Geologists discover ancient buried canyon in South Tibet

This photo shows the Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge -- the new discoveries falsify this hypothesis. -  Ping Wang
This photo shows the Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge — the new discoveries falsify this hypothesis. – Ping Wang

A team of researchers from Caltech and the China Earthquake Administration has discovered an ancient, deep canyon buried along the Yarlung Tsangpo River in south Tibet, north of the eastern end of the Himalayas. The geologists say that the ancient canyon–thousands of feet deep in places–effectively rules out a popular model used to explain how the massive and picturesque gorges of the Himalayas became so steep, so fast.

“I was extremely surprised when my colleagues, Jing Liu-Zeng and Dirk Scherler, showed me the evidence for this canyon in southern Tibet,” says Jean-Philippe Avouac, the Earle C. Anthony Professor of Geology at Caltech. “When I first saw the data, I said, ‘Wow!’ It was amazing to see that the river once cut quite deeply into the Tibetan Plateau because it does not today. That was a big discovery, in my opinion.”

Geologists like Avouac and his colleagues, who are interested in tectonics–the study of the earth’s surface and the way it changes–can use tools such as GPS and seismology to study crustal deformation that is taking place today. But if they are interested in studying changes that occurred millions of years ago, such tools are not useful because the activity has already happened. In those cases, rivers become a main source of information because they leave behind geomorphic signatures that geologists can interrogate to learn about the way those rivers once interacted with the land–helping them to pin down when the land changed and by how much, for example.

“In tectonics, we are always trying to use rivers to say something about uplift,” Avouac says. “In this case, we used a paleocanyon that was carved by a river. It’s a nice example where by recovering the geometry of the bottom of the canyon, we were able to say how much the range has moved up and when it started moving.”

The team reports its findings in the current issue of Science.

Last year, civil engineers from the China Earthquake Administration collected cores by drilling into the valley floor at five locations along the Yarlung Tsangpo River. Shortly after, former Caltech graduate student Jing Liu-Zeng, who now works for that administration, returned to Caltech as a visiting associate and shared the core data with Avouac and Dirk Scherler, then a postdoc in Avouac’s group. Scherler had previously worked in the far western Himalayas, where the Indus River has cut deeply into the Tibetan Plateau, and immediately recognized that the new data suggested the presence of a paleocanyon.

Liu-Zeng and Scherler analyzed the core data and found that at several locations there were sedimentary conglomerates, rounded gravel and larger rocks cemented together, that are associated with flowing rivers, until a depth of 800 meters or so, at which point the record clearly indicated bedrock. This suggested that the river once carved deeply into the plateau.

To establish when the river switched from incising bedrock to depositing sediments, they measured two isotopes, beryllium-10 and aluminum-26, in the lowest sediment layer. The isotopes are produced when rocks and sediment are exposed to cosmic rays at the surface and decay at different rates once buried, and so allowed the geologists to determine that the paleocanyon started to fill with sediment about 2.5 million years ago.

The researchers’ reconstruction of the former valley floor showed that the slope of the river once increased gradually from the Gangetic Plain to the Tibetan Plateau, with no sudden changes, or knickpoints. Today, the river, like most others in the area, has a steep knickpoint where it meets the Himalayas, at a place known as the Namche Barwa massif. There, the uplift of the mountains is extremely rapid (on the order of 1 centimeter per year, whereas in other areas 5 millimeters per year is more typical) and the river drops by 2 kilometers in elevation as it flows through the famous Tsangpo Gorge, known by some as the Yarlung Tsangpo Grand Canyon because it is so deep and long.

Combining the depth and age of the paleocanyon with the geometry of the valley, the geologists surmised that the river existed in this location prior to about 3 million years ago, but at that time, it was not affected by the Himalayas. However, as the Indian and Eurasian plates continued to collide and the mountain range pushed northward, it began impinging on the river. Suddenly, about 2.5 million years ago, a rapidly uplifting section of the mountain range got in the river’s way, damming it, and the canyon subsequently filled with sediment.

“This is the time when the Namche Barwa massif started to rise, and the gorge developed,” says Scherler, one of two lead authors on the paper and now at the GFZ German Research Center for Geosciences in Potsdam, Germany.

