First geoscience summer lecture draws crowd

Shayne Mazur

Approximately 50 people assembled in the library meeting room last Tuesday to attend the first installment of the Big Horn Basin Dinosaur and Geoscience Museum’s summer lecture series, which featured Dr. Aaron Wood, director of the Iowa State University geology field station, and his talk “Eocene Climate Change in the Willwood Formation, Bighorn Basin, WY.”

Wood grew up in southern Indiana, but he nurtured his geologist roots in a small farmhouse on the north side of Powell where he woke to the sight of the Willwood Formation every day. 

“The value I see in it is that it’s a great record of ancient ecosystems, environments and climate change. In other words, it serves as a nice natural experiment,” Wood said.

The formation, a sedimentary sequence that can be seen when driving to Cody or McCullough Peaks, underlies portions of the Bighorn Basin and is distinguishable by its red, pink and purple layers.

The formation also contains “quite a few fossil localities” of known mammal fossils—primarily isolated teeth and jaw fragments belonging to the ancestors to modern horses, deer and primates.

The fossils helped date the deposit’s formation at the late Paleocene to early Eocene, a significant time in history due to the Paleocene-Eocene Thermal Maximum (PETM), a large-scale global warming event where the earth reached a local maximum in temperature.

Wood’s research seeks to document climatic and environmental change and the impact both have on mammalian communities in the geologic past. He examines the effects of the PETM in order to understand how the earth responds to smaller climate events.

“I want to see how these small-scale events effected ecosystems, so we have a heads up about what’s coming with modern climate change,” he explained.

Marine sediment samples collected in oceans around the world demonstrate the PETM had a direct effect on precipitation, soils and organisms at the time. Mammal fossils in particular show a much smaller body size at the Paleocene-Eocene boundary.

“This would be an example of what’s called evolutionary dwarfing, where the body size decreased by 15-20 percent over the span of 100,000 years or so,” Wood said.

Smaller mammals were more likely to survive the dry environment and adapt to extreme conditions, since it’s easier for them to radiate excess body heat and obtain the necessary water and food.

“We have changes in the ecosystem, changes in how soils were developing, all due to these drastic changes in temperature and precipitation.”

Using evidence of a small-scale global warming event documented in marine sediments, Wood worked to identify traces of this event in the rocks of the Willwood Formation. 

His team collected samples at two localities from the same interval of time, pulling calcium carbonate modules from the formation to measure the carbon cycle by drilling powder that represented the carbon dioxide composition that existed in the soil when it was formed.

Wood determined that “the impacts on the mammals and the environment during this event were not as severe as those of the larger-scale global warming event. We don’t see any dwarfing or any major impacts in soil moisture.”

His conclusion is simple.

“If the amount of global warming is smaller, we expect the scale of the effect would also be smaller. The temperatures increased a little bit, but not to the point where it caused stress on the organisms living there.

“So if we do reduce our carbon emissions in the future, the amount of climate risks will also be reduced. Our natural experiment from the Willwood Formation seems to support that idea.”