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Dales Gorge Formation These redbeds are found in Western Australia near the northwestern corner of that continent, in the Pilbara region near the iron mining community of Pannawonica. They are all part of the Dales Gorge formation, one of the major sources of iron for mining in Australia and one of the classic Banded Iron Formations associated with the rise of oxygen on the planet.
The Most Photographed Stone East of the Mississippi
Very near the Soudan Underground State Park administered by the Minnesota Department of Natural Resources is what some people call “the most photographed outcrop in the state.” This is a pavement outcrop of folded banded iron formation. The outcrop consists of metallic hematite, red jasper and white chert. These originally horizontal layers have been folded multiple times. In some areas, the jasper and chert have fractures filled with milky quartz.
These rocks are something like 2 billion years old! They formed around the world just after the rise of oxygen.
Banded Iron Formations – an insight into early life on Earth
While the earth formed some 4.5 billion years ago in the Hadean Eon, most of the rocks we see nowadays are much younger than that. Looking at changing rocks through time we can see a number of distinct environments and time periods represented, such as the impressive exposures of white chalk from the Cretaceous Period, but relatively few opportunities to study the very oldest rocks on the planet remain. On Earth, through the combined actions of metamorphism, erosion and remelting of rocks, Hadean rocks are in very short supply. More samples exist from Earth’s next Eon, the Archaean, including fascinating examples like these that imply a very different world. Banded iron formations (BIFs for short) are distinct, layered, and often heavily deformed rocks. Typical BIFs show repeating, consecutive, iron-rich and iron-poor layers; bands of a few millimetres to centimetres of black, silver or grey iron oxides such as haematite (Fe2O3) or magnetite (Fe3O4) alternate with layers of sediment lacking in iron, like shale or chert that are often red in colour, producing a beautiful layered effect. These formations are therefore an excellent indicator of the Earth’s early environmental history.
About 2.4 billion years ago, oxygen first appeared in Earth's atmosphere, the product of organisms called cyanobacteria which first developed the process of photosynthesis around that time. Prior to this, oxygen generally reacted with dissolved iron or organic matter in the oceans, but once these sources became oversaturated O2 started to fill the atmosphere; this is often referred to as the Great Oxygenation Event, the first accumulation of biologically induced oxygen.
Without oxygen in the atmosphere, iron does something we're not familiar with today - it actually dissolves in water and can be held in the oceans like salt. Once oxygen began building up in the atmosphere, suddenly all this iron became insoluble, started precipitating out and sinking to the sea floor. This appears to have been a periodic process; periods of abundant dissolved iron alternated with periods of limited dissolved iron and formation of cherts and shales. Once enough oxygen was present to use up the iron dissolved in the oceans, BIFs could no longer form, so the planet no longer makes them today. Their age usually means that they have been subject to a number of deformation processes, producing beautiful folded effects in specimens. Banded iron formations truly are a unique insight into early planetary history. ZM
Further information:
Genesis of Banded Iron Formations: http://econgeol.geoscienceworld.org/content/89/6/1384.abstract Banded Iron Formations: http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Banded_iron_formation.html
Image credit: http://www.flickr.com/photos/jsjgeology/14872616219/
Figure: Folded jaspilite BIF (Hamersely Group, Neoarchean to Paleoproterozoic, ~2.47-2.55 Ga; Hamersley Range, Western Australia)
Mary Ellen Jasper
A beautiful rock, made of life, consisting of a banded iron formation 1.85 billion years old made of microcrystalline silica containing red haematite inclusions sandwiched between the grey haematite of the precipitated iron. What makes this rock so interesting is that the red jasper is the fossilised remnant of stromatolites, some of the earliest complex organisms in geological history. They were formed by cyanobacterial microbial mats, growing sinuously over and through layers of precipitated sediments in an ever higher stack as the sediments fell rhythmically, creating the lovely shapes of the red jasper.
They come from the Mary Ellen mine in Minessota, in a layer of rocks called the Biwabik iron formation. Originally precipitated in a shallow sea, the chemical reason for the richness in iron started with the very photosynthetic bacteria that formed the stromatolites. As their lifestyle released oxygen into the sea, the reduced iron oxidised, and being insoluble, precipitated on the sea bottom, accompanied by plenty of silica that fossilised the mats into jasper as they grew.