That picture of the river and the Tibetan Plateau, which involves the river incising deeply into the plateau millions of years ago, differs quite a bit from the typically accepted geologic vision. Typically, geologists believe that when rivers start to incise into a plateau, they eat at the edges, slowly making their way into the plateau over time. However, the rivers flowing across the Himalayas all have strong knickpoints and have not incised much at all into the Tibetan Plateau. Therefore, the thought has been that the rapid uplift of the Himalayas has pushed the rivers back, effectively pinning them, so that they have not been able to make their way into the plateau. But that explanation does not work with the newly discovered paleocanyon.

The team’s new hypothesis also rules out a model that has been around for about 15 years, called tectonic aneurysm, which suggests that the rapid uplift seen at the Namche Barwa massif was triggered by intense river incision. In tectonic aneurysm, a river cuts down through the earth’s crust so fast that it causes the crust to heat up, making a nearby mountain range weaker and facilitating uplift.

The model is popular among geologists, and indeed Avouac himself published a modeling paper in 1996 that showed the viability of the mechanism. “But now we have discovered that the river was able to cut into the plateau way before the uplift happened,” Avouac says, “and this shows that the tectonic aneurysm model was actually not at work here. The rapid uplift is not a response to river incision.”

###

The other lead author on the paper, “Tectonic control of the Yarlung Tsangpo Gorge, revealed by a 2.5 Myr old buried canyon in Southern Tibet,” is Ping Wang of the State Key Laboratory of Earthquake Dynamics, in Beijing, China. Additional authors include Jürgen Mey, of the University of Potsdam, in Germany; and Yunda Zhang and Dingguo Shi of the Chengdu Engineering Corporation, in China. The work was supported by the National Natural Science Foundation of China, the State Key Laboratory for Earthquake Dynamics, and the Alexander von Humboldt Foundation.

Fountain of youth underlies Antarctic Mountains

Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. -  Tim Creyts
Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. – Tim Creyts

Time ravages mountains, as it does people. Sharp features soften, and bodies grow shorter and rounder. But under the right conditions, some mountains refuse to age. In a new study, scientists explain why the ice-covered Gamburtsev Mountains in the middle of Antarctica looks as young as they do.

The Gamburtsevs were discovered in the 1950s, but remained unexplored until scientists flew ice-penetrating instruments over the mountains 60 years later. As this ancient hidden landscape came into focus, scientists were stunned to see the saw-toothed and towering crags of much younger mountains. Though the Gamburtsevs are contemporaries of the largely worn-down Appalachians, they looked more like the Rockies, which are nearly 200 million years younger.

More surprising still, the scientists discovered a vast network of lakes and rivers at the mountains’ base. Though water usually speeds erosion, here it seems to have kept erosion at bay. The reason, researchers now say, has to do with the thick ice that has entombed the Gamburtsevs since Antarctica went into a deep freeze 35 million years ago.

“The ice sheet acts like an anti-aging cream,” said the study’s lead author, Timothy Creyts, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory. “It triggers a series of thermodynamic processes that have almost perfectly preserved the Gamburtsevs since ice began spreading across the continent.”

The study, which appears in the latest issue of the journal Geophysical Research Letters, explains how the blanket of ice covering the Gamburtsevs has preserved its rugged ridgelines.

Snow falling at the surface of the ice sheet draws colder temperatures down, closer to protruding peaks in a process called divergent cooling. At the same time, heat radiating from bedrock beneath the ice sheet melts ice in the deep valleys to form rivers and lakes. As rivers course along the base of the ice sheet, high pressures from the overlying ice sheet push water up valleys in reverse. This uphill flow refreezes as it meets colder temperature from above. Thus, ridgelines are cryogenically preserved.

The oldest rocks in the Gamburtsevs formed more than a billion years ago, in the collision of several continents. Though these prototype mountains eroded away, a lingering crustal root became reactivated when the supercontinent Gondwana ripped apart, starting about 200 million years ago. Tectonic forces pushed the land up again to form the modern Gamburtsevs, which range across an area the size of the Alps. Erosion again chewed away at the mountains until earth entered a cooling phase 35 million years ago. Expanding outward from the Gamburtsevs, a growing layer of ice joined several other nucleation points to cover the entire continent in ice.

