Scientists stunned by colossal formations hidden under the North Sea

Using high-resolution 3D seismic (sound wave) imaging, combined with data and rock samples from hundreds of wells, researchers from The University of Manchester in collaboration with industry, identified vast mounds of sand -- some several kilometers wide -- that appear to have sunk downward, displacing older, lighter and softer materials from beneath them.

The result is stratigraphic inversion -- a reversal of the usual geological order in which younger rocks are typically deposited on top of older ones on a previously unseen scale.

While stratigraphic inversion has previously been observed at small scales, the structures discovered by the Manchester team -- now named "sinkites" -- are the largest example of the phenomenon documented so far.

The finding, published in the journal Communications Earth & Environment, challenges scientists understanding of the subsurface and could have implications for carbon storage.

Lead author Professor Mads Huuse from The University of Manchester, said: "This discovery reveals a geological process we haven't seen before on this scale. What we've found are structures where dense sand has sunk into lighter sediments that floated to the top of the sand, effectively flipping the conventional layers we'd expect to see and creating huge mounds beneath the sea."

It is believed the sinkites formed millions of years ago during the Late Miocene to Pliocene periods, when earthquakes or sudden shifts in underground pressure may have caused the sand to liquefy and sink downward through natural fractures in the seabed. This displaced the underlying, more porous but rigid, ooze rafts -- composed largely of microscopic marine fossils -- bound by shrinkage cracks, sending them floating upwards. The researchers have dubbed these lighter, uplifted features 'floatites'.

The finding could help scientists better predict where oil and gas might be trapped and where it's safe to store carbon dioxide underground.

Prof Huuse said: "This research shows how fluids and sediments can move around in the Earth's crust in unexpected ways. Understanding how these sinkites formed could significantly change how we assess underground reservoirs, sealing, and fluid migration -- all of which are vital for carbon capture and storage."

Now the team are busy documenting other examples of this process and assessing how exactly it impacts our understanding of subsurface reservoirs and sealing intervals.

Prof Huuse added: "As with many scientific discoveries there are many skeptical voices, but also many who voice their support for the new model. Time and yet more research will tell just how widely applicable the model is."

This research has been published in the journal Communications Earth & Environment.