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.

River deep, mountain high — new study reveals clues to lifecycle of worlds iconic mountains

This image shows the very steep topography of East Timor. The evolution of this mountain range is dominated by ongoing feedbacks between landslides and river erosion. -  Mike Sandiford University of Melbourne
This image shows the very steep topography of East Timor. The evolution of this mountain range is dominated by ongoing feedbacks between landslides and river erosion. – Mike Sandiford University of Melbourne

Scientists have discovered the reasons behind the lifespan of some of the world’s iconic mountain ranges.

The study conducted by the University of Melbourne, Australia, and Aarhus University, Denmark, has revealed that interactions between landslides and erosion, caused by rivers, explains why some mountain ranges exceed their expected lifespan.

Co-author Professor Mike Sandiford of the School of Earth Sciences at the University of Melbourne said the study had answered the quandary as to why there was fast erosion in active mountain ranges in the Himalayas and slow erosion in others such as the Great Dividing Range in Australia or the Urals in Russia.

“We have shown that links between landslides and rivers are important in maintaining erosion in active or ancient mountain ranges,” he said.

“This study is a great insight into the origins and topography of our globe’s mountainous landscape.”

Mountain ranges are expected to erode away in the absence of tectonic activity but several ranges, such as the Appalachians in the US and the Urals in Russia, have been preserved over several hundred million years.

Co-author, Professor David Egholm from Aarhus University said the new model study published in Nature today provided a plausible mechanism for the preservation of tectonically inactive mountain ranges.

“Computational simulations performed for the study revealed that variations in mountain erosion may relate to a coupling between river incision and landslides,” he said.

Researchers said rivers can cut through bedrock and this process is thought to be the major factor in controlling mountain erosion, however, the long-term preservation of some mountains is at odds with some of the underlying assumptions regarding river erosion rates in current models of river-based landscape evolution.

The study revealed landslides affected river erosion rates in two ways. Large landslides overwhelm river transport capacity and can protect the riverbed from further erosion; conversely, landslides also deliver abrasive agents to the streams, thereby accelerating erosion.

Feedback between these processes can help to stabilize the rates of erosion and increase the lifespan of mountains, the authors said.

Syracuse University professor argues Earth’s mantle affects long-term sea-level rise estimates

Robert Moucha is an assistant professor of Earth Sciences in Syracuse University's College of Arts and Sciences. -  SU News
Robert Moucha is an assistant professor of Earth Sciences in Syracuse University’s College of Arts and Sciences. – SU News

From Virginia to Florida, there is a prehistoric shoreline that, in some parts, rests more than 280 feet above modern sea level. The shoreline was carved by waves more than 3 million years ago-possible evidence of a once higher sea level, triggered by ice-sheet melting. But new findings by a team of researchers, including Robert Moucha, assistant professor of Earth Sciences in Syracuse University’s College of Arts and Sciences, reveal that the shoreline has been uplifted by more than 210 feet, meaning less ice melted than expected.

Equally compelling is the fact that the shoreline is not flat, as it should be, but is distorted, reflecting the pushing motion of the Earth’s mantle.

This is big news, says Moucha, for scientists who use the coastline to predict future sea-level rise. It’s also a cautionary tale for those who rely almost exclusively on cycles of glacial advance and retreat to study sea-level changes.

“Three million years ago, the average global temperature was two to three degrees Celsius higher, while the amount of carbon dioxide in the atmosphere was comparable to that of today,” says Moucha, who contributed to a paper on the subject in the May 15th issue of Science Express. “If we can estimate the height of the sea from 3 million years ago, we can then relate it to the amount of ice sheets that melted. This period also serves as a window into what we may expect in the future.”

Moucha and his colleagues-led by David Rowley, professor of geophysical sciences at the University of Chicago-have been using computer modeling to pinpoint exactly what melted during this interglacial period, some 3 million years ago. So far, evidenced is stacked in favor of Greenland, West Antarctica, and the sprawling East Antarctica ice sheet, but the new shoreline uplift implies that East Antarctica may have melted some or not at all. “It’s less than previous estimates had implied,” says Rowley, the article’s lead author.

Moucha’s findings show that the jagged shoreline may have been caused by the interplay between the Earth’s surface and its mantle-a process known as dynamic topography. Advanced modeling suggests that the shoreline, referred to as the Orangeburg Scarp, may have shifted as much as 196 feet. Modeling also accounts for other effects, such as the buildup of offshore sediments and glacial retreats.