The researchers say that the mechanism that stalled aging of the Gamburtsevs at higher elevations may explain why some ridgelines in the Torngat Mountains on Canada’s Labrador Peninsula and the Scandinavian Mountains running through Norway, Sweden and Finland appear strikingly untouched. Massive ice sheets covered both landscapes during the last ice age, which peaked about 20,000 years ago, but many high-altitude features bear little trace of this event.

“The authors identify a mechanism whereby larger parts of mountains ranges in glaciated regions–not just Antarctica–could be spared from erosion,” said Stewart Jamieson, a glaciologist at Durham University who was not involved in the study. “This is important because these uplands are nucleation centers for ice sheets. If they were to gradually erode during glacial cycles, they would become less effective as nucleation points during later ice ages.”

Ice sheet behavior, then, may influence climate change in ways that scientists and computer models have yet to appreciate. As study coauthor Fausto Ferraccioli, head of the British Antarctic Survey’s airborne geophysics group, put it: “If these mountains in interior East Antarctica had been more significantly eroded then the ice sheet itself
may have had a different history.”

Other Authors


Hugh Carr and Tom Jordan of the British Antarctic Survey; Robin Bell, Michael Wolovick and Nicholas Frearson of Lamont-Doherty; Kathryn Rose of University of Bristol; Detlef Damaske of Germany’s Federal Institute for Geosciences and Natural Resources; David Braaten of Kansas University; and Carol Finn of the U.S. Geological Survey.

Copies of the paper, “Freezing of ridges and water networks preserves the Gamburtsev Subglacial Mountains for millions of years,” are available from the authors.

Scientist Contact


Tim Creyts

845-365-8368

tcreyts@ldeo.columbia.edu

Sediment supply drives floodplain evolution in Amazon Basin

A new study of the Amazon River basin shows lowland rivers that carry large volumes of sediment meander more across floodplains and create more oxbow lakes than rivers that carry less sediment.

The findings have implication for the Amazonian river system, which may be significantly altered by proposed mega-dams that would disrupt sediment supplies.

Researchers from Cardiff University’s School of Earth and Ocean Sciences examined 20 reaches within the Amazon Basin from Landsat imagery spanning nearly 20 years (1985 to 2013).

They found rivers transporting larger amounts of sediment migrated more, and noted that channel movement did not depend on either the slope of the channel or the river discharge.

The research gives scientists insight into the contrasting behavioural properties of rivers where sediment is an imposed variable – e.g. resulting from glacial, volcanic, or human activity – and rivers were the main sediment supply is from local bank erosion.

Dr José Constantine, Lecturer in Earth Sciences at Cardiff University’s School of Earth & Ocean Sciences and lead author of the paper said: “We found that the speed at which the meanders migrated for each of the rivers studied depended on the river’s supply of sand and silt. The meanders of rivers carrying more sediment migrated faster than those carrying less sediment, and were also more frequently cut off and abandoned to form U-shaped lakes. If sediment loads are reduced — by a dam, for example — meander migration is expected to slow, and thus the reshaping of the floodplain environment is affected.

Rivers flow differently over gravel beds, study finds

River researchers used a specially constructed model to study how water flows over gravel river beds. Illinois postdoctoral researcher Gianluca Blois (left) and professor Jim Best also developed a technique to measure the water flow between the pore spaces in the river bed. -  L. Brian Stauffer
River researchers used a specially constructed model to study how water flows over gravel river beds. Illinois postdoctoral researcher Gianluca Blois (left) and professor Jim Best also developed a technique to measure the water flow between the pore spaces in the river bed. – L. Brian Stauffer

River beds, where flowing water meets silt, sand and gravel, are critical ecological zones. Yet how water flows in a river with a gravel bed is very different from the traditional model of a sandy river bed, according to a new study that compares their fluid dynamics.

The findings establish new parameters for river modeling that better represent reality, with implications for field researchers and water resource managers.

“The shallow zones where water in rivers interacts with the subsurface are critical environmentally, and how we have modeled those in the past may be radically different from reality,” said Jim Best, a professor of geology, geography and geographic information science at the University of Illinois. “If you’re a river engineer or a geomorphologist or a freshwater biologist, predicting where and when sediment transport is going to occur is very important. This study provides us with a very different set of conditions to look at those environments and potentially manage them.”

Best and postdoctoral researcher Gianluca Blois led the study at the U. of I., in collaboration with colleagues in the United Kingdom. The team published its findings in the journal Geophysical Research Letters.

