Adriatic Margin Research Articles

Middle to Late Jurassic pelagites and gravity mass flow deposits of a displaced Neotethyan margin: Microfacies and biostratigraphical studies in Northeast Hungary

Microfacies, depositional age and sedimentary environment were characterised for two Jurassic successions, which were deposited on the Adriatic microcontinental margin of the Neotethys Ocean. Investigations were carried out mostly on cores drilled in the Mesozoic basement of the eastern part of the Matra Mountains (Recsk area) and the westernmost part of the Bukk Mountains, NE Hungary. This area represents the continuation of the Inner Dinaric nappe-system, and was displaced along the Mid-Hungarian Shear Zone during the Late Oligocene to Early Miocene. The pre-Cenozoic basement of the area is characterised by three juxtaposed units: the lowermost Recsk Succession, the Tarna Olistostrome and the topmost Darnohegy Melange nappe. The Recsk Succession is made up of Upper Triassic, cherty carbonates of pelagic basin facies that are overlain by pelagic limestones of Early to early Middle Jurassic age. The carbonate sedimentation changed gradually into shale-dominated one during the late Bathonian to the early Callovian. In the Bajocian to early Callovian interval the Recsk area was located at the toe of a coeval carbonate platform, which provided gravitational mass flows reaching the investigated area. The external margin of this platform drowned and got covered by the pelagic shale in the late Bajocian. The Tarna Olistostrome is built up by a Tithonian pelagic mixed carbonatic and siliciclastic succession with breccia/ olistostrome horizons. The clasts derived from the Upper Permian-Lower Jurassic succession of a distal Adriatic margin. The Darnohegy Melange is a typical sub-ophiolitic melange comprising scrapped off blocks and slices from the lower plate and gravitationally redeposited / tectonically sheared blocks from the overriding ophiolite nappe. The age of the melange is Callovian-Oxfordian. These inferences may serve as a base for new geodynamic evaluations of the studied region.

Faulting, basin formation and orogenic arcuation at the Dinaric–Hellenic junction (northern Albania and Kosovo)

The Dinaric–Hellenic mountain belt bends where two fault systems transect the orogen: (1) the dextral Shkoder-Peja Transfer Zone (SPTZ), active sometime between the Late Cretaceous and middle Eocene; (2) the Shkoder-Peja Normal Fault (SPNF), which accommodated NW–SE directed orogen-parallel extension. The SPTZ dextrally offsets the Dinaric–Hellenic nappes by ~ 75 km, a displacement attributed to reactivation of an Early Mesozoic rift transfer zone in the Adriatic margin during Paleogene subduction of the Pindos Ocean. This subduction involved an initial counter-clockwise rotation of the Hellenides with respect to the Dinarides around a pole at the NW end of the Budva–Krasta–Cukali–Pindos Basin. The SPNF overprints the SPTZ and is a composite structure comprising five fault segments: four of them (Cukali–Tropoja, Decani, Rožaje, Istog) were active under ductile-to-brittle conditions. They downthrow the West Vardar Ophiolite in the hanging wall. The Cukali–Tropoja and Decani segments exhume domes with anchizonal-to-greenschist-facies metamorphism in their footwalls. These structures formed during a first-phase of extension and clockwise rotation, whose Paleocene age is constrained by cross-cutting relationships. A second extensional phase was accommodated mainly by the fifth (Dukagjini) segment of the SPNF, a subsurface normal fault bordering syn-rift, mid-late Miocene clastic and lacustrine sediments in the Dukagjini Basin (DB) that are sealed by Plio-Pleistocene strata. This later phase involved subsidence of Neogene basins at the Dinaric–Hellenic junction coupled with accelerated clockwise oroclinal bending. The driving force for clockwise rotation is thought to be bending and rollback of the untorn part of the Adriatic slab beneath the Hellenides.

