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Big-nosed, long-horned dinosaur discovered in Utah

This image shows the skull of the newly announced Nasutoceratops from Grand Staircase-Escalante National Monument (GSENM), which encompasses 1.9 million acres of high desert terrain in south-central Utah.Credit: Rob Gaston

A remarkable new species of horned dinosaur has been unearthed in Grand Staircase-Escalante National Monument, southern Utah. The huge plant-eater inhabited Laramidia, a landmass formed when a shallow sea flooded the central region of North America, isolating western and eastern portions for millions of years during the Late Cretaceous Period.

The newly discovered dinosaur, belonging to the same family as the famous Triceratops, was announced today in the British scientific journal, Proceedings of the Royal Society B.
The study, funded in large part by the Bureau of Land Management and the National Science Foundation, was led by Scott Sampson, when he was the Chief Curator at the Natural History Museum of Utah at the University of Utah. Sampson is now the Vice President of Research and Collections at the Denver Museum of Nature & Science.

Additional authors include Eric Lund (Ohio University; previously a University of Utah graduate student), Mark Loewen (Natural History Museum of Utah and Dept. of Geology and Geophysics, University of Utah), Andrew Farke (Raymond Alf Museum), and Katherine Clayton (Natural History Museum of Utah).

Horned dinosaurs, or “ceratopsids,” were a group of big-bodied, four-footed herbivores that lived during the Late Cretaceous Period. As epitomized by Triceratops, most members of this group have huge skulls bearing a single horn over the nose, one horn over each eye, and an elongate, bony frill at the rear. The newly discovered species, Nasutoceratops titusi, possesses several unique features, including an oversized nose relative to other members of the family, and exceptionally long, curving, forward-oriented horns over the eyes.

The bony frill, rather than possessing elaborate ornamentations such as hooks or spikes, is relatively unadorned, with a simple, scalloped margin. Nasutoceratops translates as “big-nose horned face,” and the second part of the name honors Alan Titus, Monument Paleontologist at Grand Staircase-Escalante National Monument, for his years of research collaboration.

For reasons that have remained obscure, all ceratopsids have greatly enlarged nose regions at the front of the face. Nasutoceratops stands out from its relatives, however, in taking this nose expansion to an even greater extreme. Scott Sampson, the study’s lead author, stated, “The jumbo-sized schnoz of Nasutoceratops likely had nothing to do with a heightened sense of smell — since olfactory receptors occur further back in the head, adjacent to the brain — and the function of this bizarre feature remains uncertain.”

This image shows an artist rendition of Nasutoceratops.Credit: Lukas Panzarin

Paleontologists have long speculated about the function of horns and frills on horned dinosaurs. Ideas have
ranged from predator defense and controlling body temperature to recognizing members of the same species. Yet the dominant hypothesis today focuses on competing for mates—that is, intimidating members of the same sex and attracting members of the opposite sex. Peacock tails and deer antlers are modern examples. In keeping with this view, Mark Loewen, a co-author of the study claimed that, “The amazing horns of Nasutoceratops were most likely used as visual signals of dominance and, when that wasn’t enough, as weapons for combatting rivals.”

A Treasure Trove of Dinosaurs on the Lost Continent of Laramidia

This is an image of a drawing of the skull of the Nasutoceratops found in Grand Staircase-Escalante National Monument (GSENM), which encompasses 1.9 million acres of high desert terrain in south-centralUtah. Credit: Sammantha Zimmerman

Nasutoceratops was discovered in Grand Staircase-Escalante National Monument (GSENM), which encompasses 1.9 million acres of high desert terrain in south-central Utah. This vast and rugged region, part of the National Landscape Conservation System administered by the Bureau of Land Management, was the last major area in the lower 48 states to be formally mapped by cartographers. Today GSENM is the largest national monument in the United States. Sampson proclaimed that, “Grand Staircase-Escalante National Monument is the last great, largely unexplored dinosaur boneyard in the lower 48 states.”

For most of the Late Cretaceous, exceptionally high sea levels flooded the low-lying portions of several continents around the world. In North America, a warm, shallow sea called the Western Interior Seaway extended from the Arctic Ocean to the Gulf of Mexico, subdividing the continent into eastern and western landmasses, known as Appalachia and Laramidia, respectively. Whereas little is known of the plants and animals that lived on Appalachia, the rocks of Laramidia exposed in the Western Interior of North America have generated a plethora of dinosaur remains. Laramidia was less than one-third the size of present day North America, approximating the area of Australia.

Most known Laramidian dinosaurs were concentrated in a narrow belt of plains sandwiched between the seaway to the east and mountains to the west. Today, thanks to an abundant fossil record and more than a century of collecting by paleontologists, Laramidia is the best known major landmass for the entire Age of Dinosaurs, with dig sites spanning from Alaska to Mexico. Utah was located in the southern part of Laramidia, which has yielded far fewer dinosaur remains than the fossil-rich north. The world of dinosaurs was much warmer than the present day; Nasutoceratops lived in a subtropical swampy environment about 100 km from the seaway.

Beginning in the 1960’s, paleontologists began to notice that the same major groups of dinosaurs seemed to be present all over this Late Cretaceous landmass, but different species of these groups occurred in the north (for example, Alberta and Montana) than in the south (New Mexico and Texas). This finding of “dinosaur provincialism” was very puzzling, given the giant body sizes of many of the dinosaurs together with the diminutive dimensions of Laramidia. Currently, there are five giant (rhino-to-elephant-sized) mammals on the entire continent of Africa. Seventy-six million years ago, there may have been more than two dozen giant dinosaurs living on a landmass about one-quarter that size. Co-author Mark Loewen noted that, “We’re still working to figure out how so many different kinds of giant animals managed to co-exist on such a small landmass?” The new fossils from GSENM are helping us explore the range of possible answers, and even rule out some alternatives.

During the past dozen years, crews from the Natural History Museum of Utah, the Denver Museum of Nature & Science and several other partner institutions (e.g., the Utah Geologic Survey, the Raymond Alf Museum of Paleontology, and the Bureau of Land Management) have unearthed a new assemblage of more than a dozen dinosaurs in GSENM. In addition to Nasutoceratops, the collection includes a variety of other plant-eating dinosaurs—among them duck-billed hadrosaurs, armored ankylosaurs, dome-headed pachycephalosaurs, and two other horned dinosaurs, Utahceratops and Kosmoceratops — together with carnivorous dinosaurs great and small, from “raptor-like” predators to a mega-sized tyrannosaur named Teratophoneus. Amongst the other fossil discoveries are fossil plants, insect traces, clams, fishes, amphibians, lizards, turtles, crocodiles, and mammals. Together, this diverse bounty of fossils is offering one of the most comprehensive glimpses into a Mesozoic ecosystem. Remarkably, virtually all of the identifiable dinosaur remains found in GSENM belong to new species, providing strong support for the dinosaur provincialism hypothesis.

Andrew Farke, a study co-author, noted that, “Nasutoceratops is one of a recent landslide of ceratopsid discoveries, which together have established these giant plant-eaters as the most diverse dinosaur group on Laramidia.”

Eric Lund, another co-author as well as the discoverer of the new species, stated that, “Nasutoceratops is a wondrous example of just how much more we have to learn about with world of dinosaurs. Many more exciting fossils await discovery in Grand Staircase-Escalante National Monument.”

Fact Sheet: Major Points of the Paper
(1) A remarkable new horned dinosaurs Nasutoceratops titusi, has been unearthed in Grand Staircase-Escalante National Monument, southern Utah.
(2) Nasutoceratops is distinguished by a number of unique features, including an oversized nose and elongate, forward-curving horns over the eyes.
(3) This animal lived in a swampy, subtropical setting on the “island continent” of western North America, also known as “Laramidia.”
(4) Nasutoceratops appears to belong to a previously unrecognized group of horned dinosaurs that lived on Laramidia, and provides strong evidence supporting the idea that distinct northern and southern dinosaur communities lived on this landmass for over a million years during the Late Cretaceous.

New Dinosaur Name: Nasutoceratops titusi.

  • The first part of the name, Nasutoceratops, can be translated as the “big-nosed horned face,” in reference to the oversized nose of this plant-eating dinosaur. The second part of the name honors Alan Titus, Monument Paleontologist at Grand Staircase-Escalante National Monument, for all of his work in support of paleontological research in GSENM.

Size
Nasutoceratops was about 15 feet (5 meters) long and 2.5 tonnes.

Relationships
Nasutoceratops belongs to a group of big-bodied horned dinosaurs called “ceratopsids,” the same family as the famous Triceratops. More specifically, they are members of the subset of ceratopsids known as “centrosaurines,” with Avaceratops being the closest known relative within this smaller subset of horned dinosaurs.

Anatomy

  • Nasutoceratops was a four-legged (quadrupedal) herbivore.
  • Like most other horned dinosaurs, Nasutoceratops had a large horn above each eye, although they are particularly elongate in this animal and forward facing, which is unusual. Rather than a large horn over the nose and an elaborately ornamented frill, both typical of centrosaurines, Nasutoceratops possessed a low, narrow, blade-like horn above the nose and relatively simple frill lacking well developed ornaments.

Age and Geography

  • Nasutoceratops lived during the Campanian stage of the Late Cretaceous period, which spanned from approximately 84 million to 70 million years ago. This animal lived about 76 million years ago.
  • During the Late Cretaceous, the North American continent was split in two by the Western Interior Seaway. Western North America formed an island continent called Laramidia, stretching from Mexico in the south to Alaska in the north.
  • Nasutoceratops lived in Utah at the same time that other, closely related horned dinosaurs lived in Alberta. This finding strong evidence of dinosaur provincialism on Laramidia—that is, the formation of northern and southern dinosaur assemblages during a part of the Late Cretaceous.

Discovery

  • Nasutoceratops was found in a geologic unit known as the Kaiparowits Formation, abundantly exposed in GSENM, southern Utah.
  • Nasutoceratops was first discovered by (then) University of Utah masters student Eric Lund in 2006. Additional specimens of this animal were found in subsequent years.
  • Nasutoceratops specimens are permanently housed in the collections and on public display at the Natural History Museum of Utah in Salt Lake City, Utah.
  • These discoveries are the result of a continuing collaboration between the Natural History Museum of Utah, the Denver Museum of Nature & Science, and the Bureau of Land Management.