The researchers used a specially constructed flume in the Ven Te Chow Hydrosystems Laboratory at Illinois to experimentally compare scenarios ranging from the traditional model of an impermeable river bottom to a completely permeable river bed – a collection of spheres that simulate gravel.

The researchers used a technique called particle image velocimetry (PIV), a widely used method for quantifying how water flows over a model river bed, pioneered at the U. of I. in the 1980s. Best and Blois developed a method to use PIV endoscopically to study, for the first time, fluid flow within the small spaces between the gravel. This allowed them to quantify flow within the river bed and link it to the stream flow above.

They found that, in the scenario that simulates a gravel bed, the patterns of flow velocity above the bed and the distribution of forces on the river bed were dramatically different from the models on which all previous work has been based. Their experimental scenarios also disproved one popular theory that explained the difference between classic models and field observations for the formation of bed topography, such as dunes.

“Bedforms formed in fine sediments are known to be substantially different from those formed in gravel beds, but we just didn’t know why,” Blois said. “People before us suggested that those differences were due to the roughness of the grains. But we introduced the bed permeability, just like real rivers. This, with our new measurement technique, allowed us to demonstrate that most of the stress variation is actually coming from fluid emerging from the permeable bed, rather than roughness.”

The maps of water flow that the experiments produced could lead to better predictive models, so that researchers can more accurately predict and study how nutrients and pollutants travel and accumulate in rivers. These new models also could provide insight into the growth and behavior of organisms that thrive in the narrow zone where river flow meets the river bed.

“For example, when salmon spawn in gravel-bed rivers, they basically make a depression in the gravel, into which they lay their eggs,” Best said. “By doing that, not only do they protect the eggs, but they create a bump in the sediment that creates a pressure distribution that would keep fine grains from going into the bed, which would be detrimental to the eggs. It’s fascinating that fish actually take advantage of these flow dynamics.”

The researchers are working with collaborators around the world to study how permeability affects turbulence above the bed, how this affects the organisms that grow in the pore spaces, and how tiny particles and dissolved substances accumulate in porous riverbeds.

“It’s going to change the way we conceptualize these systems and model them,” Blois said. “We’re trying to raise awareness of the fact that we are now able to measure the complex flow dynamics in these challenging environments, and that’s going to open up a new paradigm for river research.”

Star Trekish, rafting scientists make bold discovery on Fraser River

SFU geographer Jeremy Venditti (orange jacket; black hat) is among several scientists aboard a Fraser River Rafting Expeditions measuring boat passing through a Fraser River canyon. -  SFU PAMR
SFU geographer Jeremy Venditti (orange jacket; black hat) is among several scientists aboard a Fraser River Rafting Expeditions measuring boat passing through a Fraser River canyon. – SFU PAMR

A Simon Fraser University-led team behind a new discovery has “?had the vision to go, like Star Trek, where no one has gone before: to a steep and violent bedrock canyon, with surprising results.”

That comment comes from a reviewer about a truly groundbreaking study just published in the journal Nature.
Scientists studying river flow in bedrock canyons for the first time have discovered that previous conceptions of flow and incision in bedrock-rivers are wrong.

SFU geography professor Jeremy Venditti led the team of SFU, University of Ottawa and University of British Columbia researchers on a scientific expedition on the Fraser River.

“For the first time, we used oceanographic instruments, commonly used to measure three-dimensional river flow velocity in low land rivers, to examine flow through steep bedrock canyons,” says Venditti. “The 3-D instruments capture downstream, cross-stream and vertical flow velocity.”

To carry out their Star Trek-like expedition, the researchers put their lives into the experienced hands of Fraser River Rafting Expeditions, which took them into 42 bedrock canyons. Equipped with acoustic Doppler current profilers to measure velocity fields, they rafted 486 kilometres of the Fraser River from Quesnel to Chilliwack. Their raft navigated turbulent waters normally only accessed by thrill-seeking river rafters.

“Current models of bedrock-rivers assume flow velocity is uniform, without changes in the downstream direction. Our results show this is not the case,” says Colin Rennie, an Ottawa U civil engineering professor.

“We observed a complicated flow field in which high velocity flow plunges down the bottom of the canyon forming a velocity inversion and then rises along the canyon walls. This has important implications for canyon erosion because the plunging flow patterns result in greater flow force applied to the bed.”