Deep-Water Dynamics along the 2012–2020 Observations on the Continental Margin of the Southern Adriatic Sea (Mediterranean Sea)

This work presents the results of long-term deep-water observations carried out in the southwestern Adriatic margin. Hydrodynamics and thermohaline measurements were carried out in the last 100 m of the water column using two long-term moorings placed at two different locations along the western sector of the Adriatic continental margin (open slope vs. submarine canyon). The observations, carried out over a period of almost 10 years, made it possible to define the intra- and interannual deep-water dynamics, which are mainly influenced by the passage of cold, dense water. The hydrodynamic field is influenced by seasonal behavior and varies from year to year, with no clear temporal trend or periodicity. Thermohaline properties follow hydrodynamics but also show a climatological trend toward higher temperatures and salinity. The combination and variability of preconditioning factors explains the interannual variability in dense water passage at the mooring sites triggering the formation of dense water in the northern Adriatic. The impulsive nature of the dense water flow, which is difficult to capture with sporadic oceanographic surveys, and its linkage with the large-scale atmospheric circulation make continuous monitoring essential to answer open questions about cascading processes and deep-water dynamics under a global change scenario.

Carboniferous–Triassic tectonic and thermal evolution of the middle crust section of the Dervio–Olgiasca Zone (Southern Alps)

AbstractA well‐preserved remnant of the middle crust of the former Adriatic passive margin is exposed in the Southern Alps (Italy). The Dervio–Olgiasca Zone is located south of the Insubric Line along the northern part of Como Lake and, because of the lack of Alpine overprint, provides favourable conditions to investigate the pre‐Alpine (rift‐related) history. We reconstruct the P–T–t–d evolution of the Adria middle crust through petrological (petrography, mineral chemistry, thermobarometry and thermodynamic modelling) and geochronological (Lu/Hf in garnet and U–Pb in monazite) data from pegmatites and host micaschists. These data allow reconstruction of a complex tectono‐thermal evolution of the future proximal Adriatic margin at the onset of Alpine rifting. The amphibolite‐facies Carboniferous metamorphic basement (7.6–10 kbar and 610–660°C at 318–312 Ma) was affected by pervasive extensional deformation (5.1–7.6 kbar and 580–660°C) in the Middle‐ to Late‐Permian (257.5 ± 3.8 Ma). Pegmatite intruded at 249.8 ± 1.1 Ma in an extensional phase that re‐equilibrated rocks of the basement at 3.5–4.5 kbar and 560–600°C. During the Middle‐ to Late‐Triassic (241–235 Ma), the basement experienced static thermal recrystallization (T = 689 ± 41°C and ~5.0 kbar). This Late‐Anisian to Early‐Carnian thermal event was simultaneous with the emersion of carbonate platforms, volcanism and ore deposition in the future proximal Adriatic margin. The subsequent cooling of the middle crust was synchronous with large‐scale extensional detachments developed in the upper crust (e.g., the Lugano‐Val Grande Fault), which controlled the formation of the Monte Generoso Basin. This study reveals that the local post‐Carboniferous thinning and heating events recorded in the Adriatic middle crust were interconnected to other processes occurring at different crustal levels that were, in turn, induced by crustal stretching in the early stages of the Alpine rifting.

Sediment resuspension and transport processes during dense water cascading events along the continental margin of the southern Adriatic Sea (Mediterranean Sea)

The near-bottom nepheloid layer in the western margin of the Southern Adriatic Sea was monitored for 8-years by measurements acquired at two mooring sites. The two moorings, equipped with CTD probes and ADCPs, are located in the Bari Canyon and in an open slope sector along the Southern Adriatic Margin. These regions are of interest because affected by episodic dense shelf water cascading events whose dynamic has direct implications on deepwater morpho-dynamic, biogeochemical cycles and trophic networks. In this work, the sedimentation flux and its interdecadal dynamic is analysed examining in detail the sedimentary processes triggered by dense water flow through the analysis of the echo records of ADCPs.The integration of hydrodynamic, turbidity and particle grain-size data provided estimates of the sediment flux, separating phases when the flow actively erodes the seabed from phases when particles are transported to the mooring location through density flows.The frequency and velocity of dense-water cascading currents vary in time and space reflecting the capacity of sediment transport. Data analysis demonstrated that the hydrodynamic event that mostly accounts for sediment transfer to the deep basin is represented by current pulses induced by the passage of dense waters. The average annual sediment flux has been quantified and the Bari canyon shows transport more than five time larger than in the open slope sector, confirming that the canyon is the dominant pathway of sediment transfer to the deep basin. In contrast, in the open slope, albeit a minor lateral sediment advection, is impacted by currents that are able to trigger intense resuspension of seabed sediments, which can contribute over 80% of the total solid load.This study allows unravelling the role of cascading in the sediment resuspension and transport processes and is essential to support deciphering the sedimentary records in the study area. The long temporal extent of the dataset used for quantification provides a reliable contribution to the Quaternary sediment budget determination.

