Search

New seismic reflection data reveal that the south-eastward prolongation of the Apennine thrust front in the central Adriatic Sea is most likely located in a more external position with respect to the traditional interpretation. In this new interpretation, the Apennine thrust front shows a segmented geometry in correspondence to the Tremiti lithospheric transfer zone. The available data suggest that the north-eastward flexural retreat of the subducting Adriatic lithosphere and the related frontal accretion of the Apennine accretionary prism have acted during the last 5 Ma and may be considered still lively in both the Po plain and in the Central Adriatic domain, north of the Tremiti lineament. By analysing the tectonic evolution of the Apulo-Adriatic areas, it may be argued that the differential slab retreat between the central and southern sectors of the subducting Adriatic plate has been able to induce the segmentation of the Apennine thrust front. [ABSTRACT FROM AUTHOR]

Two sets of thrust compactive shear bands and one set of dip--slip compactive shear bands with, in places, associated slip surfaces have been recognized for the first time in a peculiar high-porosity grainstones of the Calcare Massiccio Fm., a Lower Jurassic platform limestone deformed during the development of the late Messinian Cingoli anticline of northern Apennines, Italy. The deformation bands have been studied by field mapping, thin section image analysis, back scatter SEM imaging, and pressure pulse decay minipermeametry. The deformation micro-mechanism in the compactive shear bands is controlled by plastic smearing and grain size reduction of soft micrite peloids with rare grain crushing and even rarer pressure solution. Plastic smearing is characteristic of the micrite peloids and is different from mechanisms occurring in other known carbonate deformation bands where the grains are bioclastic fragments and sparite ooids. The syntectonic diagenetic episode that brought to cement precipitation in the high-porosity grainstones of the Calcare Massiccio caused the loss of porosity and a change in deformation style from strain localization accommodated by banding to classical faulting along slip surfaces accompanied by thick zones of gouge and breccia. The permeability reduction from the host rock normal to the slip surfaces with associated compactive shear bands is, on average, an order of magnitude, which is less than what measured across deformation bands in other porous carbonates. We speculate that the diagenetic history provides a conceivable hypothesis to explain the high porosity in a Mesozoic platform carbonate at the time of orogenic compression (late Messinian), so that deformation bands, hitherto unknown in this type of rock, could develop. [ABSTRACT FROM AUTHOR]

Abstract: The Cingoli anticline is a late Messinian thrust-related fold that developed along the northern Apennines front (Italy). This exposed anticline represents a potential analog of hydrocarbon reservoirs located in the nearby Po Plain and Adriatic Sea areas. The folded rock multilayer of the Cingoli anticline includes a heterogeneous, Mesozoic–Cenozoic, marine succession, consisting of massive platform carbonates below, and layered pelagic carbonates on top. This article reports the results of analyses conducted on pelagic micrites cropping out in two exposures located in the anticline backlimb. There, the late Cretaceous–Eocene Scaglia Rossa Fm., which is characterized by thin beds of pelagic limestones and marly limestones, is crosscut by pervasive, closely-spaced, stratabound fractures mostly consisting of pressure solution seams (PSSs) and sheared PSSs. The fractured strata are, in places, crosscut by small-offset fault zones. Field and laboratory structural data are used to define the nature and type of the different fracture sets as well as their temporal evolution and interaction. Seven main sets of stratabound PSSs and sheared PSSs are identified and interpreted as an early background fabric crosscut by or involved in later through-going fault zones. We propose a conceptual model of fault nucleation and growth that envisions the studied faults as late-stage structures, which formed by incorporating and connecting segments of bedding surfaces and early developed PSSs. We discuss our conceptual model in terms of fault and fracture permeability, highlighting the possible role exerted by the documented structures on subsurface fluid flow. [Copyright &y& Elsevier]