A new geological study has revealed evidence of a far older chapter in the history of the waters around Formentera, identifying structures beneath the seabed that date back to the Mesozoic, the geological era commonly associated with the age of the dinosaurs.

The research focuses on the Formentera Basin, a deep submarine depression south of Formentera, and concludes that its underlying structure was largely inherited from geological processes that took place hundreds of millions of years ago.

Evidence hidden beneath the seabed

The researchers analysed offshore seismic data to investigate the layers and structures beneath the seafloor.

The Formentera Basin lies at depths of approximately 1,500 to 1,800 metres and occupies a position between the southern Formentera platform and the Émile Baudot Escarpment, one of the major underwater geological structures of the western Mediterranean.

The seismic profiles allowed the researchers to distinguish different geological units and identify faults and other structures buried beneath younger sediments.

A geological structure dating to the Mesozoic

The central conclusion of the study is that the Formentera Basin is not primarily a Neogene structure, as might have been assumed from its more recent geological evolution.

Instead, the authors interpret it as a Mesozoic half-graben system.

A half-graben is a type of geological depression formed when the Earth's crust is stretched and broken by normal faults, causing one side of the structure to sink relative to the other.

According to the study, these extensional structures formed during the Mesozoic and became part of the underlying architecture of the region.

What was the ancient Tethys?

The study links these structures to the former Ligurian-Maghrebian Tethys, an ancient oceanic domain that existed during the geological evolution of the region.

The researchers interpret the southern margin of Formentera and the basin beneath the surrounding waters as part of an ancient passive continental margin associated with the opening of this former oceanic domain.

The Tethys was not the same Mediterranean Sea that exists today. It was part of a much older geological setting that was subsequently transformed by movements of the Earth's tectonic plates.

The findings therefore provide evidence of how the area around the Balearic Islands was structured long before the present-day western Mediterranean took shape.

Triassic salt played an important role

One of the significant features identified by the researchers is the presence of Triassic evaporites, including salt, deep within the geological sequence.

The Mesozoic structures were affected by deformation above these evaporite layers.

Because geological salt can deform plastically over very long periods of time, it can act as a detachment surface along which the rocks above it move.

The seismic data also revealed structures including listric extensional faults, salt diapirs, folds and other features associated with this deformation.

The basin changed again over millions of years

The geological story did not end with the formation of the Mesozoic structures.

Much later, during the Cenozoic, the region experienced additional tectonic processes connected with the evolution of the western Mediterranean and the convergence of the African and Eurasian plates.

The new study finds that these later Neogene processes had a relatively limited effect on the Formentera Basin compared with the much older structures.

The researchers found that major older structures were sealed beneath later geological deposits and that younger sedimentary units were generally only gently deformed.

Not a dinosaur-era landscape visible on the island

The research is significant, but its findings need to be understood precisely.

It does not mean that dinosaur-era rocks have been discovered exposed across Formentera, nor that an ancient ocean survives beneath the island.

The study concerns geological structures preserved offshore beneath the seabed.

Formentera's exposed geology is considerably younger in many areas. Official geological information for the island, for example, identifies Late Miocene formations at locations such as Cala Saona, dating from roughly 11 to 7 million years ago.

The connection with the Mesozoic comes from the deeper geological architecture identified beneath the surrounding waters.

A deeper history of the Balearic Promontory

The findings also help refine understanding of the Balearic Promontory, the broad geological structure that includes the Balearic Islands and extends beneath the surrounding sea.

The area sits between the Valencia Basin to the northwest and the Algerian Basin to the southeast, making it an important location for studying the tectonic evolution of the western Mediterranean.

The Émile Baudot Escarpment is particularly important because it marks a major transition between the thinned continental crust of the Balearic Promontory and the deeper domain of the Algerian Basin.

The newly interpreted structures help researchers reconstruct how this part of the region developed before later tectonic events reshaped the western Mediterranean.

A geological archive hundreds of millions of years old

The significance of the study lies in the geological record preserved below the present-day seabed.

The deepest structures retain evidence of crustal extension during the Mesozoic, while younger sediments record the subsequent evolution of the region through the Miocene, Messinian, Pliocene and Quaternary periods.

In this sense, the Formentera Basin acts as a geological archive, preserving evidence from dramatically different stages of Earth's history.

The research offers a more detailed picture of the ancient geological setting surrounding Formentera and shows that beneath the modern Mediterranean lies a much older tectonic story, preserved in structures that began forming hundreds of millions of years ago.