The wiggling of the columns is thought to represent the tracking of the sun's position through the seasons, showing that the strategy adopted by sunflowers has along evolutionary history. Similar formations elsewhere have been used to prove the inference that the number of days in the year has shrunk through time as the Earth's rotation has slowed. These rocks also testify to one of the major events in global history, when free oxygen gradually appeared and poisoned off the existing ecosystem (who remain as some extremophile bacteria), thus paving the way for the evolution of the complex oxygen breathing life that is the most familiar feature of today's biosphere.
Our past post on banded iron formation http://tinyurl.com/p5ob9a6 and stromatolites http://tinyurl.com/nh48h3z
Loz
Image credit: Captain Tenneal
Fire, Water, Iron, Air, & Ice
Stripes of smooth gray and fiery orange give banded iron formations a striking appearance. When deformed, this special sedimentary rock can even evoke the image of a flickering flame in its bands. Despite their burning appearance, banded iron formations reveal information about air, water, and ice of the past, rather than fire. Banded iron formations are composed of alternating layers of dark-colored iron oxide minerals like hematite or magnetite, and reddish cherts or shales. Cyclicity between these two types of sediments was due to intermittent oxygen availability in the oceans where they were deposited. When oxygen levels were high, dissolved iron in the seawater would bond with the oxygen, creating insoluble oxide minerals that fell to the seafloor. When oxygen levels were low, the iron did not precipitate and sediment deposition resulted in iron-poor cherts and shales.
Many of the world’s banded iron formations were formed between 2.5 and 1.9 billion years ago. This time period contains the Great Oxygenation Event, when oxygen became more prevalent in Earth’s atmosphere and oceans. This oxygen was created by cyanobacteria, an early type of photosynthetic life. The oxygen levels of the ocean varied during the overall rise in oxygenation, as ocean currents moved water of different oxygen levels around and as cyanobacteria produced variable amounts of oxygen with seasons and populations. The shifting oxygen levels during this period created the perfect conditions to deposit banded iron formations on the seafloor.
Curiously, banded iron formations have also been found that date from 750 to 580 million years ago, long after the Great Oxygenation Event. The cyclic deoxygenation of the oceans in this case was caused by ice. This period of the past was a “Snowball Earth” era, when extensive glaciations covered a great deal of the planet’s surface. Sea ice would have limited ocean circulation, creating variably anoxic conditions conducive to banded iron formation deposition.
-Ce
More information: Western Australia Museum,https://bit.ly/1NOOT5a Image: Flickr user James St. John, CC license,https://bit.ly/2RUjTrz
Australian Iron Formation
This image shows a rock type known as a Banded Iron Formation (BIF). Hopefully the “banded” part makes sense just from the photo.
These rocks are about 2.5 billion years old and come from Dales Gorge in the Pilbara Craton of Western Australia. This is a key time in Earth’s history as it’s when oxygen first began building up in the atmosphere. There are hints from some locations on Earth that bacteria evolved the ability to generate oxygen through photosynthesis hundreds of millions of years earlier, but at around 2.5 billion years ago oxygen started rising.
Before there was oxygen in the atmosphere, iron could exist as “ferrous” iron, with a 2+ charge. When iron rusts today, it becomes “ferric” iron with a 3+ charge – extra oxygen causes the change in charges.
Ferrous iron can dissolve in ocean waters, ferric iron cannot. Prior to oxygen in the atmosphere, iron could dissolve in the oceans, but once oxygen started being generated, the iron dissolved in the world’s oceans reacted with that oxygen and formed sedimentary iron rocks. Many of the world’s economic iron deposits were produced in this way.
The other distinct characteristic of these rocks is their banding. The layers are produced by alternating patterns of iron-rich sediments and silica-rich sediments. The silica rich layers are produced by other sediments which are washed into the areas producing iron formations, possibly by storms, river inputs, or maybe other processes as well.
-JBB
Image credit: Pete Hill (Creative Commons licensed) http://www.flickr.com/photos/blundershot/5992386207
Australian Iron Formation
This image shows a rock type known as a Banded Iron Formation (BIF). Hopefully the “banded” part makes sense just from the photo.
These rocks are about 2.5 billion years old and come from Dales Gorge in the Pilbara Craton of Western Australia. This is a key time in Earth’s history as it’s when oxygen first began building up in the atmosphere. There are hints from some locations on Earth that bacteria evolved the ability to generate oxygen through photosynthesis hundreds of millions of years earlier, but at around 2.5 billion years ago oxygen started rising.
