends north into the Canadian province of Quebec. The cities of Burlington, Ve ...

; there, gentle uplift has tilted the sediments: the bedding planes now dip slightly to the north, revealing sequences of horizons in exposed rock. The black limestone of Isle La Motte takes a polish, revealing the white "bird's-eye" markings of embedded fossil shells, notably the spirals formed by sliced

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

shells. Rock of the Chazy Formation was quarried from the nineteenth century at the Fisk Quarry, Isle La Motte, the oldest

quarry A quarry is a type of open-pit mining, open-pit mine in which dimension stone, rock (geology), rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some juri ...

Vermont Vermont () is a U.S. state, state in the New England region of the Northeastern United States. It borders Massachusetts to the south, New Hampshire to the east, New York (state), New York to the west, and the Provinces and territories of Ca ...

.The blackest stone may be seen in the polished "marble" revetments—actually unmetamorphosed

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) ...

— inside Radio City Music Hall, New York, and in floors in the Vermont State House. Portions of the exposed reef on several islands in Lake Champlain were dedicated as the Chazy Fossil Reef National Natural Landmark in 2009. The system formed in warm tropical waters of the Iapetus Ocean, in low latitudes of the Southern Hemisphere. The site was in shallow waters of a continental shelf: the continental

craton A craton ( , , or ; from "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of contine ...

of Laurentia lay to the west, beyond the

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...

system that formed behind the protective reef. The time was some 480-450 Ma (million years ago), at a period when global paleoclimate was so warm that the planet was all but ice-free. Atmospheric

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

was fourteen to sixteen times more plentiful than it is today. The Chazy Reef Formation, which built up vertically from a muddy base catching fine dark silt as it grew, began as mounds deposited by bryozoans that stabilized a muddy bottom, then built up into the water column to such an extent that the connected mounds modified their surrounding environment (Mehrtens). As the reef aged, it began to offer an increasing variety of ecological niches, which fostered the first rich local

biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...

that has characterized all reef systems ever since. One dominant reef-building organism took the place of another, in a slowly evolving faunal succession. The Chazy Reef Formation has given its name to the contemporaneous mid-Ordovician

faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by conven ...

, the Chazyan.

Notes

External links

(Lamotte Preservation Trust) The Chazy Reef on Isle La Motte
* ttp://www.lcbp.org/wayside/PDFS/Chazy_Reef/Chazy_Reef.pdf Chazy Reef Formation(pdf file)

Notes

External links

Further reading