With a nod to the recent AAPG Distinguished Lecture Program talk “The Shelf is a Dangerous Place: Surfing the Cretaceous Seaway” by Distinguished Lecturer Dr. Lesli Wood, GeoLifestyle will travel back in time to the late Cretaceous.
Sharon Lyon
Editor, GeoLifestyle
The Hell Creek Formation
Prospecting for fossils in the North Dakota badlands.
During a past summer, I had the opportunity to go on dinosaur dig in the North Dakota badlands, near the town of Marmarth. It was both a great experience, and a lot of work. Let’s dig into the Hell Creek Formation:
The Hell Creek Formation of Montana, North Dakota, South Dakota, and Wyoming formed along the late Cretaceous Western Interior Seaway, approximately 67–66 million years ago. Its claystones and sandstones were deposited in swamps, river channels, and deltas.
In western North Dakota, the soft rocks of the Hell Creek have eroded into distinctive rounded hills and hoodoos topped with caprock, known as badland topography.
The K-Pg boundary separating the Cretaceous from the Paleogene is a distinct bed above, and occasionally within, the Hell Creek. Below this boundary are fossils of the last non-avian dinosaurs, and the formation is famous for its dinosaur fossils.
The Hell Creek is the type locality for Tyrannosaurus rex and Ankylosaurus magniventris. The first documented remains of T. rex were excavated in 1902 by Barnum Brown from Hell Creek in southeastern Montana. Today, 95 percent of T. rex museum skeletons have been excavated from these rocks. The formation is also known for its Edmontosaurus and Triceratops skeletons.
The oldest known true alligator, Brachychampsa montana, found in the formation, provides evidence of a subtropical to temperate climate. Its large mouth and short teeth suggest it preyed on turtles. When I scouted for new finds in the badlands, I discovered several fossil turtles, their partial carapaces exposed on the ground.
A message from AAPG Academy and Eliis
Register now to join AAPG Academy and Eliis on 28 January at 9am CST for a free webinar to learn more about downscaling seismic and geological interpretation to construct geological and reservoir models.
Expert speakers Nicolas Daynac from Eliis and Jean-Claude Dulac from Next-Shot@Geomodeling will demonstrate how to:
Use synthetic seismic data from a digitized analogue model alongside real-world basin seismic datasets to show how the Relative Geological Time method enables characterization of depositional sequences at well log resolution
Originally discovered in 2008, the Tanis fossil site documents the cataclysmic moments after the impact of the asteroid that ended the Age of Dinosaurs.
It is postulated that seismic waves from the impact created a seiche (surge of water) up to 300 feet high in the Western Interior Seaway. A bend in an ancient river along the seaway appears to have been flooded with great force. Evidence includes:
Hundreds of densely packed marine and freshwater fish mixed together with marine reptiles, miles inland. The taphonomy of the carcasses, in near-identical states of preservation, demonstrate a sudden mass-death.
Ejecta spherules lodged within the fish’s gills and embedded in amber
Why it matters: As the discoverers state in their 2019 paper, “Tanis provides a postimpact ‘snapshot,’ including ejecta accretion and faunal mass death, advancing our understanding of the immediate effects of the Chicxulub impact.” Read the paper here.
How to Experience the Cretaceous
Dinosaur bone encased in rock; phone case for scale.
In 1966, the Hell Creek Fossil Area was designated a National Natural Landmark by the National Park Service. It is important to note however, that much of the acreage is private, and access is limited.
Fossils from the Hell Creek Formation can be found in many museums including:
You can also volunteer on a field crew through the Badlands Dinosaur Museum. I reached out to Dr. Denver Fowler, curator and co-leader of the field research program, to learn more about this opportunity:
What do you look for in a volunteer?
Fowler: “People with experience digging are good, but we also get novices who've not dug before. About 50 percent of our crew is college students, and the rest is literally everyone else—Retired teachers, firefighters, military veterans, and cadets, and every kind of person. They come from all over the world: the majority are from the United States, but maybe 10 percent are from other countries.”
Where will you be digging this summer?
Fowler: “We are working the Judith River Formation in Montana. Although a famous formation, it has never been heavily collected and has great potential for improving our understanding of Campanian dinosaur ecosystems. I still have some important Hell Creek sites that need excavating, so it's possible we'll hit some in 2025.
What makes your program unique?
Fowler: “I encourage students to publish descriptive research on specimens in our collection. It's a wonderful feeling to help students who want a career in paleontology to get their first paper. Also, we're one of the only free dinosaur digs left in…the world maybe? That said, our digs are not as luxurious as [paid] digs; we work hard in the sun and our camp is very basic, but we eat well, have a lot of fun, have the best shade-tarp system imaginable, and we dig up some of the best dinosaur fossils you will see.”
The bottom line: Dr. Fowler concludes, “Ultimately, we're a scientific research dig, we work on specimens that are scientifically important, and we collect them from public lands and store them in perpetuity for the public in our public museum.”
👍 If you enjoyed this edition of GeoLifestyle, consider supporting AAPG's brand of newsletters by forwarding to a friend or colleague and signing up for our other newsletters here.
➡️ Was this newsletter forwarded to you? Sign up for GeoLifestyle here.
AAPG thanks our advertisers for their support. Sponsorship has no influence on editorial content. If you're interested in supporting AAPG digital products, reach out to Melissa Roberts.