Other

  • The fossil record of ceratopsid dinosaurs from the southern part of Laramidia has been very poorly known. The discovery of this new dinosaur in Utah helps to fill a major gap in our knowledge.
  • Nasutoceratops is part of a previously unknown assemblage dinosaurs discovered in GSENM over the past 12 years.
  • The skull of Nasutoceratops is on permanent display at the Natural History Museum of Utah.
  • The Bureau of Land Management manages more land—253 million acres—than any other federal agency, and manages paleontological resources using scientific principles and expertise.
  • In addition to serving as the Vice President of Research and Collections at the Denver Museum of Nature & Science, the paper’s lead author, Scott Sampson, is also the science advisor and on-air host of the hit PBS KIDS television series, Dinosaur Train.

 Note : The above story is reprinted from materials provided by University of Utah

Newly Discovered Flux in Earth May Solve Missing-Mantle Mystery

This artist’s rendering shows a solar system that is a much younger version of our own. Dusty disks, like the one shown here circling the star, are thought to be the breeding grounds of planets, including rocky ones like Earth. (Credit: NASA/JPL-Caltech)

It’s widely thought that Earth arose from violent origins: Some 4.5 billion years ago, a maelstrom of gas and dust circled in a massive disc around the sun, gathering in rocky clumps to form asteroids. These asteroids, gaining momentum, whirled around a fledgling solar system, repeatedly smashing into each other to create larger bodies of rubble — the largest of which eventually cooled to form the planets.

Countless theories, simulations and geologic observations support such a scenario. But there remains one lingering mystery: If Earth arose from the collision of asteroids, its composition should resemble that of meteoroids, the small particles that break off from asteroids.

But to date, scientists have found that, quite literally, something doesn’t add up: Namely, Earth’s mantle — the layer between the planet’s crust and core — is missing an amount of lead found in meteorites whose composition has been analyzed following impact with Earth.

Much of Earth is composed of rocks with a high ratio of uranium to lead (uranium naturally decays to lead over time). However, according to standard theories of planetary evolution Earth should harbor a reservoir of mantle somewhere in its interior that has a low ratio of uranium to lead, to match the composition of meteorites. But such a reservoir has yet to be discovered — a detail that leaves Earth’s origins hazy.

Now researchers in MIT’s Department of Earth, Atmospheric and Planetary Sciences have identified a “hidden flux” of material in Earth’s mantle that would make the planet’s overall composition much more similar to that of meteorites. This reservoir likely takes the form of extremely dense, lead-laden rocks that crystallize beneath island arcs, strings of volcanoes that rise up at the boundary of tectonic plates.

As two massive plates push against each other, one plate subducts, or slides, under the other, pushing material from the crust down into the mantle. At the same time, molten material from the mantle rises up to the crust, and is ejected via volcanoes onto Earth’s surface.

According to the MIT researchers’ observations and calculations, however, up to 70 percent of this rising magma crystallizes into dense rock — dropping, leadlike, back into the mantle, where it remains relatively undisturbed. The lead-heavy flux, they say, puts the composition of Earth’s mantle on a par with that of meteorites.

“Now that we know the composition of this flux, we can calculate that there’s tons of this stuff dropping down from the base of the crust into the mantle, so it is likely an important reservoir,” says Oliver Jagoutz, an assistant professor of geology at MIT. “This has a lot of implications for understanding how the Earth evolved through history.”

Jagoutz and his colleague Max Schmidt, of the Swiss Federal Institute of Technology in Zurich, have detailed their results in a paper published in Earth and Planetary Science Letters.

A mantle exposed

Measuring the composition of material that has dropped into the mantle is a nearly impossible task. Jagoutz estimates that such dense rocks would form at a depth of 40 to 50 kilometers below the surface, beyond the reach of conventional sampling techniques.

There is, however, one place on earth where such a depth of the crust and mantle is exposed: a region of northern Pakistan called the Kohistan arc. Forty million years ago, this island arc was crushed between India and Asia as the two plates collided.

“When India came in, it slammed into the arc, and the arc extended and rotated itself,” Jagoutz says. “Because of that, we now have a cross-section of the mantle-to-crust transition. This is the only place on Earth where this exists.”

On various trips from 2000 to 2007, Jagoutz trekked through the Kohistan arc region, collecting rocks from various parts of the arc’s crust and mantle. Bringing them back to the lab, he analyzed the rocks’ density and composition, discovering that some were “density-unstable” — much denser than the mantle. These denser rocks could potentially sink into the mantle, creating a hidden reservoir.

Adding up to an asteroid origin

The researchers measured the rocks’ composition, and found that the denser rocks contained much more lead than uranium — exactly the ratio predicted for the missing reservoir of material. Jagoutz then performed a mass balance (a simple conservation-of-mass calculation) to determine how much dense rock drops into the mantle, based on the composition of the region’s crust, rocks and mantle: Essentially, the mass of the Kohistan arc, minus whatever material drops into the mantle, should equal the material that comes out of the mantle.

Jagoutz and Schmidt solved the equation for 10 common elements. From their calculations, they found that 70 percent of the magma that rises from the mantle must ultimately drop back down, relatively heavy with lead. Applying this statistic to other island arcs in the world — such as the Andean volcanic belt and the Cascade Range — they found that the amount of material dropped into the mantle globally equals the composition and quantity of the so-called missing reservoir — a finding that suggests that Earth did indeed form from the collision of meteorites.

Bruce Buffett, a professor of earth and planetary science at the University of California at Berkeley, says a hidden reservoir in the mantle made of dense rocks is “interesting and plausible,” though he points out that there are other competing theories. For example, the subduction of oceanic crust into the mantle may contribute unknown material. Likewise, material may form from the cooling and solidifying of a large magma ocean.

“There are a large variety of options on the table to explain the complex structure we detect seismically at the bottom of the mantle,” says Buffett, who was not involved in the study. “The attractive aspect of [Jagoutz’s] idea is that it has testable consequences. This is how progress is made.”

“If we are right, one of the questions we have is: Why is the Earth capable of hiding something from us? Why is there never a volcano that brings up these rocks?” Jagoutz adds. “You’d think it’d come back up, but it doesn’t. It’s actually interesting.”

Note : The above story is reprinted from materials provided by Massachusetts Institute of Technology. The original article was written by Jennifer Chu. 

Volcanic ‘scream’ precedes explosive eruptions

The researchers studied the eruption of Redoubt in 2009

A change in the frequency of earthquakes may foretell explosive volcanic eruptions, according to a new study.

The seismic activity changes from steady drum beats to increasingly rapid successions of tremors.

These blend into continuous noise which silences just before explosion.

The study of tremors in the lead up to the 2009 eruption of Redoubt, a volcano in Alaska, appears in Journal of Volcanology and Geothermal Research.

Those quakes continuously rose in pitch like a volcanic glissando – a musical glide from one pitch to another.

Subterranean magma plumbing systems sit beneath volcanoes and feed pressurised molten rock toward the surface before eruptions.

As the magma flows through deep conduits and cracks, it generates small seismic tremors and earthquakes.

Scientists have noted earthquakes preceding volcanic eruptions before, for example drumbeat earthquakes were the first sign of renewed magmatic activity in Mount St Helens in April 2005.

But the new analysis of Alaska’s Redoubt volcano shows that the tremor glided to higher frequencies and then stopped abruptly less than a minute before eruption.

“The frequency of this tremor is unusually high for a volcano,” explained Alicia Hotovec-Ellis, a doctoral student involved in the study, from the University of Washington.

“Because there’s less time between each earthquake, there’s not enough time to build up enough pressure for a bigger one. After the frequency glides up to a ridiculously high frequency, it pauses and then it explodes.”

The earthquake noise sounds like a scream before eruption when the seismometer data are speeded up sixty times to make them audible. The authors suggest a simple model of brittle fracture may explain their results, although the precise details of what is going on underneath volcanoes before they erupt remain unclear.

Dr Marie Edmonds, from the University of Cambridge, who was not involved in the study, commented: “This work is probably the most intensive treatment of this phenomenon. If you can get an idea of what is causing these types of patterns then you have a route to prediction of volcanic eruptions.

“The question that arises is whether you can ever get these sorts of patterns without an eruption following?

“We had repetitive sequences of volcanic explosions in the Caribbean island of Montserrat in 1997 and 2003 which were preceded by similar tremors, with hybrid earthquakes that were periodic and then recurrence intervals decreased with time before the explosion. People are converging on a view on how magmas behave.”

Note : The above story is reprinted from materials provided by BBC News. The original article was written by Simon Redfern

T-rex tooth found embedded in prey, restoring dinosaur’s reputation

New evidence suggests T rex was capable of bringing down live prey rather than simply scavenging dinosaur carcasses. Photograph: Corey Ford/Corbis

Threats to the fearsome reputation of Tyrannosaurs rex appeared to have been seen off on Monday by fresh evidence unearthed in the US.

The dinosaur’s feeding habits have long been debated by academics, with some claiming that T rex was less a ferocious hunter and more a lumbering slowcoach that scavenged the carcasses of beasts that had died at the claws of others.

The latest evidence comes from palaeontologists who found remnants of a prehistoric skirmish in a slab of rock at the Hell Creek Formation in South Dakota. The clash, which occurred around 66m years ago, involved a T rex and a large, plant-eating hadrosaur, and ended with the tooth of the former lodged firmly in the spine of the latter.

Scans of the tooth and two surrounding tail vertebrae showed clear signs of bone healing around the wound, taken as proof that the hadrosaur was alive at the time of the attack and survived for several months or even years afterwards.

“This is unambiguous evidence that T rex was an active predator,” the authors write in the journal Proceedings of the National Academy of Sciences. “Such evidence is rare in the fossil record for good reason – prey rarely escapes.”

Tyrannosaurs shed their teeth frequently as fresh sets came through. In this case a weaker rear tooth broke free as the T rex, which was not fully-grown, chomped on the hadrosaur’s tail. The hadrosaur is believed to have been an adult Edmontosaur, which grew to around 10 metres in length.

The tooth crown is embedded between two hadrosaur vertebrae and the bone has healed over. Photograph: David A Burnham

“We not only have a broken-off tooth embedded in the bone of another animal, but the bone has healed over

The remains join a large collection of fossils that tell their own partial stories about the dining habits of T rex. Previous discoveries reveal rake, puncture and chew marks on bones, while one specimen – an impressive half-metre of fossilised faeces – contained partly digested dinosaur bones. In all of these cases, it is hard to differentiate between predation and scavenging.

