Stefano Conti

Miocene chemoherms of the northern Apennines, Italy

In the Miocene of the northern Apennines, methane-derived limestones from various geologic settings represent important examples of fossil chemoherms and provide a basis for more accurate interpretations of seepage systems. The systematic study of fossil chemoherms has allowed the definition of new field and compositional criteria for the recognition of these deposits, which were previously based almost exclusively on negative carbon isotope composition and peculiar chemosynthetic communities; this has constrained the relations between seepage and sedimentary and tectonic instability processes. We suggest that the peculiar brecciated structures associated with fossil chemoherms are related to diapirism of overpressured pelitic sediments due to fluid venting. Fluidization of sediments increases the instability of mudstones in which chemoherms are contained, thus favoring gravity slumping processes and the reworking of many chemoherms.

Possible Relationships between Seep Carbonates and Gas Hydrates in the Miocene of the Northern Apennines

In the Miocene of the northern Apennines, a widespread carbonate precipitation was induced by the expulsion of methane-rich fluids. Numerous outcrops of carbonate masses share sedimentological, textural and geochemical features with present-day gas hydrate-associated carbonates. We hypothesize the contribution of paleo-gas hydrate destabilization on the base of the heavy oxygen isotope signature, the presence of distinctive sedimentary features (breccias, pervasive nonsystematic fractures, and soft sediment deformation), the close association between seep carbonates and sedimentary instability, and the huge dimensions of seep carbonates bearing brecciated structures.

Depositional history of the Epiligurian wedge-top basin in the Val Marecchia area (northern Apennines, Italy): a revision of the Burdigalian-Tortonian succession

The Burdigalian-Tortonian Epiligurian succession in the Val Marecchia area comprehends different lithostratigraphic units deposited in a wedge-top basin during the northeastern migration of the thrust belt. The succession includes shallow-water carbonates passing to mixed carbonate-siliciclastic and to fine-grained politic sediments, capped by fluvio-deltaic coarse-grained deposits. Detailed field work and stratigraphy has allowed to characterize depositional units and unconformities and to delineate the sedimentary and tectonic evolution of the basin. Tectonics exerted a primary control at different stages. During the Burdigalian, a general uplift of the area allowed the onset of shelfal carbonate sedimentation on underlying Ligurian and Epiligurian deep-water sediments. At the Serravallian the sedimentation was influenced by the thrust reactivations which caused a marked asymmetry in the basin geometry and fill. The subsidence increase in the rear part of the basin determined the deposition of a thick succession of relatively deep fine-grained sediments (up to 800 m water-depth) (Serravallian, MNN6a through MNN6b subzones based on nannofossil biostratigraphy) and fossiliferous clays (lower Tortonian, biozones MNN8b-MNN9). Conversely, uplift is activated in the frontal part of the basin, causing the partial erosion of the Burdigalian-Langhian shallow-water carbonates. A relevant amount of this carbonate detritus is delivered to the foredeep, supplying the Marnoso-arenacea Fm. A general uplift of the area in the late Tortonian leads to the deposition of fluvio-deltaic conglomerates supplied by emerged rear sectors of the basin.

Geophysical Investigation of a Mud-Volcano in the Northern Apennines

In the frame of a co-operation between the Earth Science Department of the University of Modena and Reggio Emilia and the OGS, a geophysical investigation, including geo-electrical profiles and a 3D seismic acquisition, was detected in Nirano (Italy, Northern Apennine) where mud volcanoes are present. The aim of the investigation was to determine the geometries of the shallower structures, across a mud volcano (Fig. 1), using information obtained by tomographic inversion of first arrivals of 3D seismic data and resistivity models obtained by 2D ERT (Earth resistivity Tomography) data. The joint information from different geophysical methods furnished a detailed map of the structures of the first 30 - 50 m in depth, and the final results are in agreement.