ABQ Times

Geologists have made significant advances in understanding the Cambrian period, thanks to new research on the Grand Canyon's Tonto Group. A recent paper led by Carol Dehler of Utah State University, along with a team including UNM adjunct professor Fred Sundberg and other distinguished scientists, has been published in GSA Today's November 2024 issue. The study refines the classic stratigraphic model of marine transgression originally developed by Eddy McKee.

"The Tonto Group of Grand Canyon holds a treasure trove of sedimentary layers and fossils chronicling the Cambrian Explosion some 500 million years ago," said Dehler. This period marked a rapid proliferation of life forms with hard shells as sea levels rose.

The researchers' new model offers a more nuanced view than McKee's, showing mixed marine and non-marine settings and faster evolutionary tempos. "Even more than before, the Tonto Group of Grand Canyon remains one of the most important Cambrian type sections in the world because of its complete exposure," said Karl Karlstrom from UNM.

Supported by the National Science Foundation Division of Earth Sciences, this work underscores that science is an evolving process. James Hagadorn noted how these findings connect people personally to science through the iconic landscape of the Grand Canyon.

New dating methods provided insights into rock sedimentation speeds and species diversification rates. Mark Schmitz explained that U-Pb dating methods revealed fast radiations and extinctions of trilobite species at sub-million-year intervals.

Laurie Crossey emphasized that dating sedimentary rocks is challenging but crucial for bracketing ages. Dehler highlighted that their model provides pathways for deeper understanding among students and researchers regarding sea-level rise and environmental conditions during the Cambrian explosion.

"From the Tonto Group’s 500-meter-thick strata, we’re learning about sea-level rise and effects of catastrophic tropical storms," Dehler stated, describing conditions when Earth was ice-free and devoid of land plants.