Science Moab: Ancient Oceans, Petroleum, and Orogeny

More than 65 million years ago, a sea route crossed North America from what is now the Gulf of Mexico to what is now Alaska. Peter Flaig is a research scientist at the Bureau of Economic Geology in Austin, Texas, and has studied the geology of this seaway by examining deposits from the southwestern United States to Canada and Alaska. We spoke with Flaig about the margin of this seaway which included parts of the present Colorado Shelf.

Science Moab: Can you tell us a bit about the Western Interior Seaway, the prehistoric ocean that runs through western North America?

Flag : [The Western Interior Seaway was] a sea route that crossed the continent and then finally disappeared. It was hundreds of meters deep, but not as deep as the continental shelf. There were sediments coming out of the Sevier orogeny. The Sevier Orogenic Belt buckled the lithosphere and created this large inland basin along the continent which filled with water. In this inland seaway, the deposits of rivers and floodplains enter as deltas and shorelines along this rather complex coastline that crossed all of North America. The seaway separated Laramidia from Appalachia. [Laramidia was a landmass that stretched from modern-day Alaska to Mexico. -ed.]

Science Moab: How have the shoreline and water levels of the Seaway changed over time?

Flag : You would have tens to hundreds of meters of sea level fluctuation. different deposit stacked on top of each other. You could start with a very wide sea lane in a place with deltas, beaches and even offshore deposits. As the Seaway narrows, these shores move east [and in that location] coastal plains are forming above these ancient shorelines, so now you have trees in peat swamps and river systems and dinosaurs that lived on these coastal plains. As the Seaway expanded, [that location would again] return to more marine conditions.

Moab Science: The Mancos Shale is one of the deepest parts of the basin, isn’t it?

Flag : Think of the Mississippi Delta: if you were to walk the sub-aerial part of the delta and start walking in the Gulf of Mexico, the farthest front of the delta. Eventually you would be in hundreds of feet of water where you would lose any coarse-grained sediment, such as sand. You’re just depositing silt and mud. The Mancos Shale is that deeper part of the system, where you’ve passed all of the actual coarse-grained sediment inputs and you’re just depositing these very fine silts and muds. It’s a big part of the basin, and it saves a lot of time.

Science Moab: Do Seaway deposits have economic value?

Flag : The oil and gas industry is very interested in the Seaway deposits because the outcrops are incredible. When people drill oil and gas reservoirs, they get a Swiss view of what’s going on underground. These wells can be widely spaced and it is very expensive to drill cores. The Book Cliffs can provide us with outcrop analogues for these underground reservoirs. It’s not that they are necessarily reservoirs; they may be, but they represent what we cannot see in the basement. What could be a good reservoir and how connected it is over long distances, the Book Cliffs give us this continuous exposure.

Science Moab: What first made you want to study the Seaway?

Flaig: Well, the Bureau of Economic Geology was looking for someone to go and see these outcrops as analogous to reservoir systems. One of the best places to do this is in the Book Cliffs, so I started using them as outcrop analogs for reservoirs for people all over the world. Then I became very interested in the Seaway deposits in terms of what kind of plants and animals they preserve, what they can tell us about the evolution of the interior of South America North and the natural things that happened to this planet because of the wax. and the decline of glaciers. What does it look like when humans aren’t around? We want to understand if we are doing something with the planet and if we are causing sea levels to rise or temperatures to change.

Science Moab: What excites you about studying the Seaway?

Flag : I’m really interested in what’s going on with the repositories. It is very interesting to examine the repositories to understand why they have the characteristics that they have. The characteristics of these systems then speak of their larger geometries in the subsoil, where the shales are found. For example, in Alaska many of these systems go underground and there are very active oil and gas reservoirs. I’m really interested in looking at the outcrops of these systems and understanding how these features change, and then predicting if we’re going to see the same things underground and asking if we should change our predictions of what’s actually happening.

Science Moab is a non-profit organization dedicated to involving community members and visitors in the science that takes place in southeastern Utah and the Colorado Plateau. For more information and to listen to the rest of this interview, go to This interview has been edited for clarity.

About Lucille Thompson

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