Palaeontologists expressed mixed reactions to the latest findings. Jack Horner at the Museum of the Rockies in Montana, who served as technical adviser on the Jurassic Park movies, told the Guardian: “This one piece of evidence does seem to suggest that a tyrannosaur bit a hadrosaur, but certainly doesn’t provide any indication of the sort of carnivore the rex actually was.”

In 2011, Horner and his team reported that T rex was probably an opportunistic carnivore like hyena, which take carrion and occasional live prey. “This paper certainly offers no evidence to refute that hypothesis,” Horner added.

Paul Barrett, a dinosaur researcher at the Natural History Museum in London, expressed exasperation that the debate was still ongoing. “The whole T rex scavenger or predator debate is pretty intractable and not particularly enlightening. Work on living carnivores, like big cats and wolves, clearly show they use both strategies depending on what’s available to them. They’ll generally make do with a meal from either source if it satisfies their dietary needs. Any other extinct carnivore, including T rex, is likely to have been the same,” he said.

“This paper shows without question that a T rex bit a living hadrosaur, but it can’t show if this was a regular behaviour or not, or even if this was hunting behaviour rather than some other kind of interaction,” he added.

But Sam Turvey, a senior research fellow at the Institute of Zoology in London, called it “important and convincing” new evidence. “Even though T rex may have fed on carcasses when the opportunity arose – a behaviour also seen in modern-day carnivorous large mammals such as lions – the new findings provide strong evidence that these iconic dinosaurs were fully capable of being active predators, and help to dismiss the ecologically unrealistic hypothesis that they were restricted to a scavenging lifestyle,” he said.
the wound, and a nasty wound it was too,” said David Burnham at Palm Beach Museum of Natural History in Florida.

Note : The above story is reprinted from materials provided by guardian.co.uk. The original article was written by Ian Sample, science correspondent . 

Some Volcanoes ‘Scream’ at Ever-Higher Pitches Until They Blow Their Tops

Redoubt Volcano’s active lava dome as it appeared on May 8, 2009. The volcano is in the Aleutian Range about 110 miles south-southwest of Anchorage, Alaska. (Credit: Chris Waythomas, Alaska Volcano Observatory)

It is not unusual for swarms of small earthquakes to precede a volcanic eruption. They can reach a point of such rapid succession that they create a signal called harmonic tremor that resembles sound made by various types of musical instruments, though at frequencies much lower than humans can hear.

A new analysis of an eruption sequence at Alaska’s Redoubt Volcano in March 2009 shows that the harmonic tremor glided to substantially higher frequencies and then stopped abruptly just before six of the eruptions, five of them coming in succession.

“The frequency of this tremor is unusually high for a volcano, and it’s not easily explained by many of the accepted theories,” said Alicia Hotovec-Ellis, a University of Washington doctoral student in Earth and space sciences.

Documenting the activity gives clues to a volcano’s pressurization right before an explosion. That could help refine models and allow scientists to better understand what happens during eruptive cycles in volcanoes like Redoubt, she said.

The source of the earthquakes and harmonic tremor isn’t known precisely. Some volcanoes emit sound when magma — a mixture of molten rock, suspended solids and gas bubbles — resonates as it pushes up through thin cracks in Earth’s crust.

But Hotovec-Ellis believes in this case the earthquakes and harmonic tremor happen as magma is forced through a narrow conduit under great pressure into the heart of the mountain. The thick magma sticks to the rock surface inside the conduit until the pressure is enough to move it higher, where it sticks until the pressure moves it again.

Each of these sudden movements results in a small earthquake, ranging in magnitude from about 0.5 to 1.5, she said. As the pressure builds, the quakes get smaller and happen in such rapid succession that they blend into a continuous harmonic tremor.

“Because there’s less time between each earthquake, there’s not enough time to build up enough pressure for a bigger one,” Hotovec-Ellis said. “After the frequency glides up to a ridiculously high frequency, it pauses and then it explodes.”

She is the lead author of a forthcoming paper in the Journal of Volcanology and Geothermal Research that describes the research. Co-authors are John Vidale of the UW and Stephanie Prejean and Joan Gomberg of the U.S. Geological Survey.

Hotovec-Ellis is a co-author of a second paper, published online July 14 in Nature Geoscience, that introduces a new “frictional faulting” model as a tool to evaluate the tremor mechanism observed at Redoubt in 2009. The lead author of that paper is Ksenia Dmitrieva of Stanford University, and other co-authors are Prejean and Eric Dunham of Stanford.

The pause in the harmonic tremor frequency increase just before the volcanic explosion is the main focus of the Nature Geoscience paper. “We think the pause is when even the earthquakes can’t keep up anymore and the two sides of the fault slide smoothly against each other,” Hotovec-Ellis said.

She documented the rising tremor frequency, starting at about 1 hertz (or cycle per second) and gliding upward to about 30 hertz. In humans, the audible frequency range starts at about 20 hertz, but a person lying on the ground directly above the magma conduit might be able to hear the harmonic tremor when it reaches its highest point (it is not an activity she would advise, since the tremor is closely followed by an explosion).

Scientists at the USGS Alaska Volcano Observatory have dubbed the highest-frequency harmonic tremor at Redoubt Volcano “the screams” because they reach such high pitch compared with a 1-to-5 hertz starting point. Hotovec-Ellis created two recordings of the seismic activity. A 10-second recording covers about 10 minutes of seismic sound and harmonic tremor, sped up 60 times. A one-minute recording condenses about an hour of activity that includes more than 1,600 small earthquakes that preceded the first explosion with harmonic tremor.

Upward-gliding tremor immediately before a volcanic explosion also has been documented at the Arenal Volcano in Costa Rica and Soufrière Hills volcano on the Caribbean island of Montserrat.

“Redoubt is unique in that it is much clearer that that is what’s going on,” Hotovec-Ellis said. “I think the next step is understanding why the stresses are so high.”

The work was funded in part by the USGS and the National Science Foundation.

Note : The above story is reprinted from materials provided by University of Washington. The original article was written by Vince Stricherz. 

Improved Interpretation of Volcanic Traces in Ice

The crater of the Indonesian volcano Tombora (diameter about 7 km). Its eruption turned 1815 in to a “year without a summer” in Europe. The sulfate traces it left behind in the Greenland and Antarctic ice, served as a comparison for the current model study. (Credit: NASA)

How severely have volcanoes contaminated the atmosphere with sulfur particles in past millennia? To answer this question, scientists use ice cores, among others, as climate archives. But the results differ, particularly in some major volcanic major events of the past, depending on whether the cores come from Antarctica or Greenland. Atmospheric scientists from the GEOMAR Helmholtz Centre for Ocean Research Kiel and the Max Planck Institute for Meteorology in Hamburg have now found an explanation that could significantly improve the interpretation of ice cores.

Their study was just published in the current issue of the  Journal of Geophysical Research Atmosphere.

Storms, cold, poor harvests — the year 1816 was a “year without a summer” in European history. The reason was the eruption of the Indonesian volcano Tambora a year earlier. It had thrown huge amounts of sulfur compounds into the stratosphere (at altitudes of 15-50 km) where they spread around the entire globe and significantly weakened solar radiation for several years afterwards. Such intense volcanic eruptions are quite common in Earth’s history. To better understand their impact on the climate and the atmosphere, scientists try to reconstruct those eruptions accurately. Important archives of information are ice cores from Greenland and Antarctica because the sulfur particles ejected from the volcano fall back to the surface. A portion of that fallout is trapped in the ice of the polar regions and can be analyzed even thousands of years afterwards. The former aerosol contamination of the atmosphere is derived from it using a simple ratio calculation.

But this method has its limitations. “Volcanic aerosols in the stratosphere absorb infrared radiation, thereby heating up the stratosphere, and changing the wind conditions subsequently,” said Dr. Matthew Toohey, atmospheric scientist at GEOMAR Helmholtz Centre for Ocean Research Kiel. Using an atmospheric model, he has now tested the effects of this phenomenon. “We have found that the deposition of sulfur compounds in the Antarctic after very large volcanic eruptions in the tropics may be lower than previously thought,” the atmospheric researcher summarizes the findings of the study which has just been published in the current issue of the international “Journal of Geophysical Research — Atmosphere.”

For the study, Dr. Toohey and his colleagues from GEOMAR and the Max Planck Institute for Meteorology in Hamburg have used an aerosol-climate model to track 70 different eruption scenarios while analyzing the distribution of the sulfur particles. It was based on real volcanic eruptions during the past 200,000 years in Central America, which had been investigated in the framework of the Collaborative Research Project 574. “In our calculations, we could clearly see the differences in distribution and deposition between the northern and southern hemispheres,” explains co-author and director of the working group, Dr. Kirstin Krüger. The spatial deposition of sulfur particles in the bipolar ice cores, as calculated in the model, agrees well with the actually measured deposits of large volcanic eruptions, such as Pinatubo in 1991 or even of Tambora of 1815.

“If we know how volcanic sulfur particles affect the atmospheric winds, we can have a much improved interpretation of the traces of volcanic activities in the ice cores,” says Dr. Toohey. For one, there are better estimates of the strength of an outbreak. And secondly, the previously undetermined traces of volcanic eruptions that could not be assigned to any particular event or volcano eruption, can now be clearly traced to their origin.

“In any case, the results of our model study give a clear indication that the bipolar variability of sulfate deposits must be taken into consideration if the traces of large volcanic eruptions are to be deduced from ice cores,” says Dr. Krüger, “Several research groups that deal with this issue have already contacted us to verify their data through our model results.”

Note : The above story is reprinted from materials provided by Helmholtz Centre for Ocean Research Kiel (GEOMAR). 

Scientists cast doubt on theory of what triggered Antarctic glaciation

This is a physiographic map of the present-day Scotia Sea, Drake Passage and adjacent land masses. The white arrows show the present path of the several branches of the deep Antarctic Circumpolar Current (ACC) centered on its core. The area of study in the central Scotia Sea (CSS) is shown by the black box to the south of South Georgia island (SG). The volcano symbols mark the active South Sandwich volcanic arc (SSA). (WSS = western Scotia Sea; ESS = eastern Scotia Sea)Credit: University of Texas at Austin

A team of U.S. and U.K. scientists has found geologic evidence that casts doubt on one of the conventional explanations for how Antarctica’s ice sheet began forming. Ian Dalziel, research professor at The University of Texas at Austin’s Institute for Geophysics and professor in the Jackson School of Geosciences, and his colleagues report the findings today in an online edition of the journal Geology.

