What are banded iron formations quizlet?
Banded iron formations are special sedimentary rocks comprised of alternating layers of iron-rich (red) and iron poor (gray) layers (figure 7-4 on page 239 of your text). Most rocks of this type are older than 2 billion years. They account for most of the iron ore that is mined in the world today.
What is banded iron ore?
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).
What causes the iron to be banded?
banded-iron formation (BIF), chemically precipitated sediment, typically thin bedded or laminated, consisting of 15 percent or more iron of sedimentary origin and layers of chert, chalcedony, jasper, or quartz. Such formations occur on all the continents and usually are older than 1.7 billion years.
When and why did banded iron formations stop forming?
formation of abundant BIFs stopped once the majority of iron from oceans was used up which resulted in buildup of oxygen in the atmosphere as also suggested by the first appearance of common continental red beds of the post-BIF Earth.Nov 14, 2016
The Atmosphere and Hydrosphere
Kent C. Condie, in Earth as an Evolving Planetary System (Third Edition), 2016
Geochemistry of Mineral Deposits
E.R. Ramanaidou, M.A. Wells, in Treatise on Geochemistry (Second Edition), 2014
The atmosphere and hydrosphere
Banded iron formation ( BIF) ( Fig. 8.6) has a very distinct distribution with time ( Fig. 8.25 ).
Geochemistry of Mineral Deposits
W.C. Pat ShanksIII, in Treatise on Geochemistry (Second Edition), 2014
Sediments, Diagenesis and Sedimentary Rocks
A. Bekker, ... K.O. Konhauser, in Treatise on Geochemistry (Second Edition), 2014
Origin of Life and Energy
Banded iron formations are worldwide layered sedimentary deposits rich in iron that range in age from 1.5 to 3.8 billion years old, the age of the earliest known rocks. They contain 30–60% Fe3+. No molecular oxygen was present in the earth's atmosphere until 1.5–2.0 billion years ago. Thus, the oxidant earlier could not have been O 2.
The Precambrian Earth
P.G. Eriksson, ... O. Catuneanu, in Developments in Precambrian Geology, 2004
Description
A typical banded iron formation consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides, either magnetite (Fe 3 O 4) or hematite (Fe 2 O 3 ), alternating with bands of iron-poor chert, often red in color, of similar thickness.
Occurrence
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.
Origins
An ashtray carved out of a soft form of banded ironstone from the Barbeton Supergroup in South Africa. The red layers were laid down when Archaean photosynthesizing cyanobacteria produced oxygen that reacted with dissolved iron compounds in the water, to form insoluble iron oxide (rust).
Economic geology
Banded iron formations provide most of the iron ore presently mined. 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.
Further reading
Harnmeijer, J.P. (2003). "Banded Iron Formation: A Continuing Enigma of Geology". University of Washington. Archived from the original on 8 September 2006.
Overview
Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness and extend laterally for several hundred kilometers. Almost all of these formations are of Precambrian age and are thought to record the oxygena…
Description
A typical banded iron formation consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor chert, often red in color, of similar thickness. A single banded iron formation can be up to several hundred meters in thickness and extend laterally for several h…
Occurrence
Banded iron formations are almost exclusively Precambrian in age, with most deposits dating to the late Archean (2800-2500 Ma) with a secondary peak of deposition in the Orosirian period of the Paleoproterozoic (1850 Ma). Minor amounts were deposited in the early Archean and in the Neoproterozoic (750 Ma). The youngest known banded iron formation is an Early Cambrianformatio…
Origins
Banded iron formation provided some of the first evidence for the timing of the Great Oxygenation Event, 2,400 Ma. With his 1968 paper on the early atmosphere and oceans of the earth, Preston Cloud established the general framework that has been widely, if not universally, accepted for understanding the deposition of BIFs.
Economic geology
Banded iron formations provide most of the iron ore presently mined. 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. The term "banded ir…
See also
• Iron-rich sedimentary rocks – Sedimentary rocks containing 15 wt.% or more iron
• Stromatolite – Layered sedimentary structure formed by the growth of bacteria or algae
• Taconite – Iron-bearing sedimentary rock, in which the iron minerals are interlayered with quartz, chert, or carbonate
Further reading
• Harnmeijer, J.P. (2003). "Banded Iron Formation: A Continuing Enigma of Geology". University of Washington. Archived from the original on 8 September 2006.
• Klein, C. (October 2005). "Some Precambrian banded iron-formations (BIFs) from around the world: Their age, geologic setting, mineralogy, metamorphism, geochemistry, and origins". American Mineralogist. 90 (10): 1473–99. Bibcode:2005AmMin..90.1473K. doi:10.2138/am.2005.1871.
External links
• Media related to Banded iron formation at Wikimedia Commons
• Banded-iron formation at the Encyclopædia Britannica
• "Jaspilite" . Encyclopedia Americana. 1920.