Secondary impact crater complex discovered in Wyoming

(ORDO NEWS) — The Wyoming crater field is about 280 million years old. New research shows that the massive primary crater responsible for this is now buried deep underground near the Wyoming-Nebraska border.

Sometimes a deer hunter finds something more than a six-pointed deer.

In the mid-1990s, a hunter named Gene George, who was a petroleum geologist, discovered a strange depression in southeastern Wyoming. George speculated that the trough was formed by a cosmic impact and called geology professor Peter Hunton of the University of Wyoming to discuss his theory.

Intrigued, Hunton sent one of his undergraduate students to explore the site as part of a summer research project. The student first mapped five possible craters in the area and then detailed his findings in a 1996 report.

In 2017, the Great American Eclipse occurred: geologist Kent Sundell of Casper College in Wyoming led a pre-eclipse tour with Apollo 17 astronaut geologist Harrison Schmitt.

Sandell recently used a newly acquired drone by the college to confirm the presence of a cluster of craters first discovered two decades ago. Out there on the dry, windswept plains, Schmitt “and all the other planetary scientists agreed that these [features] were exceptional,” Sandell told Astronomy.

Shortly thereafter, Sandell began using drones, as well as his students, to find more craters. And they found. Lots of craters.

Secondary impact crater complex discovered in Wyoming 1
Drone (A, B, D, E) and Google Earth (C, F, G) images show a selection of the various craters that make up the Wyoming crater field. SM=Sheep Mountain; MC=Mule Creek; FR=Fetterman Ridge; FRX=Fetterman Road; PCR=Palmer Canyon Road

Then team member Doug Cook, an independent consultant, asked Thomas Kenkman of the Albert Ludwig University in Freiburg, Germany, to analyze samples from the craters.

Based in part on the impact quartz that Kenkmann found in the samples, he was able to confirm that they were indeed created during a cataclysmic cosmic impact. Since then, Sandell says he and his students have regularly made the hour-long drive from Kaspar to continue studying the craters.

First batch of secondary Earth craters

These hour-long trips take Sandell and his team back 280 million years to the Permian, when the impact crashed into the supercontinent Pangea. This devastating impact created several dozen small craters that make up what is now the Wyoming Crater Field.

In 2018, the team published their initial interpretation of the Wyoming Crater Field in Scientific Reports. Their theory? The accumulation of craters was the result of multiple impacts from a single massive meteoroid that exploded into many small fragments while still in the Earth’s atmosphere.

However, further research led to a different idea. On February 11, 2022, Kenkmann and his team published an article in the GSA Bulletin about the follow-up research.

In it, they suggested that the Wyoming crater field was actually the result of a secondary impact resulting from a primary impact that occurred somewhere near the present-day Wyoming-Nebraska border. A superlarge primary impact crater, if it exists, would be 31 to 40 miles (50 to 80 km) wide and filled with sediment.

“Secondary craters around large craters are well known on other planets and moons,” Kenkmann said in a statement provided by the Geological Society of America (GSA), “but have never been found on Earth.”

Secondary impact crater complex discovered in Wyoming 2
The crater Copernicus on the Moon is a prime example of how a single powerful impact can eject enough ejectors to create a chain of secondary craters, such as this set of secondary craters taken from lunar orbit during the Apollo mission. These secondary craters often have herringbone ridges that radiate outward, with the tops of their ridges pointing towards the location of the primary crater

In this case, according to the team, the width of the primary impactor should have been at least a mile (1.6 km). In comparison, the iron-nickel meteorite that crashed into the Earth and created the 0.75 mile (1.2 km) wide Meteor Crater in Arizona was only about 160 feet (50 m) across.

A closer look at the craters

The 31 secondary craters discovered to date range from 32 to 229 feet (10 to 70 m) wide and are located in a triangular area bordered by the cities of Laramie, Casper and Douglas, Wyoming.

Secondary craters are located at a distance of 93 to 124 miles (150-200 km) from the proposed main crater. According to the team, a single meteoroid air burst could not have created such an extensive set of craters.