Before there was oxygen in the atmosphere, iron could exist as “ferrous” iron, with a 2+ charge. When iron rusts today, it becomes “ferric” iron with a 3+ charge – extra oxygen causes the change in charges.
Ferrous iron can dissolve in ocean waters, ferric iron cannot. Prior to oxygen in the atmosphere, iron could dissolve in the oceans, but once oxygen started being generated, the iron dissolved in the world’s oceans reacted with that oxygen and formed sedimentary iron rocks. Many of the world’s economic iron deposits were produced in this way.
The other distinct characteristic of these rocks is their banding. The layers are produced by alternating patterns of iron-rich sediments and silica-rich sediments. The silica rich layers are produced by other sediments which are washed into the areas producing iron formations, possibly by storms, river inputs, or maybe other processes as well.
-JBB
Image credit: Pete Hill (Creative Commons licensed) http://www.flickr.com/photos/blundershot/5992386207
I got to see this gorgeous banded iron formation again
BIF In our last post (see http://tinyurl.com/nmynqyo) we discussed evidence of an early whiff of oxygen in a 2.98 billion year old soil as an early prelude to the great oxygenation event 2.6 billion years ago. When the latter event happened, the oxygen oxidised iron dissolved in the oceans and sank to the bottom alongside layers of silica. The resulting rocks are known as banded iron formations, and are our main source of iron, as they contain easily mined high concentrations of the metal. Here is a lovely specimen, with tiger eye chalcedony in between the red iron rich layers. Loz Image credit: Maitri
An extremely crisp and detailed photograph by James St. John of a jaspilite banded iron formation in Soudan Underground Mine State Park, St. Louis County, Minnesota.
Banded Iron formation. Jasper Knob, Ishpeming, Michigan.
That is some awesome iron formation.
Jasper Knob, Ishpeming, Michigan. Basically an entire hill comprised of bands of hematite and jasper. Unusual and beautiful. #rockgeek #geology #geologyrocks #geologyporn #travelmqt #PureMichigan #jasper
Banded Iron Formation!
Fortescue falls, a long exposure just for something different.
Northwest Australia in the Pilbara Craton. The waterfall is tumbling over banded ironstone, which is a ~2 billion year old rock type formed when oxygen first appeared in the atmosphere and reacted with iron in the ocean to form solid, sedimentary rust.
Banded Iron Formations – an insight into early life on Earth While the earth formed some 4.5 billion years ago in the Hadean Eon, most of the rocks we see nowadays are much younger than that. Looking at changing rocks through time we can see a number of distinct environments and time periods represented, such as the impressive exposures of white chalk from the Cretaceous Period, but relatively few opportunities to study the very oldest rocks on the planet remain. On Earth, through the combined actions of metamorphism, erosion and remelting of rocks, Hadean rocks are in very short supply. More samples exist from Earth’s next Eon, the Archaean, including fascinating examples like these that imply a very different world. Banded iron formations (BIFs for short) are distinct, layered, and often heavily deformed rocks. Typical BIFs show repeating, consecutive, iron-rich and iron-poor layers; bands of a few millimetres to centimetres of black, silver or grey iron oxides such as haematite (Fe2O3) or magnetite (Fe3O4) alternate with layers of sediment lacking in iron, like shale or chert that are often red in colour, producing a beautiful layered effect. These formations are therefore an excellent indicator of the Earth’s early environmental history. About 2.4 billion years ago, oxygen first appeared in Earth's atmosphere, the product of organisms called cyanobacteria which first developed the process of photosynthesis around that time. Prior to this, oxygen generally reacted with dissolved iron or organic matter in the oceans, but once these sources became oversaturated O2 started to fill the atmosphere; this is often referred to as the Great Oxygenation Event, the first accumulation of biologically induced oxygen. Without oxygen in the atmosphere, iron does something we're not familiar with today - it actually dissolves in water and can be held in the oceans like salt. Once oxygen began building up in the atmosphere, suddenly all this iron became insoluble, started precipitating out and sinking to the sea floor. This appears to have been a periodic process; periods of abundant dissolved iron alternated with periods of limited dissolved iron and formation of cherts and shales. Once enough oxygen was present to use up the iron dissolved in the oceans, BIFs could no longer form, so the planet no longer makes them today. Their age usually means that they have been subject to a number of deformation processes, producing beautiful folded effects in specimens. Banded iron formations truly are a unique insight into early planetary history. ZM Further information: Genesis of Banded Iron Formations: http://econgeol.geoscienceworld.org/content/89/6/1384.abstract Banded Iron Formations: http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Banded_iron_formation.html Image credit: http://www.flickr.com/photos/jsjgeology/14872616219/ Figure: Folded jaspilite BIF (Hamersely Group, Neoarchean to Paleoproterozoic, ~2.47-2.55 Ga; Hamersley Range, Western Australia)
