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Giant sand structures at the bottom of the North Sea have puzzled scientists for years. Now researchers have learned that they were formed as a result of geological process, which has never been observed on such a scale before.
Seismic data and rock samples from the northern part of the North Sea, off the coast of Norway, show, that sand dunes several kilometers wide sank many millions of years ago and brought up even older, less dense silt. The findings may allow scientists to learn more about the options for burial and storage of CO₂.
Researchers have been aware of these giant sand mounds for many years, but have not yet had a consensus on their formation. It has been suggested that these mounds were formed as a result of landslide deposits, pushing sandstone from below or pushing dirt through fragile rock.
Using a three-dimensional seismic dataset from the northern North Sea and rock samples, the scientists investigated these mounds and the surrounding area. They found that these geological structures was surrounded by ancient dilute liquid mud, consisting mainly of fossilized remains of ancient microorganisms.
The chemical composition of these mounds resembled the sands around them, which are found in geological deposits that appeared later. In some places, the mounds were connected to these sands through cracks in the rock. In this regard, the researchers suggested that. The hills were formed by younger sands that were buried under ancient, lighter silt. These sands differ from the usual geological pattern of deposits, as ancient rocks usually lie deeper than younger deposits.
«This discovery reveals a geological process that we have not previously observed on this scale. We found structures where dense sand had sunk into lighter sediments that had floated to the surface, effectively inverting the usual layers we would expect to see and creating huge hills on the seabed», — the study’s co-author notes, is a geophysicist at the University of Manchester, Mads Huus.
Earthquakes or sudden pressure changes could have caused the sands to become liquid-like, allowing them to easily slip through cracks in the seabed and slipped beneath the solid areas of silt. The researchers called these sand hills settling on the bottom, «synkites», and silt layers rising to the surface — «floatites».
Initially, scientists explored these hills as a potential CO₂ storage site. However, before Before any carbon storage work can begin in this region, scientists need to understand how well and safely the area can store it.
The results of the study are published in the journal Communications Earth and Environment
Source: LiveScience