Virtual outcrop modeling has emerged as a tool for supporting geological field activities such as geological mapping and stratigraphic investigations. Here we show how this technique can be used to support the detailed stratigraphic logging and sampling with a case history from the Eocene carbonate platform succession exposed in the Val Rosandra gorge, in the vicinity of the city of Trieste, NE Italy. The biostratigraphic analysis highlighted the occurrence of Shallow Benthic zones (SBZ) 10 to 12 and the planktonic zones E7/E8. An upwards-deepening trend, from inner platform to a hemipelagic domain, is observed through the studied stratigraphic interval and is in accordance with the vertical evolution recorded in other Eocene successions of the Adriatic Carbonate Platform. Aerial drone imaging was used to produce a virtual outcrop model of the studied succession that provided a high- resolution geometrical framework for field measurements, sample geotagging and observations. For instance, the virtual outcrop model assisted in determining the true thickness of beds, a task that can be subject to significant imprecisions when measurements are taken by hand. Ultimately, the integration of virtual outcrop modeling with classical sampling and measuring methods resulted in accurate stratimetry and in the precise spatial positioning of samples that were taken for biostratigraphy and facies characterization.

The evolution of the Apennine wedge has seen the time‐space migration of the forebulge, foredeep, thrust wedge, and back‐arc extension phases in the wake of the Eastward rollback of the subducting Adria slab. In this framework, thrusting and post‐orogenic extensional faulting have occurred in two parallel forelandward‐migrating ribbons, with extensional deformation overprinting or partly exploiting anisotropies of the inherited thrust system. Here, we explore the tectonic framework and the timing of thrusting and subsequent negative inversion of the Circeo thrust, one of the major thrusts in the inner portion of the central Apennines, with the main aim to constrain the timing and mode of the compression to extension switch. Structural analysis, carbonate C and O and clumped isotopes analysis, X‐ray diffraction of clay minerals, and U‐Pb dating of calcite slickenfibers have been integrated with seismic interpretation, cross‐section balancing, and 1D burial and thermal modeling. We show that the Circeo thrust developed during Langhian‐Serravallian time. Its extensional reactivation is dated at the Serravallian, during the stacking of an underlying thrust slice, before the onset of Pliocene back‐arc extension in the area. Combination of our data with the age of thrusts, extensional basins, and base of the foredeep infill of the central Apennines, demonstrates that forelandward migration of the foredeep‐thrust system occurred at variable velocities. Accelerations and decelerations are synchronous, respectively, with the opening of the Liguro‐Provençal and Tyrrhenian back‐arc basins and with the interluding quiescent period.

During the late Early Cretaceous, at the beginning of the Africa-Europe convergence, some portions of Adria experienced an enigmatic post-rift subsidence acceleration. According to many, this event is likely associated with extensional tectonics, which, however, hardly fits the Aptian-Cenomanian convergent framework of the central Mediterranean area and suffers from the apparent lack of coeval faults unquestionably linked to crustal stretching. Here we reconcile the tectonic and geodynamic records of Adria by introducing a syn-sedimentary extensional fault system exposed in the Lattari Mts. (southern Italy), currently forming the largest exposed Aptian-Cenomanian extensional system of Adria. Our structural reconstruction shows that the extensional displacement of the main fault is 2 km, at least 0.7 km of which was acquired during the Cretaceous. Radiometric dating indicates that reactivation and further growth of the fault occurred at 12.8 +/- 0.5 Ma and 5.8 +/- 3.4 Ma. To explain extensional tectonics in the framework of Africa-Europe convergence, we propose a slab pull mechanism, in which the traction exerted by the subducting Neotethys Ocean was responsible for the stretching of continental ribbons of Adria.