The scientists conclude that river flow in bedrock canyons is far more complex than first thought and the way scientists have linked climate, bedrock incision and the uplift of mountains needs to be rethought. They say the complexity of river flow plays an important role in deciding bedrock canyon morphology and river width.

“The links between the uplift of mountain ranges, bedrock incision by rivers and climate is one of the most important open questions in science,” notes Venditti. “The incision that occurs in bedrock canyons is driven by climate because the climate system controls precipitation and the amount of water carried in rivers. River flow drives the erosional mechanisms that cut valleys and allow the uplift of majestic mountain peaks.”

Venditti adds that river flow velocity in bedrock canyons also influences the delivery of sediment from mountain-rivers to lowland rivers.

“Sediment delivery controls water levels and stability of lowland rivers, which has important implications for lowland river management, flooding impacts to infrastructure, availability of fish habitat and more.

“Lowland river floodplains and deltas are the most densely populated places on earth, so understanding what is happening in mountain rivers is important because our continued development of these areas is significantly affected by what is happening upstream.”

‘Fracking’ wastewater that is treated for drinking produces potentially harmful compounds

Concerns that fluids from hydraulic fracturing, or “fracking,” are contaminating drinking water abound. Now, scientists are bringing to light another angle that adds to the controversy. A new study, appearing in the ACS journal Environmental Science & Technology, has found that discharge of fracking wastewaters to rivers, even after passage through wastewater treatment plants, could be putting the drinking water supplies of downstream cities at risk.

William A. Mitch, Avner Vengosh and colleagues point out that the disposal of fracking wastewater poses a major challenge for the companies that use the technique, which involves injecting millions of gallons of fluids into shale rock formations to release oil and gas. The resulting wastewater is highly radioactive and contains high levels of heavy metals and salts called halides (bromide, chloride and iodide). One approach to dealing with this wastewater is to treat it in municipal or commercial treatment plants and then release it into rivers and other surface waters. The problem is these plants don’t do a good job at removing halides. Researchers have raised concern that halide-contaminated surface water subsequently treated for drinking purposes with conventional methods, such as chlorination or ozonation, could lead to the formation of toxic byproducts. Mitch’s team set out to see if that was indeed the case.

The researchers diluted river-water samples of fracking wastewater discharged from operations in Pennsylvania and Arkansas, simulating real-world conditions when wastewater gets into the environment. In the lab, they then used current drinking-water disinfection methods on the samples. They found that even at concentrations as low as 0.01 percent up to 0.1 percent by volume of fracking wastewater, an array of toxic compounds formed. Based on their findings, the researchers recommend either that fracking wastewater should not be discharged at all into surface waters or that future water treatment include specific halide-removal techniques.

Snail shells show high-rise plateau is much lower than it used to be

This is the Zhada Basin on the southwest Tibetan Plateau, with the Himalayas to the south. -  Joel Saylor
This is the Zhada Basin on the southwest Tibetan Plateau, with the Himalayas to the south. – Joel Saylor

The Tibetan Plateau in south-central Asia, because of its size, elevation and impact on climate, is one of the world’s greatest geological oddities.

At about 960,000 square miles it covers slightly more land area than Alaska, Texas and California combined, and its elevation is on the same scale as Mount Rainier in the Cascade Range of Washington state. Because it rises so high into the atmosphere, it helps bring monsoons over India and other nations to the south while the plateau itself remains generally arid.

For decades, geologists have debated when and how the plateau reached such lofty heights, some 14,000 feet above sea level, about half the elevation of the highest Himalayan peaks just south of the plateau.

But new research led by a University of Washington scientist appears to confirm an earlier improbable finding – at least one large area in southwest Tibet, the plateau’s Zhada Basin, actually lost 3,000 to 5,000 feet of elevation sometime in the Pliocene epoch.

“This basin is really high right now but we think it was a kilometer or more higher just 3 million to 4 million years ago,” said Katharine Huntington, a UW associate professor of Earth and space sciences and the lead author of a paper describing the research.

Co-authors are Joel Saylor of the University of Houston and Jay Quade and Adam Hudson, both of the University of Arizona. The paper was published online in August and will appear in a future print edition of the Geological Society of America Bulletin.

