Scientists have made a groundbreaking discovery regarding an ancient tsunami in Japan, revealing compelling evidence hidden within tree amber that dates back to the time of the dinosaurs. The research team found that the amber samples exhibited distinct deformations, suggesting that trees and organic debris were rapidly swept into the ocean and subsequently sank to the seafloor approximately 115 million years ago. This finding, published in the journal Scientific Reports on May 15, indicates that one or more significant tsunamis may have occurred during this period.
Historically, scientists have estimated the occurrence of tsunamis by examining geological evidence, such as massive fossilized boulders that have been transported and deposited along coastlines. Additionally, they analyze abrupt changes in sediment deposits. However, differentiating between tsunami traces and the effects of severe storms can be particularly challenging, as both can leave similar sedimentary patterns. The unique properties of amber, which is fossilized tree resin, provide a valuable record of these catastrophic events, as it can be carried to the ocean when a tsunami displaces trees and other vegetation.
The research team conducted a detailed analysis of amber-rich silica deposits from the Shimonakagawa Quarry located in northern Hokkaido, Japan. These deposits were formed during the Early Cretaceous period, roughly between 116 million and 114 million years ago, at a time when the region was submerged under deep ocean water. Using advanced fluorescence imaging techniques, which involve photographing the amber while exposing it to ultraviolet light, the scientists observed the amber's structural characteristics.
The amber samples revealed a pattern reminiscent of what geologists refer to as flame structures. This deformation occurs when soft sediment is deposited and changes shape before it fully hardens, leading to flame-like tongues emerging between sediment layers. The researchers concluded that the amber was likely swept from land into the ocean by one or more tsunamis, remaining sheltered from air exposure that would have caused it to harden before sinking to the seafloor. This amber was then covered by a layer of silt, preserving it for millions of years.
Identifying tsunamis in the geological record is often a complex task. According to Aya Kubota, a paleontologist at Chuo University in Tokyo and co-author of the study, it was not immediately clear that the unusual amber samples were indicative of tsunami activity. By integrating detailed field observations with the amber's internal structures, the team was able to determine that the most plausible explanation was indeed the occurrence of tsunamis. Supporting evidence from the area further corroborated this hypothesis, including indications of a nearby landslide likely triggered by an earthquake and large chunks of mud that appeared to have been violently displaced from the seafloor.
The findings suggest that examining geological and fossil evidence from the ocean floor—beyond just coastal areas—provides a more comprehensive understanding of past tsunamis. Researchers proposed that analyzing amber deposits can help differentiate between prehistoric tsunamis and severe storms, offering a rare glimpse into depositional processes. As Kubota noted, the emerging field of amber sedimentology holds exciting potential for gaining unique insights into sedimentological processes, moving beyond the traditional focus on organisms trapped within amber samples.
