Messinian evaporites in Sicily and nearby Ionian Sea: Linking basin tectonics, evaporite facies variations and their impact on subsequent deformation

Messinian evaporites in the seabed of the modern Mediterranean are generally inferred to influence the structure ofthe overlying Plio-Quaternary sediments. Hummocky deformation of these sediments (so-called “cobblestone”morphology) characterizes much of Mediterranean sea-floor. With improvements in seismic imaging, it is increasinglyevident that original stratigraphic variations in evaporite formations can play important roles in their deformation.Critical in this regard is the relative abundance of halite, together with other high-solubility salts, and the less solublecalcium sulfates and carbonates. Our aim is to demonstrate the length-scale of variations in evaporite stratigraphiesdeposited in thrust-top basins and how these variations have controlled subsequent deformation of these basins. We useMessinian examples that integrate outcrop observations with extensive subsurface data from Sicily to provide newstructural interpretations and apply these insights to interpret seismic data (in the absence of well control) from thenearby Ionian Sea. These Messinian basins are excellent sites for studying lateral variations in evaporite successionsand their subsequent deformation. Two areas of the Sicilian thrust system are used here, linked to three major mineareas (Realmonte, on the south coast; Corvillo and Mandre in the centre of the island). Thrust-top mini-basins controlfractionation of carbonate-evaporite facies that then continue to influence post Messinian deformation. Gypsum andcarbonate units develop broad single-layer buckle-fold trains, wavelengths reflecting layer thickness. The developmentof deformation appears limited by bending resistance at fold hinges – which can be overcome by syn-tectonic erosion.In contrast, the thick halite deposits that accumulated in growth synclines have deformed with short-wavelength foldsand distributed strain. These structures can display rapid lateral variations over length scales of a few hundred metres.Similar structural styles – with buckle fold trains passing laterally into more homogeneously shortened, short wavelengthfolding - are evident on seismic data from the buried Messinian interval beneath the Ionian sea. Using theSicilian outcrop as analogues, the structural styles for the Ionian may be used to infer evaporite type in these subsurfaceexamples and assist interpretation of evaporites beneath the sea-bed of Mediterranean.