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. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

limestone deposit in northeastern

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. 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 processes— deposition of sand, wave erosion planing down rock out ...

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 formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). The ...

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 invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a l ...

, some of the oldest known bryozoans, but

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...

s made an early appearance, and stromatoporoids. The formation is named for the small town of

Chazy, New York Chazy is a town in northeastern Clinton County, New York, United States. The population was 4,284 at the 2010 census. The closest city is Plattsburgh, to the south. Chazy is south of the Canada–United States border. The ZIP code is 12921 ...

, 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 Elkanah Billings (May 5, 1820 – June 14, 1876) is often referred to as Canada's first paleontologist. Billings was born on a farm by the Rideau River outside Bytown (Ottawa), now known as Billings Estate Museum, Billings Estate. His parents w ...

(1858, 1859). The reef extends from

Tennessee Tennessee ( , ), officially the State of Tennessee, is a landlocked state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to th ...

Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee ...

and

Newfoundland Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...

, but its most easily studied outcropping is at Goodsell Ridge,

Isle La Motte Isle La Motte is an island in Lake Champlain in northwestern Vermont, United States. At 7 mi (11 km) by 2 mi (3 km), it lies close to the place that the lake empties into the Richelieu River. It is incorporated as a New England town in Grand Isle ...

, the northernmost island in

Lake Champlain , native_name_lang = , image = Champlainmap.svg , caption = Lake Champlain-River Richelieu watershed , image_bathymetry = , caption_bathymetry = , location = New York/Vermont in the United States; and Quebec in Canada , coords = , type = , ...

; there, gentle uplift has tilted the sediments: the

bedding plane In geology, a bed is a layer of sediment, sedimentary rock, or pyroclastic material "bounded above and below by more or less well-defined bedding surfaces".Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds., 2005. ''Glossary of Geology'' ...

s 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 The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

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 mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their envi ...

Vermont Vermont () is a state in the northeast New England region of the United States. Vermont is bordered by the states of Massachusetts to the south, New Hampshire to the east, and New York to the west, and the Canadian province of Quebec to ...

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

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

— inside

Radio City Music Hall Radio City Music Hall is an entertainment venue and Theater (structure), theater at 1260 Sixth Avenue (Manhattan), Avenue of the Americas, within Rockefeller Center, in the Midtown Manhattan neighborhood of New York City. Nicknamed "The Showplac ...

, New York, and in floors in the

Vermont State House The Vermont State House, located in Montpelier, is the state capitol of the U.S. state of Vermont. It is the seat of the Vermont General Assembly. The current Greek Revival structure is the third building on the same site to be used as the Sta ...

. Portions of the exposed reef on several islands in Lake Champlain were dedicated as the

Chazy Fossil Reef Chazy Fossil Reef is a United States National Natural Landmark spanning three Lake Champlain islands in Clinton County, New York and Grand Isle County, Vermont. The site is recognized as the oldest known diverse fossil reef in the world, and cont ...

National Natural Landmark The National Natural Landmarks (NNL) Program recognizes and encourages the conservation of outstanding examples of the natural history of the United States. It is the only national natural areas program that identifies and recognizes the best ...

in 2009. The system formed in warm tropical waters of the

Iapetus Ocean The Iapetus Ocean (; ) was an ocean that existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). The Iapetus Ocean was situated in the southern hemisphere, between the paleoco ...

, in low latitudes of the Southern Hemisphere. The site was in shallow waters of a

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

: the continental

craton A craton (, , or ; from grc-gre, κράτος "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 ...

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although ...

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'') a ...

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 (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

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 or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...

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 principle of faunal succession, also known as the law of faunal succession, is based on the observation that sedimentary rock strata contain fossilized flora and fauna, and that these fossils succeed each other vertically in a specific, reli ...

. 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 convent ...

, 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