The Zhada Basin has rugged terrain, with exposed deposits of ancient lake and river sediments that make fossil shells of gastropods such as snails easily accessible, and determining their age is relatively straightforward. The researchers studied shells dating from millions of years ago and from a variety of aquatic environments. They also collected modern shell and water samples from a variety of environments for comparison.

The work confirms results of a previous study involving Saylor and Quade that examined the ratio of heavy isotope oxygen-18 to light isotope oxygen-16 in ancient snail shells from the Zhada Basin. They found the ratios were very low, which suggested the basin had a higher elevation in the past.

Oxygen-18 levels decrease in precipitation at higher elevations in comparison with oxygen-16, so shells formed in lakes and rivers that collect precipitation at higher elevations should have a lower heavy-to-light oxygen ratio. However, those lower ratios depend on a number of other factors, including temperature, evaporation and precipitation source, which made it difficult to say with certainty whether the low ratios found in the ancient snail shells meant a loss of elevation in the Zhada Basin.

So the scientists also employed a technique called clumped isotope thermometry, which Huntington has used and worked to refine for several years, to determine the temperature of shell growth and get an independent estimate of elevation change in the basin.

Bonding, or “clumping” together, of heavy carbon-13 and oxygen-18 isotopes in the carbonate of snail shells happens more readily at colder temperatures, and is measured using a tool called a mass spectrometer that provides data on the temperature of the lake or river water in which the snails lived.

The scientists found markedly greater “clumping,” as well as lower ratios of oxygen-18 to oxygen-16 in the ancient shells, indicating the shells formed at temperatures as much as 11 degrees Celsius (20 F) colder than average temperatures today, the equivalent of as much as 5,000 feet of elevation loss.

Just why the elevation decline happened is open to speculation. One possibility is that as faults in the region spread, the Zhada Basin lowered, Huntington said. It is unknown yet whether other parts of the southern plateau also lowered at the same time, but if elevation loss was widespread it could be because of broader fault spreading. It also is possible the crust thickened and forced large rock formations even deeper into the Earth, where they heated until they reached a consistency at which they could ooze out from beneath the crust, like toothpaste squeezed from the tube.

She noted that climate records from deep-sea fossils indicate Earth was significantly warmer when the cold Zhada Basin snail shells were formed.

“Our findings are a conservative estimate,” Huntington said. “No one can say this result is due to a colder climate, because if anything it should have been warmer.”

Most of the sand in Alberta’s oilsands came from eastern North America, study shows

Christine Benyon is completing her Master's degree in Geoscience in the Faculty of Science. -  Riley Brandt, University of Calgary
Christine Benyon is completing her Master’s degree in Geoscience in the Faculty of Science. – Riley Brandt, University of Calgary

They’re called the Alberta oilsands but most of the sand actually came from the Appalachian region on the eastern side of the North American continent, a new University of Calgary-led study shows.

The oilsands also include sand from the Canadian Shield in northern and east-central Canada and from the Canadian Rockies in western Canada, the study says.

This study is the first to determine the age of individual sediment grains in the oilsands and assess their origin.

“The oilsands are looked at as a Western asset,” says study lead author Christine Benyon, who is just completing her Master’s degree in Geoscience in the Faculty of Science.

“But we wouldn’t have oilsands without the sand, and some of that sand owes its origin to the Appalachians and other parts of Canada.”

The research, which also involved study sponsor Nexen Energy ULC and the University of Arizona LaserChron Center, was published last week in the Journal of Sedimentary Research.

The findings contribute to geologists’ fundamental understanding of the oilsands.

They also help oilsands companies better understand the stratigraphy, or layers, of sand and the ancient valleys where sediment was deposited, “and that could lead to better production techniques,” Benyon says.

To determine the origin of the sand, the researchers used a relatively new technique called “detrital zircon uranium-lead geochronology.”

They used a mass spectrometer to date the age of tiny and extremely durable crystallized minerals called zircons that are present in the oilsands.

“The age of those zircons tells us how long since they crystallized. And knowing that, we can infer their place of origin,” Benyon explains.

Researchers dated the zircons in nine core samples from three wells drilled into the oilsands’ McMurray Formation.

Lowermost deposits contained zircons ranging from 1,800 to 2,800 million years old. These zircons, and thereby the associated sand, originally came from the Canadian Shield, which contains rocks of those ages, Benyon says.

