Tyrrhenian Basin

The volcanism associated with these islands occurs at the northeast closure of the downgoing slab and began approximately during the late Pliocene to early Pleistocene (1.5–1.7 Ma).

Seismic reflection surveys across the Upper Sardinia Margin exhibit a stratigraphic geometry suggestive of pre-rift, syn-rift, and post-rift sequences.

[6] Drill cores penetrating to the base of the syn-rift sediments identified a transgressive sequence related to subsidence of the continental crust during the rifting stage of the Tyrrhenian Basin opening.

[6] Late Tortonian to Early Messinian calcareous ooze and claystone with benthic foram assemblages overlays the sandstone formation; this indicates that water depth increased,[6] perhaps due to subsidence at the end of the syn-rift period.

The boundary between the syn-rift and post-rift periods is believed to be located in a 50-meter section of late Messinian gypsum that overlays the calcareous ooze and claystone formations.

At the top of the stratigraphic section are 243 meters of Pliocene to Pleistocene post-rift sediment containing calcareous mud with occasional terrigenous clastics and volcanic ash.

[6] A drill core to the base of the syn-rift sediments revealed 533 meters of thinly-bedded, calcareous, siltstone and sandstone with dispersed detrital gypsum grains and anhydrite nodules.

[6] Immediately above the basalt is a 100-meter-thick section of Pleistocene sedimentary cover, consisting primarily of nannofossil-rich mud with occasional reworked volcanogenic debris.

[1][3][5][6] K-Ar dating of peripheral oceanic basalts, drilled at the southeast edge of the Vavilov plain, estimates the beginning of extension to be 7.3 ± 1.3 Ma.

[3][6] This lower age limit, along with the presence of a saddle containing continental crust (the "Issel bridge") between the Vavilov and Marsili plains, implies that there were two distinct episodes of back-arc extension.

Between the Tortonian and middle Pliocene, W-E directed extension opened the Vavilov plain and Sardinia margin in the northwest portion of the present day basin.

This rapid shift in the direction and spatial location of extension may be due to how the relative velocities of interacting tectonic plates change over time.

[1] Post-Pliocene migration was eventually driven through the narrow corridor (250 km) represented by the present Ionian Sea and thus separated the Adriatic and Sicilian sectors.

This is primarily due to the basin's high geothermal gradient which pushes the oil window to very shallow depths where structural and stratigraphic traps are uncommon.