How was the banded iron formed?
A nearly 3-billion-year-old banded iron formation from Canada shows that the atmosphere and ocean once had no oxygen. Photosynthetic organisms were making oxygen, but it reacted with the iron dissolved in seawater to form iron oxide minerals on the ocean floor, creating banded iron formations.
Where is banded iron formation found?
Banded iron formations were first discovered in northern Michigan in 1844. Banded iron formations account for more than 60% of global iron reserves and provide most of the iron ore presently mined. Most formations can be found in Australia, Brazil, Canada, India, Russia, South Africa, Ukraine, and the United States.
When did banded iron formations appear?
Banded Iron formations occur in Proterozoic rocks, ranging in age from 1.8 to 2.5 billion years old. They are composed of alternating layers of iron-rich material (commonly magnetite) and silica (chert).
Are banded iron formations metamorphic?
Such formations occur on all the continents and usually are older than 1.7 billion years. They also are highly metamorphosed.
Why did banded iron formations form between 2.4 and 1.8 Ga?
Why did banded iron formations form between 2.4 and 1.8 Ga? a. The oceans became oversaturated in iron. The oceans began to absorb large amounts of oxygen.
Is banded iron formation magnetic?
Magnetite-rich banded iron-formations (BIFs) exhibit characteristic magnetic properties, including strong anisotropy.
What is the texture of banded iron?
Banded iron-formations are sedimentary rock formations with alternating silica-rich layers and iron-rich layers that are typically composed of iron oxides (hematite and magnetite), iron-rich carbonates (siderite and ankerite), and/or iron-rich silicates (e.g., minnesotaite and greenalite).
Where can you find banded iron formation?
More than 60% of global iron reserves are in the form of banded iron formation, most of which can be found in Australia, Brazil, Canada, India, Russia, South Africa, Ukraine, and the United States. Different mining districts coined their own names for BIFs.
What are the itabarite banded iron formations of Brazil?
The Itabarite banded iron formations of Brazil cover at least 80,000 square kilometers (31,000 square miles) and are up to 600 meters (2,000 feet) thick. These form the Quadrilatero Ferrifero or Iron Quadrangle, which resembles the Iron Range mines of United States in that the favored ore is hematite weathered out of the BIFs.
What is banded iron formation (BIF)?
The distribution of banded iron formation (BIF) with geologic time provides a constraint on O2 levels in the oceans and atmosphere ( Ohmoto et al., 2006 ). BIFs also commonly contain layers of chert and generally have Fe 3+ /Fe 2+ + Fe 3+ ratios in the range of 0.3 to 0.6, reflecting an abundance of magnetite (Fe 3 O 4 ).
Why did the banded iron deposits end?
The requirement of an anoxic, but not euxinic, deep ocean for deposition of banded iron formation suggests two models to explain the end of BIF deposition 1.8 billion years ago. The “Holland ocean” model proposes that the deep ocean became sufficiently oxygenated at that time to end transport of reduced iron.