Most of the oilsands’ sediment contains zircons that range from 300 to 1,200 million years old – the same zircon signature found in Appalachian sources in eastern North America.

The uppermost oilsands contain zircons that are less than 250 million years old, indicating the Canadian Rockies as their most likely place of origin.

So how did so much of the sand, deposited during the Cretaceous geological time period about 145 to 66 million years ago (before the sand was emplaced with oil), get to Alberta from the other side of the continent?

No one knows for sure, but Benyon and her co-authors propose three theories, all involving sediment transported by a continental-sized river system:

  • The massive river system transported the sediment directly from eastern North America to the present-day oilsands region during the Cretaceous;

  • The river system transported the sediment from eastern North America during an earlier geological time period and deposited it in the southwestern United States; later, in the Cretaceous, rivers flowing northward ‘recycled’ the sediment and deposited it in western Canada;
  • An older (perhaps Jurassic or Permian) river system coming from the Appalachians deposited the sediment in western Canada; later, during the Cretaceous, the sediment was eroded by smaller rivers and re-deposited in northeastern Alberta.

No matter how and when the sand got to the present location of the oilsands, “the study tells us that the Appalachians were an important source of sediment in the geological history of North America,” Benyon says.

Soil production breaks geologic speed record

This is a photo of the researcher hiking down the ridge at Rapid Creek to collect soil samples.  The dense bush and heavy 10 kilogram soil samples slowed uphill progress to less than 200 meters per hour. -  Andre Eger
This is a photo of the researcher hiking down the ridge at Rapid Creek to collect soil samples. The dense bush and heavy 10 kilogram soil samples slowed uphill progress to less than 200 meters per hour. – Andre Eger

Geologic time is shorthand for slow-paced. But new measurements from steep mountaintops in New Zealand show that rock can transform into soil more than twice as fast as previously believed possible.

The findings were published Jan. 16 in the early online edition of Science.

“Some previous work had argued that there were limits to soil production,” said first author Isaac Larsen, who did the work as part of his doctoral research in Earth sciences at the University of Washington. “But no one had made the measurements.”

The finding is more than just a new speed record. Rapidly eroding mountain ranges account for at least half of the total amount of the planet’s weathering and sediment production, although they occupy just a few percent of the Earth’s surface, researchers said.

So the record-breaking production at the mountaintops has implications for the entire carbon cycle by which the Earth’s crust pushes up to form mountains, crumbles, washes with rivers and rainwater to the sea, and eventually settles to the bottom to form new rock.

“This work takes the trend between soil production rates and chemical weathering rates and extends it to much higher values than had ever been previously observed,” said Larsen, now a postdoctoral researcher at the California Institute of Technology in Pasadena.

The study site in New Zealand’s Southern Alps is “an extremely rugged mountain range,” Larsen said, with rainfall of 10 meters (33 feet) per year and slopes of about 35 degrees.

To collect samples Larsen and co-author André Eger, then a graduate student at Lincoln University in New Zealand, were dropped from a helicopter onto remote mountaintops above the tree line. They would hike down to an appropriate test site and collect 20 pounds of dirt apiece, and then trek the samples back up to their base camp. The pair stayed at each of the mountaintop sites for about three days.

“I’ve worked in a lot of places,” Larsen said. “This was the most challenging fieldwork I’ve done.”

Researchers then brought soil samples back to the UW and measured the amount of Beryllium-10, an isotope that forms only at the Earth’s surface by exposure to cosmic rays. Those measurements showed soil production rates on the ridge tops ranging from 0.1 to 2.5 millimeters (1/10 of an inch) per year, and decrease exponentially with increasing soil thickness.

The peak rate is more than twice the proposed speed limit for soil production, in which geologists wondered if in places where soil is lost very quickly, the soil production just can’t keep up. In earlier work Larsen had noticed vegetation on very steep slopes and so he proposed this project to measure soil production rates at some of the steepest, wettest locations on the planet.

The new results show that soil production and weathering rates continue to increase as the landscape gets steeper and erodes faster, and suggest that other very steep locations such as the Himalayas and the mountains in Taiwan may also have very fast soil formation.

“A couple millimeters a year sounds pretty slow to anybody but a geologist,” said co-author David Montgomery, a UW professor of Earth and space sciences. “Isaac measured two millimeters of soil production a year, so it would take just a dozen years to make an inch of soil. That’s shockingly fast for a geologist, because the conventional wisdom is it takes centuries.”