The Antarctic Circumpolar Current (ACC), an ocean current flowing clockwise around the entire continent, insulates Antarctica from warmer ocean water to the north, helping maintain the ice sheet. For several decades, scientists have surmised that the onset of a complete ACC played a critical role in the initial glaciation of the continent about 34 million years ago.

Now, rock samples from the central Scotia Sea near Antarctica reveal the remnants of a now-submerged volcanic arc that formed sometime before 28 million years ago and might have blocked the formation of the ACC until less than 12 million years ago. Hence, the onset of the ACC may not be related to the initial glaciation of Antarctica, but rather to the subsequent well-documented descent of the planet into a much colder “icehouse” glacial state.

“If you had sailed into the Scotia Sea 25 million years ago, you would have seen a scattering of volcanoes rising above the water,” says Dalziel. “They would have looked similar to the modern volcanic arc to the east, the South Sandwich Islands.”

Using multibeam sonar to map seafloor bathymetry, which is analogous to mapping the topography of the

his is a reconstruction of the Scotia Sea area 25 million years ago, showing volcanoes of the ancestral South Sandwich arc (ASSA). They are now submerged, but were active at that time and possibly emergent. They may have blocked the onset of the Antarctic Circumpolar Current. (NSR = North Scotia Ridge; SSR = South Scotia Ridge; SG = South Georgia island)Credit: University of Texas at Austin

land surface, the team identified seafloor rises in the central Scotia Sea. They dredged the seafloor at various points on the rises and discovered volcanic rocks and sediments created from the weathering of volcanic rocks. These samples are distinct from normal ocean floor lavas and geochemically identical to the presently active South Sandwich Islands volcanic arc to the east of the Scotia Sea that today forms a barrier to the ACC, diverting it northward.
Using a technique known as argon isotopic dating, the researchers found that the samples range in age from about 28 million years to about 12 million years. The team interpreted these results as evidence that an ancient volcanic arc, referred to as the ancestral South Sandwich arc (ASSA), was active in the region during that time and probably much earlier. Because the samples were taken from the current seafloor surface and volcanic material accumulates from the bottom up, the researchers infer that much older volcanic rock lies beneath.

Combined with models of how the seafloor sinks vertically with the passage of time, the team posits that the ASSA originally rose above sea level and would have blocked deep ocean currents such as the ACC.

Two other lines of evidence support the notion that the ACC didn’t begin until less than 12 million years ago. First, the northern Antarctic Peninsula and southern Patagonia didn’t become glaciated until less than approximately 12 million years ago. And second, certain species of microscopic creatures called dinoflagellates that thrive in cold polar water began appearing in sediments off southwestern Africa around 11.1 million years ago, suggesting colder water began reaching that part of the Atlantic Ocean.

Note : The above story is reprinted from materials provided by University of Texas at Austin

Dinosaurs, Diets and Ecological Niches: Study Shows Recipe for Success

Dr. Jordan Mallon in the museum’s fossil collections with three of the skulls he examined for his study on niche partitioning. Front to back: Lambeosaurus clavinitelis (a hadrosaur), Chasmosaurus belli, and Styracosaurus albertensis, both ceratopsids (horn-faced dinosaurs). (Credit: Dan Smythe © Canadian Museum of Nature)

A new study by a Canadian Museum of Nature scientist helps answer a long-standing question in palaeontology — how numerous species of large, plant-eating dinosaurs could co-exist successfully over geological time.

Dr. Jordan Mallon, a post-doctoral fellow at the museum, tackled the question by measuring and analyzing characteristics of nearly 100 dinosaur skulls recovered from the Dinosaur Park Formation in Alberta, Canada. The specimens now reside in major fossil collections across the world, including the collections of the Canadian Museum of Nature.

The work was undertaken as part of his doctoral thesis at the University of Calgary under the supervision of Dr. Jason Anderson.

Mallon’s results, published in the July 10, 2013 issue of the open-access journal PLOS ONE, indicate that these megaherbivores (all weighing greater than 1,000 kg) had differing skull characteristics that would have allowed them to specialize in eating different types of vegetation. The results support a concept known as niche partitioning, which dates to the 19th-century studies of Charles Darwin and came into its own in the 1950s with the development of the science of ecology.

The Dinosaur Park Formation is between 76.5 and 75 million years old and is known for its rich concentration of dinosaur remains. The rock unit has yielded nearly 20 species of megaherbivores from the Late Cretaceous period. Of these, six species would have coexisted at any one time, including two types of ankylosaurs (tank-like armoured dinosaurs), two types of hadrosaurs (duck-billed dinosaurs), and two types of ceratopsids (horn-faced dinosaurs).

Dr. Jordan Mallon in the museum’s fossil collections with three of the skulls he examined for his study on niche partitioning. Front to back: Lambeosaurus clavinitelis (a hadrosaur), Chasmosaurus belli, and Styracosaurus albertensis, both ceratopsids (horn-faced dinosaurs).

Modern megaherbivores include elephants, giraffes, hippos and rhinos. “Today’s megaherbivore communities are not nearly as diverse as those from the Late Cretaceous of Alberta, and most other fossil communities also pale by comparison. So the question is: how does an environment support so many of these large herbivores at once?” asks Mallon.

Mallon tested two competing hypotheses. The first is that availability of food was not a limiting factor in species survival. Plants may have been either super-abundant, so the megaherbivores did not have to compete for food, or the dinosaurs’ metabolisms were relatively low, so the environment could support more species relative to a fauna comprised entirely of high-metabolic animals.

The second hypothesis is that the available food resources were limiting and that niche partitioning came into play; in other words, there weren’t that many plants to go around so that the species had to share available food sources by specializing on different types of vegetation.

“If niche partitioning was in effect, then you would expect to see various dietary adaptations among the coexisting dinosaur species, ” explains Mallon. “So you would look for differences in the shapes of the skull, in the teeth, and in the beaks that might reflect adaptations for feeding on diverse plants or plant parts. ” These differences, for example, would reflect whether a dinosaur was adapted to feeding on soft or hard plant tissues.

Until Mallon’s study, neither of these hypotheses had been rigorously tested with such a large sample size. For each of the nearly 100 dinosaur skulls he studied, Mallon measured 12 characteristics that are known to relate to diet in modern animals. These include depth of the jaw, angle of the beak, size of muscle insertions, and length of the tooth row. “We can apply those same functional and mechanical principles to dinosaurs to see what they might tell us about niche partitioning,” he explains.

Styracosaurus albertensis, a ceratopsid (horn-faced dinosaur), was one of the many skulls studied by Dr. Jordan Mallon for his study on niche partitioning. This specimen is in the museum’s collections in Gatineau, Quebec.

Not unexpectedly, differences were found between the three major groups (ankylosaurs, hadrosaurs and ceratopsids). But more striking were the subtle yet significant differences within each of the three groups that were probably related to feeding. “We found those differences that were previously suspected but never demonstrated, ” explains Mallon.

As an example, the palaeontologist suggests that ankylosaurs probably specialized on eating ferns, because they stood low to the ground, and their wide beaks would have allowed them to feed efficiently on abundant, relatively low-nutrient plants. However, within this group, the family known as nodosaurids (clubless ankylosaurs) had more efficient jaw mechanics that might have enabled them to include tougher plants in their diets. In contrast, ceratopsids had skulls that suggest they were adapted to feeding on mid-sized shrubs, while the taller hadrosaurs were less picky and would have fed on anything within reach.

Although different species came and went, the same ecological roles were filled over the 1.5 million year span of the Dinosaur Park Formation. “This tells us that niche partitioning was a viable strategy for the coexistence of these animals,” adds Mallon. “The study provides further evidence to explain why dinosaurs were one of the most successful groups of animals to live on this planet.”

The study was funded by an NSERC Alexander Graham Bell Canada Graduate Scholarship, Alberta Innovates Technology Futures graduate student scholarship, Queen Elizabeth II scholarship, and a research grant from the Jurassic Foundation. The dinosaur specimens examined reside in the collections of the Canadian Museum of Nature (Ottawa), Royal Ontario Museum (Toronto), Royal Tyrrell Museum of Palaeontology (Drumheller, Alberta), University of Alberta (Edmonton), American Museum of Natural History (New York), Field Museum (Chicago), Yale Peabody Museum (New Haven, Connecticut), National Museum of Natural History (Washington), and Natural History Museum (London).

Note : The above story is reprinted from materials provided by Canadian Museum of Nature. 

Earth’s Core Affects Length of Day

The form of core motions giving rise to variations in Earth’s length of day. (Credit: Image courtesy of University of Liverpool)

Researchers studied the variations and fluctuations in the length of day over a one to 10 year period between 1962 and 2012

Research at the University of Liverpool has found that variations in the length of day over periods of between one and 10 years are caused by processes in Earth’s core.
Earth rotates once per day, but the length of this day varies. A year, 300million years ago, lasted about 450 days and a day would last about 21 hours.

Length of day increases

As a result of the slowing down of Earth’s rotation the length of day has increased.

The rotation of Earth on its axis, however, is affected by a number of other factors — for example, the force of the wind against mountain ranges changes the length of the day by plus or minus a millisecond over a period of a year.

Professor Richard Holme, from the School of Environmental Sciences, studied the variations and fluctuations in the length of day over a one to 10 year period between 1962 and 2012. The study took account of the effects on Earth’s rotation of atmospheric and oceanic processes to produce a model of the variations in the length of day on time scales longer than a year.

Professor Holme said: “The model shows well-known variations on decadal time scales, but importantly resolves changes over periods between one and 10 years.

“Previously these changes were poorly characterised; the study shows they can be explained by just two key signals, a steady 5.9 year oscillation and episodic jumps which occur at the same time as abrupt changes in the Earth’s magnetic field, generated in the Earth’s core.

He added: “This study changes fundamentally our understanding of short-period dynamics of the Earth’s fluid core. It leads us to conclude that the Earth’s lower mantle, which sits above the Earth’s outer core, is a poor conductor of electricity giving us new insight into the chemistry and mineralogy of the Earth’s deep interior.”

The research was conducted in partnership with the Université Paris Diderot and is published in Nature.

Note : The above story is reprinted from materials provided by University of Liverpool.

