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UWRF geology professors involved in rare fossil find

February 5, 2009

A rare fossil was discovered near River Falls in December, and since the find, the fossils have been promoted by the UW-River Falls geology department in multiple ways. As a result, more interesting things have been uncovered in the area.

Steve Thompson, a geologist from the Minnesota Pollution Control Agency, called the UWRF geology department after he uncovered some unusual sandstone formations on his property while digging a foundation in December. Little did Thompson know that the unusual sandstone housed two leaf fossils that turned out to be the only known fossils of their kind found in Wisconsin.

Geology professors Kerry Keen and Mike Middleton were two of the people called to the site. Keen found the first leaf, the larger of the two, and later Middleton discovered the second, a small imprint. The team was able to determine the fossils dated back to the Cretaceous period.

Middleton estimated the fossils are between 135 and 165 million years old.

These are the first reported fossils found from the Cretaceous period in Wisconsin. There have been only a handful of iron-rich stone and sands found in Wisconsin. Two samples of rock were found just a few miles away from River Falls, in Spring Valley, Wis. Spring Valley used to be an iron mining area, so the discovery of these sediments was not unexplainable.

It is not unusual to find fossils from this period in Minnesota, Middleton said.

“There used to be a giant sea that covered what is now Minnesota and lots of land to the west,” Middleton said.

The fossils that are commonly found in western Wisconsin are marine fossils. It is rare to find plant fossils in this region that date back to the Cretaceous period.

“It’s their geographic occurrence that makes them so rare,” Middleton said. “It’s going to be hard to identify them specifically. There isn’t a lot of great detail in the veins of the leaves.”

Middleton and Keen have been promoting their find vigorously. The two teamed up with fellow UWRF geology professors Bill Cordua and Bob Baker as well as UWRF junior geology major Amy Nachbor to write a paper and create an elaborate and detailed poster on the fossils. The paper and poster were presented at the regional meeting of the Geological Society of America in April.

“The find has sparked a lot of professional interest,” Middleton said.

The leaf fossil samples are being held in the UWRF paleontology collection. Upon appointment, anyone can come and view them.