Linking basin tectonics, evaporite facies variations and their impact on subsequent deformation: insights from the Messinian.

With improvements in seismic imaging, it is increasingly evident 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 soluble calcium sulfates and carbonates. Our aim is to demonstrate the length-scale of variations in evaporite stratigraphies deposited in thrust-top basins and how these variations have controlled subsequent deformation of these basins. We use Messinian examples that integrate outcrop observations with extensive subsurface data from Sicily to provide new structural interpretations and apply these insights to interpret seismic data (in the absence of well control) from the nearby Ionian Sea. These Messinian basins are excellent sites for studying lateral variations in evaporite successions and their subsequent deformation. Two areas of the Sicilian thrust system are used here, linked to three major mine areas (Realmonte, on the south coast; Corvillo and Mandre in the centre of the island). Thrust-top mini-basins control fractionation of carbonate-evaporite facies that then continue to influence post Messinian deformation. Gypsum and carbonate units develop broad single-layer buckle-fold trains, wavelengths reflecting layer thickness. The development of 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 folds and 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 wave-length folding - are evident on seismic data from the buried Messinian interval beneath the Ionian sea. Using the Sicilian outcrop as analogues, the structural styles for the Ionian may be used to infer evaporite type in these subsurface examples.