Scientists in northern Japan have resolved the mystery behind the amber layer on the seafloor. They uncovered evidence that a powerful tsunami may have carried large amounts of tree resin into the ocean more than 100 million years ago, leaving behind one of the oldest known geological traces of such an event.
The discovery was made in the Shimonakagawa Quarry on the island of Hokkaido, where layers of amber, a fossilized form of tree resin, were found embedded in rock that once lay at the bottom of the sea. The sediment dates back to the Cretaceous period, approximately 114 to 116 million years ago.
Amber typically forms on land, as it originates from tree resin that hardens after exposure to air. Its presence in ancient deep-sea rock has long puzzled researchers.
In a new study published in Scientific Reports, geologist Aya Kubota of the Geological Survey of Japan and her team propose a striking explanation: a massive tsunami swept the resin from land into the ocean, where it became trapped in seafloor sediment.
Clues point to sudden submersion during a tsunami
The team found flame-like distortions in some amber, suggesting the resin had not yet fully hardened when it was engulfed by water. These stress marks, visible under fluorescence analysis, indicated the resin was still soft—a key clue pointing to sudden submersion.
The study adds to a growing body of research on paleotsunamis, ancient tsunamis that predate written records. While tsunamis have shaped coastlines for millions of years, physical evidence from earlier geological periods is rare and difficult to confirm. Most known tsunami deposits date to the past 10,000 years, during the Holocene.
“What they show in this study is super exciting, because this is obviously a deposit from a tsunami,” said Beverly Goodman, a tsunami expert at the University of Haifa who was not involved in the study.
Japan’s geology supports the tsunami theory
Japan’s geography supports the theory. Hokkaido lies at the meeting point of four tectonic plates, making it one of the most earthquake-prone regions in the world. According to the study, the likely trigger was a massive landslide several hundred kilometers from the quarry.
The collapse of a large marine platform, once the biggest in the Northwest Pacific during the Jurassic-Cretaceous era, may have generated the waves that carried the resin out to sea.
In the ancient forest, trees produced thick resin layers, some fossilized into amber. Much of it likely fell to the forest floor. When the tsunami struck, the resin, along with bark and other forest material, was dragged into the sea, where it became sealed in time.
As researchers continue refining methods for identifying tsunami deposits, they expect to uncover more examples hidden in the rock record.
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