Search

Pressure solution processes taking place during diagenesis deeply modify the hydraulic properties of carbonates, affecting their mechanical layering and hence the dimension, distribution, and connectivity of high-angle fractures. The formation of stylolites is controlled by the texture of the host rock and therefore by the depositional environment and the diagenetic processes that involve it. This study reports the results of a multidisciplinary study carried out on a Jurassic–Cretaceous carbonate platform in southern Italy. The goal is to unravel the control exerted by single carbonate textures and specific diagenetic processes on the formation of bed-parallel stylolites. Microfacies analyses of thin sections are aimed at obtaining information regarding the composition and texture of the carbonates. Petrographic observations coupled with CL analyses are key to deciphering their diagenetic history. Results are consistent with carbonates originally deposited in a shallow-water realm in which carbonate mud is occasionally abundant. In this environment, early cementation inhibits their chemical compaction. In grain-supported facies, pressure solution is only localized at the grain contacts. During shallow burial diagenesis, precipitation of blocky calcite predates the formation of bed-parallel stylolites in the grain-supported facies. Contrarily, mud-supported facies favor chemical compaction, which results in stylolites showing a good lateral extension and thick sediment infill. A classification of different types of stylolite morphology is attempted in relation to facies texture. In detail, rougher morphology (sharp-peak) characterizes the stylolites nucleated in grain-supported facies, while smoother morphology (rectangular to wave-like) is observed in stylolites on mud-supported facies. Application of this knowledge can be helpful in constraining the diagenetic history of carbonate rocks cored from depth, and therefore predict the fracture stratigraphy properties of carbonates buried at depth. [ABSTRACT FROM AUTHOR]

Aiming at assessing the porosity and permeability properties, we present the results of microstructural and laboratory measurements of density, porosity, VP, VS, and electrical resistivity performed in dry and in saturated conditions on 54 blocks of Mesozoic carbonate host rocks and fault breccias. Host rocks consist of carbonate mudstones, wackestones, packstones, and sedimentary breccias pertaining to the Senonian and Vigla formations. These rocks show average density values, low values of porosity, and medium-to-high P- and S-wave velocities. Fault breccias derive from high-angle extensional and strike-slip fault zones, and are characterized by a wider range of density, porosity values up to 5–10 times higher than host rock, and low ultrasonic velocities. Independently on lithology, the carbonate host rocks might include vugs due to selective dissolution. Differently, the fault breccia samples include microfractures. A slight textural anisotropy is documented in the carbonate host rocks, whereas a higher degree of anisotropy characterizes the fault breccias. Selected samples were also tested in pressure vessels with confining pressure up to 80 MPa, showing that transport properties along microcracks in fault breccias can significantly increase with increasing depth. In order to assess rock permeability and porosity-permeability relations, three different protocols are employed. Two of them are based on the Effective Medium Theory, so that permeability is computed by inverting ultrasonic measurements and assuming an array of penny-shaped cracks embedded in an impermeable host matrix. Accordingly, the aspect ratio and crack width are obtained by the seismic measurements. Two end terms have been modelled by assuming all cracks isolated, and unconnected or all cracks connected into the network. Application of these two protocols shows a systematic variation of permeability with porosity, whereas the results of the third one, based on the digital image analysis outcomes, do not exhibit systematic variation. We interpret this behavior as due to the not-selective dissolution of the outcropping carbonates causing a wide range of measured fracture aperture values. [ABSTRACT FROM AUTHOR]

We combined field mapping, structural and microstructural analyses, stable‐clumped isotope geochemistry, and U‐Pb dating of calcite veins and syn‐tectonic slickenfibres, to assess the regional scale fault‐related fluid flow during the evolution of the External Hellenides fold‐and‐thrust belt. We show that fluid circulation during forebulge uplift was characterized by cold meteoric water‐derived fluids, from which calcite precipitated and sealed bed‐perpendicular joints. Fluid circulation during foreland flexuring and early layer‐parallel shortening was characterized by warm fluids buffered by the carbonate host rock, which circulated through normal faults and bed‐parallel veins. Mixing with meteoric‐derived fluids also occurred at this stage of tectonic evolution. Fluid circulation during the late stage of thrust wedge accretion and post‐orogenic extension at 1.6 ± 1 Ma was characterized by increasing dominance of cold meteoric water circulating in strike‐slip and normal faults. The ingress of meteoric‐derived fluids was controlled by throughgoing fault conduits, while host rock‐buffered fluids were confined in isolated structures such as minor faults and veins. We developed a conceptual model of fault‐related fluid circulation, which invokes a transition from an open fluid system during forebulge uplift, to a semi‐closed fluid system during foreland flexuring and early layer‐parallel shortening, and to an open system during late thrust wedge accretion and post‐orogenic extension. This type of fluid circulation may have impacted fluid migration/leakage, including hydrocarbons, into or outside potential reservoirs in the highly prospective Hellenides‐Albanides fold‐and‐thrust belt, a renovated frontier for hydrocarbon exploration in the Mediterranean area. Key Points: Throughgoing faults are fluid conduits for external, meteoric‐derived fluids, minor faults and veins host rock‐buffered warm fluidsBed‐perpendicular joints sealed during forebulge uplift, rock‐buffered fluids circulated during foreland flexure and wedge accretionMeteoric water moved through strike‐slip faults during late wedge accretion and through post‐orogenic (at 1.6 Ma) normal faults [ABSTRACT FROM AUTHOR]

The Southern Apennines consist of a Cenozoic to Quaternary fold and thrust belt characterized by a complex structural architecture. In the axial portion of the chain, corresponding to the Agri Valley, folds and faults with multiple styles formed during the progressive emplacement of various tectonic units, derived from different paleodomains. In the available geological maps, the geometry of these tectonic structures is often hindered by scarce cartographic detail due to the use of basic stratigraphic subdivisions. Therefore, at the aim to better define these structures and contextually update the outcropping stratigraphic units, we realized a detailed geological map, which take into consideration not only the formation as basic stratigraphic units, but also finer subdivisions such as members or beds. Using this approach, we improved the stratigraphy of the area, we recognized new geological units and, eventually, we reconstructed the structural setting, and the tectonic evolution of the Agri Valley in detail. [ABSTRACT FROM AUTHOR]