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Scientists deepen understanding of ancient rivers


Nebraska’s rivers can be viewed as places for quiet contemplation, familiar local landmarks, or valuable natural resources to be protected. To Jesse Corus, the state’s rivers are everything, but also more: they are ambassadors of Nebraska’s deep geological past. Messages from innovative analyzes of remaining river channels preserved in modern topography and rock outcrops are important in helping Nebraskans understand the current geological dynamics affecting the state.

Korus, an associate professor in the School of Natural Resources at the University of Nebraska-Lincoln, is deepening his knowledge of Nebraska’s geological past by co-authoring two recent studies on ancient river systems in the Great Plains.

“This is the first time we have directly observed the flow of ancient river channels across a large area of ​​the Great Plains and linked them to past landscapes and events,” Korus said. said.

An article published in the journal Geosphere notes that the landscapes of the Great Plains “are the product of a long-lived system of continental sedimentary routing along rivers, and yet remarkably little is known about these ancient rivers.” Article by Corus and Matt

Yokel, senior assistant director at the School of Natural Resources and a Nebraska geologist, is helping fill a knowledge gap about the history of the Platte River’s ancient river system, which dates back 33 million years.

“Rivers were the building blocks of the Great Plains,” said Korus, who is also a groundwater geologist with the Nebraska Department of Conservation and Research. Yokel is the director of CSD.

The second article of two scientists has been published Sedimentary RecordExplains how fluvial sediment accumulation patterns from the Rocky Mountains to the Gulf of Mexico convey important geological information about upstream conditions.

Corus and Joeckel write that large fan-shaped sedimentary deposits in Nebraska’s ancient High Plains stabilized the river’s sediment distribution system, retaining sediment for millions of years and preventing climate fluctuations from rapidly altering the landscape downstream.

“These rivers carried not only sediments and the water itself, but also information about the geological past (past environments, past events),” Korus said. “For example, uplift of the Rocky Mountains could have caused a sediment pulse that eventually resulted in the accumulation of thick sediment in a sink below the Gulf of Mexico.”

Korus and Joeckel found that giant “megafans” of sediments in ancient southwestern Nebraska, as well as parts of Colorado and Wyoming, acted as a “signal buffer,” delaying the transfer of information.

Giant fan-shaped structures, up to 56 miles wide, accumulated sediments eroded from the Rocky Mountains over perhaps 5 million years, some of which was transported downward. This geological process delayed the transmission through streams of signals of uplift and climate change that affected the ancient river basin.

Nebraska scientists’ analysis advances understanding of how rivers respond to tectonic movement, geomorphological upheaval, and climate change over geologic time scales. Their work also sets the stage for Korus and Joeckel to conduct a comprehensive geological analysis in western Nebraska, eastern Wyoming and northeastern Colorado. The sediments exposed at the surface in these areas are similar to the Ogallala aquifer at depth to the east. This future research may improve understanding of the aquifer, Nebraska’s primary natural resource.

Korus said such research could “improve our understanding of subsurface sediments, the same sediments that are part of the Ogallala High Plains aquifer.” “So it helps us better understand our larger aquifer systems in Nebraska.”

For both of these projects, Korus and Yokel used a remote sensing technology known as lidar, or light detection and ranging, that allows terrain to be analyzed in extremely fine detail. For the first paper, Korus and Yokel identified more than 3,100 river ridges, eroded remains of ancient river channels that provide important information about ancient hydrology and drainage patterns.

A careful analysis of these “fossil rivers” dating from 2 million years ago to about 33 million years ago revealed the evolution of the Platte River system. This suggests that the flows of the ancient South Platte river system were initially small and diverse, following a very different route than the modern river system.

“The earliest South Platte was very different from what it is today,” Korus said.

“Some rivers flowed perpendicularly from northwest to southeast to the present-day South Platte River in eastern Colorado. This indicates that the river system was not yet fully established. It was still in its early stages. Later, young ridges told us that the river was growing, which led to the cutting of the present-day South Platte valley.” “The modern North Platte valley began to develop only after the modern route of the South Platte was established.”

Understanding these ancient geological details depends on understanding the messages contained in Nebraska geology.

“Sedimentary deposits and rocks as a whole can be read like books and tell us about the geological past,” Korus said.

Source: Port Altele



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