All secondary craters were formed by ejecta (from the primary impact) 13 to 26 feet (4 to 8 km) wide. These ejected fragments hit the Earth at speeds ranging from approximately 1,500 mph (930 km/h) to over 2,200 mph (1,370 km/h).

Smaller impacts line up in a typical secondary chain, and some of the craters are elliptical, indicating a low-angle impact. The classic herringbone pattern of secondary strikes may also be present.

The craters the team has explored so far show impact features associated with impacts, but another 60 suspected troughs still await further study. Some craters contain inclusions of accretionary lapilli, tiny spherical objects composed of concentric layers of ash that form around condensing liquids or other particles.

They form in giant plumes over volcanic eruptions or impacts in the seconds and minutes immediately following violent events. They form in sandstones of varying degrees of preservation, and in some of them even ejection blankets are visible, consisting of materials destroyed by impact near the rim of the crater.

Confirmation of the Origin History of the Wyoming Crater Field

Despite a growing body of evidence, more work needs to be done before the team can say with certainty that the Wyoming crater field is indeed the site of a secondary impact.

First of all, the researchers want to find a massive primary impact crater that has been obscured by sediment deposited over the past few hundred million years. In addition, the team also plans to find more associated secondary craters, which could further limit the parameters used in their impact models.

Meanwhile, one of the team members, Sandell, is particularly intrigued by the possibility that the Wyoming crater field could be the result of “a meteor storm that has hit the entire Earth for a significant period of time,” he said.

While such a storm would no doubt have resulted in multiple impacts around the world, Sandell suggests “we just found an area that has preserved these fast-moving small impactors very well.”

However, despite some evidence that the impacts were distributed over a negligible period of time, and evidence that the Moon was the victim of an intensified cosmic squall about 290 million years ago, Kenkmann and Cook disagree with Sundell’s meteorite hypothesis. storm.

Secondary impact crater complex discovered in Wyoming 3
This elevation map of southeastern Wyoming shows the location of possible primary impact craters as well as several identified secondary crater fields. SM=Sheep Mountain; MC=Mule Creek; FR=Fetterman Ridge; FRX=Fetterman Road; PCR=Palmer Canyon Road; WR=Wagonhound Ridge; BR=Box Elder Canyon; and MR=Manning Ridge

What Secondary Craters Can Teach Us

Kelsey N. Singer, a senior scientist at the Southwestern Research Institute who specializes in secondary craters and was not involved in the study, tells Astronomy that “theoretically, most primary impacts should form secondary craters, but we may not see them that often on Earth because they are more easily eroded than large primary ones.”

If the Wyoming crater field is confirmed to be a secondary crater field, Singer says, it would be “a great comparison to craters on other planets.” Secondary craters are a record of all the fragments ejected from the parent crater, so they are really useful for understanding how craters form and how physics works.”

“This article is very interesting and important…” says planetary geologist Stephen Jaret of the American Museum of Natural History, who was not involved in the new study. “Although scientists have assumed that secondary craters also occur on Earth, it is now nice to have direct evidence that they can occur even in dense atmospheres.”

Jareth added that “Detecting impact quartz in these secondary craters is very important. Impact quartz only naturally occurs when hit by a very fast moving object. Even meteorites hitting the ground don’t fall fast enough to shock the quartz. material ejected from the primary crater returns downward with sufficient velocity and energy to generate a shock wave.”

Another outside researcher, Canadian planetary scientist Gordon Oskinsky of the University of Western Ontario, agrees that the paper is strong. However, he was also struck by the age of the crater field. “This is evidence of an element of luck in geology.

In this case, it turned out that this field was not only preserved, but also was exposed on the surface in an area with a large amount of rocks in this period of the Earth’s history – when there are scientists nearby to study them”.

As always, additional data is needed for confirmation. In particular, finding a primary crater would support the team’s hypothesis, Singer said. But in the end, finding new evidence is what Sandell calls “exciting science in the making.”

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