Cover page Figure The side facing the Velebit channel in the northwestern part of the mapped area, showing multiple thrust faults verging in opposite directions.
It is largely accepted that in the Dinaric shallow foredeep basin, the onset of Cenozoic synorogenic sedimentation is diachronous along strike and shows orogenparallel southward younging, creating a large uncertainty in the age of the Dalmatian flysch. Calcareous nannofossil biostratigraphy was studied to investigate a turbiditic succession exposed in Pag Island (Croatia) with the main purpose of constraining its age, which is still a matter of debate. The age assignment for the turbiditic deposition bears important implications for better understanding of the geodynamic and paleoenvironmental evolution of the External Dinarides.We logged a well-exposed sedimentary section in the south-western limb of the Pag anticline and performed calcareous nannofossil quantitative analyses revealing a high species diversity and abundant assemblage. The age diagnostic species indicate CNE14-CNE15 biozones, suggesting that flysch deposition occurred in the Lutetian-Bartonian. This age can be further restricted to the CNE14 (42.37-40.51 Ma) by means of the lowest occurrence of Reticulofenestra reticulata and the highest occurrence of Sphenolithus furcatolithoides. Vertical facies variation and paleoecological indications suggest an increase in paleobathymetric depth during deposition. Our data support a post-Lutetian age of folding and thrusting for the Pag Island region and suggest a relatively short time span during the middle-late Eocene period for the main contractional stage in this sector of the External Dinarides. This result has important implications for the evolution of the Dinaride foreland basin system in Cenozoic times. K E Y W O R D S calcareous nannofossils, Dalmatian flysch, Eocene, External Dinarides, Pag anticline
OBJECTIVES To select the "best outcrop analogue" of a subsurface field/prospect is always challenging, especially when dealing with fractured carbonatic reservoirs. The candidate should match the mechanical stratigraphy, the depositional conditions, the diagenetic history, the tectonic evolution. This is almost impossible, considering that at least the exhumation phase and the associated diagenetic features will not be shared between the outcropping analogue and the buried reservoir. Nevertheless, the analysis of natural analogues can provide useful indications particularly in a complex matter as fracture distribution; in fact, large-scale outcrop analogues reveal their potential when trying to fill the gap between seismic- and borehole-scale structural characterization. METHODS, PROCEDURES, PROCESSES In order to start building an "Atlas of Fracturing Facies" as a digital interactive catalogue of natural fractured analogues, three main cases have been studied: Pag (Croatia) and Parmelan (France) anticlines as analogues for folded and faulted platform carbonates affected by pre-folding extensional faulting, and the Gozo Island (Maltese Archipelago) as an example of carbonatic sequences affected by extensional tectonics. An integrated multiscale approach has been applied, from thin sections to outcrop scale analysis, from drone-based surveys to satellite image interpretation. This workflow leads to the reconstruction of 3D models, and to the quantification of the main parameters characterizing the fracture pattern and its variability. RESULTS, OBSERVATIONS, CONCLUSIONS The Island of Pag, External Dinarides of Croatia, is a thrust-related anticline that involves Upper Cretaceous to Eocene shallow-water carbonate platform sequences affected by tight folding during Eocene – Oligocene times. The fold evolution is multiphase, expressed by pre-folding features developed during a layer-parallel shortening with a strong influence of structural inheritance, followed by fold- and thrust-related cataclastic flow in hinge zones. The Parmelan Anticline, in the Bornes Massif, Western Alps, is a box-fold involving Lower Cretaceous massive platform carbonates. It is characterized by steeply-dipping limbs, separated by a wide crestal plateau, delimited by narrow hinge zones localized on inherited extensional faults. Its polyphasic tectonic history has been reconstructed by analyzing the fracture and vein pattern, which highlighted the strong influence of structural inheritance during folding. The Gozo Island is a Late Oligocene-Late miocene carbonatic sequence, composed by platform carbonates with different facies, affected by two extensional events associated to a mult-sets fracture pattern. In Gozo, spectacular coastal outcrops allowed analyzing the structural and statistical relationships between fractures and faults, in terms of density, length, orientation, spatial distribution patterns, and topology. NOVEL/ADDITIVE INFORMATION The Pag, Parmelan and Gozo case studies, together with several literature case studies, are the starting point of the implementation of an Atlas of Fracturing Facies, providing a multidisciplinary knowledge management and data repository platform to improve the prediction of fracture patterns in the subsurface, and its impact on porosity and permeability in reservoirs.
<p>The NW-SE striking Pag anticline, in the External Dinarides fold and thrust belt, provides an appropriate field site for studying fold- and fault-related deformation patterns at different scales in a transpressional setting due to outstanding exposures. We performed a multiscale structural analysis together with petrographic and isotopic characterization of syntectonic calcite cements. Results indicate that the Pag anticline, is a box fold developed mainly by detachment folding in response to NE-SW oriented compression. Depth-to-detachment calculation indicates that the basal thrust of the anticline is located in the Upper Jurassic evaporitic complex, at a depth of about 2.5 km. The geometry of the fold is strongly controlled by the interaction and overstepping of a major thrust-backthrust fault pair. In the northern sector, backthrust activity produced a northeastern facing, steeply dipping to near vertical backlimb. Moving southward, the forelimb gradually becomes vertical to overturned and fold asymmetry switches to a southwestward facing. Late- to post-folding tightening resulted in non-cylindrical and compartmentalized deformation by near vertical N-S right-lateral, and E-W, left-lateral, strike-slip faults trending oblique to the fold axis. These fault sets make a wider angle than expected for transversal conjugate strike-slip faults commonly associated with folding, possibly due to lateral propagation from inherited, folded soft-sediment extensional faults. Paleostress analysis indicates that the evolution of the Pag anticline occurred in a stress field that switched from contractional to transpressional configuration, maintaining a N40-50&#176; oriented major stress axis. Petrographic and isotopic data support infiltration of meteoric fluids into exposed carbonates in the pre-folding stage, followed by mixing with marine fluids during folding at shallow burial conditions and, eventually, meteoric fluid circulation along strike-slip faults in the late to post-folding stage. Stable isotope ratios suggest that fluid flow evolved from a bedset confined system to an open one in the late to post-folding stage. As such, a major role to control paleofluid flow is played by the transversal sets of low-displacement near orthogonal strike-slip faults. This suggests that, in reservoir structural characterization, particular attention should be paid to the presence of low-displacement strike-slip faults because of their role to enhance fluid flow mixing and channeling. The presence and, particularly, the abundance of such deformation features are difficult to constrain in buried fractured reservoirs by seismic reflection imaging because of low displacement values. We, consequently, stress the importance of studying field analogues by multidisciplinary approaches for better understanding the relationships between folding, faulting, the associated incremental deformation patterns, and the impact on fluid flow.</p>
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