Friday, 15 July 2016 15:36

Secrets in the Sandstone of Capitol Reef National Park

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Published in Microbial Sciences

Figure 1 Scott Chimileski Capitol Reef
Figure 1. A very helpful and friendly ranger, Rick Thorum, signs our backcountry camping permit. Photo by: Scott Chimileski

“So, you're like Indiana Jones?” asked Rick, one of the rangers at Capitol Reef National Park, as he signed our backcountry camping permit. I had just been explaining to Rick how my brother and I were in Utah to find fossilized stromatolites—a record of microbial life in the Navajo Sandstone from the early Jurassic—located deep within the park. I told him how we were also going to Yellowstone in Wyoming to see living stromatolites, and that it was all part of a microbial science photography expedition in celebration of the National Park Service centennial.

But let’s hold back on the adventure for a moment. To appreciate the fossils that we were looking for, we need to reimagine life on Earth as we know it. We’re used to thinking about ecosystems as pyramids of trophic levels, with large predators and herbivores at the top. But what if all macroscopic plants and animals suddenly cleared off the pyramid, leaving only microbes? It seems strange, yet this is exactly how ecosystems existed before the Cambrian explosion. And it remains the way of life in some places on Earth today—places that are too hot or cold, too acidic or alkaline, or too salty for animals to live.

Figure 2 Scott Chimileski Capitol ReefFigure 2. Screenshot of a satellite map (left) and view of the terrain (right) as we drove off-road towards the entry point. Photos by: Scott Chimileski.

In the absence of snails and other grazing macrofauna, microbial primary producers like cyanobacteria take in energy from the sun and produce thick biofilms, establishing the base of a different kind of food web. The visible form of this ecosystem is a multispecies microbial mat. When microbial mats develop in layers and solidify in place over time (due to interactions with minerals and sediment), we call them stromatolites. Part rock, part microbe, stromatolites are often shaped as mounds or columns and were once common in shallow waters across the planet. 

We were searching for a trace of one of these bizarre microbial worlds from the past.

Now, back to Rick’s question. I have to admit, the real Indiana Jones in this context would be Len Eisenberg: the geologist who discovered the stromatolite fossils in Capitol Reef. Yes, it would be the most physically demanding segment of the trip, in the hottest, most arid, and isolated location we would visit. We would be hiking on unmarked trails that are traveled more frequently by wildlife than by people. To reach the trails, we would drive off-road for ten miles. The key difference was, Len found the fossils during an extended backpacking trip over 15 years ago. My brother and I, however, had been in contact with Len and had the advantage of following his maps.

Figure 3Figure 3. Backcountry area within Capitol Reef National Park showing carbonate outcrops containing stromatolite fossils. These formations stick out as more delicate sandstone erodes around them. Photo by: Scott Chimileski.

There was one slight complication: it was forecast to be dangerously hot in southern Utah that weekend.

Our first objective was to reach the parking location. We drove down a narrow 4x4 road for one hour, through river crossings and over some seriously sketchy inclines, declines, and rocky ledges. I knew the topography of the canyon that we needed to hike into and tracked our GPS position with the landscape. We arrived at the parking location with about two hours of light left, which meant we had to move with a purpose to find a campsite, although at least the midday heat had dissipated.

We climbed to a natural wash and followed it through the canyon for a few miles, hoping to get close to the stromatolite outcrops before dark. As the sun set, I recalled some of Len’s last bits of advice: “Bighorn sheep are around, as well as cougars, so if alone, look up when you go under a tree or a ledge.” While it would have enlivened the story … we did not encounter any mountain lions. Instead, we set up our tent in a soft bed of sand beside a rock wall, and after watching the stars in the Utah dark sky, we went to sleep.

Figure 4Figure 4. Closer views of the stromatolite outcrop in Figure 3 (left; white marker is 2 meters) and its laminated texture (right). Photos by: Len Eisenberg

It was surprisingly cool early the next morning. We wasted no time, packed up and pushed further into the backcountry. As we scaled a small cliff and into a hidden valley near the outcrops, the sun began to heat the land. The cool air was gone in what seemed like minutes and just when we reached the first area of interest, it was 100 degrees Fahrenheit.

I photographed several stromatolite fossils at this site, with the air getting hotter and the sun more intense. Though we had prepared for the heat and had enough water, we decided to be on the safe side and head back to escape the afternoon sun, rather than hiking to any further outcrops. Nevertheless, the short visit was worth every speck of dust and drop of sweat. Because these aren’t just any fossils.

The stromatolites in Capitol Reef have the potential to change a longstanding view of this entire paleo environment. If we went back to the early Jurassic, as our mammalian ancestors were just beginning to evolve, the Navajo Sandstone in what is now Utah would be one giant sea of blowing sand dunes. This prehistoric domain is known as the Navajo erg and has been compared to present-day hyperarid deserts like the African Sahara.

But how could stromatolites form in the Navajo erg without any water? Based on growth rates of modern analogs, the stromatolites in Capitol Reef arose within an aquatic setting for anywhere from 2,000 to 10,000 years. These estimations suggest that there was once a stable network of freshwater lakes between the dunes. The lakes likely accumulated as rainfall pooled behind a blocked drainage. And as the theory continues, when this dam eventually breached, the stromatolites became buried by a massive flow of wet sand, only to reemerge after eons of erosion.

Figure 5 1Figure 5. Millimeter-scale laminations and convex forms within Capitol Reef stromatolite fossils. Cross-section from L. Eisenberg collection, Photo by: Scott Chimileski

I will return to Capitol Reef to see the other stromatolite outcrops. In the meantime, I feel grateful for this national park. To hike into a majestic desert landscape, to envision life as it was 200 million years ago, within a lake so ancient that it existed on the supercontinent of Pangea—it really was about as close to an “Indiana Jones” experience as a microbiologist can get.


Further Reading

A few places where you can find stromatolites forming today



Last modified on Tuesday, 16 May 2017 15:02
Scott Chimileski

Senior Contributor Scott Chimileski is a Research Fellow in Roberto Kolter’s laboratory at Harvard Medical School and a member of the ASM Writer Team. Scott's research is focused on imaging biofilms and other microbial multicellular forms. He is a photographer, coauthor of the book Life at the Edge of Sight: A Photographic Exploration of Microbial World, and is currently spearheading several exhibitions on microbial life at the Harvard Museum of Natural History. You can find him on Twitter @socialmicrobes.