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RESEARCH PRODUCT

Formation mechanisms of Neptunian dikes in the Jurassic carbonates of Monte Maranfusa (western Sicily)

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Younger sediment infilling open fissures exposed on the sea floor are defined as neptunian dikes. These are peculiar features of carbonate platform successions deposited along the plate margins bounding the western Tethys during the Late Triassic time. During middle-Early Jurassic, a large part of these carbonate platforms were drowned, and became submerged plateaux covered by pelagic sediments during Jurassic (“Rosso Ammonitico”) and Cretaceous times (“Scaglia”). In western Sicily, several Neptunian dikes crop out (Monte Kumeta, Rocca Busambra, Monte Maranfusa, Monte Magaggiaro, etc.). They cut across mainly the carbonate sediments of the Inici Formation and in some cases the pelagic limestone “Rosso Ammonitico”, located along the paleo-margin which separated the platform sectors of Hyblean-Saccense and Panormide domains and the basinal areas of the Imerese-Sicanian domains. In this work, we focused on the geometric, dimensional and kinematic properties of Neptunian dikes outcropping in the north-western side of Monte Maranfusa, with the aim to obtain new information relative on their formation processes. The Jurassic succession of Monte Marafusa is made up of peritidal limestones about 20 meters thick of the Inici Formation (Hettangian to Sinemurian) topped by a discontinuous thin layer (0,5-1 m) of pink-white crinoidal packstone/grainstone (Pliensbachian) and, subsequently, by a 27 meter thick sequence of Rosso Ammonitico-type pelagic limestones (Toarcian to Thitonian). Within this succession, we have identified four sets of Neptunian dikes showing four main orientations: N-S, NW-SE, NE-SW and E-W. The N-S and NW-SE sets are the most developed in terms of number of dikes and relative size. In fact, the dikes show thickness up to 2 m, heights up to 10 m, and are also characterized by offsets ranging from 0.5 to 2 m. The two other sets are oriented EW and NE-SW, respectively. The latter ones are thinner (up to 0,2 m) than the aforementioned dike sets, show variable heights, which range from a few m up to more than 10 m, and do not show significant displacement (always less than one meter). In general, some dikes show an heterogeneous infilling consisting of upper pelagic limestone (Rosso Ammonitico and/or Scaglia) and calcite. Differently, others are filled by a homogeneous material. Ongoing research is aimed at deciphering , as far as possible, the loading conditions that led to the dikes formation, as well as the relative timing of the different dike sets.