Most plate kinematic reconstructions concerning the Iberian plate imply a major (>400 km) left-lateral displacement between Iberia and Eurasia during the opening of the Bay of Biscay (Late Jurassic-Early Cretaceous). In the past, authors identified the North Pyrenean Zone (NPZ) as the domain accommodating this lateral displacement, while more recent works tend to distribute the deformation in two or three transtensional corridors located in the NPZ and in the Iberian Chain basins. Nevertheless, field evidence contrasts with such models, since no structure seems to have accommodated such huge amount of displacement. Moreover, debate exists concerning the timing of the left-lateral displacement between Iberia and Eurasia (Late Jurassic vs Early Cretaceous).

We present a review of the tectono-sedimentary and kinematic evolution of rift basins distributed across the wide Iberia-Eurasia plate boundary that recorded the Late Jurassic-Early Cretaceous rifting phase, from the Iberian Chain basins (in the southwest) to the northern part of the Aquitaine domain aligned with the Armorican Margin (to the northeast). To the first order, these basins experienced the same tectonic evolution, with an initial Permian-Triassic rifting phase related to the breakup of Pangea, and a subsequent Late Jurassic-Early Cretaceous rifting phase related to the opening of the Bay of Biscay. For this latter phase, authors have proposed contrasting kinematic models, with opening mechanisms varying between orthogonal rifting and transtensional/pull-apart tectonics. Our review allows to propose a reappraisal of the kinematic evolution of the Iberia-Eurasia diffuse plate boundary during the Late Jurassic-Early Cretaceous rifting, which consists in four phases: (i) a Late Jurassic phase of transtensional deformation localized at the borders of the system (Asturian Basin/Southwesternmost Iberian Chain basins and Armorican Margin), while the rest of the basins underwent orthogonal rifting, contemporaneous with rifting in the Bay of Biscay margins; (ii) a Neocomian phase of generalized marine regression; (iii) a Barremian-Early Albian phase of distributed left-lateral transtension, contemporaneous with crustal breakup in the Bay of Biscay; (iv) an Albian-Cenomanian phase of left-lateral transtension localized in the Basque-Cantabrian/North Pyrenean corridor, contemporaneous with ocean spreading in the Bay of Biscay, while the rest of the rift basins within the plate boundary became tectonically inactive. This evolution highlights a trend of progressive localization of the plate boundary from the Late Jurassic to the Early Cretaceous in response to the different tectonic phases of the Bay of Biscay margins. This work also allows to highlight the role of some rift basins in accommodating part of the deformation between Iberia and Eurasia which have been often disregarded, due to their position below the Cenozoic cover of the Pyrenean foreland basins, such as the Ebro and Aquitaine domains.

How to cite: Asti, R., Saspiturry, N., and Angrand, P.: Progressive localization of a diffuse transtensional plate boundary: the example of the Iberia-Eurasia plate boundary during the opening of the Bay of Biscay (Late Jurassic-Early Cretaceous), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2691, https://doi.org/10.5194/egusphere-egu23-2691, 2023.

In the Peloritani Mountains (North-Eastern Sicily, Italy), evidence of several fractured pebbles and cobbles was found in the coarse-grained siliciclastic deposits of the middle-upper Miocene San Pier Niceto Formation. The pattern of this pebble/cobble fracturing is analogous in type and orientation. These broken pebbles and cobbles appear fractured and affected by normal subparallel faults in a single clastic element, with mm- to cm offset. Such peculiar structures have been commonly associated with active tectonics in recent deposits. 
The present research is therefore devoted to the study of the middle-upper Miocene San Pier Niceto Fm. in Peloritani Mountains for i) characterizing the morphologic properties and orientation of clasts, ii) defining the spatial orientation of faults and principal stresses, iii) understanding their tectono-sedimentary genesis. The goal is to ascertain that broken clasts may or may not represent paleoseismic evidence and coseismic deformation during the initial stages of the extensional tectonics in the still active area of the Calabrian Arc.

How to cite: Maniscalco, R., Somma, R., and Spoto, S. E.: Broken pebbles and cobbles from the middle-upper Miocene siliciclastic deposits of the Peloritani Mountains (Sicily, Italy): evidence of extensional paleotectonics?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9397, https://doi.org/10.5194/egusphere-egu23-9397, 2023.