The middle Paleozoic (similar to 420-350 Myr) records a major increase in ocean-atmosphere oxygen levels; however, the timing and pattern of oxygenation are poorly constrained. Two well-dated North American locations in Nevada and Illinois were used to generate a high-resolution U-isotopic profile (delta U-238) spanning similar to 70 Myr of the middle Paleozoic. Stratigraphic and geochemical data support the interpretation that the Nevada profile represents a near-primary record of global-ocean redox variations. First-order delta U-238 trends indicate strongly reducing oceans during the late Silurian and Early Devonian, terminated by a major oxygenation event near the Emsian-Eifelian boundary (similar to 395 Ma). More oxic seawater conditions persisted for the next 30+ Myr, but were punctuated by multiple Myr-scale anoxic events during the Middle-Late Devonian and Early Mississippian that correlate with known global biotic crises, positive delta C-13 excursions, and widespread organic-rich facies deposition. The timing of the similar to 395 Ma oxygenation event suggests that the O-2 rise was the result of increased photosynthesis and organic carbon burial linked to diversification of late Silurian to earliest Middle Devonian terrestrial plants, rather than to subsequent Devonian increases in terrestrial plant root depth, tree height, lignin content, or seed reproduction. These findings demonstrate that early colonization of continents by relatively small, shallowly rooted plants with geographically limited ranges was sufficient to drive long-term oxygenation of the ocean-atmosphere system, paving the way for the evolution of large, mobile animals that have dominated the Earth's surface since the middle Paleozoic. (c) 2022 The Author(s). Published by Elsevier B.V.

The Apennine Carbonate Platform of southern Italy witnesses nearly 150 Myr (Late Triassic to Late Cretaceous) of shallow-water carbonate sedimentation in the subtropical central Tethys. During this field trip, you will have a look at the stratigraphy and facies across some key intervals of global palaeoenvironmental perturbation and at some important stratigraphic discontinuities in the history of the platform.During the first day, you will visit three localities of the Matese Mts. At San Lorenzello you will look at Milankovitch cyclicity expressed in Lower Cretaceous (Valanginian-Hauterivian) peritidal carbonates. At Pietraroja you will have a look at the foramol facies of the Cusano formation, marking the Early Miocene transgression on top of the eroded Cretaceous substrate. Moving north, at the Regiapiana you will see the abandoned mines that exploited the mid-Cretaceous karst bauxites, which mark a prolonged subaerial exposure. Moreover, you will walk through the Middle Miocene synorogenic history of the platform, from its exposure and erosion in the forebulge to its incipient flexural subsidence, highlighted by the Lower Miocene carbonates of the Cusano formation, to its drowning below the photic zone, marked by a phosphatic hardground overlain by the "Orbulina marls" of the Longano formation.During the second day, you will head south toward Salerno. In a quarry at Mercato San Severino, you will look at the record of the early Toarcian oceanic anoxic event, marked by the abrupt demise of lithiotid bivalves and dasycladalean algae, the major carbonate producers of the Lower Jurassic carbonate platforms. At the base of Mt Tobenna, you will look at the Aptian Orbitolina level: a marker bed whose palaeoenvironmental meaning has been long debated. From Mt Tobenna you will move south toward Monteforte Cilento where you will look at the record of the Cenomanian-Turonian OAE2 in the Apennine Carbonate Platform.

The Tyrrhenian back‐arc basin developed at the rear of the E‐ward migrating Apennine fold‐and‐thrust belt, with northward decreasing rollback of the subducting Adria slab leading to northward fading of back‐arc extension. The northern portion of the Tyrrhenian basin is made of thinned continental crust, whereas in the central/southern portion extension eventually evolved to oceanic crust production. In this framework, a long‐lasting debate concerns the existence of a >200 km long transform zone along the 41st parallel, which should separate the two portions of the Tyrrhenian basin. At its eastern termination, a branch of the presumed transform zone enters the Tyrrhenian margin of the Apennine belt and occurs as an accommodation zone made of a ribbon of extensional faults and related basins. This accommodation zone, which separates areas of mutually perpendicular extension directions, is here introduced, described, and named the Ponza‐Alife accommodation zone. Interpretation of seismic lines and new structural and stratigraphic data from this accommodation zone have been used to constrain the pre‐orogenic and syn‐orogenic architecture of the subducting plate and the Plio‐Quaternary back‐arc extensional stage. Our data indicate that the studied zone retraces a deep‐seated transform fault system located in the subducting plate and inherited from an Early Jurassic rifting episode, which caused the lateral juxtaposition of different rift domains in the subducting plate. We propose that during collision and trench retreat, this lateral juxtaposition has controlled differential retreat of the subducting plate across the studied zone, forcing the development of the Ponza‐Alife accommodation zone in the overlying back‐arc basin's margin.

