Enormous structures discovered under the North Sea

 Scientists stunned by enormous structures and colossal formations discovered under the North Sea

Beneath the North Sea, scientists have uncovered colossal sand formations, dubbed “sinkites,” which have mysteriously sunk into lighter sediments, flipping the usual geological order. Formed millions of years ago by ancient earthquakes or pressure shifts, these giant structures could reshape how we locate oil, gas and safe carbon storage sites. The discovery not only challenges established geology but also introduces a new partner phenomenon, “floatites,” and sparks debate among experts. A new peer reviewed study shows that heavy, younger sands sank downward while older, lighter layers rose, forming hidden hills under the seafloor. The team stitched together a huge three dimensional seismic dataset with evidence from many wells to show that the mounds occupy an area of roughly 19,000 square miles. The work points to a process that can scramble the usual order of layers and change how scientists judge the safety of places which might store captured carbon. Geologists usually rely on the law that older layers sit below younger ones unless the rocks have been overturned. In the North Sea case, the rule is broken locally because dense sand pushed downward while lighter material rose. The lighter layer is a stiff, low density mud known as ooze which grew from the remains of tiny sea life. The heavier layer is younger, loose sand which slumped down through cracks and then spread, propping up rafts of ooze from below. The result is stratigraphic inversion, a flip in the expected stacking order. The team names the sand bodies that sank sinkites and the ooze blocks that floated up floatites.

Massive buried sand mounds under the North Sea, formed millions of years ago, are defying geological norms and could change energy exploration and carbon storage strategies. These hundreds of giant sand bodies beneath the North Sea which appear to defy fundamental geological principles and could have important implications for energy and carbon storage. 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 km's 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. These features do not look like simple landslides or standard sand intrusions. Their scale, shape and relationship to fractures in the ooze point to a different driver. During strong shaking, wet sand can lose strength and move like a fluid, a process called liquefaction. If that liquefied sand rests above a stiffer but lighter layer, the dense slurry tends to sink and the lighter layer tends to rise. That push and pull creates buoyancy driven instability. The ooze, cut by natural polygon patterns of small faults, breaks into rafts that lift while sand funnels down along the fractures.

While stratigraphic inversion has previously been observed at small scales, the structures discovered by the Manchester team, 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." Earthquakes in the region millions of years ago likely triggered multiple rounds of movement. Each pulse would have let more sand drop and more ooze lift until the energy died away and the system locked in place. Seismic reflections reveal sharp boundaries between the ooze and the sand intrusions. The mounded zones are confined to a specific slice of the rock record, while layers above and below remain mostly undisturbed.

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'. In places, thin fractures filled with sand connect the intrusions below to sands above, a sign of downward movement rather than sand injected from great depth. The chemistry and grain makeup of some buried sands also match nearby overlying sands, backing the same conclusion. The mounds form ridges and pods that mirror the size and orientation of the surrounding polygonal faults. The map view geometry fits the idea of sand sinking along fracture networks while ooze rafts rise between them. Engineers are already injecting carbon dioxide into a large North Sea sandstone known as the Utsira, part of the long running Sleipner project. Any new process which moves fluids or shifts layers underground matters when picking safe, durable storage targets. Understanding whether sands could move and whether seals remain tight helps planners estimate long term behaviour. It also guides where to avoid injecting and where to watch most closely.

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." The North Sea stores of pore space are huge, but safety depends on the details of the rocks at each site. Findings like these sharpen the checklist used to evaluate storage security. Regional and detailed maps of mounds and sinkites under the North Sea, illustrating their distribution, orientation and morphology. “This discovery reveals a geological process we haven’t seen before on this scale. This research shows how fluids and sediments can move around in Earth’s crust in unexpected ways,” said Mads Huuse, a geophysicist at the University of Manchester who led the study. The data favour a model where sand sank as a slurry while ooze rose as rigid rafts. Even so, scientists want to test how often such flipping happens, how large the units can grow, and what levels of shaking are needed to start movement. Another question is timing. Evidence suggests activity clustered in the late Miocene and Pliocene, but the exact sequence of pulses and pauses varies across the basin.

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." Geologists mapping buried landscapes use shape, texture and context to decide whether a body is a channel, a landslide or an intrusion. Sinkites add a new category with its own fingerprints, such as serrated edges where sand fills polygonal fractures. For industry and storage projects, the work adds new cues for spotting zones where density contrasts once rearranged the stack. It also warns against assuming that all thick sands formed where they now sit. Future surveys can target other continental margins where light biogenic mud sits below younger sand. If similar structures appear elsewhere, the process is not a North Sea quirk but part of a broader pattern. More lab tests and computer models can explore how liquefied sand moves through fractured layers. This would helps turn a striking field observation into rules which can be predicted, when and where inversion will occur in the future ahead.