The Empordà basin is located in NE Catalonia (Spain), overprinting the Eastern Pyrenees where this mountain belt reaches the Mediterranean Sea. The area offers an opportunity to study cycles of orogenic evolution, from mountain building to destruction, although with some peculiar features. Following Pyrenean contractional structures that ceased in the Oligocene, earlier than in the Central and Western Pyrenees finished during the lower Miocene, the extension that depressed the Empordà basin seems to be a younger event (late Miocene-Pliocene) than the opening of the Western Mediterranean (Gulf of Lyon and Valencia trough; late Oligocene-Miocene). The regional NE-SW extensional fault systems that dominate from the Gulf of Lion to the Catalan Coastal Ranges and Valencia grabens contrast with the NW-SE normal faults in the Empordà basin, which are also associated with alkali volcanism during the Neogene. This feature is still poorly understood, together with the absence of crustal root in the adjacent relict relief of the Pyrenees despite the relatively high elevation.

To gain insights into these questions and into the detailed geochronology and mechanisms of the transition from convergence to extension, we have revisited the tectono-sedimentary record of the South-Pyrenean and Empordà basins. First, the provenance of the clastic deposits from the Paleogene to the Neogene gives information about the evolution of the sedimentary systems, as well as the tectonic changes in the source regions. This data combined with low-temperature thermochronology of source reliefs and basin sedimentary units allows characterizing part of the geodynamic evolution from the NW Mediterranean realm. Complementary, new structural data from field observations and seismic profile interpretation provide us with inferences on a new structural model of the region.

How to cite: Peris, S., Griera, A., Gómez-Gras, D., and Teixell, A.: The transition from convergence to extension in the NW Mediterranean: insights from the thermochronologic and tectono-sedimentary record in the Eastern Pyrenees and Empordà basin (NE Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7642, https://doi.org/10.5194/egusphere-egu23-7642, 2023.

During the Burdigalian the North Alpine Foreland Basin, as part of the central and western Paratethys, underwent various paleogeographic and paleoenvironmental changes which led to the deposition of different sedimentary facies. For instance, the Ottnangian regional stratigraphic stage (18.2 – 17.3 Ma) was characterized by a major transgression in the beginning, with the deposition of several littoral facies along the northern coastline of the North Alpine Foreland Basin. Successively, the late Ottnangian documents the final retreat of the Paratethys Sea from the North Alpine Foreland Basin and the deposition of widely distributed fluviatile units. The outcrop Neustift in southeast Germany bears many different siliciclastic facies and shows the transition of the Ottnangian marine realm towards a riverine-deltaic environment. Despite the exceptional size and complexity of the succession, this outcrop is only poorly studied. Anyhow, this section gives unique potential for the understanding of the facies evolution during the terminal Ottnangian. In total a 70 m long and 15 m high sedimentary log was recorded together with several micropaleontological samples (1 kg each) for the reconstruction of the depositional environment and stratigraphic positioning. The micropaleontological samples yielded 164 genera of benthic foraminifera and 144 species of ostracods. Moreover, these deposits are extremely rich in macrofossils (elasmobranchia, mollusca, brachiopoda, echinoidea) which are also poorly studied. We found out, that the lowermost segment of the section belongs to the marine “Littoral Facies of Holzbach-Höch”, which deposited directly on top of a transgressive layer on the crystalline basement. Several of the observed ostracod species are new to these deposits. Large-scale cross-bedding structures show that this shallow marine environment was affected by strong tidal currents along the rocky shoreline. The fine-grained sediments with wavy and lenticular bedding on top of the littoral deposits show an ongoing transgression, with neritic foraminiferal assemblages and bioturbation. They were assigned by biostratigraphy to the uppermost Neuhofen Formation. Finally, the marine deposition is replaced by a large-scale deltaic system, resulting into the deposition of the fluviatile Ortenburg gravel. This preliminary study should draw some more attention to this unique outcrop in the North Alpine Foreland Basin and the potential for further studies in the realm of sedimentology and paleontology. 

How to cite: Drießle, T. and Hofmayer, F.: From shoreface to riverbed – Facies evolution in Burdigalian deposits of the North Alpine Foreland Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8123, https://doi.org/10.5194/egusphere-egu23-8123, 2023.

Continental subduction and collision are not merely follow-ups of oceanic subduction but mark the transition from lithospheric-scale deformation localized along the subduction interface to crustal-scale deformation distributed across the orogen. In order to unravel the processes typifying the dynamic changes from oceanic subduction to collision, we have characterized pressure-temperature (P-T) and spatio-temporal evolution of rocks on either side of the tectonic contact (Briançonnais/Liguro-Piemont contact – Br/LP contact) separating the subducted oceanic remnants from the subducted continental fragments along the length of the Western Alps. West of the contact, the Briançonnais zone is considered as a micro-continent composed of pre-Alpine basement and Paleozoic to Meso-Cenozoic cover units. East of the contact, the Liguro-Piemont zone corresponds to a nappe-stack, with three groups of oceanic (upper, middle and lower) units. The Piemont zone is pinched in between the two in the southern part of the Western Alps and correspond to the distal part of the Briançonnais continental margin.