The Apennines form an active fold and thrust belt that develops as part of the W-Mediterranean subduction zone. The evolution of the collisional system is driven by the retreating subduction of the alpine Tethys, which has caused the migration of compressive fronts and the opening of the Liguro-Provençal and Tyrrhenian back-arc basins, along with the rotation and translation of the Sardinia-Corsica and Calabria blocks. The Apennines make the northern limb of the Apennines-Calabria-Sicily orocline, developed due to the differential SE-ward retreat of the subduction system. In such a context, the central-southern Apennine system develops a foreland basin floored by a subaerial forebulge unconformity followed by a trinity of diachronous lithostratigraphic units: (i) shallow-water carbonates, (ii) hemipelagic marls, and (iii) siliciclastic turbidites. Previous studies have used the following datasets for reconstructing the evolution of the orogenic-foreland basin system: paleomagnetic data; the age of the siliciclastic syn-orogenic deposits filling the foredeep and wedge-top depozones; the age of the late-orogenic extensional basins. In this study, we highlight the importance of dating with high precision the onset of the Apennine orogenesis by means of Sr-isotope stratigraphy applied to the first carbonate sediments overlying the forebulge unconformity. In this regard, we have investigated a transect of the Apennine belt, extending from inner to outer sectors, in order to constrain the timing and style of migration of the belt and foreland basin. Our results show progressive rejuvenation of the forebulge unconformity toward the outer portions of the belt. More importantly, we highlight a time delay between the onset of syn-orogenic shallow-water carbonate deposition and the onset of siliciclastic turbidite deposition that ranges between 1 and 11 myr. In detail, the trends in the delay point at three main evolutive steps: 1) rapid evolution from forebulge to foredeep during the Burdigalian, 2) higher delays from the Serravallian until the latest Miocene, and 3) progressive decrease of the delay from the Zanclean. We associate the different velocity of migration with the differential slab retreat and spreading of the back-arc basins.

The polyphase structural evolution of a sector of the internal Central Apennines, where the significance of pelagic deposits atop neritic carbonate platform and active margin sediments has been long debated, is here documented. The results of a new geological survey in the Volsci Range, supported by new stratigraphic constraints from the syn-orogenic deposits, are integrated with the analysis of 2D seismic reflection lines and available wells in the adjacent Latin Valley. Late Cretaceous syn-sedimentary faults are documented and interpreted as steps linking a carbonate platform to the adjacent pelagic basin, located to the west. During Tortonian time, the pelagic deposits were squeezed off and juxtaposed as mélange units on top of the carbonate platform. Subsurface data highlighted stacked thrust sheets that were first involved into an initial in-sequence propagation with top-to-the-ENE, synchronous to late Tortonian foredeep to wedge-top sedimentation. We distinguish up to four groups of thrust faults that occurred during in-sequence shortening (thrusts 1–3; about 55–60 km) and backthrusting (thrust 4). During Pliocene to recent times, the area has been uplifted and subsequently extended by normal faults cross-cutting the accretionary wedge. Beside regional interest, our findings bear implications on the kinematic evolution of an orogenic wedge affected by far-traveled units.