TRIASSIC-JURASSIC RIFT-RELATED DEFORMATION AND TEMPERATURE-TIME EVOLUTION OF THE FOSSIL ADRIATIC MARGIN: A REVIEW FROM OSSOLA AND STRONA DI OMEGNA VALLEYS (IVREA-VERBANO ZONE)

The direct observation and investigation of rift-related structures at the mesoscale is uncommon. Hence, detailed constraints on the evolution of the main faults and shear zones developed during crustal extension are not always available.The Ivrea-Verbano Zone, in the Italian Southern Alps, samples remnants of the former lower crust of the rifted margins surrounding the Alpine Tethys and therefore provides the opportunity to directly investigate rift-related tectonics. Here, several shear zones have been recognized and interpreted as related to Mesozoic rifting. However, even if there is a general agreement with this interpretation, the precise age of activity of many of those shear zones is not well constrained.In this paper we present a review of the Triassic-Jurassic geochronological and thermochronological data available for two sections of the Ivrea-Verbano Zone, the Strona di Omegna and Ossola valleys, where at least two extensional shear zones are exposed. Ductile deformation occurred under amphibolite-facies conditions and it was alternatively attributed to late Variscan deformation or to Triassic-Jurassic rifting-related tectonics.We discuss the available chronological data and the different interpretations provided for the shear zones considering also new geochronological studies on other lower crustal shear zones exposed in other sectors of the Ivrea-Verbano Zone. This review allows us to strengthen the more recent interpretations indicating that these shear zones are important tectonic structures related to Late Triassic-Jurassic deformation in the lower crust of the Adriatic margin.

An outline of the geology of the Northern Apennines (Italy), with geological map at 1:250,000 scale

An outline of the geology of the Italian Northern Apennines, to accompany a geological map at 1:250,000 scale covering the Emilia- Romagna, Marche, Tuscany and Umbria regions, is presented herein. The map is intended as a first result of a longer term project carried out by the Geological Surveys of the above regions, aimed to create a common geological map at 1:10,000 scale, useful for environmental planning and management.The lithostratigraphic units are grouped in domains and successions (with references to main tectonic units), and a special effort was made to correlate similar lithostratigraphic units across the area. The enclosed geological map distinguishes stratigraphic successions deposited in: a) Ligurian Domain (Internal and External Ligurian domains); b) Subligurian Domain; c) Tuscan Domain (Tuscan Succession, Tuscan Metamorphic Succession, Cervarola- Falterona Succession, Modino Succession, Rentella Succession, Pseudoverrucano Succession); Umbria-Marche-Romagna Domain. Tectonic units derived from regional tectonic mélanges and shear zones (Sestola-Vidiciatico Unit), and units affected by HP metamorphism in the Tuscan Archipelago and southern Tuscany have been mapped. Distinguished younger successions are: a) Epiligurian Succession; b) Miocene-Pleistocene succession of the Tyrrhenian margin; c) Miocene- Pleistocene succession of the Po Plain and Adriatic margin. The main outcrops of magmatic rocks (Miocene-Pleistocene in age) and Quaternary alluvial, continental and coastal deposits have also been mapped. Main tectonic contacts (high-angle normal faults, main thrust and low-angle normal faults) are indicated. The 1:250,000 geological map of the Northern Apennines is freely available as PDF, raster and vector GIS data from the web site: https://www.geological-map.it.

A brachiopod biotope associated with rocky bottoms at the shelf break in the central Mediterranean Sea: Geobiological traits and conservation aspects

Abstract In the Recent, brachiopods only seldom occur in benthic communities. A biotope dominated by Megerlia truncata was identified in 2013 by exploration of the south‐easternmost Adriatic margin by Remotely Operated Vehicle (ROV). Emerging rocky substrates next to the shelf break at approximately 120 m appear intensively exploited by this eurybathic rhynchonelliformean brachiopod, attaining a population of more than 300 individuals per m2. Calcareous red algae are almost ubiquitous at this site and preferentially encrust sectors of the substrate where brachiopods are minimal. This Megerlia biotope is a novel finding for this part of the Mediterranean Sea, similar to a situation previously observed in the Western Basin, off the Mediterranean French coast. It is proposed that this remarkable brachiopod biotope and the adjacent rhodolith bed are considered important for conservation management.

Historical sedimentary deposition and flux of PAHs, PCBs and DDTs in sediment cores from the western Adriatic Sea.