Results indicate that the maximum temperature and pressure difference on each side of the contact is generally < 30°C and < 0.3 GPa, evidencing that (i) no significant metamorphic gap exists between both sides and that (ii) offscraping of the continental fragments occurred at the same depth as the oceanic ones. The dataset also shows a northward increase of peak P-T conditions from ~300°C-1.2 GPa to ~500°C-2.0 GPa. The preservation of similar P-T conditions on both sides of the Br/LP contact can tentatively be assigned to either (1) offscraping of the Liguro-Piemont and later of the Briançonnais at similar depths or (2) entrainment and joint burial of the Liguro-Piemont (previously accreted or subducted) fragments together with the Briançonnais margin. The latter hypothesis, however, is not supported by the ~10 My gap between the peak burial of the Briançonnais and Liguro-Piemont zones. The recurrent depth range of the various units, which reflects systematic variations of slicing and mechanical coupling along the plate interface (Herviou et al., 2022), suggests that (1) similar slicing mechanisms and strain localization prevailed during both oceanic and continental subduction and (2) shows that the Br/LP contact represents a frozen-in subduction interface. The end of high-pressure and low-temperature metamorphism and continental subduction at ~33 Ma would thus mark the stalling of subduction interface dynamics and the onset of strain distribution across the plate interface and into the lower plate.

• Herviou, C., Agard, P., Plunder, A., Mendes, K., Verlaguet, A., Deldicque, D., Cubas, N., 2022. Subducted fragments of the Liguro-Piemont ocean, Western Alps: Spatial correlations and offscraping mechanisms during subduction. Tectonophysics 827, 229267. https://doi.org/10.1016/j.tecto.2022.229267

How to cite: Mendes, K., Agard, P., Plunder, A., and Herviou, C.: Plate interface frozen at the very end of continental subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11990, https://doi.org/10.5194/egusphere-egu23-11990, 2023.

The Eastern Sardinian margin consists in a hyper-extended rifted margin, located in the western Tyrrhenian Sea, a recent back-arc basin (late Neogene). This area was affected by strong aerial erosion during the Messinian Salinity Crisis (MSC, 5.96 – 5.33 My) associated with the drop of sea level (> 1500 m) which occurred throughout the whole Mediterranean. The Gulf of Orosei and surrounding offshore areas are characterized by small and diffuse drainage systems input, where the Messinian Erosion Surface (MES) has rarely been studied while it has been in large fluvial systems (Rhone, Ebro). The MES was already found in the Cendrino valley (which flows in the Gulf) and in the East-Sardinia Basin but the link between onshore and offshore was never been studied in the area. The “METYSS 4” cruise (June 2019, R/V “Téthys II”) allowed acquiring more than 2000 km of very high-resolution (VHR) seismic data (Sparker), following a dense grid (1.5 km average profile spacing), on the Eastern Sardinian continental shelf, and especially in the Orosei Gulf area, that has been little explored until now. While the main limitation on seismic data (air-gun) interpretation is often due to the occurrence of sea bottom multiple, the limitation for Sparker data may also be due to very short shot intervals at greater water depth. The seismic trace ends where there still is signal of interest. Thus, we applied a simple method to increase investigation depth for short shot intervals (0.333 - 0.533 ms), which allowed interpretation on the continental slope. This approach consists in copying the raw data and concatenating the copied data under the raw data with a shift of 1 shot point. To constrain the MES depth on the continental slope and shelf we compared air-gun seismic data from previous METYSS surveys, where the MES has already been interpreted by a strong erosional discordance between Plio-Quaternary deposits and pre-MSC units, with the new VHR data. The restoration of the morphological features of the Orosei canyon at Messinian times shows that the former Messinian canyon network is very similar to the present-day one. The present-day canyon and its tributaries show sub-marine erosion in the talwegs. The heads of the canyons present gravitational features, highlighted by chaotic deposits near the talweg of the canyon or in-between the Plio-Quaternary strata. Offshore Arbatax, south Orosei, the seismic profiles show no significant Plio-Quaternary deposits (thickness < 0.1 sTWT), which allows polygenic pre-MSC units to occur at the seafloor. In the Gulf, we observe thick deposits (0.4 - 0.5 sTWT) on the right bank of Orosei Canyon, making it more complicated to image the MES in this area. The sedimentation rate on this margin is very low (c.a. 9 cm/ka in the Gulf of Orosei), which is consistent with previous studies on the East-Sardinian basin (3-20 cm/ka). These preliminary results will allow correlating for the first time the MES distribution from the onshore to the offshore continental slope of the Eastern Sardinian Margin in order to improve the MSC understanding in this key area.