Uranium isotope variations ( δ 238 U) recorded in marine carbonates are emerging as a potentially powerful tracer of redox conditions in ancient oceans. In order for these proxies to be interpreted as a record of ocean oxygenation, the data must first be corrected for syndepositional and early diagenetic processes which result in an offset between seawater and syngenetic carbonate. The existing paradigm for interpreting these variations is based mainly on observations from modern and Early-Triassic age sediments where U-rich aragonite is the primary carbonate polymorph. Congruence of δ 238 U trends recorded in multiple widely spaced early Triassic carbonates suggests that early diagenetic behavior of U isotopes deposited during periods of aragonite seas is consistent between sites and relatively well-understood. In contrast, U isotope records from carbonates deposited during periods of calcite seas show increased sample-to-sample variability as well as increased variation between corelative sections. Here, we use an isotope-enabled early diagenetic model of uranium geochemistry to demonstrate that the diagenetic behavior of U isotopes in shallow-water calcite sediments differs significantly from that in aragonite, necessitating a qualitatively different paradigm for the interpretation of δ 238 U records spanning large portions of the Paleozoic and Mesozoic Eras. Over a broad range of depositional conditions, low initial concentrations of U(VI) in calcite are overwhelmed by the addition of early diagenetic U(IV). Rather than reflecting the U(VI) composition of seawater and primary calcite, the bulk composition of these sediments is expected to predominantly reflect the isotopically heavy reduced U(IV) component similar to black shales. We show that the variability of δ 238 U observed in shallow-water calcite sediments most likely reflects variations in depositional conditions

The Apennines are a retreating collisional belt where the foreland basin system, across large domains, is floored by a subaerial forebulge unconformity developed due to forebulge uplift and erosion. This unconformity is overlain by a diachronous sequence of three lithostratigraphic units made of (a) shallow-water carbonates, (b) hemipelagic marls and shales and (c) siliciclastic turbidites. Typically, the latter two have been interpreted regionally as the onset of syn-orogenic deposition in the foredeep depozone, whereas little attention has been given to the underlying unit. Accordingly, the rate of migration of the central-southern Apennine fold-thrust belt-foreland basin system has been constrained, so far, exclusively considering the age of the hemipelagites and turbidites, which largely post-date the onset of foredeep depozone. In this work, we provide new high-resolution ages obtained by strontium isotope stratigraphy applied to calcitic bivalve shells sampled at the base of the first syn-orogenic deposits overlying the Eocene-Cretaceous pre-orogenic substratum. Integration of our results with published data indicates progressive rejuvenation of the strata sealing the forebulge unconformity towards the outer portions of the fold-thrust belt. In particular, the age of the forebulge unconformity linearly scales with the pre-orogenic position of the analysed sites, pointing to an overall constant migration velocity of the forebulge wave in the last 25 Myr.

We present a structural study on late Miocene-early Pliocene out-of-sequence thrusts affecting the southern Apennine orogenic belt. The analyzed structures are exposed in the Campania region (southern Italy). Here, thrusts bound the N-NE side of the carbonate ridges that form the regional mountain backbone. In several outcrops, the Mesozoic carbonates are superposed onto the unconformable wedge-top basin deposits of the upper Miocene Castelvetere Group, providing constraints to the age of the activity of this thrusting event. Moreover, a 4-km-long N-S oriented electrical resistivity tomography profile, carried out along the Caserta mountains, sheds light on the structure of this thrust system in an area where it is not exposed. Further information was carried out from a tunnel excavation that allowed us to study some secondary fault splays. The kinematic analysis of out-of-sequence major and minor structures hosted both in the hanging wall (Apennine Platform carbonates) and footwall (Castelvetere Group deposits and Lagonegro-Molise Basin units) indicates the occurrence of two superposed shortening directions, about E-W and N-S, respectively. We associated these compressive structures to an out-of-sequence thrusting event defined by frontal thrusts verging to the east and lateral ramp thrusts verging to the north and south. We related the out-of-sequence thrusting episode to the positive inversion of inherited normal faults located in the Paleozoic basement. These envelopments thrust upward to crosscut the allochthonous wedge, including, in the western zone of the chain, the upper Miocene wedge-top basin deposits.