The sources and depositional history of polycyclic aromatic hydrocarbons (PAHs) and organochlorine compounds (OCs) over the last century were investigated in sediment cores from the North Adriatic Sea (Po River prodelta) and the South-Western Adriatic Margin (SWAM). Contaminant concentrations were higher in the Po River prodelta. ∑16PAHs ranged from 193 to 533 ng g-1, ∑5PCBs ranged from 0.9 to 5.2 ng g-1 and ∑DDTs (p,p'-DDD+p,p'-DDE) ranged from 0.1 to 2.5 ng g-1. In the SWAM, ∑PAHs ranged from 11 to 74 ng g-1 while ∑PCB and ∑DDT concentrations were close to the MQL. Accordingly, contaminant fluxes were much higher in the northern (mean values of 152 ± 31 ng cm2 y-1 and 0.70 ± 0.35 ng cm2 y-1 for PAHs and OCs, respectively) than in the southern Adriatic (2.62 ± 0.9 ng cm2 y-1 and 0.03 ± 0.02 ng cm2 y-1 for PAHs and OCs, respectively). The historical deposition of PAHs seemed to be influenced by the historical socioeconomic development and by changes in the composition of fossil fuel consumption (from petroleum derivatives to natural gas) in Italy from the end of the 19th century to the present. Similarly, vertical variations in DDT concentrations matched its historical use and consumption in Italy, which started around in the mid-late 1940s to fight typhus during the II World War. Contaminant concentrations detected in sediments does not seem to pose ecotoxicological risk for marine organisms in the Adriatic Sea.

Transfer of deformation during indentation: Inferences from the post- middle Miocene evolution of the Dinarides

Understanding the structural and kinematic effects of indentation is still debated due to the large number of competing mechanisms associated with the complex orogenic build-up. Among the many examples available worldwide, the evolution of the Adriatic continental microplate in the Mediterranean domain provides one of the best places to understand the mechanics of indentation. This understanding is hampered by the lack of structural and kinematic data in the Dinarides, an orogen situated at the critical transition between the Alps, Albanides and Hellenides, and across the Adriatic margin of the Apennines. We have studied the less known area of the central and south-eastern Dinarides by focussing on collecting a new kinematic dataset for structures formed during the Adriatic indentation, which postdates the main Late Jurassic – Paleogene orogenic structuration. Our results are in agreement with previous interpretations of an early-middle Miocene period of extension that affected the entire orogen across its strike and is incompatible with indentation effects in the studied parts of the Dinarides. More importantly, we demonstrate for the first time that the post- middle Miocene Dinarides deformation was characterized by a coherent regional system of large offset dextral strike-slip faults, which transfer gradually their offsets to thrusts and high-angle reverse faults. The overall deformation transfer mechanism can be described as a special class of continental restraining bends or stepovers, whose geometry is controlled by rheological distribution. The integration of our results in the larger geodynamic context shows that the post-middle Miocene Dinarides fault system accommodates the differential motion between the N- to NE-wards Adriatic indentation and the rapid S- to SW- ward movement of a Hellenides area situated SE of the Kefalonia Fault, driven by the Aegean slab-roll back.

The syn-rift stratigraphic record across a fossil hyper-extended rifted margin: the example of the northwestern Adriatic margin exposed in the Central Alps

To understand the overall spatial and temporal evolution and resulting sedimentary stacking patterns within an evolving hyper-extended rift system, we investigated the Austroalpine and Upper Penninic nappes in the Central Alps. These nappes preserve pristine remnants of the northwestern Adriatic rifted margin showing the transition from stretched and hyper-extended continental crust to exhumed mantle of a sediment-starved, magma-poor rifted margin. Our paper reviews sedimentological and structural data that enable us to determine a general chrono-tectono-stratigraphic framework for the syn-rift succession of the margin. The detailed study of the facies distribution within the different rift domains, including proximal, necking, hyper-extended, and exhumed mantle domains, allow us to identify syn- and post-tectonic sedimentary packages. The correlation of these sedimentary packages between the rift domains is based on the identification of basin-wide correlative stratigraphic intervals linked to global or basin-wide Jurassic events: (1) the Early Toarcian Oceanic Anoxic Event; (2) an Early Bajocian bio-siliceous event; and (3) the onset of Tithonian carbonate-dominated sedimentation. Using these timelines, we could recognize the oceanward propagation of the syn-tectonic package from the proximal to the exhumed mantle domains as a function of time. A key observation is that syn-tectonic packages can be compartmentalized into four tectonic system tracts across the margin. Each system tract and their associated bounding surfaces record the stratigraphic evolution and change in deformation mode related to distinct and successive syn-rift phases that correspond to the stretching (~ 10My), necking (~ 6My), hyper-extension (~ 15My), and mantle exhumation (~ 18My) phases.

