Banded iron formation dating

banded iron formation dating

How old is banded iron formation?

2.1 billion year old rock showing banded iron formation. Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock that are almost always of Precambrian age.

Why study banded iron formations in the oceans?

One important piece of this puzzle is determining when oxygen production began, and how early oxygen was consumed by reduced species, such as iron (Fe (II)), in the oceans. One way of tracing the Fe redox cycle through time has been studying banded iron formations ( BIF s).

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.

How are bands of iron formed?

Banded-iron formation. Their formation has been variously ascribed to volcanic activity; rhythmic deposition from iron and silica solutions due to seasonal variations; oxidation of iron-rich sediments contemporaneous with deposition; and precipitation from solution as a result of special oxidation-reduction conditions.

What is the oldest type of banded iron formation?

Banded iron formations are found worldwide, in every continental shield of every continent. The oldest BIFs are associated with greenstone belts and include the BIFs of the Isua Greenstone Belt, the oldest known, which have an estimated age of 3700 to 3800 Ma.

What is the origin of banded rock formations?

Each band is similar to a varve, resulting from cyclic variations in oxygen production. Some of the Earths oldest rock formations, which formed about 3,700 million years ago ( Ma ), are associated with banded iron formations. They were first discovered in northern Michigan in 1844.

Why are there banded iron formations in the ocean?

Almost all of these formations are of Precambrian age and are thought to record the oxygenation of the Earths oceans . Banded iron formations are thought to have formed in sea water as the result of oxygen production by photosynthetic cyanobacteria.

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.

How are bands of iron formed in the ocean?

Banded iron formations are thought to have formed in sea water as the result of oxygen production by photosynthetic cyanobacteria. The oxygen combined with dissolved iron in Earths oceans to form insoluble iron oxides, which precipitated out, forming a thin layer on the ocean floor.

What are banded iron formations?

The history of banded iron formations is also the history of our planet’s journey from anaerobic to aerobic ecosystems. These formations trace the fluctuating levels of free oxygen in Earth’s atmosphere and oceans. Banded iron formations are chemically derived sedimentary deposits.

What type of rock is iron found in?

Most of the major iron deposits worldwide occur in rocks called banded iron formations (or BIFs for short), which are finely layered sedimentary rocks composed of alternating chert (a form of quartz) and iron oxide bands. Banded iron formations (BIFs) are chemically precipitated sedimentary rocks .

What is the dominant type of iron formation in geologic record?

Abundance of banded iron formation in the geologic record. Color indicates dominant type. Light yellow = older Archean formations; dark yellow = Greater Gondwana formations; brown = granular iron formations; red = Snowball Earth formations. Adapted from Trendall 2002. Location of occurrences. Color indicates dominant type.

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