Red rocks of the Chinle Formation at Petrified Forest National Park
The Chinle Formation at Petrified Forest National Park provides a “living laboratory” for studying the Triassic period. Credit: National Park Service

Reddish rock formations pervade the American Southwest. Their coloration is associated with the mineral hematite, through which a recent Rutgers University–led study uncovered a powerful link to climate.

According to lead author Christopher Lepre, conventional understanding attributes redness in the rock formations to diagenesis, a process of oxidation that occurs well after rocks are formed. Lepre’s team asked whether the coloration was due not to diagenesis but to a different process altogether. Lepre is an assistant instructor in Earth and planetary sciences at Rutgers.

“Nobody’s ever thought about using hematite as a paleoproxy for understanding seasonal climate parameters like precipitation.”

“My coauthor, Paul Olsen, and his colleagues demonstrated some years ago that the color changes in Triassic rocks from the Newark Basin in New Jersey correlate with ancient monsoonal climate changes,” said Lepre. Applying that correlation to rocks on the Colorado Plateau, Lepre’s team identified a healthy concentration of similarly ancient, colored hematite. “That revises how we start to think about how these rocks got these wonderful colors.”

Celina A. Suarez, an associate professor in the Department of Geosciences at the University of Arkansas not involved in the new research, called the study “a really interesting application.” “Diagenesis is such an amorphous term that researchers tend to shy away from…. Chris saw a pattern in the ‘redness data’ and thought about what it really means. There is a pattern that correlates with other proxy patterns related to precipitation, and he dug into it [to] find what controls hematite formation…. Nobody’s ever thought about using hematite as a paleoproxy for understanding seasonal climate parameters like precipitation.”

Climate Impacts on Seasonality, Paleontology

Lepre and his colleagues examined part of a 518-meter-long rock core from the Chinle Formation in Petrified Forest National Park in Arizona. Using diffuse reflectance spectroscopy, they obtained the wavelengths of various colors to find the concentration of hematite as well as grain size, which pushes the color to be more blue or red. (A more arid climate corresponds to a more reddish hue.) By looking at color cycles recorded in the rock formations, the team evaluated climate behavior during the Late Triassic, about 216 million to 213 million years ago.

Morgan Schaller, an associate professor at Rensselaer Polytechnic Institute not involved with the study, noted the importance of the work: “There are scant few mechanisms of determining hydrological conditions like rainfall on the ancient Earth, especially ones that have the potential to be calibrated quantitatively with so few confounding controls.”

In addition to understanding climate change in the Late Triassic, the new data might be used to imagine how future climate changes might affect monsoonal environments. “Atmospheric [carbon dioxide] levels were very high in the Late Triassic—this is probably not analogous to what’s going to happen in our lifetime but is certainly relevant for [future] projections,” Lepre said.

Suarez said the new research also has a strong impact on understanding seasonality. “That’s something that a lot of paleoclimatologists are grappling with,” she said. “If you can apply this [methodology] to multiple other climate crises throughout Earth’s history, it has the potential for being highly impactful for understanding climate change impacts on extreme seasonality.”

Bill Parker, chief scientist at Petrified Forest National Park, was interested in applying lessons from the study to paleontology: “The ability of dinosaurs over other animal groups to thrive through the climatic effects from the Triassic probably was a major factor of [their] success, and we need to [learn] more about the effects of climate on animal populations.”

The new study was published in the Proceedings of the National Academy of Sciences of the United States of America.

Mentorship and Collaboration with the Navajo Nation

Although this study took place on federal land, part of the project’s sequel proposes coring on Navajo lands, opening the door to deepening an ongoing relationship between outside geologists and the Navajo Nation. Although COVID-19 disrupted plans for in-person collaboration and virtual meetings are difficult because of a lack of Internet access, the research team has formed a working group of seven scientists, including three members of the Navajo Nation, who have been meeting virtually.

“There is a lot of interest from students, and they learn a lot, present at conferences, and talk to their local community.”

One member of this working group, Lavina Becenti, is a geologist with the Navajo Nation. “My involvement is to speak to the community and to tell them how this will affect the Navajo Nation,” Becenti said. “It brings underrepresented minority students from community colleges on the Navajo reservation to opportunities they wouldn’t find anywhere else…. There is a lot of interest from students, and they learn a lot, present at conferences, and talk to their local community.”

Becenti also mentioned that the project would be used to find viable aquifers, a crucial task, as the pandemic has exacerbated water scarcity. Additional concerns include testing for soil and water quality, understanding how climate change will affect the Southwest, and expanding youth training opportunities. In addition, undergraduate students are setting up a website in Navajo that communicates the recent findings to the community. It is scheduled to go live in a couple of months, and Becenti noted that the team has plans to speak to the community as the pandemic comes to a close.

“As the nation begins to open up, we will hold town halls and invite the Navajo community to join our project as consultants and scientists,” Lepre said. “There are a lot of opportunities to get young people involved—not just because of the environmental implications for their own communities, but because it’s exciting stuff.”

“We are looking forward to continued partnership with tribal members that has been ongoing since 2009,” said Jessica Whiteside, an associate professor of ocean and Earth sciences at the University of Southampton. Whiteside has worked with the Navajo Nation on similar projects and is a co–principal investigator on the current project’s sequel. “We have plans for a cross-cultural field school setting, science communication workshops, and continued internship programs.”

“There’s an old saying when you do fieldwork: You take only pictures and you leave only footsteps,” recalled Lepre. “But I think we can leave something besides footsteps—make relationships, bring some science that takes root there and is managed by the people rather than outsiders like us.”

—Ria Mazumdar (@riamaz), Science Writer


Mazumdar, R. (2021), Red rocks: Using color to understand climate change, Eos, 102, Published on 30 March 2021.

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