Upper Triassic\u2012Middle Jurassic resedimented toe-of-slope and hemipelagic basin deposits in the Dinaridic Ophiolite Belt, Zlatar Mountain, SW Serbia

In the Dinaridic Ophiolite Belt, small (m-scale) to large (km-scale) blocks of Middle to Upper Triassic, and Middle to Upper Jurassic, more or less silicified bedded limestone are widely present, both as parts of para-autochthonous successions and as redeposited blocks in ophiolitic mélanges. The studied, approximately 230-m-thick succession in the wider area of Zlatar Mountain, is one of the most important para-autochthonous sections in the Serbian part of the Dinaridic Ophiolite Belt. The succession is made up of an alternation of redeposited carbonate toe-of-slope deposits, sand to clay-sized siliciclastic rocks, hemipelagic mudstones and radiolarite–spongiolite basin facies. In the lower part of the sequence, the components of the siliciclastic beds were derived mostly from low- and medium-grade metamorphic rocks. Similar components, together with sand-sized fragments of ophiolitic rocks, were encountered in small amounts in some redeposited carbonate beds. The chronostratigraphic assignment of the succession is based mostly on foraminifers, but age-diagnostic radiolarians and other microfossil groups were also considered. In the lower part of the probably continuous succession, a Norian–Rhaetian assemblage was recognized; a Sinemurian–Pliensbachian assemblage was encountered up-section, whereas the upper part of the succession could be assigned to the Bajocian–Bathonian. Considering the paleogeographic reconstructions and the analogies of age-equivalent sections, the succession records the depositional history of the Bosnian Basin during the Late Triassic to Middle Jurassic period and may contribute to the understanding of the evolution of the Adriatic margin of the Neotethys Ocean in the transition interval from passive to active margin stages.

Phase equilibrium modelling of the amphibolite to granulite facies transition in metabasic rocks (Ivrea Zone, NW Italy)

AbstractThe development of thermodynamic models for tonalitic melt and the updated clinopyroxene and amphibole models now allow the use of phase equilibrium modelling to estimate P–T conditions and melt production for anatectic mafic and intermediate rock types at high‐T conditions. The Permian mid‐lower crustal section of the Ivrea Zone preserves a metamorphic field gradient from mid amphibolite facies to granulite facies, and thus records the onset of partial melting in metabasic rocks. Interlayered metabasic and metapelitic rocks allows the direct comparison of P–T estimates and partial melting between both rock types with the same metamorphic evolution. Pseudosections for metabasic compositions calculated in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O (NCKFMASHTO) system are presented and compared with those of metapelitic rocks calculated with consistent end‐member data and a–x models. The results presented in this study show that P–T conditions obtained by phase equilibria modelling of both metabasic and metapelitic rocks give consistent results within uncertainties, allowing integration of results obtained for both rock types. In combination, the calculations for both metabasic and metapelitic rocks allows an updated and more precisely constrained metamorphic field gradient for Val Strona di Omegna to be defined. The new field gradient has a slightly lower dP/dT which is in better agreement with the onset of crustal thinning of the Adriatic margin during the Permian inferred in recent studies.

Macrofaunal assemblages in canyon and adjacent slope of the NW and Central Mediterranean systems

Macrofaunal assemblages were studied along bathymetric transects in six canyons and four adjacent open slopes of the Mediterranean Sea. The different areas investigated were located approximately along a longitudinal gradient at similar latitudes. Three regions were investigated: the Catalan (from 334 to 1887 m depth), the Ligurian (from 222 to 2005 m depth) and the South Adriatic margins (from 196 to 908 m depth). The analysis of the meso-scale distribution of assemblage structure and biomass showed significant differences among regions, which resulted in high values of δ-diversity. Clear differences in trophic composition were also observed, and a decreasing pattern in the individual body size of macrofaunal organisms moving Eastward. These patterns were apparently linked to changes in food supply, whereas macrofaunal abundance and number of taxa showed a decrease pattern with increasing water depth. When the assemblage structure was compared between canyons and adjacent open slope, a very high β-diversity was observed, indicating that the bottom topography exerted a strong effect on the assemblage characteristics.

