The discovery of the “small” deep groundwater tells an amazing tale

Groundwater at a depth of hundreds of meters or more can be hundreds of millions of years old and is often thought to be stagnant and isolated from the atmosphere and the water cycle — which is why these subsurface areas are targeted as potential subsurface waste disposal sites, Ferguson said. .

“But things are much more dynamic there than we thought,” said Ferguson, professor of civil, geological and environmental engineering at the University of Osaka’s School of Engineering and co-author of the research paper in the journal. Geophysical Research Letters.

The paper describes the surprising findings in the Paradox Basin, located in southeastern Utah and southwestern Colorado, where the research team found unexpected groundwater at a depth where ancient aquifers existed.

Said co-author Dr. Jennifer McIntosh (Ph.D.), a U of A Distinguished Researcher in the Department of Hydrology and Atmospheric Sciences and an assistant professor at USask.

“We expected to find that groundwater would gradually age as you got deeper,” Macintosh said. “Instead, we found a million-year-old groundwater, which is relatively young, about three kilometers below the surface in sediments hundreds of millions of years old.”

Mackintosh headed the team that Ferguson pioneered in physical hydrology. Dr. Jihyun Kim (PhD), now a graduate student at the University of Calgary and a Ph.D. at the University of Calgary previously. The candidate, supervised by Macintosh and Ferguson, was the first author.

This study is among the first to use a relatively new Krypton 81 technology to date in deep groundwater. Unlike carbon-14, which scientists use to determine the age of materials up to 40,000 years, the longer decay period of radioactive krypton 81 can be used to calculate the age of water up to 1.2 million years.

The results of the study correlate with rapid geological changes over the past 3 million to 10 million years in the Colorado Plateau, where the dramatic fissure (slope, or erosion under the river bed) of the Great Colorado River, which formed the Grand Canyon, began. Expel old groundwater.

Before the incision of the Colorado River, the Colorado Plateau was relatively flat and seawater from the Paleozoic (500 million to 250 million years ago) was trapped within the sediments for hundreds of millions of years, Ferguson said.

“Essentially, what the fissure did was to create drains that would allow water from the surface to permeate the ancient, highly saline waters into and below the aquifers, above and below the saline sediments in the center of the deep groundwater system.”

McIntosh explains that this research shows that landscape evolution can radically change the subsurface environment within a few million years — a short period of geological time. She said the study is useful because the same methods can be applied to characterize sites elsewhere to see how they relate to the atmosphere and the surface.

A newly funded project in the Colorado Plateau led by McIntosh is examining the relationship between underground hydrology and life in more detail, testing the hypothesis that deep circulation of water from the surface can re-inoculate microbial life in sediments that have been deeply buried and sterilized by high temperatures in the geological past.

The team plans to extend this work to other areas including the Canadian Prairies, where geologic events, such as the rise of the Rockies 80 million to 50 million years ago, and the glaciation that covered most of North America about 2.8 million years ago, Ferguson said. Huge hydrological changes would have occurred.

“Especially from a Saskatchewan perspective, we’re thinking about the different ways we use the Earth’s subsoil, whether it’s storing fluids from oil and gas, or sequestering carbon, we’re going to have these legacies in the future,” he said. “I don’t think we’ve actually checked these systems in ways that we can or should.”


Scientists measure new depths at the bottom of the hydrological cycle


more information:
Ji‐Hyun Kim et al, Krypton‐81 dating constrains the timing of deep groundwater flow activation, Geophysical Research Letters (2022). doi: 10.1029/2021GL097618

Presented by the University of Saskatchewan

the quote: Discovery of Deep Groundwater ‘Young’ tells a surprising story (2022, July 20) Retrieved on July 21, 2022 from https://phys.org/news/2022-07-discovery-young-deep-groundwater-tale.html

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