KU team solves century-old Kansas geological mystery
Age of red beds at Point of Rocks was last remaining stratigraphy dispute in state
Hikers, birders and Santa Fe Trail buffs head to Point of Rocks in extreme southwest Kansas — a key landmark for pioneers — for the wildflowers, wildlife and wagon ruts.
But many a geologist has fixated instead on the mysterious streak of exposed red sandstone at the base of the famous rock formation.
For more than a century they’ve debated, how old are these so-called “red beds?”
Finally, a team of Kansas University researchers applying new dating technology believes it has answered that question with certainty.
“This is pretty much the last gap, the last hole in the geologic map of Kansas,” said Rex Buchanan, interim director of the KU-based Kansas Geological Survey. “This has sat there for a long time waiting for somebody to come by and answer the question.”
The red beds are located at the foot of the bluff topped by a formation known as Point of Rocks — a welcome landmark for pioneers on the Santa Fe Trail’s Dry Route because natural springs were located nearby. Point of Rocks lies within the Cimarron National Grassland in Morton County.
The red beds were long thought by many to be the only Jurassic Period rocks exposed on the surface in all of Kansas, said Jon Smith, assistant scientist at the Kansas Geological Survey.
“We know that’s not the case now,” Smith said. “It’ll change the maps a little bit.”
The rocks are actually millions of years older, according to the research team’s paper, for which Smith was lead author. Testing revealed they were deposited in the Permian Period, which lasted from about 298 million to 252 million years ago.
Previous scientists had posited everything from Permian to the later Triassic, Jurassic and Cretaceous periods — but all were virtually guesses.
Scientists often use fossils embedded in rocks to date them, or perhaps ash layers embedded along with said fossils, Smith said.
“In this case we had no fossils,” Smith said. “There’s no ash. There’s no anything.”
Instead, past geologists had basically looked at the red rock and compared it to similar-looking rock they’d seen in, say, New Mexico or Colorado, Smith said. If they knew the age of the lookalike rocks, then they based their red beds age guess on that.
The KU researchers applied a dependable dating technique based on radioactive decay, which Smith called “one of the best measured things in science.”
The team took samples of the rocks, sent them to a lab to be crushed and suspended in a liquid that would allow tiny zircon crystals to be isolated by sinking to the bottom, Smith said. Those microscopic zircons were then tested for lead and uranium content. Over time, uranium decays into lead, so scientists can date material by the amount of lead in the zircons.
This testing was started several years ago, although KU has since added equipment that enables it to do such testing in-house today, Smith said.
Radioactive dating isn’t new, but it’s just now starting to be used to date sedimentary rocks, Smith said.
Although, it’s definitely too new to have been an option for the first geologists stumped by the red beds at Point of Rocks.
“One hundred years ago they were doing all this on horseback,” Smith said. “They had to focus on great big swaths of area.”
The seemingly “esoteric” study of stratigraphy — the branch of geology dealing with the order and position of strata and their relationship to the geologic timescale — can shed light on how environmental and geological aspects of the world may change in the future, Smith said.
“The present is the key to the past,” he said. “In the same way, the past is also predicting the future.”
In the red beds project, applying a new technique to an old question was key, Smith said.
“People have been kicking this around like a football for 100 years. Let’s apply some of these new techniques to get an answer,” he said. “I think it was a real success.”