How Early Earth Kept Warm Enough to Support Life

An artist’s conception of the Earth during the late Archean, 2.8 billion years ago. Weak solar radiation requires the Earth have increased greenhouse gas amounts to remain warm. CU-Boulder doctoral student Eric Wolf Wolf and CU-Boulder Professor Brian Toon use a three-dimensional climate model to show that the late Archean may have maintained large areas of liquid surface water despite a relatively weak greenhouse. With carbon dioxide levels within constraints deduced from ancient soils, the late Archean may have had large polar ice caps but lower latitudes would have remained temperate and thus hospitable to life. The addition of methane allows the late Archean to warmed to present day mean surface temperatures. (Credit: Charlie Meeks)

Solving the “faint young sun paradox” — explaining how early Earth was warm and habitable for life beginning more than 3 billion years ago even though the sun was 20 percent dimmer than today — may not be as difficult as believed, says a new University of Colorado Boulder study

In fact, two CU-Boulder researchers say all that may have been required to sustain liquid water and primitive life on Earth during the Archean eon 2.8 billion years ago were reasonable atmospheric carbon dioxide amounts believed to be present at the time and perhaps a dash of methane. The key to the solution was the use of sophisticated three-dimensional climate models that were run for thousands of hours on CU’s Janus supercomputer, rather than crude, one-dimensional models used by almost all scientists attempting to solve the paradox, said doctoral student Eric Wolf, lead study author.

“It’s really not that hard in a three-dimensional climate model to get average surface temperatures during the Archean that are in fact moderate,” said Wolf, a doctoral student in CU-Boulder’s atmospheric and oceanic sciences department. “Our models indicate the Archean climate may have been similar to our present climate, perhaps a little cooler. Even if Earth was sliding in and out of glacial periods back then, there still would have been a large amount of liquid water in equatorial regions, just like today.”

Evolutionary biologists believe life arose on Earth as simple cells roughly 3.5 billion years ago, about a billion years after the planet is thought to have formed. Scientists have speculated the first life may have evolved in shallow tide pools, freshwater ponds, freshwater or deep-sea hydrothermal vents, or even arrived on objects from space.

A cover article by Wolf and CU-Boulder Professor Brian Toon on the topic appears in the July issue of Astrobiology.

Scientists have been trying to solve the faint young sun paradox since 1972, when Cornell University scientist Carl Sagan — Toon’s doctoral adviser at the time — and colleague George Mullen broached the subject. Since then there have been many studies using 1-D climate models to try to solve the faint young sun paradox — with results ranging from a hot, tropical Earth to a “snowball Earth” with runaway glaciation — none of which have conclusively resolved the problem.

“In our opinion, the one-dimensional models of early Earth created by scientists to solve this paradox are too simple — they are essentially taking the early Earth and reducing it to a single column atmospheric profile,” said Toon. “One-dimensional models are simply too crude to give an accurate picture.”

Wolf and Toon used a general circulation model known as the Community Atmospheric Model version 3.0 developed by the National Center for Atmospheric Research in Boulder and which contains 3-D atmosphere, ocean, land, cloud and sea ice components. The two researchers also “tuned up” the model with a sophisticated radiative transfer component that allowed for the absorption, emission and scattering of solar energy and an accurate calculation of the greenhouse effect for the unusual atmosphere of early Earth, where there was no oxygen and no ozone, but lots of CO2 and possibly methane.

The simplest solution to the faint sun paradox, which duplicates Earth’s present climate, involves maintaining roughly 20,000 parts per million of the greenhouse gas CO2 and 1,000 ppm of methane in the ancient atmosphere some 2.8 billion years ago, said Wolf. While that may seem like a lot compared to today’s 400 ppm of CO2 in the atmosphere, geological studies of ancient soil samples support the idea that CO2 likely could have been that high during that time period. Methane is considered to be at least 20 times more powerful as a greenhouse gas than CO2 and could have played a significant role in warming the early Earth as well, said the CU researchers.

There are other reasons to believe that CO2 was much higher in the Archean, said Toon, who along with Wolf is associated with CU’s Laboratory for Atmospheric and Space Physics. The continental area of Earth was smaller back then so there was less weathering of the land and a lower release of minerals to the oceans. As a result there was a smaller conversion of CO2 to limestone in the ocean. Likewise, there were no “rooted” land plants in the Archean, which could have accelerated the weathering of the soils and indirectly lowered the atmospheric abundance of CO2, Toon said.

Another solution to achieving a habitable but slightly cooler climate under the faint sun conditions is for the Archean atmosphere to have contained roughly 15,000 to 20,000 ppm of CO2 and no methane, said Wolf. “Our results indicate that a weak version of the faint young sun paradox, requiring only that some portion of the planet’s surface maintain liquid water, may be resolved with moderate greenhouse gas inventories,” the authors wrote in Astrobiology.

“Even if half of Earth’s surface was below freezing back in the Archean and half was above freezing, it still would have constituted a habitable planet since at least 50 percent of the ocean would have remained open,” said Wolf. “Most scientists have not considered that there might have been a middle ground for the climate of the Archean.

“The leap from one-dimensional to three-dimensional models is an important step,” said Wolf. “Clouds and sea ice are critical factors in determining climate, but the one-dimensional models completely ignore them.”

Has the faint young sun paradox finally been solved? “I don’t want to be presumptuous here,” said Wolf. “But we show that the paradox is definitely not as challenging as was believed over the past 40 years. While we can’t say definitively what the atmosphere looked like back then without more geological evidence, it is certainly not a stretch at all with our model to get a warm early Earth that would have been hospitable to life.”

“The Janus supercomputer has been a tremendous addition to the campus, and this early Earth climate modeling project would have impossible without it,” said Toon. The researchers estimated the project required roughly 6,000 hours of supercomputer computation time, an effort equal to about 10 years on a home computer.

The study was funded by two NASA grants and by the National Science Foundation, which supports CU-Boulder’s Janus supercomputer used for the study.

Note :  The above story is reprinted from materials provided by University of Colorado at Boulder.

New idea tackles Earth core puzzle

Lying 5,000km beneath our feet, the core is beyond the reach of direct investigation

Scientists have proposed a radical new model for the make-up of the Earth’s core.The study may explain a longstanding puzzle about the most inaccessible part of our planet.

It suggests that differences between the east and west hemispheres of the core are explained by the way iron atoms pack together.
Details appear in the journal Scientific Reports.

Lying more than 5,000km beneath our feet, at the centre of the Earth, the core is beyond the reach of direct investigation. Broadly speaking, it consists of a solid sphere of metal sitting within a liquid outer core.

The inner core started to solidify more than a billion years ago. It has a radius of about 1,220km, but is growing by about 0.5mm each year.

But the stuff that the core is made from remains a longstanding unresolved problem.

Clues come from the speeds that seismic waves generated by earthquakes pass through the core.

These tell us its density and elasticity, but the precise arrangement of iron atoms forming the crystalline core controls these numbers.

How those atoms are arranged remains unclear, since the conditions of extreme pressure and temperature at the core cannot easily be replicated in the laboratory.

Seismic data indicate that the western and eastern hemispheres of Earth’s inner core differ, and this has led some to suggest that the core was once subjected to an impulse – presumably from the collision of a space rock or planetoid which shook the whole Earth.

The core, it is suggested, is constantly moving sideways. As it does, the front side is melting and the rear side crystallising, but the core is held centrally by gravity.

With all these seismic complexities, the link between the crystal structure and the geophysical observations has yet to be resolved.

In Scientific Reports, Maurizio Mattesini from the Complutense University of Madrid, Spain, and colleagues propose a novel possibility for the structure of the core: that it is composed of mixtures of different iron arrangements distinguished by the way their atoms pack together.

By comparing seismic data from over one thousand earthquakes across the globe with quantum mechanical models for the properties of iron, they suggest that seismic variations directly reflect variations in the iron structure.

They propose that the eastern and western sides of the core differ in the extent of mixing of these distinct structures, and suggest their results account for the dynamic eastward drift of the core through time.

Their complicated picture of the core contrasts with earlier suggestions of a more uniform mineralogy. It has yet to incorporate the effects of minor amounts of other elements in the iron alloy actually thought to be there.

But Dr Arwen Deuss, a seismologist from the University of Cambridge, commented: “This is a step in the right direction, directly comparing seismology with mineral physical properties.” She added that it should eventually provide a better understanding of the birth and evolution of our planet.

Note : The above story is reprinted from materials provided by Simon Redfern For BBC News

Evidence That Elemental Fluorine Occurs in Nature

Antozonite or “Stinkspat” (Credit: Photo: Dr. Rupert Hochleitner, Mineralogische Staatssammlung München)

Fluorine is the most reactive chemical element. That is why it is not found in nature in its elemental form, but only in compounds, such as fluorite — that was the accepted scientific doctrine so far. A special fluorite, the “fetid fluorite” or “antozonite,” has been the subject of many discussions for nearly 200 years.

This mineral emits an intensive odor when crushed. Now, for the first time, scientists from the Technische Universitaet Muenchen (TUM) and the Ludwig-Maximilians-University Munich (LMU) have successfully identified natural elemental fluorine in this fluorspar.

They report their results in the international edition of the scientific journal Angewandte Chemie.

Fluorine is the most reactive of all chemical elements and calls for extremely careful handling. It is so aggressive that glass laboratory instruments cannot resist it and even bricks burn when exposed to fluorine gas. Yet elemental fluorine has numerous industrial applications including corrosion prevention or fuel tank diffusion barriers and it is used for the production of sulphur hexafluoride, which serves as insulating material in high voltage switches.

Because of its extreme properties, until now chemists were convinced that fluorine cannot occur in nature in its elemental form, but only as a fluoride ion, for instance in minerals such as fluorite (CaF2), also known as fluorspar. A certain variety of it, the so-called “fetid fluorite” or “antozonite” from the “Maria” mine in Woelsendorf in the Upper Palatinate (Germany), has been an object of contention in science for some 200 years. When crushed, it emits an unpleasant, pungent smell.

A number of eminent chemists, among them Friedrich Woehler (1800-1882) and Justus von Liebig (1803-1873), proposed various substances to explain the odor. Over the years, scientists resorted to olfactory tests, chemical analyses and complex mass spectrometer studies — coming to very different conclusions. Next to elemental fluorine, substances like iodine, ozone, phosphorus compounds, arsenic, sulphur, selenium, chlorine, hypochlorous acid and hydrofluorocarbons were made responsible for the smell. Direct evidence that this fluorspar has inclusions of fluorine and that the gas does not form during crushing was lacking hitherto.

