Brazos River Fossils of Southeast Texas

Adriane here-

A simple location map (inset) and aerial view of the Whiskey Bridge fossiliferous outcrops on the Brazos River.

At the end of January, I was in College Station, Texas sampling sediment cores from my recent IODP expedition (more to come on that soon!) and editing our science chapters. It just so happened that while I was in Texas, I also celebrated my birthday. Of course, I had to do something extra fun, so my friend and I (who also sailed with me last summer in the Tasman Sea) went fossil collecting!

College Station is a relatively small town in southeast Texas, made famous as it is the home of Texas A & M University. There’s plenty of bars and restaurants, dancing spots and cowboy hats (seriously, I’ve never seen so many people wearing cowboy boots!). But if you know where to look, College Station is also home to another gem: Eocene-aged (~41 million years ago) fossils!

My snazzy rental car I drove around College Station !

It just so happened that while I was visiting College Station, I was given a 2018 silver Camaro by the rental car company. Needless to say, we were paleontologists cruising around in style! So my friend and I hopped in the car in our best fossil-collecting gear and made the 15 minute trip to find the ‘most fossiliferous site in Texas’. The outcrop itself is under the Whiskey Bridge on the Brazos River, a bit closer to Bryan, TX than College Station, really. The parking area was located near the bridge, which required pulling off the interstate on a dirt road to get to. Once we were there, it was a short hike under the bridge, and we were instantly in fossil haven!

A view of the outcrop on the Brazos River, under the Whiskey Bridge. Notice how fine-grained and dark the sediments are towards the bottom, then get coarser (chunkier-looking) towards the top. The coarser-grained sediments indicate a sea level fall.

During the Eocene, this part of Texas was covered by a shallow sea, probably between the shore and the shelf-slope margin, with the shoreline estimated to be about 50 miles away. So, this area was never very deep, but comparable to the continental margin of the east coast U.S. today. Because the water was deep enough that energy from waves didn’t reach the bottom, fine-grained sediments accumulated here. Most of the outcrop was very fine-grained and dark in color, which geologists would call a mudstone. The dark color indicates that the rock is high in organic material from animals, plankton, algae, and bacterial that lived in the upper water column when the sea was here. There are also sandstones preserved at this location, indicating that sea level dropped at one point, and that major storms likely brought in thin sands from shore.

A close-up view of the fine-grained sediments that contained fossils.

It’s partly due to the fine-grained material that tons of delicate, tiny fossils were preserved in the strata. The dominant fossils that can be  found at this location are invertebrates, including gastropods (snails), bivalves, scaphopods, bryozoa, and corals. There are few vertebrate fossils preserved, such as shark teeth, gar teeth, otoliths (fish ear bones), and squid beaks. Even rare trace fossils (preserved movements and burrows from animals) can be found, including coiled worm tubes. We didn’t have much time to collect, as we were just supposed to be gone for about an hour over lunch.

Even though we didn’t have much time at the outcrop, we sure did leave with some awesome fossils! Most of what we found were gastropods- species of Pseudoliva, Latirus, Protosurcula, and Turritella. All were small, with some only being about 3 mm in length! There were few clam shells, as they were mostly delicate and fell apart when we tried to pry them out of the sediments. I felt pretty lucky to have found a fish otolith, or inner ear bone (I didn’t realize that’s what it was until I took it out to write this post)! Towards the end of our trip, my friend found a large (~2 inch) shark tooth! It was her first time finding one, so that was pretty thrilling! Content with our finds, we hopped in the car, muddy and happy, to head back to sample cores in College Station.

A small preview of the fossils found under the Whiskey Bridge on the Brazos River. All of these fossils are invertebrates, except the rounded fossil at top center; that is a fish ear bone!

But unfortunately, that wasn’t the end of our journey that day. After being on the interstate for 2 minutes, I was pulled over by a state trooper for speeding 3 mph over the speed limit. The officer asked us where we were going, and that he was only going to give me a warning. I then had to get out of the car to get my license (it was in my book bag in the trunk, with my fossils) when the officer asked what was in my bags. Happy for the distraction, I enthusiastically showed him my fossils and began prattling on about the Eocene, in hopes he would lose interest and let us go. Instead, he was totally interested in the geologic facts I was spouting at him! He then said, ‘I wondered what you two were doing under the bridge’.

So as it turns out, driving a new Camaro onto a muddy dirt road near a bridge is a great way to gain the attention of state troopers.  I’ll be sticking to my muddy, beat up Jeep for future fossil collecting trips 🙂

Click here for a link to field trip guides, fossil ID guides, an outcrop guide, and a link to a paper about the Whiskey Bridge outcrop!

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