The Bakken Shale Formation—a 200,000-square-mile shale deposit below parts of Canada and North Dakota—has supplied billions of barrels of oil and natural gas to North America for 70 years. A new discovery reveals that the rocks also open a uniquely informative window into Earth's complicated geological history.
A research team, which included geologists from the University of Maryland, George Mason University and the Norwegian oil and gas company Equinor, developed a new framework for analyzing paleontological and biogeochemical data extracted from the formation's rock.
Using this technique, the team pinpointed a major trigger of several closely spaced biotic crises during the late Devonian Period almost 350 million years ago: euxinia, or the depletion of oxygen and expansion of hydrogen sulfide in large bodies of water. Published in the journal Nature on March 8, 2023, the team's findings demonstrate links between sea level, climate, ocean chemistry and biotic disruption.
"For the first time, we can point to a specific kill mechanism responsible for a series of significant biotic disruptions during the late Devonian Period," said UMD Geology Professor Alan Jay Kaufman, a senior author of the paper. "There have been other mass extinctions presumably caused by expansions of hydrogen sulfide before, but no one has ever studied the effects of this kill mechanism so thoroughly during such a critical period of Earth's history."
According to Kaufman, the late Devonian Period was a "perfect storm" of factors that played a large role in how Earth is today. Vascular plants and trees were especially crucial to the process; as they expanded on land, plants stabilized soil structure, helped spread nutrients to the ocean, and added oxygen and water vapor to the atmosphere while pulling carbon dioxide out of it.
"The introduction of terrestrial plants capable of photosynthesis and transpiration stimulated the hydrological cycle, which kick-started the Earth's capacity for more complex life as we know it today," Kaufman said.
The Devonian Period ended around the same time the Bakken sediments accumulated, allowing the layers of organic-rich shale to 'record' the environmental conditions that occurred there. Because the Earth's continents were flooded during that time, various sediments including black shale gradually accumulated in inland seas that formed within geological depressions like the Williston Basin, the preserved the Bakken formation.
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