Now, finally, a scientific team led by Florian Kraus, head of the Fluorine Chemistry Work Group at the Department of Chemistry of the Technische Universitaet Muenchen, and by Joern Schmedt auf der Guenne, head of the Emmy-Noether Work Group for Solid State NMR at the Department of Chemistry of the Ludwig-Maximilians-University Munich, have succeeded in directly proving the presence of fluorine in “antozonite” beyond any doubt. Using 19F-NMR spectroscopy, they were able to identify the fluorine “in-situ,” i.e. non-destructively in its natural environment, and thereby put an end to the long discussions about the cause for the odor of “stinking fluorspar.”

“It is not surprising that chemists doubted the existence of elemental fluorine in fetid fluorite,” explain the researchers. “The fact that elemental fluorine and calcium, which would normally react with each other at once, are found here side by side is indeed hard to believe.” However, in the case of “antozonite” there are very special conditions: The elemental fluorine is generated through minute uranium inclusions in the mineral, which constantly emit ionizing radiation and thus split the fluorite into calcium and elemental fluorine. The fluorine remains in minute inclusions, separated from the calcium by the non-reactive fluorite and thus retains its elemental form. The ionizing radiation also leads to the formation of calcium clusters, which give “antozonite” its dark color.

Note : The above story is reprinted from materials provided by Technische Universitaet Muenchen.

Earthquakes make gold veins in an instant

Veins of gold, such as this one trapped in quartz and granite, may deposit when the high-pressure water in which they were dissolved suddenly vaporises during an earthquake. Credit: Shutterstock

Scientists have long known that veins of gold are formed by mineral deposition from hot fluids flowing through cracks deep in Earth’s crust. But a study published today in Nature Geoscience1 has found that the process can occur almost instantaneously — possibly within a few tenths of a second.
The process takes place along ‘fault jogs’ — sideways zigzag cracks that connect the main fault lines in rock, says first author Dion Weatherley, a seismologist at the University of Queensland in Brisbane, Australia.

When an earthquake hits, the sides of the main fault lines slip along the direction of the fault, rubbing against each other. But the fault jogs simply open up. Weatherley and his co-author, geochemist Richard Henley at the Australian National University in Canberra, wondered what happens to fluids circulating through these fault jogs at the time of the earthquake.

What their calculations revealed was stunning: a rapid depressurization that sees the normal high-pressure conditions deep within Earth drop to pressures close to those we experience at the surface.

For example, a magnitude-4 earthquake at a depth of 11 kilometres would cause the pressure in a suddenly opening fault jog to drop from 290 megapascals (MPa) to 0.2 MPa. (By comparison, air pressure at sea level is 0.1 MPa.) “So you’re looking at a 1,000-fold reduction in pressure,” Weatherley says.

Flash in the pan

When mineral-laden water at around 390 °C is subjected to that kind of pressure drop, Weatherley says, the liquid rapidly vaporizes and the minerals in the now-supersaturated water crystallize almost instantly  — a process that engineers call flash vaporization or flash deposition. The effect, he says, “is sufficiently large that quartz and any of its associated minerals and metals will fall out of solution”.

Eventually, more fluid percolates out of the surrounding rocks into the gap, restoring the initial pressure. But that doesn’t occur immediately, and so in the interim a single earthquake can produce an instant (albeit tiny) gold vein.

Big earthquakes will produce bigger pressure drops, but for gold-vein formation, that seems to be overkill. More interesting, Weatherley and Henley found, is that even small earthquakes produce surprisingly big pressure drops along fault jogs.

“We went all the way to magnitude –2,” Weatherley says — an earthquake so small, he adds, that it involves a slip of only about 130 micrometres along a mere 90 centimetres of the fault zone. “You still get a pressure drop of 50%,” he notes.

That, Weatherley adds, might be one of the reasons that the rocks in gold-bearing quartz deposits are often marbled with a spider web of tiny gold veins. “You [can] have thousands to hundreds of thousands of small earthquakes per year in a single fault system,” he says. “Over the course of hundreds of thousands of years, you have the potential to precipitate very large quantities of gold. Small bits add up.”

Weatherley says that prospectors might be able to use remote sensing techniques to find new gold deposits in deeply buried rocks in which fault jogs are common. “Fault systems with lots of jogs can be places where gold can be distributed,” he explains.

But Taka’aki Taira, a seismologist at the University of California, Berkeley, thinks that the finding might have even more scientific value. That’s because, in addition to showing how quartz deposits might form in fault jogs, the study reveals how fluid pressure in the jogs rebounds to its original level — something that could affect how much the ground moves after the initial earthquake.

“As far as I know, we do not yet incorporate fluid-pressure variations into estimates of aftershock probabilities,” Taira says. “Integrating this could improve earthquake forecasting.”

Note: The above post is reprinted from materials provided by Nature. The original article was written by Richard A. Lovett.

OpenStereo

OpenStereo is an open source, cross-platform software for structural geology analysis.

The software is written in Python, a high-level, cross-platform programming language and the GUI is designed with wxPython, which provide a consistent look regardless the OS. Numeric operations (like matrix and linear algebra) are performed with the Numpy module and all graphic capabilities are provided by the Matplolib library, including on-screen plotting and graphic exporting to common desktop formats (emf, eps, ps, pdf, png, svg).
OpenStereo is released under the GNU General Public License v.3.

An abstract about the software was presented at the AGU 2010 Fall Meeting. A ful paper is being prepared for publication.

Screenshots

Main interface. Left panel: file tree Right panel: tabs for each operation (stereonet, rose diagram, statistics and histogram)
Rose diagram tab. Full rose (360 deg). The highlighted file (left panel) is the one being ploted.
Statistics tab (1). The descriptive statistics are for the highlighted file. The text can be copied to the clipboard or save as a txt file. 2-axis (modified Flinn) diagram on the right. The color (and the symbols) are the same as those selected for the poles of the file.
Grid. Equal-area (Schmidt) projection.

Download :

Windows binaries (version 0.1.2f)
Python source code (version 0.1.2f)

More Info :  Instituto de Geociências – Universidade de São Paulo

After millennia of mining, copper nowhere near ‘peak’

A former copper mine in Andalucia, Spain is currently seeking regulatory approval to recommence production. Credit: ThinkStock

New research shows that existing copper resources can sustain increasing world-wide demand for at least a century, meaning social and environmental concerns could be the most important restrictions on future copper production.
Researchers from Monash University have conducted the most systematic and robust compilation and analysis of worldwide copper resources to date. Contrary to predictions estimating that supplies of this important metal would run out in around 30 years, the research has found there are plenty of resources within the reach of current technologies.

The database, published in two peer-reviewed papers, was compiled by Dr Gavin Mudd and Zhehan Weng from Environmental Engineering and Dr Simon Jowitt from the School of Geosciences. It is based on mineral resource estimates from mining companies and includes information vital for carbon and energy-use modelling, such as the ore grade of the deposits.

Dr Jowitt said the database could change the industry’s understanding of copper availability.

“Although our estimates are much larger than any previously available, they’re a minimum. In fact, figures for resources at some mining projects have already doubled or more since we completed the database,” Dr Jowitt said.

“Further, the unprecedented level of detail we’ve presented will likely improve industry practice with respect to mineral resource reporting and allow more informed geological exploration.”

Dr Mudd said the vast volumes of available copper meant the mining picture was far more complex than merely stating there were ‘x’ years of supply left.

“Workers’ rights, mining impacts on cultural lands, issues of benefit sharing and the potential for environmental degradation are already affecting the viability of copper production and will increasingly come into play,” Dr Mudd said.

Despite examples like the Ok Tedi mine in Papua New Guinea, where mining has continued despite widespread environmental degradation that has affected thousands of residents, non-economic factors have constrained some mining operations and the researchers believe this will become increasingly important in the near future. An example is the Pebble copper-gold project in Alaska, which after more than a decade still doesn’t have the necessary approvals due to the environmental and cultural concerns of nearby residents.

“Pressingly, we need to acknowledge that with existing copper resources we’re not just going to be dealing with the production of a few million tonnes of tailings from mining a century ago; we are now dealing with a few billion tonnes or tens of billions of tonnes of mine waste produced during modern mining,” Dr Mudd said.

The researchers will now undertake detailed modelling of the life cycles and greenhouse gas impacts of potential copper production, and better assessment of future environmental impacts of mining.

They will also create similar databases for other metals, such as nickel, uranium, rare earths, cobalt and others, in order to paint a comprehensive picture of worldwide mineral availability.

Note : The above story is reprinted from materials provided by Monash University.

Mars had an oxygen-rich atmosphere four billion years ago

Scientists inferred the presence of oxygen in the atmosphere by comparing Martian meteorites with data from rocks examined by Nasa’s Spirit Mars rover. Image: Nasa

Mars had an oxygen-rich atmosphere more than a billion years before the Earth, say scientists. An examination of meteorites and rocks on the planet suggests that oxygen was affecting the Martian surface four billion years ago.
On Earth, oxygen did not build up to appreciable quantities in the atmosphere for at least another 1.5bn years.

The researchers compared Martian meteorites that have crashed onto the Earth with data from rocks examined by Nasa’s Spirit Mars rover. Differences in their composition can best be explained by an abundance of oxygen early in Martian history.

Spirit was exploring an ancient part of Mars containing rocks more than 3.7bn years old. The rocks bear the hallmarks of early exposure to oxygen before being “recycled” – drawn into shallow regions of the planet’s interior and then spewed out in volcanic eruptions.

Volcanic Martian meteorites, on the other hand, originate from deeper within the planet where they would be less affected by oxygen. The meteorites travel to Earth after being flung into space by massive eruptions or impacts.

The new research, published in the journal Nature, has implications for the possibility of past life on Mars. On early Earth, the atmosphere was gradually filled with free oxygen by photosynthesising microbes. Scientists call this the Great Oxygenation Event.

The link between oxygen and life on Mars is less certain. Oxygen could have been produced biologically, or by a chemical reaction in the atmosphere.

Lead scientist Professor Bernard Wood of Oxford University said: “The implication is that Mars had an oxygen-rich atmosphere at a time, about 4,000 million years ago, well before the rise of atmospheric oxygen on Earth around 2,500 million years ago.

“As oxidation is what gives Mars its distinctive colour, it is likely that the ‘red planet’ was wet, warm and rusty billions of years before Earth’s atmosphere became oxygen-rich.”

Note : The above story is reprinted from materials provided by Press Association

Ancient Jigsaw Puzzle of Past Supercontinent Revealed

Image from video. The coloured polygons represent different geological units that have been mapped (and inferred) by geologists over many years. These geological units formed before the continents broke apart, so we can use their position to put the “jigsaw pieces” back together again. Many other reconstructions do not use the geological boundaries to match the continental “jigsaw pieces” back together – so they don’t align properly. (Credit: Image courtesy of University of Royal Holloway London)

A new study published today in the journal Gondwana Research, has revealed the past position of the Australian, Antarctic and Indian tectonic plates, demonstrating how they formed the supercontinent Gondwana 165 million years ago.

