Dating banded iron formation

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.

What are some examples of banded iron-formations?

Banded iron-formations are rocks of mostly Precambrian age that are composed of interlaminated quartz and iron minerals. 1. Algoma deposits, which are relatively small with an obvious volcanic association, and 2. Lake Superior, which are much larger and have a shallow-shelf, orthoquartzite-carbonate association.

What is bedded iron formation?

Banded iron formations (BIFs) are iron ores defined as layered, bedded, or laminated stratigraphic units composed of ≥15% weight iron that often contain quartz, chert, or carbonate interlayers (James, 1954; Gross, 1980). Kent C. Condie, in Earth as an Evolving Planetary System (Third Edition), 2016

How thick can a banded iron formation be?

A single banded iron formation can be up to several hundred meters in thickness and extend laterally for several hundred kilometers. Banded iron formation is more precisely defined as chemically precipitated sedimentary rock containing greater than 15% iron.

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.

What is a banded iron formation?

Banded iron formation contains layers of iron oxides (essentially either hematite or magnetite) isolated by layers of chert (silica-stocked sedimentary rock). Each layer is generally narrow (millimeters to few centimeters). The rock has a characteristically banded appearance due to differently colored darker iron-rich and lighter silica layers.

What is the thickness of an iron band?

Individual bands may vary in thickness from less than a millimetre to metres, and the overall succession of bands may be hundreds of metres thick. The principal iron minerals are the iron oxides hematite and magnetite.1BIFs have a chemical composition unlike any sedimentary material being deposited in significant quantities on the modern earth.2

How thick is the thickest piece of iron on Earth?

The banded iron formations here were deposited from 2470 to 2450 Ma and are the thickest and most extensive in the world, with a maximum thickness in excess of 900 meters (3,000 feet).

What are the characteristics of a hematite banded iron?

Banded iron formation contains layers of iron oxides (essentially either hematite or magnetite) isolated by layers of chert (silica-stocked sedimentary rock). Each layer is generally narrow (millimeters to few centimeters).