Impact of dense bottom water on a continental shelf: An example from the SW Adriatic margin

Dense shelf waters have been recognised as a key factor in transporting sediment and organic matter across continental slopes; however, the effect of their circulation on continental shelves is still overlooked. The Adriatic Sea is one of the areas in the Mediterranean where dense shelf water forms and flows as a bottom-hugging gravity current along the continental margin. A fraction of this dense water passes beyond the shelf break and flows downslope through cascading, while a large (lighter and faster) portion remains on the shelf, with a principal vein flowing between 80 and 120 m water depth.This paper presents the 3D shape, internal architecture and sediment facies of a variety of large-scale sedimentary features detected on the continental shelf and at the shelf edge, between 50 and 300 m water depth. These features include giant comet marks, large flute-shaped scours, muddy sediment waves, very large dunes with superimposed bedforms, active and relict sand ridges and shelf edge contourites. Both erosional and depositional features show an overall internal geometry and orientation consistent with water masses flowing southward, and are located where flows become accelerated by topographic constraints and deviated by the curvature of the shelf edge.In this study, the morphology and seismic stratigraphic structure of large-scale bedforms are investigated in an effort to place constraints on bedform evolution and preservation, especially as predictive tools for sand resource management, and to bring new evidence of the interaction between unidirectional hydrodynamic processes and seafloor dynamics on the shelf.

Meiofaunal biodiversity in submarine canyons of the Mediterranean Sea: A meta-analysis

Deep-sea canyons include highly heterogeneous habitats characterised by a large variability in terms of geomorphological, oceanographic end ecological features. Despite the increasing efforts conducted in the last decade to investigate deep-sea canyon ecology, patterns and drivers of their biodiversity are still controversial. Here, we carried out a meta-analysis of meiofaunal abundance, biomass, richness of higher taxa and taxonomic composition from 18 Mediterranean canyons, located in the Western (Balearic, Catalan, Ligurian margins), Central (South Adriatic margin) and Eastern (Cretan margin) basins. We also compared Mediterranean canyons with 3 canyons located in the European margins of the Northern Atlantic Ocean at similar latitudes. Our results revealed the presence of weak differences in terms of meiofaunal abundance and biomass among canyons and adjacent slopes. However, their biodiversity (expressed as expected richness of higher meiofaunal taxa) was typically similar or higher in canyons than in open slopes. High levels of dissimilarity were also observed between canyons and slopes in terms of taxonomic composition. The variability of meiofaunal assemblages in canyons appear linked to their geomorphological heterogeneity. The results of the meta-analysis also indicate that the most important drivers of the observed patterns were water depth, regional setting (i.e., differences among Mediterranean Western, Central and Eastern sub-basins) and geomorphological characteristics of the canyons. We conclude that deep-sea Mediterranean canyons contribute significantly to the deep-sea biodiversity at both regional and whole-basin scale.

Detrital signatures of impending collision: The deep-water record of the Upper Cretaceous Bordighera Sandstone and its basal complex (Ligurian Alps, Italy)

Despite intensive research efforts and significant advances in the understanding of subduction and obduction processes that affected several units which at the present day compose the Western Alps, the paleogeographic evolution of the Alpine Tethys represents a debated topic in Alpine geology. The role of the opposing continental margins (passive European margin and active Adriatic margin) as source regions for Cretaceous siliciclastic turbidites bordering the convergent system remains disputed. To address this question along the Ligurian Alps transect, a multi-proxy provenance analysis is applied to the two terrigenous superimposed units (Hauterivian-Campanian San Bartolomeo Fm. and Campanian-Maastrichtian Bordighera Sandstone) of the San Remo-Monte Saccarello Unit of the Western Ligurian Flysch complex. Petrographic analyses characterize the basal San Bartolomeo Fm. as quartz-rich mature sandstones. By contrast, the overlying Bordighera Sandstone represents texturally and compositionally immature first-cycle arkosic arenites. This change records the evolution of the sediment provenance from a stable craton into a continental basement uplift setting, reflecting erosion of granitoid plutons and the low-grade metamorphic basement. Geochronological data (UPb detrital zircon ages) indicate that virtually the same source terranes provided the source for both formations. The detrital age spectra display age peaks are compatible with well-documented magmatic and metamorphic pulses that affected the Southern Variscides in the Paleo-European margin. The strong affinity of clastic detritus with the Paleo-European margin basement rocks underlines the importance of the lower plate passive continental margin in supplying sand-rich turbidite systems prior to the arrival of the passive margin in the subduction zone.