The researchers believe plant roots may be responsible here. The mountain landscape was covered with low, dense vegetation. The roots of those plants reach into cracks in the rocks, helping break them apart and expose them to rainwater and chemical weathering.

“This opens up new questions about how soil production might happen in other locations, climates and environments,” Larsen said.

Shale sequestration, water for energy & soil microbes

Scientists from the Department of Energy’s Pacific Northwest National Laboratory will present a variety of their research at the 2013 American Geophysical Union Fall Meeting, which runs Monday, Dec. 9 through Friday, Dec. 13 at the Moscone Convention Center in San Francisco. Among the noteworthy PNNL research scheduled to be discussed are carbon sequestration in empty shale reservoirs, water needs for future energy production and how soil microbes adjust to climate change. More information is below.

Chemistry informs economics of carbon sequestration at shale gas sites

Shale formations – underground mixes of mud, minerals and gas that have sparked a natural gas drilling boom in the United States – could also help power plants meet proposed EPA emission regulations by permanently storing carbon dioxide. But while many pollution-emitting power plants are located near shale formations, little is known about the complex chemistry of shales reacting with pumped-in carbon emissions. The issue is complicated by the variety of different clay minerals that make up shales. PNNL scientists are getting to the bottom of these details by conducting laboratory experiments and computer modeling research to determine how carbon dioxide, methane and common power plant byproducts such as sulfur dioxide react with the four clays common in shales. Early results show the clay mineral montmorillonite expands to hold more carbon emissions under certain conditions. Tests also show the clay kaolinite has a sweet spot to absorb emissions with an ideal combination of pressure and carbon dioxide concentrations. PNNL geologist Todd Schaef will present these and other results, including a preliminary cost-benefit analysis of carbon sequestration at the United States’ shale gas reservoirs.

MR21B-5: “CO2 Utilization and Storage in Shale Gas Reservoirs,” 9-9:15 a.m., Tuesday, Dec. 10, 301 (Moscone South).

Water consumption to increase with future U.S. energy needs

Future power plants can use more water-efficient cooling technologies to withdraw less water from rivers and ponds, but PNNL research shows there is a tradeoff. Water-efficient cooling technologies typically reuse water instead of using it just once, but they also warm the reused water and cause evaporation that removes water from the local ecosystem. PNNL used a computer model to estimate future energy generation and associated water use for each of the 50 states. The detailed analysis found while the nation’s energy sector could withdraw less water with advanced cooling technologies, the amount of water consumed through evaporation would increase. The study also identified several other trends, such as energy-related water withdrawals decreasing in the Eastern U.S. while they increase in the West. PNNL environmental scientist Lu Liu will present a poster on this research.

H11J-1274: “An integrated assessment of energy-water nexus at the state level in the United States: Projections and analyses under different scenarios through 2095,” 8 a.m. – 12:20 p.m., Tuesday, Dec. 10, Hall A-C (Moscone South).

Climate change alters bacteria behavior

Climate change doesn’t affect just polar bears and ice caps; it also impacts the tiny microbes that help plants soak up nutrients in the soil. New research shows transplanted soil bacteria adjust their enzyme production to better survive in a new climate. The findings are a result of a unique study where soil samples were transplanted between two elevations about 1700 feet apart on an isolated mountain in rural Washington state. The scientists gave the transplanted soil about 17 years to settle into its new surroundings and then compared its bacteria with bacteria in unmoved soil samples. The researchers found bacteria made more of some enzymes in the higher-up soil, where it’s wetter and cooler and there’s more vegetation. The enzymes found in greater abundance break down cellulose – the tough, pithy material that gives plants structure – and chitin – another tough material that strengthens fungal cell walls. The researchers hypothesize the higher-elevation bacteria produce more of those enzymes because the richer soils there are home to more plants and fungi for the bacteria to digest. Better understanding how climate impacts microbes can also help us better understand climate change, as many of the greenhouse gases that contribute to climate change occur as a result of interactions with microbes. PNNL microbiologist Vanessa Bailey will present a poster on this research.

B51D-0311: “Bacterial Community Structure after a 17-year Reciprocal Soil Transplant Simulating Climate Change with Elevation,” 8 a.m. – Noon, Friday, Dec. 13, Hall A-C (Moscone South).