Ricci, Simone (2015) Geometrie deposizionali in una piattaforma Oligo-Miocenica nel sottosuolo del Mediterraneo: espressione sismica e confronto con geometrie di affioramento. [Magistrali biennali]
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Defining depositional geometries of an Oligo-Miocene carbonate platform buried in southern Mediterranean sea is the goal of this study. The examined sedimentary basin consists of a passive continental margin which formation is related to Tethys ocean geodynamic history. In this basin the study area has an areal extent of 30 x 32,5 km; it experienced compressional first and then weakly extensional tectonic regimes. In this framework four sedimentary mega-sequences were deposited and the last one (mega-sequence D) contains a thick carbonate succession (800-900 meters) that is the subject of this thesis. Lithological data were obtained from the study of perforation cuttings from two wells that show lithologies ranging from marls and shale to fossiliferous limestone. Identified grains are initially of macroforaminiferal grainstone and later packstone-wackestone containing corals and ostreidae. In addition to them log data (master log, composite log, caliper log, natural γ ray log, sonic log, density log and three types of resistivity log) from eight wells were analyzed. Five of these wells (wells A, B, C, D and E) perforate platform carbonate whereas the other three (wells F, G and H) have basinal successions. Emerged data allowed the individuation of 17 litho-types used to describe wells successions. A seismic dataset was analyzed to describe the geometrical arrangement and correlations with basinal areas. A gradually steepening platform structure with well defined margins composed by coral reefs emerges. From seismic data seven seismic facies were defined and six Seismic Horizons (SH) were identified and tracked. They have allowed platform subdivision in five Seismic Units (SU) that were mapped and analyzed also with use of seismic attributes. Litho-type data were plotted on seismic sections which intercept wells locations to give a lithologic and stratigraphic meaning to reconstructed SH and to understand what litho-types may give rise to the observed seismic facies. To better populate geometries inferred from the litho-types spatial distribution, detailed analysis of potential outcrop analogues from literature was performed. A range of potentially present facies was extrapolated and thirteen of them were identified based on present litho-types and seismic facies. A depositional model of the platform was reconstructed and exposed in two key-sections intersecting studied wells. The distribution of inferred depositional environments shows open platform geometries in the lower part and the transition to a shelf platform in the upper one. Well correlation displays the complex lateral relationships between the various platform facies. Finally depositional environment maps were realized to allow an areal view of platform growing steps and dynamics.
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