Rossella Capozzi

Pliocene sequence stratigraphy, climatic trends and sapropel formation in the Northern Apennines (Italy)

Abstract The Pliocene stratigraphy of the Romagna Northern Apennines foredeep has been reconstructed through mapping and measuring the different lithostratigraphic units. The physically correlated sedimentary bodies have been chronologically calibrated through biostratigraphic analyses. Analysis of facies and fossil content allowed reconstructing the main depositional systems and their evolution. The co-occurrence of shallow- to deep-water environments and carbonate to siliciclastic systems allowed understanding fully the role of eustasy and climate vs. continuous tectonic deformation controlling the accommodation and basin morphology. Following a limited sea-level lowering at 4.2 Ma, associated with the first signal of cooling in the Early Pliocene, a fast growing subtropical type carbonate platform developed, in response to warm and oligotrophic surface waters. Furthermore, a significant drop in sea-level at 3.75 Ma points to an important Pliocene continental glaciation in the Northern Hemisphere. During the subsequent transgression, warm and possibly humid climate favoured the deposition of the first Pliocene sapropel around 3.3 Ma. The growth of a second generation of carbonate platform between 3.3 and 3.042 Ma suggests a renewed warm period and limited runoff. At the top of this highstand, thick sapropels developed, which can easily be correlated across the Mediterranean. The platform abruptly drowned, was overwhelmed by bio-erosion and was covered by iron–phosphate crusts; whereas in the adjacent basins numerous sapropel layers occurred, rich of biosiliceous forms, documenting the shift from Ccarb to Corg deposition. Strong oscillations of climate, due to precessionally controlled seasonality, and increased precipitation and runoff are considered as the main causes of the increase of surface water fertility. After the 2.87 Ma sea-level drop, again very significant, the sapropel rapidly disappears, in conjunction to the development of the lowstand wedge. After this cold period, which ended around 2.6 Ma, carbonate platforms never recovered due to the enduring cooler surface waters and the onset of an active drainage on the Apenninic range. This study documents the role of the eustatic variations on the Pliocene deposition of the actively deforming Northern Apennines foredeep. The abrupt lithostratigraphic changes appear also controlled by palaeoproductivity variations associated with climate and runoff.

The Miocene Petroleum System of the Northern Apennines in the Central Po Plain (Italy)

We describe the Miocene petroleum system in the context of the geology of the Northern Apennines as a system fed by multiple sources including some potential for deep oil accumulation. The presence of sources deeper than the Miocene reservoir is required by the high thermal maturity of the oils, the thermogenic nature of methane and the high ion content, in the reservoir brines, deriving from decaying organic matter. This is in contrast with the lower thermal maturity measured in the Miocene reservoir coupled with its low organic matter content. A Miocene secondary source, however, is required by the presence of a Tertiary organic marker in the oil. The deeper sources charged reservoirs of different age, geometry and sediment provenance, mostly as a function of stepwise migration of the foredeep and the overlying Ligurian units toward the foreland, which provided rapid overburden. The porosity of the reservoir was preserved in the anticlines mostly because of up-dip migration into early formed structures in the foredeep units. Therefore, the structural evolution of the area, especially the time interval between deposition and deformation of the foredeep units, is crucial for the definition of the quality of the reservoirs. Finally, the Quaternary reactivation of the thrust sheets in the foothills changed the geometry of the reservoirs, inducing new accumulations and/or dismigration from deeper and older traps.

Spontaneous fluid emissions in the Northern Apennines: geochemistry, structures and implications for the petroleum system

Abstract Natural seeps in the Northern Apennines document a variability of fluids and reservoirs in terms of origin, age and evolution. Their spatial distribution appears controlled by the presence or absence of the tectonic overburden provided by the Ligurian nappe. The general trend of deepening of the Mesozoic basement toward the internal part of the thrust belt is reflected by the nature of the seeps, characterized by thermogenic methane and oil at the foothills, whereas the innermost seeps show occurrence of dry thermogenic gas suggesting overcooking of the residual oil. At the front of the Ligurian nappe, or in places never covered by it, the seepages are associated with biogenic methane related to bacterial degradation of the organic-rich intervals occurring in the Pliocene and Pleistocene marine succession. The coupling of geochemical and structural analysis allows reconstructing the tectono-thermal evolution of the belt, improving our knowledge on the processes acting within the reservoir and controlling important parameters of the petroleum system, such as the reservoir porosity and its modifications, and the migration patterns.

Cold seepages: An economic tool for hydrocarbon appraisal

Spontaneous cold fluid seepages are a renowned phenomenon occurring in a wide range of geologic and geodynamic settings, including deep sea fans, rapidly subsiding basins, and compressive tectonic settings (e.g., Dimitrov, 2002; Morley et al., 2011; Oppo et al., 2013, 2014). Cold seepages are marked by various structures, both on land and offshore, such as mud volcanoes (MVs), methane-derived authigenic carbonates (MDACs), and chemosymbiotic communities. Their formation mechanism requires the increase of pore-fluid pressure above the lithostatic gradient with the subsequent upward fluid migration through hydrofracturing or along carrier beds and tectonic discontinuities. Cold seepages have long been investigated, especially for the information that they may provide for the exploration of hydrocarbons present in different types of reservoirs associated with this phenomenon (e.g., Link, 1952; Heggland, 1998; Abrams, 2005). Although the relation between cold seepages and hydrocarbon reservoirs has not been completely enlightened in numerous settings, as in fold and thrust belts, it is established that the occurrence of gas, frequently associated with oil, is a common characteristic that most of the seepage areas show. In particular, the spontaneous leakage of oil and gas represents a prime indication of hydrocarbons occurrence in the subsurface and valuable source of information on the petroleum system. The associated fluids also provide evidence of the geochemistry of deep-seated hydrocarbons. A useful example of this association is represented by the oil and gas field exploited near MVs along the coast and offshore in the Caspian Sea (e.g., Planke et al., 2003; Davies and Stewart, 2005; Oppo et al., 2014; Oppo and Capozzi, 2016). The spontaneous cold seepages of the northern Apennines illustrated here and in Capozzi et al. (2017) represent a long-lasting phenomenon, mainly characterized by present-day MVs activity. According to a renowned definition, MVs are …

Biostratigraphy as a Tool to Validate High-Resolution OSL, CRN, and Sequence-Stratigraphic Data

We present a biostratigraphic study of the Enza section that provides robust constraints on the timing of deposition in a case where the lack of magnetic polarity reversals in the marine part of the section does not allow palaeomagnetic age constraints to be obtained.

Mechanisms of Fluid Emissions - The Case Study of Regnano Mud Volcano

The seep of Regnano mud volcano, where mud is extruded in association with saline water and light hydrocarbons, is located at the surface emergence of a normal fault making part of art extensional system active after the arly Pleistocene. Chemical analysis and geological setting indicate that this system cuts previous chain thrusts and drains a Miocene reservoir which trapped deeper fluids migrated from the underlying Mesozoic units.