UWs Vietti Leads Student Expedition Into Three Kemmerer Fossil Fish Quarries

Laura Vietti and two University of Wyoming researchers recently accompanied some UW students to three fossil fish quarries near Kemmerer. Their mission: to gather ash samples in the fossil fish layers to discover how quickly the fossil lake filled up millions of years ago.

“We focused on a new and promising research project to collect ash samples from the fossil fish layers to determine the age -- possibly for the first time ever -- of the fossil fish layers that yield some of the best fossils in the world,” says Vietti, museum and collections manager for the UW Geological Museum.  

During its field trip June 13-17, the research group, made up of Vietti; Lily Jackson, a postdoctoral researcher in the UW Department of Geology and Geophysics; Kevin Chamberlain, a research professor of geology and geophysics; and three UW students, visited American Fossil quarry, Fossil Fish Adventures quarry and the Green River Stone Co. quarry, all of which are located in and around Kemmerer.  

Arvid Aase, curator with Fossil Butte National Monument, guided the group to remote locations “to capture as much of the ancient lake strata as we could,” Vietti says.

“Since we are interested in learning how fast fossil lakes filled up, we tried to sample ash from the very oldest layers (beginning of lake); at the middle of the lake; and at the youngest (end of the lake) layers,” Vietti explains. “To sample the mid- and youngest layers of the lake, we visited three commercial quarries.”

The quarries are part of Wyoming’s Green River Formation that was created during the Eocene era, approximately 56 million to 33.9 million years ago. The formation boasts the country’s best-preserved Eocene bats, birds, caimans, crocodiles, dragonflies, ferns, mammals, snakes and turtles.

During the 2-million-to-3-million-year lifetime of the approximately 50-million-year-old lake, eruptions from nearby volcanoes were frequent. These eruptions laid down several layers of volcanic ash throughout the lake sediment. The ash contains minerals that can be dated by radioisotopic methods, Chamberlain says. This method dates geological or archaeological specimens by determining the relative proportions of particular radioactive isotopes present in a sample.

“By dating multiple ash layers within the sediment pile, the ages of any fossils that are between the ash layers also can be determined, as well as how long it took for the sediments containing the fossils to accumulate,” Jackson explains. “This will be the first study to date multiple ash layers within the fossil basin and to precisely constrain the ages.”

The team collected ash layers from different parts of the ancient lake. The ash layers represent different times in the lake’s depositional history and are associated with different fossil species.

When sampling the oldest ash in the fossil lake, the group discovered several small fish fossils that likely represent some of the first fish deposited in the lake. These fish are undescribed and are a type of percoid, a group of fish that contains snapper, grouper, bass, goatfish and perch, Vietti says. These specimens were given to Fossil Butte National Monument for curation and will be scientifically described.

“Students learned much on this trip, including how to identify and sample ash units; how to quarry for fossil fish; about the overall stratigraphy of the ancient fossil lake; and how the lake environment and chemistry changed over time,” Vietti says.

The discoveries the group made will be made available to the public next spring, when the UW Geological Museum holds its annual Fossil Fish Festival. The collaborative outreach event is free and open to the public, with the target audience being schoolkids.

“We spent a day collecting teaching specimens to use in our annual Fossil Fish Festival,” Vietti says.

UW students who participated in the field trip, listed by hometown, are:

Boulder, Colo. -- Sarah Hurrell, a sophomore majoring in geology and geophysics.

Monticello, Fla. -- Claudia Richbourg, a third-year Ph.D. student in the Program in Ecology.

Rancho Cucamonga, Calif. -- Julian Hernandez Diepenbrock, a second-year Ph.D. student in paleontology.

“Sarah Hurrell is playing a very large part in this project,” Vietti says of the UW student who has been selected as a 2022-23 Wyoming Research Scholar. “Through the program, they are helping fund Sarah assisting us in the field and especially helping fund her to work in the lab processing the samples. We are very appreciative and excited for her to be part of this program.”