The Miocene transgression in central and southern Apennines is commonly represented by a sharp contact between shallow-water open-marine bioclastic limestones and the underlying Cretaceous or Eocene bedrock. Only in a few areas, very proximal marine or paralic deposits, witnessing the first stage of the transgression, have been preserved. These deposits contain rich foraminiferal assemblages commonly dominated by specimens of the genus Ammonia. The paleontological and paleoenvironmental analysis revealed that the Miocene Ammonia shared the same habitat and ecological requirements of living representatives from recent shoreline environments. Small Ammonia forma ‘tepida’ have been found in Miocene marginal paralic organic-rich bottoms with restricted water circulation and possibly under natural metal pollution. Big Ammonia forma ‘beccarii’ characterize Miocene nearshore marine bottoms with vegetated areas under fresh water inputs. The endoskeletal lamellar folding called tooth-plate, which characterizes recent representatives, is observed in fossil specimens of both tepida and beccarii morphogroups, testifying that there were no major changes in the shell architecture of Ammonia since the early Miocene.

In fold and thrust belts developing at convergent margins, the migration of the advancing wedge is accompanied by bulging of the downgoing plate, followed by the development of a foredeep basin filled by a thick succession of syn-orogenic sediments. The transition from forebulge to foredeep marks a key moment in the evolution of the orogenic system. In deep water environments, the record of this transition is typically complete and progressive. Conversely, in the shallow-water/continental environment of many collisional systems, the uplift of the forebulge area can imply emersion and erosion, obliterating the stratigraphic record of key steps of the evolution of the orogenic system. The southern Apennines constitute one of these collisional fold and thrust belts where the development of the forebulge has implied emersion and erosion, with the development of a Miocene forebulge erosional unconformity, accompanied by extensional deformation associated with the bending of the lithosphere during the forebulge stage. In this paper, we use strontium isotope stratigraphy to constrain with unprecedented time-resolution the age of the forebulge unconformity in areas presently incorporated in the northern sector of the southern Apennines fold and thrust belt. Integration of our results and those of previous studies indicates, at the regional scale, a younging toward the foreland of the forebulge unconformity across the belt. Our high-resolution ages also reveal a diachronous onset of the flexural subsidence over short distances, associated with the occurrence of horst and graben structures, possibly resulting from inherited paleotopography along with forebulge extension. This work highlights how high-resolution dating is critical to unravel the evolution of foreland basin systems at different scales.

Mountain building in the Al-Hajar Mountains (NE Oman) occurred during two major shortening stages, related to the convergence between Africa-Arabia and Eurasia, separated by nearly 30 Ma of tectonic quiescence. Most of the shortening was accommodated during the Late Cretaceous, when northward subduction of the Neo-Tethys Ocean was followed by the ophiolites obduction on top of the former Mesozoic margin. This shortening event lasted until the latest Santonian - early Campanian. Maastrichtian to Eocene carbonates unconformably overlie the eroded nappes and seal the Cretaceous foredeep. These neo-autochthonous post-nappe sedimentary rocks were deformed, along with the underlying Cretaceous tectonic pile, during the second shortening event, itself including two main exhumation stages. In this study we combine remotely sensed structural data, seismic interpretation, field-based structural investigations and apatite (U-Th)/He (AHe) cooling ages to obtain new insights into the Cenozoic deformation stage. Seismic interpretation indicates the occurrence of a late Eocene flexural basin, later deformed by an Oligocene thrusting event, during which the post-nappe succession and the underlying Cretaceous nappes of the internal foredeep were uplifted. This stage was followed by folding of the post-nappe succession during the Miocene. AHe data from detrital siliciclastic deposits in the frontal area of the mountain chain provide cooling ages spanning from 17.3 to 42 Ma, consistent with available data for the structural culminations of Oman. Our work points out how renewal of flexural subsidence in the foredeep and uplift of the mountain belt were coeval processes, followed by layer-parallel shortening preceding final fold amplification.

