Western Interior Seaway
Over 65 million years ago, a seaway existed across North America from the present-day Gulf of Mexico to present-day Alaska. Peter Flaig, Research Scientist at the Bureau of Economic Geology in Austin, TX, has studied the geology of this seaway by looking at deposits from the southwest US into Canada and Alaska. We talk with Peter about the margin of this seaway that includes parts of the present-day Colorado Plateau.
Meet the Scientist: Peter Flaig
Peter P. Flaig is a Research Scientist at the Bureau of Economic Geology. His Master’s work took him to the Central Transantarctic Mountains of Antarctica where he examined sedimentation across the Permian-Triassic boundary. Peter collaborated with paleontologists during his PhD research on the North Slope of Alaska that involved identifying the ancient depositional systems and ecosystem of the dinosaur-bearing Prince Creek Formation. He joined the Bureau of Economic Geology in 2009 for a 2 year Jackson School postdoctoral fellowship, and then spent 7 years as lead scientist on fluvial, deltaic, and shallow marine research at the Quantitative Clastics Laboratory Industrial Associates Consortium. Peter now works for the State of Texas Advanced Resource Recovery program and Alaska North Slope Integrated Projects program.
Peter’s research focuses on deposits of clastic and mixed carbonate clastic systems and typically integrates sedimentology, ichnology, paleopedology, high-resolution image capture and analysis, and petroleum geology. He has worked extensively on deposits of the Cretaceous Western Interior Seaway from Texas through the southwestern US (UT, CO, WY), Canada, and into Alaska.
Relevant Links
Follow Science Moab wherever you get your podcasts
Interview Transcript - Where the Sea Used to Be
Science Moab: Can you speak a bit about the Western Interior Seaway, the prehistoric ocean across Western North America?
Flaig: So it’s an epeiric seaway that cut through the continent and then ultimately disappeared. It was hundreds of meters deep, but not as deep as the continental shelf-slope-deepwater system, and didn’t have an abyss. There were sediments that were coming off of the Sevier Orogeny. The loading of the lithosphere by the Sevier Orogenic Belt buckled the lithosphere and created this big interior basin along the continent, and then it filled up with water. And into this Interior Seaway, river and floodplain deposits enter as deltas and shorelines along this pretty complex coastline that ran all across North America. The Seaway divided Laramidia from Appalachia.
Science Moab: How did the shoreline and water level of the Seaway change over time?
Flaig: It was a greenhouse time period, so you’d have tens to hundreds of meters of sea level fluctuation. The shorelines moved towards the center of the Seaway as the Seaway shrank and then backed up towards the outskirts of the seaway as the seaway rose, creating a lot of different depositional environments stacked one on top of another. You might start out with a very wide Seaway. And in one location, you might have deltas and the beach and even offshore deposits. As the Seaway shrinks, those shorelines move to the east. And then you start to prograde coastal plains over the top of those ancient shores and deltas, so now you have trees in peat swamps, and river systems, and the dinosaurs that lived on those coastal plains. As the Seaway again expanded, you returned to more marine conditions.
Science Moab: The Mancos Shale represents one of the deepest parts of the basin, is that correct?
Flaig: Think of the Mississippi Delta: if you were to walk on the actual sub-aerial part of the delta, and you started walking out into the Gulf of Mexico, you would be in the river systems, and then you’d walk to the furthest delta front. Eventually, you would be in hundreds of meters of water, where you’ve lost all of your coarse grained sediments, like sands. You’re just depositing silts and muds. The Mancos Shale is that deeper part of the system, where you are past all of your real coarse grain sediment input, and you’re just depositing those very fine silts and muds in the deepest part of the basin and that’s a large part of the basin, and it records an awful lot of time.
Science Moab: Is there any economic value to the Seaway’s deposits?
Flaig: The oil and gas industry is very interested in the deposits of the Seaway, because the outcrops are amazing. When folks drill oil and gas reservoirs, they have a Swiss cheese view of what’s going on in the subsurface. These wells might be widely spaced, and it’s very expensive to drill core. And the Book Cliffs provide us with outcrop analogs for these subsurface reservoirs. It’s not that they are necessarily reservoirs; they can be, but they represent what we can’t see in the subsurface. What might be a good reservoir and how connected it is over long distances, the Book Cliffs provide us with that continuous exposure.
Science Moab: What are you passionate about studying, with regards to the Seaway?
Flaig: I’m really interested in what the controls are behind what’s going on with the deposits. It’s very interesting to look at deposits to figure out why these deposits have the characteristics that they do. And the characteristics of these systems then speak to their broader geometries in the subsurface, where the shales are. For example, in Alaska, a lot of these systems dip into the subsurface, and there are very active oil and gas reservoirs in the subsurface. I’m really interested in looking at the outcrops of these systems, and understanding how these characteristics change, and what’s driving the changes in these characteristics. And then predict, if we are going to see the same things in the subsurface, and should we change our predictions about what’s actually happening. So I’m really interested in that.
Science Moab: What first made you want to study the Seaway?
Flaig: Well, the Bureau of Economic Geology was looking for someone to go out and take a look at these outcrops as analogs for reservoir systems. We wanted to broaden the outcrop based analog program. One of the best places to do that is in the Book Cliffs, so I initially started just using these as outcrop analogs for reservoirs for people all around the world. But then I became very interested in the deposits of the Seaway with respect to the kind of plants and animals they preserve, what they can tell us about the evolution of the interior of North America, and the natural things that happened to this planet based on waxing and waning of glaciers. What does that look like when humans aren’t around? We want to understand if we’re doing something with the planet and causing sea levels to rise or temperatures to change.