“Dynamic topography is a very important contributor to Earth’s surface evolution,” says Rowley. “With this work, we can demonstrate that even small-scale features, long considered outside the realm of mantle influence, are reflective of mantle contributions.”

Moucha’s involvement with the project grew out of a series of papers he published as a postdoctoral fellow at the Canadian Institute for Advance Research in Montreal. In one paper from 2008, he drew on elements of the North American East Coast and African West Coast to build a case against the existence of stable continental platforms.

“The North American East Coast has always been thought of as a passive margin,” says Moucha, referring to large areas usually bereft of tectonic activity. “[With Rowley], we’ve challenged the traditional view of passive margins by showing that through observations and numerical simulations, they are subject to long-term deformation, in response to mantle flow.”

Central to Moucha’s argument is the fact that viscous mantle flows everywhere, all the time. As a result, it’s nearly impossible to find what he calls “stable reference points” on the Earth’s surface to accurately measure global sea-level rise. “If one incorrectly assumed that a particular margin is a stable reference frame when, in actuality, it has subsided, his or her assumption would lead to a sea-level rise and, ultimately, to an increase in ice-sheet melt,” says Moucha, who joined SU’s faculty in 2011.

Another consideration is the size of the ice sheet. Between periods of glacial activity (such as the one from 3 million years ago and the one we are in now), ice sheets are generally smaller. Jerry Mitrovica, professor of geophysics at Harvard University who also contributed to the paper, says the same mantle processes that drive plate tectonics also deform elevations of ancient shorelines. “You can’t ignore this, or your estimate of the size of the ancient ice sheets will be wrong,” he says.

Moucha puts it this way: “Because ice sheets have mass and mass results in gravitational attraction, the sea level actually falls near the melting ice sheet and rises when it’s further away. This variability has enabled us to unravel which ice sheet contributed to sea-level rise and how much of [the sheet] melted.”

The SU geophysicist credits much of the group’s success to state-of-the-art seismic tomography, a geological imaging technique led by Nathan Simmons at California’s Lawrence Livermore National Laboratory. “Nathan, who co-authored the paper, provided me with seismic tomography data, from which I used high-performance computing to model mantle flow,” says Moucha. “A few million years may have taken us a day to render, but a billion years may have taken several weeks or more.”

Moucha and his colleagues hope to apply their East Coast model to the Appalachian Mountains, which are also considered a type of passive geology. Although they have been tectonically quiet for more than 200 million years, the Appalachians are beginning to show signs of wear and tear: rugged peaks, steep slopes, landslides and waterfalls-possible evidence of erosion, triggered by dynamic topography.

“Scientists such as Rob, who produce increasingly accurate models of dynamic topography for the past, are going to be at the front line of this important research area,” says Mitrovica.

Adds Rowley: “Rob Moucha has demonstrated that dynamic topography is a very important contributor to Earth’s surface evolution. ? His study of mantle contributions is appealing on a large number of fronts that I, among others of our collaboration, hope to pursue.”

Appalachia in the limelight

A new memoir from the Geological Society of America, 'From Rodinia to Pangea: The Lithotectonic Record of the Appalachian,' contains 36 original papers reporting the results of research performed throughout nearly the entire length and breadth of the Appalachian region, including all major provinces and geographical areas. -  The Geological Society of America
A new memoir from the Geological Society of America, ‘From Rodinia to Pangea: The Lithotectonic Record of the Appalachian,’ contains 36 original papers reporting the results of research performed throughout nearly the entire length and breadth of the Appalachian region, including all major provinces and geographical areas. – The Geological Society of America

The Appalachians have served as a springboard for innovative geologic thought for more than 170 years. A new volume from The Geological Society of America contains 36 original papers reporting the results of research performed throughout nearly the entire length and breadth of the Appalachian region, including all major provinces and geographical areas.

Memoir 206, From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region, grew out of GSA’s 2007 Northeastern Section meeting in Durham, New Hampshire, and commemorates the (near) fortieth anniversary of the publication of the classic Studies of Appalachian Geology volumes that appeared just prior to the application of plate tectonic concepts to the region.

Contributions in structural evolution, sedimentation, stratigraphy, magmatic processes, metamorphism, tectonics, and terrane accretion illustrate the wide range of ongoing research in the area and collectively serve to mark the considerable progress in scientific thought that has occurred during the past four decades.

Research highlights 3D perspectives, sequence stratigraphic techniques, and improved geochemical databases for the exploration of regional-scale modeling.