Researchers from Royal Holloway University, The Australian National University and Geoscience Australia, have helped clear up previous uncertainties on how the plates evolved and where they should be positioned when drawing up a picture of the past.

Dr Lloyd White from the Department of Earth Sciences at Royal Holloway University said: “The Earth’s tectonic plates move around through time. As these movements occur over many millions of years, it has previously been difficult to produce accurate maps of where the continents were in the past.

“We used a computer program to move geological maps of Australia, India and Antarctica back through time and built a ‘jigsaw puzzle’ of the supercontinent Gondwana. During the process, we found that many existing studies had positioned the plates in the wrong place because the geological units did not align on each plate.”

The researchers adopted an old technique used by people who discovered the theories of continental drift and plate tectonics, but which had largely been ignored by many modern scientists.

“It was a simple technique, matching the geological boundaries on each plate. The geological units formed before the continents broke apart, so we used their position to put this ancient jigsaw puzzle back together again,” Dr White added.

“It is important that we know where the plates existed many millions of years ago, and how they broke apart, as the regions where plates break are often where we find major oil and gas deposits, such as those that are found along Australia’s southern margin.”

Video :

Note : The above story is reprinted from materials provided by University of Royal Holloway London.

Grand Canyon at least 70 Million Years Old

A new study from the University of Colorado Boulder and the California Institute of Technology has analyzed mineral grains from the bottom of the western Grand Canyon. The findings indicate that the canyon was largely carved out about 70 million years ago, putting it in a time when dinosaurs were around and might have peeked over the rim.
CU-Boulder Assistant Professor Rebecca Flowers says that this new research, using a dating method that exploits the radioactive decay of uranium and thorium atoms to helium atoms in a phosphate mineral known as apatite, pushes back the accepted formation date of Arizona’s Grand Canyon by more than 60 million years.

During the carving of the Grand Canyon, the mineral grains cooled and moved closer to the surface, locking the helium atoms away inside the grains. Topography influences temperature variations at shallow levels beneath the Earth’s surface, and the thermal history recorded by the apatite grains allowed Flowers and her team to infer how much time had passed since there was significant natural excavation of the Grand Canyon.

“If you can document cooling through temperatures only a few degrees warmer than the earth’s surface, you can learn about canyon formation,” says Kenneth Farley, who is chair of the Division of Geological and Planetary Sciences at the California Institute of Technology.

“Our research implies that the Grand Canyon was directly carved to within a few hundred meters of its modern depth by about 70 million years ago,” said Flowers.

According to Alicia Chang of the Associated Press (AP), the age and evolution of the Grand Canyon causes significant controversy among scientists, with a variety of data suggesting the Grand Canyon has had a complicated history. This evidence also suggests the modern canyon might not have been carved all at the same time. Different segments of the canyon may have formed separately before coalescing into the Grand Canyon visitors see today.

In a previous study published in 2008, Flowers and colleagues revealed that parts of the eastern Grand Canyon likely developed some 55 million years ago. Before it eroded to its current depth, that segment of the canyon’s bottom was above the height of the current rim.

The steeply sided Grand Canyon is over a mile deep in places and about 280 miles long with a width of up to 18 miles wide in certain locations. More than 5 million people visit the geographic wonder every year. The Grand Canyon was carved, in large part, by an ancestral waterway of the Colorado River that was flowing in the opposite direction millions of years ago.

“An ancient Grand Canyon has important implications for understanding the evolution of landscapes, topography, hydrology and tectonics in the western U.S. and in mountain belts more generally,” said Flowers.

Flowers says that whether individual apatite crystals retain or lose helium is a function of temperatures in the rocks of Earth’s crust. If the temperatures of the apatite grains are below 86F, all of the helium is retained. Conversely, if the temperatures reach over 158F, all of the helium is lost.

“The main thing this technique allows us to do is detect variations in the thermal structure at shallow levels of the Earth’s crust,” she said. “Since these variations are in part induced by the topography of the region, we obtained dates that allowed us to constrain the timeframe when the Grand Canyon was incised.”

Past experiments used only the amount of helium produced in the radioactive decay of apatite grains to date samples. Flowers and Farley, however, also analyzed the spatial distribution of helium atoms near the margin of individual apatite crystals in order to take their uranium/thorium/helium dating technique to a more sophisticated level.

In recent years, a number of studies have reported various ages for the Grand Canyon, with the most popular theory placing the age at 5 million to 6 million years based on the age of the gravel washed downstream by the ancestral Colorado River. A 2008 study, however, estimated the age to be some 17 million years old based on dating mineral deposits inside of caves carved in the canyon walls.

Paleontologists believe that dinosaurs were wiped out when a giant asteroid collided with Earth some 65 million years ago, in a so-called “extinction event.” The collision resulted in huge clouds of dust that blocked the sun from reaching Earth’s surface, cooling the planet and killing most plants and animals.

Geologists have redoubled their efforts, according to Flowers, because of the wide numbers of theories, dates and debates regarding the age of the Grand Canyon.

“There has been a resurgence of work on this problem over the past few years because we now have some new techniques that allow us to date rocks that we couldn’t date before,” Flowers said.

The dating research for this current study was performed at CalTech, however, Flowers has recently set up her own lab at CU-Boulder capable of conducting uranium/thorium/helium dating.

“If it were simple, I think we would have solved the problem a long time ago,” said Flowers. “But the variety of conflicting information has caused scientists to argue about the age of the Grand Canyon for more than 150 years. I expect that our interpretation that the Grand Canyon formed some 70 million years ago is going to generate a fair amount of controversy, and I hope it will motivate more research to help solve this problem.”

The team hopes to continue their research, moving from “when” to “how” the canyon was formed, claiming the genesis of the canyon has important implications for understanding the evolution of many geological features in the western United States. This would include the features’ tectonics and topography.

“Our major scientific objective is to understand the history of the Colorado Plateau–why does this large and unusual geographic feature exist, and when was it formed,” says Farley. “A canyon cannot form without high elevation–you don’t cut canyons in rocks below sea level. Also, the details of the canyon’s incision seem to suggest large-scale changes in surface topography, possibly including large-scale tilting of the plateau.”

AP’s Chang reports that not everyone is convinced by the findings of Flowers and Farley’s study, however. The study ignores a mountain of evidence pointing to a geologically young landscape, the critics contend, giving rise to doubts about the technique used to date the team’s samples.

Karl Karlstrom, University of New Mexico in Albuquerque geologist, calls the notion of the Grand Canyon being 70 million years old “ludicrous.” Most scientists agree that though the exposed rocks are ancient, the Canyon was forged relatively recently in geologic time through tectonic uplift.

The oldest gravel and sediment that washed downstream date to about 6 million years ago, making it hard for most scientists to imagine an ancient Grand Canyon, especially since there are no signs of older deposits. Geologists are always happy to have new methods of dating, however, Karlstrom thinks the newest efforts are highly inaccurate. It defies logic that a fully formed canyon would sit unchanged for tens of millions of years without undergoing further erosion, Karlstrom protests.

Richard Young, geologist at the State University of New York at Geneseo, suggested an entirely different scenario to Chang; that of a cliff in the place of the ancient Grand Canyon.

According to Young, Flowers “wants to have a canyon there. I want to have a cliff there. Obviously, one of us can’t be right.”

There might be a middle ground, suggested Utah State University geologist Joel Pederson to Chang. Older canyons in the region were cut by rivers flowing in the opposite direction of the Colorado River. Perhaps, he says, a good portion of the Grand Canyon was chiseled by these smaller rivers and the younger Colorado finished the job.

If Flowers and Farley are right, however, and the Canyon existed when dinosaurs roamed, it would be a much different environment than today because the climate at that time was more tropical. Smaller tyrannosaurs, horned and dome-headed dinosaurs and duckbills patrolled the American West.

University of Maryland paleontologist Thomas Holtz told Chang that the dinosaurs would not see “the starkly beautiful desert of today, but an environment with more lush vegetation”

The results of this study were recently published online in the journal Science Express.

Note : The above story is reprinted from materials provided by April Flowers for redOrbit

Fossil insect traces reveal ancient climate, entrapment, and fossilization

The La Brea Tar Pits is the only constantly active, urban excavation site in the world.Credit: Page Museum at the La Breat Tar Pits

Fossil insect traces reveal ancient climate, entrapment, and fossilization at La Brea Tar Pits

Scientists use live insect colonies and forensic entomology to determine

LOS ANGELES — The La Brea Tar Pits have stirred the imaginations of scientists and the public alike for

This image shows a horse sesamoid (foot bone) riddled with insect damage. The bone, between 33,000-36,000 years old, is housed at the Page Museum at the La Brea Tar Pits. Credit: Page Museum at the La Brea Tar Pits

over a century. But the amount of time it took for ancient animals to become buried in asphalt after enduring their gruesome deaths has remained a mystery. Recent forensic investigations, led by Anna R. Holden of the Natural History Museum of Los Angeles County (NHM) and colleagues, reveal new insights into fossilization and the prevailing climate at the Rancho La Brea Tar Pits toward the end of the last Ice Age. The paper, entitled “Paleoecological and taphonomic implications of insect-damaged Pleistocene vertebrate remains from Rancho La Brea, southern California,” will be published in the journal PLoS One on July 3, 2013. 

The first step was to identify the insect traces. Holden and colleagues determined that different larval beetles were responsible for the exceptionally preserved traces on the bones of ancient mammals. By identifying those traces and researching the biology of the trace-maker, the team was able to pinpoint the climatic conditions and the minimum number of days it took for some of the carcasses to become submerged in the entrapping asphalt. Even after 10,000-60,000 years, the traces provide clear evidence that submergence took at least 17-20 weeks and occurred during warm to hot weather. 

Holden conducted the study with paleontologist Dr. John M. Harris, Chief Curator of the Page Museum at the La Brea Tar Pits, and Robert M. Timm, from Kansas University, who manages a dermestid beetle colony for research specimen preparation. They fed bones to insect colonies and used forensic entomology to decipher fossil insect traces. Because the insects that made the fossil traces still live today, the team was able to link the climate restrictions of these culprits to late Ice Age environmental conditions. “These are rare and precious fossils because they provide a virtual snapshot of a natural drama that unfolded thousands of years ago in Los Angeles,” Holden said.

