Scientists from Brazil and Britain were investigating the ocean floor near a volcanic plateau called the Rio Grande Rise. As they observed footage from their remotely operated submersible 650 meters (2,100 feet) below, they noticed some unusual rocks.
These rocks had layers of red clay, something not commonly found on the seabed. Bramley Murton, a marine geologist from the National Oceanographic Centre in Southampton, U.K., who was part of the team, described the deposits as resembling soils found in tropical regions.
A recent study conducted by the team revealed that the unique minerals present in the clay could have only been created through weathering in tropical conditions. This discovery adds to a series of findings suggesting that this particular area of the ocean, located 1,200 kilometers (750 miles) from Brazil’s coast, may have been an island in the past.
“Imagine a lush tropical island slipping beneath the waves and lying frozen in time. That’s what we’ve uncovered,” said Murton, the study’s co-author.
He and his colleagues believe that this island would have been approximately the size of Iceland, which is about a fifth of the total area of the Rio Grande Rise.
Rio Grande Rise goes back to 80 million years
The Rio Grande Rise has a history dating back 80 million years. At that time, a massive mantle plume existed beneath the mid-ocean ridge of the South Atlantic, leading to a period of intense volcanic activity.
Murton explains that initially, the rise resembled a Cretaceous version of Iceland and was situated closer to the mid-ocean ridge than its current location near South America. Over time, as volcanic activity decreased, the plateau slowly drifted westward across the Atlantic Ocean and eventually submerged beneath the waves.
Around 40 million years ago, the mantle plume experienced a final burst of volcanic activity, but this time, it was confined to the western part of the rise.
It was in this specific area that the researchers discovered the red clays, which were sandwiched between lavas known to be approximately 45 million years old, as reported by Live Science.
Underwater ancient beach terraces and drowned waterfalls
The research represents the outcome of two scientific expeditions conducted in 2018 to explore the Rio Grande Rise.
The first expedition aboard the Brazilian research vessel Alpha Crucis focused on mapping the underwater terrain of the rise using sonar technology. Initially, the project aimed to study mineral-rich ferromanganese crusts found on the rise’s seafloor.
During the mapping process, the researchers made several significant discoveries. They identified a steep-sided canyon called the Cruzeiro do Sul Rift, which stretches for 30 kilometers (about 20 miles) and divides the rise.
Additionally, they found evidence of ancient beach terraces, wave-cut platforms, and submerged waterfalls.
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