Anomaly in Deep Sea Sediments May Serve as Geological Time Marker

Anomaly in Deep Sea Sediments May Serve as Geological Time Marker
by Robert Schreiber
Berlin, Germany (SPX) Feb 12, 2025
Beryllium-10, a rare radioactive isotope formed by cosmic rays in the atmosphere, is providing new insights into Earth's geological past. A research team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), in collaboration with TUD Dresden University of Technology and the Australian National University (ANU), has identified an unexpected concentration of this isotope in deep-sea samples from the Pacific Ocean. This anomaly, dating back approximately 10 million years, may have resulted from shifts in ocean currents or astrophysical phenomena. The findings, published in Nature Communications (DOI: 10.1038/s41467-024-55662-4), suggest that this event could serve as a global chronological marker for dating geological records.

Radionuclides, which decay into other elements over time, are commonly used for dating archaeological and geological samples. Radiocarbon dating, for example, relies on the decay of carbon-14 (14C) in organic material. However, its effectiveness is limited to samples up to 50,000 years old.

"For dating beyond this range, other isotopes like cosmogenic beryllium-10 (10Be) are necessary," explains HZDR physicist Dr. Dominik Koll. This isotope forms when cosmic rays interact with atmospheric oxygen and nitrogen, eventually accumulating in marine sediments through precipitation. With a half-life of 1.4 million years, 10Be is a useful tool for dating events that occurred over the past 10 million years.

Unusual Beryllium-10 Accumulation Detected

Koll's team analyzed geological samples retrieved from several kilometers beneath the Pacific Ocean. These ferromanganese crusts, composed mainly of iron and manganese, have formed steadily over millions of years. Using Accelerator Mass Spectrometry (AMS) at HZDR, the researchers detected an unexpected spike in 10Be levels at around 10 million years ago-almost twice the anticipated concentration.

"To our surprise, we found nearly double the expected amount of 10Be at this point in time," says Koll. "This represents a previously unknown anomaly." Additional samples from different Pacific locations exhibited the same pattern, confirming the phenomenon's authenticity and ruling out contamination.

Possible Explanations: Oceanic or Astrophysical Origins?

Koll and his colleagues propose two possible explanations for this anomaly. The first involves changes in ocean circulation. Around 10 to 12 million years ago, significant shifts in currents near Antarctica may have altered the global distribution of 10Be, leading to its concentration in certain regions like the Pacific.

Alternatively, the anomaly might have astrophysical origins. A nearby supernova could have temporarily increased cosmic radiation levels, leading to enhanced 10Be production. Another possibility is that Earth temporarily lost the shielding effect of the heliosphere due to an encounter with a dense interstellar cloud, exposing it to greater cosmic radiation.

"To determine whether oceanic processes or astrophysical events caused this anomaly, further research is needed," notes Koll. "Our goal is to analyze additional samples, and we encourage other research groups to investigate this phenomenon." If the anomaly is detected worldwide, an astrophysical cause is likely. If it is localized, changes in ocean currents would be the more probable explanation.

A New Geological Time Marker?

If confirmed globally, this anomaly could provide a valuable tool for synchronizing geological records. "One of the biggest challenges in geochronology is aligning different archives over vast time periods," Koll explains. "Currently, no cosmogenic time markers exist for such long spans. This anomaly might change that."

Research Report:A cosmogenic 10Be anomaly during the late Miocene as independent time marker for marine archives