Aside from adding to the documented list of insects that eat bone, research by Holden et al. also sheds light

 This is an exterior view of one of the asphalt seeps at the La Brea Tar Pits. Credit: Page Museum at the La Brea Tar Pits

on the conditions under which such insects will feed, and why mammalian herbivores offer a great setting for larval development. Although carnivorans vastly outnumber the amount of mammalian herbivorans excavated from the tar pits, no insect damage was found on their bones. The team believes that the thicker skin surrounding mammalian herbivore feet dried out and provided a stable, protected, and humid sub-environment complete with the right balance of tendons, muscle and fat for dermestid and tenebrionid larvae.

These unique specimens, housed at the Page Museum, were recovered from multiple asphalt deposits from excavations that took place over the last century and continue today. “Most people associate the tar pits with research on saber-toothed cats and mammoths.” Holden said. “But we show that the insects offer some the most valuable clues for our ongoing efforts to reconstruct Los Angeles’s prehistoric environment.”

Note : The above story is reprinted from materials provided by Natural History Museum of Los Angeles County

Playa Deposits

Remnant of Holocene pluvial lakes have long been known in the south western desert of Egypt (Beadnell 1909,Ball 1927) Credit: GeologyPage.com
Remnant of Holocene pluvial lakes have long been known in the south western desert of Egypt (Beadnell 1909,Ball 1927) Credit: GeologyPage.com

Playa,  also called pan, flat, or dry lake,  flat-bottom depression found in interior desert basins and adjacent to coasts within arid and semiarid regions, periodically covered by water that slowly filtrates into the ground water system or evaporates into the atmosphere, causing the deposition of salt, sand, and mud along the bottom and around the edges of the depression.

Playas are among the flattest known landforms. Their slopes are generally less than 0.2 metre per kilometre. When filled with only a few centimetres of water, many kilometres of surface may be inundated. It is the process of inundation that develops and maintains the near-perfect flatness so characteristic of these arid-region landforms.

Playas occupy the flat central basins of desert plains. They require interior drainage to a zone where evaporation greatly exceeds inflow. When flooded, a playa lake forms where fine-grained sediment and salts concentrate. Terminology is quite confused for playas because of many local names. A saline playa may be called a salt flat, salt marsh, salada, salar, salt pan, alkali flat, or salina. A salt-free playa may be termed a clay pan, hardpan, dry lake bed, or alkali flat. In Australia and South Africa small playas are generally referred to as pans. The low-relief plains of these lands contrast with the mountainous deserts of North America, resulting in numerous small pans instead of immense playas. The terms takyr, sabkha, and kavir are applied in Central Asia, Saudi Arabia, and Iran, respectively.

Saline flats are specialized forms located adjacent to large bodies of water, as, for example, along coasts, lakeshores, and deltas. They flood during storms, either with surface runoff or with surges from the nearby body of water. The saline crusts of saline flats are quite similar to those that develop in playas.

Physical characteristics

Enclosed basins of salt and clay accumulation may originate from numerous causes. Tectonic causes include faulting, as in the East African Rift Valley and Death Valley, and warping, as in Lake Eyre in Australia, Lake Chad in central Africa, and Shaṭṭ al-Jarīd (Chott Djerid) in Tunisia. Wind deflation can produce shallow basins with downwind dunes, as in southeastern Australia. Even very large basins, such as the Qattara Depression of Egypt, have been ascribed to deflation. Local cataclysmic disruptions of drainage (e.g., volcanism, landslides, and meteorite impacts) may produce playas in desert regions.

Modern playa surfaces are not passive receptors of sediment as they were once believed to be. They serve as important sources of dust and salts, which are blown to the surrounding uplands. Complex assemblages of minerals and sediments occur on the playa surfaces. These directly reflect their environment of deposition and may be used to interpret ancient environmental conditions.

Modern playa surfaces are not passive receptors of sediment as they were once believed to be. They serve as important sources of dust and salts, which are blown to the surrounding uplands. Complex assemblages of minerals and sediments occur on the playa surfaces. These directly reflect their environment of deposition and may be used to interpret ancient environmental conditions.

Two broad classes of playas may be defined on the basis of past histories. One type develops from the desiccation of a former lake. Sediments in such a playa are primarily lacustrine, rather than derived from modern depositional processes. The second type of playa has no paleolacustrine heritage. Small salt pans in South Africa, called vokils, are of this type.

The supply of material, basin depth, and duration of accumulation all contribute to variations in the thickness of playa deposits. Very thick playa sequences may have alternating layers of lacustrine clays and salt beds. The former generally reflect periods of high floodwater runoff into the closed basins, perhaps induced by higher rainfall (so-called pluvial periods). Saline sediments or pure evaporite beds reflect arid climatic phases. The precise climatic interpretation of paleolacustrine playa sequences, however, can be problematic.

Role of flooding and groundwater

Playas affected by occasional surface floods are usually dry. Their surfaces consist of silt and clay deposited by the floodwaters that enter closed basins during the occasional flow events. Salts develop as ponded floodwater in the centre of such a basin gradually evaporates. Water also can be supplied to closed basins by groundwater flow. In basins dominated by groundwater inputs, sediment influxes are minimized, and saline crusts dominate. Moist areas may persist as groundwater flows to the lowest portion of playas. Very large playas may exhibit dry, sediment-dominated sections and moist, salt-dominated sections.

Saline minerals

 The salt deposits of a salt pan are zoned like bathtub rings, with less-soluble sulfates and carbonates at the outer margin and highly soluble sodium chloride (table salt) at the centre. The crystallization of these salts can be compared with the evaporation of brine in a dish. The first precipitates from the evaporating brine are calcium carbonate (CaCO3) and magnesium carbonate (MgCO3). These form the outer “bathtub ring.” The next ring consists of sulfates of calcium and sodium (CaSO4 and Na2SO4, respectively). If sufficient calcium is present, gypsum (CaSO4·2H2O) will form. If less calcium is present, thenardite (Na2SO4) and sodium carbonate (Na2CO3) may be deposited. The last remaining brines of exceptionally high salinity precipitate highly soluble chlorides of sodium, calcium, magnesium, and potassium.

Another kind of zoning occurs in saline playas with respect to the hydration of different minerals. Dehydrated minerals, such as anhydrite (CaSO4), occur on surface areas protected against flooding and in wet saline areas.

Some playas also contain exotic minerals. The Death Valley playa is famous for borate minerals, including borax (Na2B4O7·10H2O) and Meyerhofferite (Ca2B6O11·7H2O).

Surface relief and structures

Surface properties of playas depend on sediments (sand, silt, and clay) and salts. Near-surface groundwater may give rise to evaporite crusts formed by rigorous evaporative concentration. Thick salts may form rugged crusts, as at Devil’s Golf Course in Death Valley. Regular flooding of evaporative layers may form a very smooth surface, as at Bonneville Salt Flats in Utah. For thick, soluble crusts, dissolution may occur during fluctuations of a high water table. Solution cavities in the crust can produce a salt karst topography.

The muds deposited on playas are subject to drying and shrinking. The amount of volume change varies with the clay minerals present. Smectite clays experience the greatest shrinkage on drying. The presence of salts enhances the effect, since deposition and crystallization of salts in the cracks creates a polygonal network of salt wedges.

Some clay-rich playas have experienced unusually deep drying and sediment contraction during prolonged droughts. Giant desiccation polygons formed under these conditions are as large as 90 metres across. Individual cracks more than one metre wide and 15 metres deep have been observed.

Geomorphic evolution

Impact of climatic change

Playas are exceptionally sensitive to environmental change. They have been most profoundly influenced by changes in hydrologic regimen induced by the climatic variations of the Quaternary Period (i.e., the past 2.6 million years). All have experienced episodes of expanded lake levels in the past. Such predecessors are often called pluvial lakes, thereby implying periods of increased rainfall. It is also possible, however, that lakes could have expanded because of other factors, including increased groundwater inflow and/or decreased evaporation/transpiration.

Paleolake chronologies

Modern geochronologic techniques, such as radiocarbon dating, permit the comparison of fluctuations in the paleolakes that were predecessors to many modern playas. In northern Africa lakes were at a moderately high level from 30,000 to 22,000 years ago. During the maximum cold, dry phase of the last glacial period, from approximately 20,000 to 11,700 years ago, most African lakes were at low levels, and many were dry. From 10,000 to 8,000 years ago, lakes rose to maximum high levels. Lake Chad expanded to the size of the modern Caspian Sea. Small volume lakes, however, are more sensitive to climatic change, recording higher frequency oscillations in the hydrologic balance. Since about 4,000 years ago, the north African lakes have fallen to the range of their modern lows.

Pluvial lakes in the southwestern United States, including Lake Lahontan in western Nevada and the lakes of eastern California draining to Death Valley, seem to have achieved their most recent high levels between 14,000 and 11,000 years ago. The period from 30,000 to 24,000 years ago was marked by low lake levels. Another low was reached about 7,000 years ago. Many of the lakes of the southwestern United States, however, seem to have been not quite in phase with one another.

Effects of wind action

Playas and saline flats are particularly susceptible to wind action. Clays and salts form crusts that curl and flake upon drying. The flakes and curls are readily deflated, and these wind-eroded sediments are then deposited leeward of the playas and saline flats from which they were removed. This process is increasingly recognized as a source of dust hazard, as studies around Owens Lake, California, and in western China have shown.

In Australia many playas have large transverse crescentic foredunes on their leeward side. Because of their silt and clay composition, these features are sometimes called clay dunes. In Australia they are known as lunettes. James M. Bowler, an Australian Quaternary stratigrapher, produced a precise chronology of playa development and associated eolian activity in the desert of western New South Wales, Australia. There, numerous small lakes reached their maximum extent 32,000 years ago, approximately coincident with the age of the first human remains in Australia. From about 26,000 years ago, the lakes fell to low levels. Playas formed roughly 16,000 years ago at a time when eolian activity peaked. High lakes again occurred about 9,000 to 5,000 years ago, but playas were reestablished after that.

The present association of playas, lunettes, and linear dunes in the Australian deserts may imply a causative association. C.R. Twidale proposed that the linear dunes developed as lee-side accumulations of sand trapped by the growth of lunettes. Climatic change is critical to the association.

Photo :

Note : The above story is reprinted from materials provided by Victor R. Baker ” Regents Professor of Geosciences and of Planetary Sciences; University of Arizona”
Image Credit : © GeologyPage.com

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