Lovers of Big Bend National Park know it’s inexhaustible: There’s always something new to discover here. That’s abundantly true in the realm of geology.
Visible in the park’s southeastern corner, near the hot springs and Boquillas Canyon, the Boquillas Formation is a series of limestones and shales, in white, tan, yellow and brown. These rocks were laid down in shallow ocean waters across 10 million years, and they abound in fossils, which capture the emergence and extinction of countless creatures. Here, geologists are tracing a vivid account of an ancient chapter in Earth’s history.
Jordan Todes is a University of Chicago PhD student.
“When I personally think of Big Bend, the things that stand out to me are the Chisos Basin, that bit of the park,” Todes said, “and in many ways that Boquillas area is somewhat of an afterthought. But in terms of the types of work we're doing it is – I wouldn't even just say world-class, but probably unmatched globally. It's that remarkable of a place.”
In 2018, as a Fulbright scholar in Poland, Todes connected with Irenuesz Walaszczyk, an expert on the Cretaceous Period. The Cretaceous lasted 80 million years. It ended 66 million years ago, with the extinction event that decimated the dinosaurs. Details of that immense timespan remain mysterious. And as Todes and his mentor considered how to unravel those mysteries, Big Bend called.
When the Boquillas Formation was created, between 97 and 86 million years ago, Big Bend was a marine crossroads. Here, the Western Interior Seaway, which cut North America in half, met the Atlantic and the ancient Tethys Ocean. The fossils testify to a teeming diversity of sea life – with creatures like ammonites, crinoids and shelled mollusks known as inoceramids.
The Boquillas Formation is 600 feet thick. It s fossil record reveals the development of life in stunning detail, Todes said.
“It's so expanded that you're able to really kind of pick up on these subtle trends that you really wouldn't be able to pick up on elsewhere,” he said. “Already we can tell that the evolutionary trends in this time interval were a lot more complicated than we thought they were beforehand.”
The inoceramids are especially important. These marine bivalves had a global distribution. In the Boquillas Formation, the geologists can trace their evolution, linking individual species with specific times. Big Bend could become a reference point – if geologists find the same inoceramids elsewhere in the world, they’ll know the age of the rock they’re working with.
Todes’s samples will be sent to Poland. There, scientists will use isotope analysis to date the rocks. And they’ll examine “microfossils” – the tiny shell remains of single-celled creatures. The fossils with ultimately be housed at the Smithsonian Institution.
In fact, one especially beautiful ammonite – its spiral form 18-inches wide – is already there.
“That one got shipped straight to the Smithsonian,” Todes said. “They weren't even going to let us take that to Poland, which is absolutely fair. This thing is magnificent.”
The geology is spectacular. But part of what makes these rocks so valuable is that they’re in a national park, Todes said. The park not only offers access to researchers, but it supports them, including providing lodging at its field station.
“It might seem like a trivial thing to have a small house where you can go back to at the end of the day instead of camping,” Todes said. “But it genuinely is a really big part of why we're able to accomplish as much as we can.”
The research is a reminder – that Big Bend always rewards close attention.
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