Crisi e ripresa di sistemi carbonatici e potenziale per la formazione di reservoir: i ruoli di clima, tettonica e magmatismo

Depositional architecture and crisis of high-relief carbonate systems: greenhouse (Triassic) and Icehouse (Carboniferous) case studies. Environmental control and implications for the development of petroleum systems.

Carbonate depositional systems represent favourable data repositories that can document type, timing and sedimentological features of environmental changes because carbonate producing biota and processes are sensitive to such changes. The causes and effects of environmental changes recorded in carbonate deposits can be compared for importance and rates with the global changes that are now affecting the Earth. Episodes of carbonate production crisis are particularly interesting as they generally favour the preservation of the geometry of the systems immediately before the crisis. In order to reconstruct the controlling factors on the crisis of carbonate

systems, three different case studies, where the geodynamic setting and the global climate conditions at the time of deposition are known, have been identified:

1) Carboniferous of Spain (Fig. 1): tropical carbonate system, in a converging setting (Variscan Orogeny in the Cantabrian Mountains), in the distal part of a peripheral foreland basin. High-relief platform to carbonate ramp, interfingering with siliciclastic deposits (filling stage of the foredeep basin). Carbonate productivity driven by microbial boundstone (reef and slope) in high-relief platforms, microbial mounds with algae and corals in ramp settings, with mixed carbonate-siliciclastic deposits (Della Porta et al., 2003, 2004; Bahamonde et al., 1997, 2004, 2007). Icehouse (= present) global climate conditions. The crisis of the carbonate systems results from the interaction of tectonics, siliciclastic input and paleoceanographic changes.

2) Ladinian-Carnian (Middle-Upper Triassic) of the Central Southern Alps (Fig. 2): crisis of the high-relief greenhouse platform of the Esino Limestone (Jadoul et al., 1992; Berra, 2007; Berra et al., 2011), marked by a major subaerial exposure at the top of the platform and by an abrupt shift from carbonate to shale deposits in the basin. Climate control has been identified (Berra, 2012) and the study points to define the timing and way of the environmental change by an integrated sedimentological approach.

3) Norian-Rhaetian (Upper Triassic) of the Central Southern Alps (Fig. 3): crisis of the Dolomia Principale system (high relief, greenhouse), affected by syndepositional extensional-transtensional tectonics (Jadoul, 1985; Jadoul et al., 1992), and transition from pure carbonates (from platform to basin) to prevailing shale deposits (Riva di Solto Shale). Climate control is documented (Berra et al., 2010; Berra, 2012) and the research will focus on the responses of the carbonate system in terms of facies, microfacies and early diagenesis.

The aim of the project is to define the way environmental changes triggered the crisis of these three carbonate systems in their different subenvironments, following a multidisciplinary approach. In detail, the goals are to: 1) define modes and rate of the crisis with sedimentological, geochemical, mineralogical and diagenetic analyses; 2) reconstruct the depositional architecture of the carbonate systems at the time of the crisis by producing 3D models with professional software packages; 3) verify using 3D forward modelling software productivity and transport able to honour field data.

The detailed knowledge of events that abruptly and significantly changed in the past the depositional processes and the environments of our Planet can be an important contribution for the understanding of the significance of the environmental changes that are affecting the Earth now, whereas the reconstruction of the effects of a carbonate productivity crisis on the final geometry of carbonate systems may be a tool to identify possible favourable conditions for the generation of petroleum systems.