INTEGRATING SEDIMENTOLOGY, STRATIGRAPHY, GEOCHEMISTRY AND 3D GEOLOGICAL MODELLING: CONTRIBUTION TO GEOLOGICAL MAPPING FOR LAND KNOWLEDGE (CARG SHEET 081 ¿ROVERETO¿)
Geological maps are thematic representations illustrating the distribution of geological features exposed at the Earth’s surface. They are essential tools for land use planning, natural hazard mitigation, groundwater management, mineral resource exploration and environmental protection. In Italy, a country characterized by considerable geological fragility, the need for detailed geological knowledge and mapping has long been recognised. Shortly after its national unification, geological mapping was entrusted to the Italian Geological Survey, nowadays part of ISPRA (Istituto Superiore per la Protezione e la Ricerca Ambientale-Institute for Environmental Protection and Research). The whole national territory is currently covered by a 1:100000 scale geological map (surveyed since the XIX century and completed in the ‘70s of the last century) but the necessity for a larger-scale map led ISPRA to launch the Geological CARtography project (CARG). The CARG project aims to produce a geological map of Italy at a 1:50000 scale, made up of 634 map sheets, in collaboration with territorial authorities, research centres and universities. The project represents an essential and strategic long-term investment in scientific knowledge, with direct socio-economic benefits that ultimately support sustainable land management and decision-making. In this framework, the compilation of the CARG sheet 081 “Rovereto” provided an opportunity to promote collaboration between the Provincia Autonoma di Trento (Autonomous Province of Trento), representing the territorial administration, and the University of Milan, along with other universities and research centres, providing scientific support. Based on this collaboration, the present PhD thesis focuses on the Rhaetian(?)-Tithonian carbonate succession of the Trento Platform, one of the Jurassic structural highs of the Western Tethys Ocean, cropping out in the Folgaria plateau and in the Pasubio Massif areas (Trentino-Alto Adige region, N Italy). The Trento Platform carbonate succession, characterized by abrupt vertical facies changes, is now exposed in the Southern Alps, a fold-and-thrust belt that developed between the Late Cretaceous and the latest Eocene in response to the Alpine orogenesis. One of the most striking aspects of the studied sedimentary succession is the sharp vertical transition from shallow-water carbonates to red, condensed pelagic deposits rich in ammonites across a flat erosional unconformity, which marks the drowning of the Trento Platform. Despite extensively studied, the causes driving the drowning of the Trento carbonate platform are still poorly understood. Results from this study suggests that this sector of the platform underwent subaerial exposure possibly during the middle Aalenian, as testified by the local and limited occurrence of pendant cements and dissolution vugs filled with crystal silt immediately below the unconformity. This exposure, attributed to tectonic uplift, halted carbonate sediment production and led to the formation of a platform-scale erosional surface. Subsequent extensional tectonics caused platform subsidence at depths still above the effective wave base, which evolved into a submerged current swept paleostructural high. The relative sea-level rise and the consequent marine transgression resulted in the development of a transgressive wave-ravinement surface, which enhanced the planarity of the unconformity and removed much of the meteoric diagenetic evidence. The following Bajocian sea-level rise, possibly amplified by tectonic subsidence, favoured the abrupt transition of the wave-cut carbonate platform to bathyal settings outside the carbonate productivity window, resulting in the deposition of the red, condensed pelagic sediments directly above the unconformity. The role of extensional tectonics is manifested with the occurrence of neptunian dykes filled with red pelagic sediment. The red, condensed pelagic deposits rich in ammonites of the Trento Platform (Rosso Ammonitico Veronese) are characterized by Fe-Mn concretions occurring as nodules, crust and dendrites which, according to the literature, mark short- to long-term hiatal intervals characterized by non-deposition and erosion. In the last decades, Fe-Mn concretions have received increasing attention, both for their economic potential due to high concentrations of critical raw materials, and for their scientific significance in understanding genetic processes. However, considering that these concretions typically form at depths of hundreds to thousands of metres on the ocean floor and are difficult to sample directly, the study of comparable “fossil” deposits exposed on land is particularly valuable, providing insights into the paleoceanographic conditions prevailing at the time of their formation. Geochemical analyses revealed a hydrogenetic origin for Fe-Mn nodules, a hydrogenetic origin overprinted by diagenetic fluids for the Fe-Mn crust and a diagenetic origin for the dendrites. Carbonates hosting Fe-Mn concretions were precipitated in oxygenated conditions. Furthermore, the occurrence of Frutexites shrubs associated with Fe-Mn crust and nodules suggests a possible biotic contribution in the oxidation of Fe and Mn. Moreover, the stratigraphic and sedimentological study of the Rhaetian(?)-Tithonian sedimentary succession of the Trento Platform allowed the identification of 47 distinct depositional facies, forming the basis for the characterization of key features of each geological unit at both the meso- and microscale. The understanding of facies and unit features then facilitated the elaboration of a detailed geological map of the Pasubio Massif and the subsequent realization of a 3D model from surface geological data, adopting an iterative method using an explicit approach with the Move software. Particular attention was given in validating the 3D model, using both field-based and control geological constraints to critically assess the interpolation results performed by the software and to produce a more reliable geological model. Based on field data and stratigraphic constraints, the resulting geological map and 3D model of the study area depict a monoclinal gently dipping towards the north, characterized by geological units showing constant thicknesses. This last observation contrasts with previous interpretations, which envisaged abrupt thickness changes of the Lower Jurassic geological units as related to syn-depositional tectonics. By integrating sedimentology, stratigraphy, geochemistry and 3D geomodelling, this study provides novel insights for a better knowledge of the land and may represent a basis for the future compilation of the explanatory notes accompanying the ongoing sheet 081 “Rovereto” of the official geological map of Italy at 1:50000.
sedimentology, diagenesi, 3D geomodelling, CARG project, Trento Platform, Southern Alps, Settore GEOS-02/B - Geologia stratigrafica e sedimentologia
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