How to cite: Sylvain, R., Gaullier, V., Watremez, L., Chanier, F., Caroir, F., Graveleau, F., Lofi, J., Maillard, A., Sage, F., Thinon, I., and Travan, G.: The Messinian Erosion Surface along the Eastern Sardinian Margin, Western Tyrrhenian: New Insights from Very High-Resolution Seismic Data (METYSS 4), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13909, https://doi.org/10.5194/egusphere-egu23-13909, 2023.

We present a study of a Mio-Pliocene marine to a continental clastic sedimentary succession of the southern Apennines Foreland Basin System well exposed in the Miscano River in the Irpinia sector of the chain. These well-bedded wedge-top basin deposits host a significant angular unconformity between a post-evaporitic succession (uppermost Messinian-lowermost Pliocene), developed on top of the evaporite deposits related to the Messinian Salinity Crisis, and an overlying upper part of the Zanclean sediments. The unconformity witnesses a major tectonic shortening stage of the southern Apennines characterized by out-of-sequence thrusting that involved the Mio-Pliocene wedge-top basin deposits. Meio-microfaunal and nannofloral fossil assemblages were analyzed to define the depositional environments and biostratigraphy of the two successions. In addition, benthic foraminiferal and ostracod assemblages were studied in detail, and their autochthonous/allochthonous provenience was discussed from a paleoecological point of view. The relative response of these assemblages to environmental parameters, such as salinity, oxygenation, paleobathymetry and climatic changes, allowed us to reconstruct the paleoenvironmental evolution of these wedge-top basin deposits.

How to cite: Infante, A., Aiello, G., Barra, D., Ciarcia, S., Di Donato, V., Morabito, S., Prinzi, E. P., and Vitale, S.: Palaeoenvironmental reconstruction of the Mio-Pliocene succession of the Miscano River: insights on sedimentation after the Messinian salinity crisis in the southern Apennines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4235, https://doi.org/10.5194/egusphere-egu23-4235, 2023.

We present a study on the mud volcanoes of Bolle della Malvizza located in the Irpinia sector of the southern Apennines (southern Italy). These structures are hosted in the Upper Cretaceous-Upper Miocene Fortore succession (Lagonegro-Molise Basin) and emit mud and bubbles of methane and CO2. Mud volcanoes are focused in a narrow area of ca. 5000 m², consisting of eight main emission centres and several minor craters. We approached this research with a multidisciplinary study, including stratigraphic and structural surveys, geophysical and geochemical investigations and morphometric analyses. This study aims to investigate the origin of fluid migration and shed light on the pathways mainly controlled by faults.

How to cite: Fabozzi, C., Albanese, S., Ambrosino, M., Ciarcia, S., Cicchella, D., Natale, J., Prinzi, E. P., Verrilli, F., and Vitale, S.: A multidisciplinary study of the “Bolle della Malvizza” mud volcanoes (southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2648, https://doi.org/10.5194/egusphere-egu23-2648, 2023.

We present a study of the synorogenic deposits associated with the orogenic construction of the southern Apennines. This orogen is a segment of the Alpine chain system bounding the central-western Mediterranean Sea. Southern Apennines form an orogenic belt consisting of the superposition of some successions of the downgoing Adria plate, made of shallow-water to pelagic sedimentary successions. The synorogenic sedimentation was ruled by the migration of the forebulge-foreland basin system, with the flexure of the continental part of the Adria plate since the Oligocene (forebulge stage), mainly due to the slab retreat process. The thrust front-foredeep-forebulge system migrated toward E/NE until the middle Pleistocene. We focussed our attention on the Foreland Basin System synorogenic deposits mainly consist of back-bulge, foredeep, and wedge-top basin sediments.

How to cite: Ciarcia, S. and Vitale, S.: Neogene synorogenic stratigraphic evolution of southern Apennines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1865, https://doi.org/10.5194/egusphere-egu23-1865, 2023.