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Gunflint Chert

 

 
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Gunflint Chert
 
 
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The Gunflint chert (1.88 Ga
Annum

Annum is one form of the Latin noun meaning year, not a form normally used for derivatives in modern languages: the accusative case Grammatical number of the second declension grammatical gender noun annus , anni ....
) is a sequence of banded iron formation
Banded iron formation

Banded iron formations are a distinctive type of rock often found in primordial sedimentary rocks. The structures consist of repeated thin layers of iron oxides, either magnetite or hematite , alternating with bands of iron-poor shale and chert....
 rocks that are exposed in the Gunflint Range
Gunflint Range

The Gunflint Range is an Iron_ore deposit in northern Minnesota in the United States and western Ontario, Canada. The range extends from the extreme northern portion of Cook County, Minnesota into Canada....
 of northern Minnesota
Minnesota

Minnesota is a U.S. state in the Midwestern United States of the United States. The twelfth largest state by area in the U.S., it is the twenty-first most populous, with just over five million residents....
 and western Ontario
Ontario

Ontario is a Provinces and territories of Canada located in the Central Canada part of Canada, the largest by population and second largest, after Quebec, in total area....
 along the north shore of Lake Superior
Lake Superior

Lake Superior is the largest of the five Great Lakes of North America. It is bounded to the north by Ontario, Canada and Minnesota, United States, and to the south by the U.S....
. The black layers in the sequence contain microfossils that are 1.9 to 2.3 billion years in age. Stromatolite
Stromatolite

Stromatolites are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria ....
 coloni
Colony (biology)

In biology, a colony refers to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defences or the ability to attack bigger prey....
es of cyanobacteria
Cyanobacteria

Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis....
 that have been converted to jasper
Jasper

Jasper is an Opacity , impure variety of silica, usually red, yellow or brown in color. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone....
 are found in Ontario. The banded ironstone
Ironstone

Ironstone is a fine-grained, heavy and compact sedimentary rock. Its main components are the carbonate or oxide of iron, clay and/or sand. It can be thought of as a concretionary form of siderite....
 formation consists of alternating strata
Stratum

In geology and related fields, a stratum is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers....
 of iron oxide
Iron oxide

Iron oxides are chemical compounds composed of iron and oxygen. Altogether, there are sixteen known iron oxides and oxyhydroxides....
-rich layers interbedded with silica-rich zones.






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The Gunflint chert (1.88 Ga
Annum

Annum is one form of the Latin noun meaning year, not a form normally used for derivatives in modern languages: the accusative case Grammatical number of the second declension grammatical gender noun annus , anni ....
) is a sequence of banded iron formation
Banded iron formation

Banded iron formations are a distinctive type of rock often found in primordial sedimentary rocks. The structures consist of repeated thin layers of iron oxides, either magnetite or hematite , alternating with bands of iron-poor shale and chert....
 rocks that are exposed in the Gunflint Range
Gunflint Range

The Gunflint Range is an Iron_ore deposit in northern Minnesota in the United States and western Ontario, Canada. The range extends from the extreme northern portion of Cook County, Minnesota into Canada....
 of northern Minnesota
Minnesota

Minnesota is a U.S. state in the Midwestern United States of the United States. The twelfth largest state by area in the U.S., it is the twenty-first most populous, with just over five million residents....
 and western Ontario
Ontario

Ontario is a Provinces and territories of Canada located in the Central Canada part of Canada, the largest by population and second largest, after Quebec, in total area....
 along the north shore of Lake Superior
Lake Superior

Lake Superior is the largest of the five Great Lakes of North America. It is bounded to the north by Ontario, Canada and Minnesota, United States, and to the south by the U.S....
. The black layers in the sequence contain microfossils that are 1.9 to 2.3 billion years in age. Stromatolite
Stromatolite

Stromatolites are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria ....
 coloni
Colony (biology)

In biology, a colony refers to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defences or the ability to attack bigger prey....
es of cyanobacteria
Cyanobacteria

Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis....
 that have been converted to jasper
Jasper

Jasper is an Opacity , impure variety of silica, usually red, yellow or brown in color. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone....
 are found in Ontario. The banded ironstone
Ironstone

Ironstone is a fine-grained, heavy and compact sedimentary rock. Its main components are the carbonate or oxide of iron, clay and/or sand. It can be thought of as a concretionary form of siderite....
 formation consists of alternating strata
Stratum

In geology and related fields, a stratum is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers....
 of iron oxide
Iron oxide

Iron oxides are chemical compounds composed of iron and oxygen. Altogether, there are sixteen known iron oxides and oxyhydroxides....
-rich layers interbedded with silica-rich zones. The iron oxides are typically hematite
Hematite

Hematite, Spelling differences#Simplification of ae .28.C3.A6.29 and oe .28.C5.93.29 h?matite, is the mineral form of Iron oxide , one of several iron oxides....
 or magnetite
Magnetite

Magnetite is a ferrimagnetism mineral with chemical formula Iron3Oxygen4, one of several iron oxides and a member of the spinel group....
 with ilmenite
Ilmenite

Ilmenite is a weakly Magnetism titanium-iron oxide mineral which is iron-black or steel-gray. It is a crystalline iron titanium oxide . It crystallizes in the trigonal system, and it has the same crystal structure as corundum and hematite....
, while the silicates are predominantly cryptocrystalline
Cryptocrystalline

Cryptocrystalline is a rock Texture which is so finely crystalline, being made up of such minute crystals, that its crystalline nature is only vaguely revealed even microscopically in thin section by transmitted polarized light....
 quartz
Quartz

Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
 as chert
Chert

Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements present in the rock, and both red and green ar...
 or jasper
Jasper

Jasper is an Opacity , impure variety of silica, usually red, yellow or brown in color. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone....
, along with some minor silicate minerals.

Stanley A. Tyler examined the area in 1953, and noted the red-colored stromatolites. He also sampled a jet-black chert layer which, when observed petrographically, revealed some life-like small spheres, rods and filaments less than 10 micrometres in size. Elso Barghoorn, a paleobotanist at Harvard, subsequently looked at these same samples. Barghoorn concluded that "they were indeed structurally preserved unicellular organisms." In 1965 the two scientists published their finding, and named a variety of the Gunflint flora. This created an academic "stampede" to explore Precambrian
Precambrian

The Precambrian is an informal name for the supereon comprising the eon of the geologic timescale that came before the current Phanerozoic eon....
 microfossils from similar Proterozoic
Proterozoic

The Proterozoic is a eon representing a period before the first abundant complex life on Earth. The Proterozoic Eon extended from 2500 annum to 542.0 ? 1.0 Ma , and is the most recent part of the old, informally named ?Precambrian? time....
 environments.

See also

  • Oxygen catastrophe
    Oxygen Catastrophe

    The Oxygen Catastrophe was a massive environmental change believed to have happened during the Siderian geologic period at the beginning of the Paleoproterozoic era of the Precambrian, about 2.4 billion years ago....