The history of the Permian Basin reads like a detective novel in reverse. Geoscientists know how the story turns out. They’re trying to determine exactly how it started.
Robert Stern thinks he and a group of fellow scientists have solved one important part of the mystery. Stern, a professor of geosciences at the University of Texas at Dallas, can draw on a solid scientific basis for that detective work.
He has 3,259 clues.
Over the past decade, unconventional resource development brought back into focus just how prolific the Permian Basin is for hydrocarbons. An area that seemingly topped out in oil production in the 1970s has become the major driver for U.S. crude output growth.
“We need to think about how productive the Permian Basin is. It’s hard for me to get my brain around it,” Stern said.
“If the Permian Basin was an oil-producing country, it would be the fifth largest oil producing country” in the world, he noted.
How Did All Those Nutrients Get There?
Because of that, geoscientists know the Permian Basin had the thermal history to cook up large amounts of crude oil and natural gas. And they know the basin was filled with organic materials – Stern calls them “nutrients” – as a basis for those hydrocarbons.
“We know oil is limited by the nutrients. Oil just doesn’t suddenly appear,” Stern said.
That raises the question, “How did all those nutrients get there?” he observed.
Stern traced the basin’s development back to a critical time as the Carboniferous Pennsylvanian gave way to the Permian period.
“If you think about the tectonic setting at the end of the Paleozoic, you have a big collision to the south,” he said.
That collision involved Gondwana and Laurentia, as the ancient land masses came together and created a new landscape in what is now North America.
Topography and drainages changed. The Ouachita and Alleghanian orogenies occurred. Foreland basin systems developed. And geologic evidence shows Gondwandan sediments were dispersed on southern Laurentia, he noted.
“It’s that Gondwana signal that’s of interest,” Stern explained. “It implies a drainage that reached that area.”
Based on geological and geochemical studies, Stern and five co-authors prepared the paper, “Detrital zircon provenance evidence for an early Permian longitudinal river flowing into the Midland Basin of West Texas.” The paper was in peer review in February for publication.
“We’re arguing that there was major drainage that transported material from Gondwana. There was a major trunk steam flowing into the eastern part of the basin,” he said.
The Zircons Tell the Story
Stern and his fellow scientists base their Big River theory in large part on their study of detrital zircons. Because zircon grains contain uranium, they’ve become important geochronometers through uranium-decay-to-lead (U-Pb) radioisotopic dating.
Traces of Hafnium in zircons also provide information about the rocks from which zircons eroded, with differences from bulk Earth values expressed as epsilon Hafnium (ɛHf) values.
In the abstract to their Permian Basin paper, the authors wrote, “A total of 3,259 detrital zircon U-Pb and 357 ɛHf data from 12 samples show prominent groups of zircon grains derived from the Appalachian (500-270 Ma) and Grenville (1250-950 Ma) provinces in eastern Laurentia and the peri-Gondwana terranes (800-500 Ma) incorporated in the Alleghenian-Ouachita-Marathon orogen.”
That detrital zircon data suggests delivery of Appalachia and Gondwana detritus by a longitudinal river system flowing along the Appalachian-Ouachita-Marathon foreland into the Midland Basin throughout the early Permian, they noted.
“We know that, especially, the Pennsylvanian was a time of heavy biologic activity. Any stream that flows through this will carry a lot of nutrients, just as the Amazon River does today,” Stern said.
In this view, fluvial transport occurred off the Permian highlands to the south and fed into a major river flowing roughly southeast to northwest. What would become the bulk of the North American continent was rotated and situated at the Paleo-equator at the time.
“Tributary channels draining the uplifted Ouachita-Marathon hinterland brought Gondwana detritus into the longitudinal river with headwaters in the Appalachians or farther northeast. This drainage extended downstream westward and delivered sediments into the Permian Basin near the west terminus of the Laurentia-Gondwana suture,” the authors wrote.
The late Paleozoic era was a time of significant geological and climatic change, Stern observed.
Gondwana’s ice sheet “would have been melting and reforming in this period. That would have influenced sea levels,” he noted.
River strength decreased throughout early Permian time, the study found, and Stern said the entire regional system went into “full collapse by the Triassic, to open the Atlantic and Gulf of Mexico.”
In addition to the detrital zircon evidence, the study used sedimentological data and wireline log correlation to analyze early Permian deposits in the Midland Basin.
“We’re mostly interested in the early Permian, the Sprayberry (formation) and the Dean (sandstone). That’s where a lot of the action is,” Stern said.
In the Interest of Science
He credited Pioneer Natural Resources for providing the material that contained the detrital zircons and other inputs for study – in the interest of science.
“We couldn’t imagine that this was going to give them any economic advantage, but companies used to give people science just to keep them thinking,” Stern said.
And he would value additional scientific work by the oil and gas industry to reveal more about the early Permian Basin, without great hope of that happening. An industry that “used to invest” in pure-science research seems to have shifted its position, he noted.
Today, “no company is going to drill for science in the Permian Basin. People would say, ‘You’re crazy. Are you kidding? You drill here for oil,’” Stern said.
To stimulate scientific interest in the basin and raising public awareness, the UT-Dallas Geoscience Department last year formed the Permian Basin Research Laboratory.
“What we want to do is talk to our students and the general public about the Permian Basin, all aspects of it,” Stern said.
The latest study contributed to that mission in looking more broadly and much deeper into the Permian Basin’s origins and early history, he noted.
“That’s part of the idea – starting to think bigger about the basin,” Stern said. “The whole point is trying to start a scientific conversation about the Permian Basin.”