Cretaceous Marine Deposits Reveal Evidence of a Massive Ancient Tsunami

Significant amber deposits found in northern Japan may have been propelled from the forest into the sea by tsunamis occurring between 116 million and 114 million years ago during the early Cretaceous period. This is according to a recent study conducted by geological surveys at Japan and Chuo University.

Identifying traces of ancient tsunamis can be challenging, as the powerful waves tend to reshape coastlines. The sediment left behind often resembles deposits created by other high-energy events, like storms.

Nevertheless, amber, which originates on land and is then transported to the sea, acts as a historical record of tsunami occurrences, illuminating the physical processes influencing sediment movement during these events.

“A tsunami is a destructive ocean wave primarily caused by significant changes in submarine or coastal crust, as well as impacts from asteroids,” explains Dr. Aya Kubota, a researcher at geological surveys at Japan and Chuo University.

“They have been extensively studied during the Holocene (the last 11,700 years) due to their relevance in disaster prevention.”

“Aside from asteroid sediments, accurately identifying ancient tsunamis before major vegetation growth is extremely difficult for two key reasons.”

“First, coastal tsunami deposits are easily eroded in their dynamic environments. Second, well-defined criteria for identifying tsunami deposits have not been established, as they can be difficult to differentiate from other high-energy coastal events, such as cyclones.”

In their research, Dr. Kubota and colleagues examined amber-rich silica deposits from the Shiko River Quarry in northern Hokkaido, which formed during the early Cretaceous period around 115 million years ago.

Using fluorescence imaging, the authors discovered that the amber samples exhibited clear deformation in what is known as the flame structure. This occurs when the amber is still pliable at the time of deposition, allowing it to change shape before solidifying.

This suggests that a substantial quantity of amber was swiftly transported from land into the open ocean due to the backwash from one or more tsunamis, experiencing minimal exposure to air.

The amber then settled at the seabed, becoming covered with a layer of silt, which helped to preserve it.

“Other terrestrial sediments carried into open water could be instrumental in studying significant ancient catastrophic events, such as tsunamis,” the researchers concluded.

Their study was published in the journal Scientific Reports on May 15th.

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A. Kubota et al. 2025. Amber, a deep-sea sediment from the Cretaceous period, reveals a massive tsunami. Sci Rep 15, 14298; doi:10.1038/s41598-025-96498-2