Evidences for pre-orogenic passive-margin extension in a Cretaceous fold-and-thrust belt on the basis of combined seismic and field data (western Transdanubian Range, Hungary)

Combined sedimentological and structural analysis was carried out in the field and on 2D seismic reflection profiles to recognize pre-orogenic structures in a Cretaceous fold-and-thrust belt. Detailed field observations were made in the Keszthely Hills, Western Hungary, while 2D seismic interpretation was carried out in the neighbouring Zala Basin. As a result, a fault-controlled intraplatform basin system was identified by a detailed analysis of bounding faults, and related outcrop-scale structures. The Norian–Rhaetian (227–201.3 Ma) synsedimentary faulting was associated with talus breccia formation, small-scale faulting, and dyke formation, in addition to slumping and other soft-sediment deformations. Based on the distribution of talus breccia, WNW–ESE-trending map-scale normal faults were identified in the Keszthely Hills, which is in agreement with the directly observed outcrop-scale synsedimentary faults. On seismic sections, similar WNW- or NW-trending Late Triassic normal faults were identified based on thickness variations of the syn-rift sediments and the presence of wedge-shaped bodies of talus breccia. Normal faulting occurred already in the Norian, and extensional tectonics was active through the Early and Middle Jurassic. The Late Triassic grabens of the western Transdanubian Range could be correlated with those in western part of the Southern Alps, and the Bajuvaric nappe system of the Northern Calcareous Alps. These grabens were situated on the proximal Adriatic margin, and they represent the first sign of the Alpine Tethys rifting. The locus of extension was laterally migrated westward, towards the distal Adriatic margin during Early and Middle Jurassic.

Understanding fossil fore-arc basins: Inferences from the Cretaceous Adria-Europe convergence in the NE Dinarides

Abstract The evolution of relict fore-arc basins and their kinematic relationships with sedimentation is often less well understood due their fragmentation or amalgamation of individual basins and continental units by the subsequent collision or other post-orogenic deformation. One example is the Cretaceous–Paleogene closure and associated sedimentation of the Neotethys Ocean that was located between the European and Adriatic continental units. Our combined structural, lithostratigraphic and sedimentological study in the NE Dinarides of Serbia demonstrates a variable Cretaceous fore-arc deposition on the European plate that correlates with the shallow- to deep-water sedimentation over the subducting Adriatic margin. The fore-arc was affected by an initial Early Cretaceous–Cenomanian period of contraction, followed by Turonian–Santonian extension, the basin being exhumed by contraction during the latest Cretaceous–Early Paleogene collision. The collisional geometry was subsequently fragmented by structures associated with the Neogene evolution of the Pannonian Basin. The correlation with the preserved amount and depositional character of Cretaceous trench sediments documents an interplay between subduction accretion and subduction erosion associated with external tectonic forcing, slab retreat and back arc extension.

Framing Continental Shelf Waves in the southern Adriatic Sea, a further flushing factor beyond dense water cascading

Continental Shelf Waves (CSWs) are oscillatory phenomena migrating along the continental margins, controlled by the interplay of rotation and bathymetric gradients. Here we combine observational data from five moored current meters and high-resolution hydrodynamic model fields for describing the generation and propagation of CSWs along the Southern Adriatic Margin (SAM, eastern Mediterranean Sea), where the possibility of their occurrence has been theoretically hypothesised but not experimentally observed up to now. Results show that in spring 2012 a train of CSWs with 35–87 km wavelength and 2–4 day period was generated on the northern sectors of the SAM and propagated southwards along its western slope. Along their path, CSWs modify their apparent frequency and oscillation mode as an effect of the background current and scattering caused by changes in the continental margin morphology. This signal appears as a persistent feature triggered by the inflow of a dense water vein formed in the northern Adriatic Sea, propagating upwelling and downwelling patterns along broad sectors of the continental slope. CSWs thus appear as an additional remote-controlled mechanism for cross-shelf exchange of water, sediment and nutrients in the SAM, besides the well-acknowledged dense water downflow along preferential pathways driven by local topographic constraints.