Wyoming’s Bighorn Basin unlocks secrets to massive global warming events some 50M years ago

JACKSON HOLE, WYO – Wyoming is world famous for its extensive fossil records. Various dinosaurs, for example, died here and left us with abundant oil and gas plays after their anaerobic decomposition.

But why did all these animals live here in Wyoming? Did they prefer a colder climate?

Actually, flora and fauna thrived in Wyoming some 56 million years ago precisely because it was not typically cold Wyoming. In fact, it looked a lot more like modern-day Florida complete with palm trees and alligators.

The Paleocene and Eocene (66-34 million years ago) periods were times of numerous rapid and extreme warming events. These hothouse intervals known as ‘hyperthermals’ were series of transient greenhouse warming events caused by the release of carbon into the atmosphere that increased both temperatures and precipitation.

Ellen Currano, Assistant Professor of Botany and Geology & Geophysics with University of Wyoming, will share what she has learned studying the Bighorn Basin in particular.

Biotic change during hyperthermals provides insight into how present-day ecosystems will respond to anthropogenic CO2 release, Currano states.

Sediments in the Bighorn Basin in northwest Wyoming preserve fossil leaves from the first two Eocene hyperthermal events, the Paleocene-Eocene Thermal Maximum (PETM, 56 Ma) and the Eocene Thermal Maximum 2 (ETM2, ~53.7 Ma).

Sedimentary layers characteristic of PETM are readily found and studied in the Bighorn Basin.

During the PETM, carbon dioxide levels at least doubled, causing, in part, a temperature increase by about 8oF in the Bighorn Basin. There was a nearly complete change in vegetation, according to an observable increase in the diversity of insect herbivore damage traces observed on fossil leaves, and an increase in the amount of leaf area consumed by insect herbivores.

After the PETM, both floral composition and insect herbivory returned to pre-PETM states. Changes in CO2 and temperature during the ETM2 were about half that of the PETM, and vegetation and insect herbivore damage at the ETM2 site is intermediary between PETM and background Eocene conditions.

Currano’s results demonstrate that ecosystem change scales with the magnitude of change to the carbon cycle and temperature. Because anthropogenic CO2 release is 10-100x faster than that during the PETM, ecosystem change is likely to be even more drastic than that observed 56 million years ago.


Don’t miss Currano’s presentation titled, “Eocene Hyperthermals: Rapid & Extreme Warming Events as documented in Wyoming,” at the Teton County Library Tuesday, October 16 at 6pm.


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