Mary Ellen Jasper A beautiful rock, made of life, consisting of a banded iron formation 1.85 billion years old made of microcrystalline silica containing red haematite inclusions sandwiched between the grey haematite of the precipitated iron. What makes this rock so interesting is that the red jasper is the fossilised remnant of stromatolites, some of the earliest complex organisms in geological history. They were formed by cyanobacterial microbial mats, growing sinuously over and through layers of precipitated sediments in an ever higher stack as the sediments fell rhythmically, creating the lovely shapes of the red jasper. They come from the Mary Ellen mine in Minessota, in a layer of rocks called the Biwabik iron formation. Originally precipitated in a shallow sea, the chemical reason for the richness in iron started with the very photosynthetic bacteria that formed the stromatolites. As their lifestyle released oxygen into the sea, the reduced iron oxidised, and being insoluble, precipitated on the sea bottom, accompanied by plenty of silica that fossilised the mats into jasper as they grew. The wiggling of the columns is thought to represent the tracking of the sun's position through the seasons, showing that the strategy adopted by sunflowers has along evolutionary history. Similar formations elsewhere have been used to prove the inference that the number of days in the year has shrunk through time as the Earth's rotation has slowed. These rocks also testify to one of the major events in global history, when free oxygen gradually appeared and poisoned off the existing ecosystem (who remain as some extremophile bacteria), thus paving the way for the evolution of the complex oxygen breathing life that is the most familiar feature of today's biosphere. Once again, these rocks demonstrate the ever spiralling links through geological history between chemistry and physics, rock, sea and life that are the theme of this year's AGI Earth Science week.....for more detail on these links see our past post on mineral evolution at http://tinyurl.com/ovd7w2l. Our past post on banded iron formation http://tinyurl.com/p5ob9a6 and stromatolites http://tinyurl.com/nh48h3z Loz Dear Readers, Image credit: Captain Tenneal http://www.agatelady.com/photo-gallery-mineral-of-the-month-january-2012.html
Australian Iron Formation This image shows a rock type known as a Banded Iron Formation (BIF). Hopefully the “banded” part makes sense just from the photo. These rocks are about 2.5 billion years old and come from Dales Gorge in the Pilbara Craton of Western Australia. This is a key time in Earth’s history as it’s when oxygen first began building up in the atmosphere. There are hints from some locations on Earth that bacteria evolved the ability to generate oxygen through photosynthesis hundreds of millions of years earlier, but at around 2.5 billion years ago oxygen started rising. Before there was oxygen in the atmosphere, iron could exist as “ferrous” iron, with a 2+ charge. When iron rusts today, it becomes “ferric” iron with a 3+ charge – extra oxygen causes the change in charges. Ferrous iron can dissolve in ocean waters, ferric iron cannot. Prior to oxygen in the atmosphere, iron could dissolve in the oceans, but once oxygen started being generated, the iron dissolved in the world’s oceans reacted with that oxygen and formed sedimentary iron rocks. Many of the world’s economic iron deposits were produced in this way. The other distinct characteristic of these rocks is their banding. The layers are produced by alternating patterns of iron-rich sediments and silica-rich sediments. The silica rich layers are produced by other sediments which are washed into the areas producing iron formations, possibly by storms, river inputs, or maybe other processes as well. -JBB Image credit: Pete Hill (Creative Commons licensed) http://www.flickr.com/photos/blundershot/5992386207 Read more: http://www.newark.osu.edu/facultystaff/personal/jstjohn/Documents/Cool-Rocks/Banded-iron-formations.htm http://www.sciencedirect.com/science/article/pii/0301926893900513
