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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 early whiff of oxygen
The history of oxygen in Earth’s atmosphere has been a difficult one for scientists to understand. We know that early in Earth’s history, there was virtually no oxygen in the atmosphere and reduced gases like methane could exist. We know now that oxygen contents have risen substantially and that gas makes up 20% of the atmosphere.
Sometime between those points oxygen began being produced as a byproduct of chemical reactions by bacteria and started rising in the atmosphere. The general name of that time is the “Great Oxygenation Event” (GOE) and it is generally believed to have happened around 2.6 billion years ago.
When oxygen is present it leaves many chemical signatures. Iron, for example, rusts and becomes a solid when oxygen is presnet and can dissolve in water when oxygen is low. Similar chemical signatures for a number of elements were what produced the 2.6 billion years ago estimates for the GOE. In fact, there is some pretty decent evidence out there suggesting that oxygen levels were quite low before this time (mainly in the behavior of sulfur isotopes, but I won’t go into further details on that in this post).
The rocks you’re looking at here are 2.98 billion years old. They come from the Nsuze group, near the coast of South Africa, in a region of very old crust known as the Kaapvaal craton. They are a rock type geologists would call a “paleosol”; they are actually remnants of 3 billion year old soils. Eventually the soils were covered by water and lithified to form these rocks.
New research led by scientists from the University of Southern Denmark just published in the journal Nature makes a fascinating claim based on these rocks; the scientists argue these rocks record the presence of oxygen 2.98 billion years ago, nearly 400 million years before oxygen was generally believed to have appeared.
They looked at a number of geochemical features including isotopes of chromium and the abundance of elements sensitive to the presence of oxygen like iron and uranium. In each case, they find evidence that those elements behaved in these rocks the way they would have if oxygen was present. Chromium isotope ratios change when oxygen is present and the isotope ratios were consistent with the soil forming in the presence of oxygen. Uranium can be dissolved if oxygen is present and the soil was low in uranium. Iron tends to form solids when oxygen is present and iron is quite high in the soil; there are even layers of banded iron formation in the soil which you can see in the image.
Altogether, their evidence makes a strong case that something was producing oxygen at the time this soil was made. That is a striking claim considering this soil pre-dates when other sections indicate the rise of oxygen occurred by nearly 400 million years.
Something must have been going on geologically we don’t understand at these times. We’re not quite sure when the ability to produce oxygen evolved, but if this evidence is correct, life was producing oxygen at 3.0 billion years ago. Yet, somehow, oxygen was present during the formation of this paleosol but yet did not build up substantially in the atmosphere during that long time period before the date of the Great Oxygenation Event.
This is a very complicated period in Earth’s history and one that needs continuing research. Understanding the history of oxygen on Earth is key to assembling both the planet’s geologic history and the tree of life itself. This is fascinating science and should spark additional study of other outcrops from this time period to look for more indicators of the earliest rise of oxygen.
-JBB
Image credit: Nic Beukes http://phys.org/news/2013-09-atmospheric-oxygenation-billion-years.html
These are a few of the cool rocks I found at the rock shop located at the Broadmoor Hotel in Colorado Springs. Top left is a Tiger Iron table from Australia, 1.6 billion years old, top right is a Blue agate end table(my favorite color), middle is a fossil bed writing table, bottom left is a pyrite dollar in matrix, and finally bottom left is pyrite and quartz on a sphalerite matrix. All so cool and so expensive.
Photoset 1 from the Melbourne Zoo with @captain-amaezing!
1. Cast of Inostrancevia, a Permian gorgonopsid and a relative of ours
2. A beautiful Banded Iron Formation with pyrite. My finger there for scale.
3. Phar Lap, the famous Australian racehorse.
4. A paper-mache(!!!) model of the human body. If that wasn’t labor intensive enough, it opens up to show the internal organs.
5. Neoceratodus forsteri, or the Queensland lungfish. One of the few surviving lungfish, this guy is truly a living fossil.
6. The magnificent skull of Physeter macrocephalus, or the sperm whale.
7. The skull of Janjucetus, a stem mysticete with teeth!
8. Aboriginal sculpture of my favorite marsupial, the tassie devil.
9. A quality rancho.
10. The arching skull of the pygmy blue whale, a subspecies, Balaenoptera musculus brevicauda.
(Part 1) (Part 2)
I got to see these really cool rocks. It’s composition is Hematite and Jasper but the formation itself is more commonly known as Banded Iron. It just blows my mind that these rocks are over a billion years old and that they only formed once in Earth’s history. It’s absolutely beautiful to see and to think that this rock has seen so many living creatures and was around before any life on Earth. It just blows my mind.
Well, they formed more than once - that’s the only edit I’d give, bye were most abundant about 2.5 billion years ago when oxygen first rose in the atmosphere. They formed over a period of more than a billion years, stopped, then started again during the putative “snowball Earth” events.
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.
Probably my favourite sight the whole day. Bright red rocks and a couple little waterfalls. Damn, Newfoundland you try too hard.
Mickeleen’s Path - East Coast Trail
Check out that iron formation!
Banded Iron Formation at Jasper Knob, Ishpeming, MI
