Wrinkles in Time: The Jurassic Mystery Beneath Morocco
The outcrop in Morocco where Associate Professor Rowan Martindale noticed the wrinkle structures formed by microbial communities. Note that the large ripples on the rock slab were formed by turbidity currents. The wrinkle structures are a more subtle texture that overlays the larger ripples. Credit: Rowan Martindale.
A chance discovery on a Moroccan hillside challenges long-held assumptions about mysterious wrinkle-like textures preserved in ancient rocks.
In 2016, while hiking in Morocco, geologist Rowan Martindale, associate professor at The University of Texas at Austin’s Jackson School of Geosciences, spotted a slab of sedimentary rock etched with a pattern resembling elephant skin. “I looked at the wrinkles and I was like, ‘These aren’t supposed to be in rocks like this. What the heck is going on?’
To Martindale, former postdoctoral researcher in Professor Emeritus Andrew Knoll's lab, the textures were unmistakable: fossilized microbial mats dating back more than 180 million years to the Early Jurassic. She had seen similar examples during graduate school. But there was a problem. The rocks formed nearly 600 feet below the ocean’s surface, in deepwater conditions. Conventional wisdom holds that microbial wrinkle structures are limited to shallow, sunlit waters or stressful environments following mass extinctions. In deepwater settings, geologists typically attribute such ridges and furrows to underwater landslides.
Martindale wasn’t convinced. In a recent paper published in Geology, Martindale and co-authors, including Professor Peter Girguis — whose research focuses on modern deep-sea chemosynthetic communities — propose that an underwater landslide did occur, but instead of sculpting the wrinkles directly it delivered nutrients that fueled chemosynthetic microbial mats on the seafloor. These microbes derived energy from chemicals rather than sunlight and may have emitted toxic sulfur compounds that kept predators away. Modern analogs include microbial mats that flourish on whale falls in the deep ocean.
“This study shows the value, and challenges, of using modern ecosystems to better understand paleontological data," said Girguis. "When Dr. Martindale and her paleontology colleagues showed us pictures of “wrinkles” in ancient sediments we noticed some similarities to features we had seen at our deep-sea study site off Southern California. Rowan brought together a team of collaborators to think critically about what the modern observations can, and cannot, tell us about the ancient sediments. The study discusses these details and reminds us that science benefits from a diversity of perspectives and expertise.”
Martindale says the findings suggest chemosynthetic microbial fossils may be more common than previously recognized — and that some may have been misclassified due to vague terminology surrounding “wrinkly” rock textures.