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Salt Tectonics Controlled by Pre-, Syn- and Post-salt Basement Normal Faulting in the Tyrrhenian Sea

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

The Tyrrhenian Basin opened by eastward migration of the Apennine subduction system. Rifting along the Eastern Sardinian margin was diachronous (Tortonian to Pliocene), and hence this timing partly overlapped the Messinian Salinity Crisis. The METYSS 1 and 3 cruises were carried out to use the deformation of the Messinian salt and its overburden as a proxy for better delineating the tectonic history of the sub-salt basement.

Two typical Messinian units have been identified in the study area : the Mobile Unit (MU; salt, mainly halite), overlain by the more competent Upper Unit (UU: alternating dolomitic marls and evaporites). This series is covered by brittle Plio-Quaternary sediments.

We illustrate how in the Cornaglia Terrace, slip along N-S-trending crustal normal faults bounding basement troughs has controlled salt and overburden deformation in three different manners:

- First, basement fault activity before or during deposition of the MU controlled local salt distribution thickness by forming highs and troughs. In these troughs (SE Cornaglia Terrace), the mobile salt was thicker and passive salt diapirism occurred spontaneously.

- Second, post-salt basement faulting (typically after deposition of the Upper Unit and during early Pliocene), and some crustal-scale southward tilting, triggered along-strike (southward) thin-skinned, gliding of salt and overburden recorded by upslope extension and downslope shortening.

- Third, when salt movements are constrained by basement highs and trough morphology. This is the case in another basement trough, located East of the Baronie Ridge. This trough is narrower, trends N-S and is bounded by crustal faults. Local basement highs prevented any along-strike (N-S) gliding. The narrow width of the trough also allowed for only minor across-strike (E-W) gliding. Instead, basement fault slip and tilting (Eastward or Westward) was accommodated by lateral flow of salt, which thinned upslope and inflated downslope, while the overlying sediments remained sub-horizontal.

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