Mesozoic to Paleogene tectonic evolution of Sardinia

During the Mesozoic and Paleogene, following the Variscan Orogeny and the assembly of Pangea, and prior to the Sardinia-Corsica drift associated with the opening of the western Mediterranean, the Sardinia lithospheric block formed part of the southern European continental margin. Reconstructing the tectonic evolution of Sardinia in this time interval is therefore essential to better understand the large-scale geodynamic processes and plate kinematics involving Europe, Iberia, Adria and Africa that ultimately lead to the Pyrenean, Alpine and Apennine orogenesis. However, the Mesozoic and Paleogene tectonic evolution of Sardinia remains poorly constrained. This contribution summarizes the main structural evidence for Mesozoic-Paleogene tectonics in Sardinia and attempts to correlate it with the major geodynamic events affecting the southern European margin.

The Mesozoic to Paleogene stratigraphic succession of Sardinia is characterized by unconformity-bounded stratigraphic gaps, folds and faults that record tectonic activity throughout this time interval. Notably, no evidence of syn-tectonic magmatic activity has been recognized. The tectono-stratigraphic record differs among the southwest, central-eastern and northwestern areas of Sardinia.

In southwestern Sardinia, the Mesozoic-lower Paleogene succession is deformed by N-S-trending folds and top-to-the-east thrusts. In particular, Upper Triassic dolostones and Lower Jurassic limestones are thrust over the lower Eocene succession. These structures are sealed by the Upper Eocene-Oligocene successions.

In central eastern Sardinia, the Mesozoic carbonate succession is affected by low-angle sinistral transtensional faults, along which several metres of the Jurassic and Cretaceous formations have been tectonically elided, and by superimposed top-to-the-SSE thrusts. The age of the deformation is constrained between the Santonian, represented by the youngest deformed strata, and the Oligocene-Lower Miocene strike-slip faults that crosscut the earlier structures. Farther south, Ypresian shallow-marine deposits lie unconformably above the Variscan basement and the Permian-to-Jurassic stratigraphic succession.

In northwestern Sardinia, an angular unconformity marked by bauxite deposits between the Lower and Upper Cretaceous records a tectonic event characterized by NW-SE-trending folds and ENE-striking sinistral transpressional faults, both coherent with a NE-SW shortening direction.

These observations indicate that Sardinia experienced a spatially heterogeneous tectonic evolution during the Mesozoic and Paleogene. The contrasting structural features likely reflect distinct paleogeographic positions relative to the evolving southern European margin. The compressional deformation in southwestern Sardinia is broadly coeval and is consistent with the main collision phase in the Pyrenees. Also, the Upper Eocene sediments that seal the structures in southwestern Sardinia may have been derived from the erosion of the eastern Pyrenean belt. The central-eastern and northwestern Sardinia tectonic evolution shows similarities with that of Provence, including a transition from transtensional to transpressional deformation from the Lower to the Upper Cretaceous. This transition may be related to the onset of subduction in the western Tethys along the southern European margin.

These correlations suggest that different sectors of Sardinia recorded the effects of distinct geodynamic processes operating simultaneously along the southern European margin. Further integration of the Sardinian record with those from the Eastern Pyrenees and Provence will provide new constraints on the tectonic evolution of the region prior to the opening of the western Mediterranean.