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Messinian Seismic Markers Offshore Eastern Sardinia: Important Tools for the Understanding of the Basin Geodynamical History

Gaël Lymer, Johanna Lofi, Agnès Maillard, Isabelle Thinon, Virginie Gaullier, Françoise Sage, Frank Chanier, Bruno C. Vendeville, and Lies Loncke

We acquired seismic data during the METYSS* cruises (Messinian Event in the Tyrrhenian from Seismic Study), part of a multi-site comparison of the Messinian Salinity Crisis (MSC) seismic markers in the western Tyrrhenian basin. Typical Messinian seismic markers include several erosion surfaces and depositional units, such as the Upper Unit (UU; alternating dolomitic marls and evaporites) and Mobile Unit (MU; mainly halite). These MSC markers provided important tools for understanding the evolution of the Tyrrhenian Basin.

The western region (East-Sardinia basin) opened earlier than the eastern region (Cornaglia terrace). In the East- Sardinia basin, MSC units are present in the South and absent in the North, where the presence of erosion surfaces and detrital bodies suggests that this area locally emerged during the MSC.

In the southern Cornaglia terrace, the proximal area contains both MU and UU, indicating that there, the water depth was already significant during the MSC. However, farther east (distally), only the UU are present (MU is missing), even though both proximal and distal regions presently lie at the same depth. This suggests that distal regions were too high to allow for deposition of MU (and probably bathymetrically disconnected from proximal areas), while still allowing for deposition of the UU. The area later subsided in response to renewed basement faulting during the Pliocene.

Our observations confirm that rifting in the Eastern Sardinian margin partly controlled the distribution of MSC seismic markers. Moreover this distribution allows us to constrain the amount and timing of vertical movements during rifting: first, between the northern and southern Sardinia Basins and, second, between proximal and distal parts of the margin. Indeed, the MSC seismic units depocenters widen Eastward (proximal to distal) in the Cornaglia Terrace, thus recording the easward diachronous subsidence of the margin during the MSC.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013