Research indicates Mississippi River is older than thought

The Mississippi River above Sartell, Minn. (Minnesota DNR photo)

CARBONDALE, Ill. — Research by a Southern Illinois University instructor and her graduate student indicates the Mississippi River is more than three times older than previous records suggested.

Sally Potter-McIntyre, an associate professor in SIU’s School of Earth Systems and Sustainability, said in 2013 her then-graduate student, Jeremy Breeden, wanted to date deposits of sedimentary rock in his native Southern Illinois. So, she led a team of researchers, including Breeden, to begin dating sedimentary rock found at Illinois’ southernmost tip.

To do this, Potter-McIntyre said the researchers separated particles, called zircons, from bags of sedimentary rock collected by her team. These particles are found as grains of sand.

After separating the zircons from the other sedimentary materials, Potter-McIntyre said she and Breeden went to the University of Arizona to perform the dating analyses.

A Thursday news release from SIU announcing the research said the uranium found in zircons eventually breaks down and forms lead. By calculating the amount of uranium and lead in the zircons, the researchers were able to date the particles, which Potter-McIntyre said produces a specific fingerprint based on the different ages and formation of the sand grains. She said this fingerprint was statistically compared to other rock units and it was determined that the closest match was to older rocks in the Illinois Basin – a geographic area centered in Illinois that contains significant deposits of coal and other minerals. Potter-McIntyre said this suggests that a river was eroding those rocks and transporting the grains to the south.

Summarizing this, Potter-McIntyre said what her team’s research showed was that the Mississippi River was flowing long before it was commonly believed to have been. Initially, it was believed the Mississippi River began flowing about 20 million years ago. However, because of Potter-McIntyre’s and Breeden’s work, it is now believed to have started flowing 70 million years ago.

The discovery was significant enough to earn a nod from Smithsonian Magazine last month. The article said the “extraordinary new findings” are “helping us better understand the monumental events, beginning in late Cretaceous North America, that gave rise to the Mississippi, swelling it to gargantuan proportions.”

In practical terms, Potter-McIntyre said this could have implications for the oil industry in the region.

“What it says is that the oil could have … become mature in places that they really wouldn’t have thought prior to this,” she said.

Potter-McIntyre said this research was a good example of how science works.

“This isn’t something that we go out, ‘oh hey, look at this,’ and 10 minutes later it’s a thing. It’s a yearslong process of trial and error,” she said. She said the research didn’t start until 2013, wasn’t completed and published until 2017, and wasn’t even recognized until this year.

“Science is a long process,” she said. However, no matter how long it took, Potter-McIntyre said there was still joy and excitement in realizing they had found something significant.

“It was pretty cool to go, ‘Wait a minute wow, we’ve got something here,”’ she said.

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