Along convergent plate boundaries, the negative buoyancy of the lithosphere pulls the slab into subduction. Bending and offscraping of the downgoing plate are processes occurring at subduction zones and acting against plate motions. These localised dissipative processes cause extensional deformation in the bulge-foredeep region and thrusting and folding in the thrust wedge respectively. Within this framework, widespread early subduction-related extensional structures affecting pre-orogenic rocks of the downgoing plate of fossil subduction systems, are commonly interpreted as induced by extension occurring in the forebulge-foredeep zone. Slab pull is to date, rarely considered as a potential causative process when interpreting basin-scale pre-shortening extensional structures. The problem of distinguishing slab-pull and foreland flexuring induced extensional structures relates to the fact that for most belts, slab pull and forebulge-foredeep flexuring are expected to produce extension roughly in the same direction (i.e. parallel to the foredeep-belt system) and, when syn-kinematic strata are not available, discriminating between these two processes is arduous. In this work we present a field investigation of basin-scale extensional faults from the downgoing plate of the Oman Mts. fossil subduction system. Syn-kinematic strata indicate that normal fault development largely predated extension in the bulge-foredeep region. Herein, we argue that such faulting occurred during the transition from induced to self-sustained subduction, when the negative buoyancy of the slab started to exceed the resisting forces and the downgoing plate began to be pulled towards the trench.

We present a geological survey of the southwestern sector of the Mt. Massico (southern Apennines), which allowed us to reconstruct the stratigraphy and tectonic architecture of this area. The Mt. Massico is a key area to study the out-of-sequence thrusting stage that affected the southern Apennine chain since the late Miocene, which despite the wide occurrence of these structures in the whole chain, is a tectonic process up to now poorly investigated. This area deserves to be analyzed also for the occurrence of marble detritus within a wedge-top basin deposit, representing the only place in the southern Apennines, where such a kind of metamorphic rocks occurs. Historically, this area is known for the extraction of an ornamental stone, named Mondragone Marble. The marble is hosted as olistoliths and clasts within the deposits of the Caiazzo Fm. unconformably covering a Jurassic–middle Miocene succession, mostly made of shallow water-to-deep-basin carbonates. The wedge-top basin deposit mainly consists of a chaotic assemblage of conglomerates, olistostromes, and olistoliths of Meso-Cenozoic limestones, deep-basin rocks, and marbles, embedded in a quartzose matrix. The structural setting results from a polyphase deformation related to the superposition of two thrust systems. The first thrust system includes a duplex verging to east, with the Cenozoic carbonates thrusted onto the Caiazzo Fm. and the roof thrust cut by several breaching thrusts. The late thrust system encompasses ramp-dominated faults verging to the north. Folds, minor thrusts, and S–C structures are associated with the major compressional structures. To date the Caiazzo Fm. and put a temporal constraint to the thrust fault activity, we performed a nannoplankton content analysis that furnished, for the base of this deposit, an age not-older than the upper Tortonian. These out-of-sequence thrusts hence have acted since the late Miocene. Similar structures are widespread in the southern Apennines and are interpreted as the surficial expression of envelopment thrusts formed at deeper structural levels with respect to the thrust front. We envisage that the marble and plutonic supply was provided by the Mesomediterranean continental crust in the late Tortonian when this microcontinent was passing close to the Apennine Platform domain during its orogenic migration toward SE.

In this work we present data on fractures and mesoscale folds exposed in the Triassic to Miocene sedimentary succession of the Lurestan region (Zagros Belt). Data have been collected in tens of field sites, in a 10(4) km(2) area extending across the High Zagros Zone and the Folded Belt. Fractures and mesoscale folds have been characterised in terms of orientation, cross-cutting and abutting relationships with the other structures, and relative timing with respect to sedimentation. Outcrop-scale folds, stylolites, and reverse faults are NW-SE oriented and developed during NE-SW directed shortening. Extensional fractures, including joints, veins, and normal faults, are arranged into two assemblages including: (i) NE-SW and NW-SE striking fractures and (ii) NNW-SSE and WSW-ENE striking fractures. Syn-sedimentary fractures of the two extensional assemblages occur in pre- and syn-rift Jurassic rocks, but also in post-rift Cretaceous rocks and Cenozoic syn-orogenic rocks. We infer that the development of these extensional fractures in the Lurestan region was controlled by: (i) NE-SW-directed extension during both Early Jurassic rifting and early orogenic foreland extension; and (ii) WSW-ENE-directed stretching caused by differential compaction and related subsidence above NNW-SSE elongated basement structures, during tectonically quiescent periods.