United States

Early Palaeozoic represents a crucial period in Earth history, marked by intervals of life spread alternated with short-lasting crisis in biological activity. The Zagros Basin (SW Iran) could be a key area for the study of this time interval, due to the widespread and well-exposed Cambrian-Ordovician successions; nevertheless, these are still poorly constrained from a sedimentological and stratigraphic point of view. This study, carried out through a high-resolution facies and microfacies analysis of the Zard Kuh section, aims to give a contribution to the palaeogeographic evolution of this area. The studied section (296 m thick) includes the upper Mila C Member and Ilebeyk Formation, referred to the late Cambrian (Furongian) based on acritarch assemblages. The upper Mila C Member (23 m thick) is mainly characterized by medium to thin-bedded bioclastic packstones to mudstones grading upward into a nodular limestone unit. A sharp horizon marks the contact with the overlying Ilebeyk Formation, represented by a shale-dominated interval in the lower part. These mudrocks grade upward into heterolithic lithofacies, generating a coarsening upward sequence with an increase of siltstone and sandstone intercalations in the lower-middle part. The coarser-grained layers display scoured basal surfaces, with common gutter casts, capped by plane parallel lamination and hummocky cross-stratification (HCS). In the middle part of Ilebeyk Formation, siliciclastic deposits are alternated with relatively thick carbonatic intervals, showing similar features with Mila C Member. The upper part of the Ilebeyk Formation is dominated by shales, overlain at the topmost by a 28 m thick unit of micaceous sandstone and siltstone. The sandstone layers include plane-parallel bedding, trough cross-stratification and long-wavelength HCS. Based on the facies and microfacies analysis, the depositional system of the studied section is interpreted as a mixed carbonate-siliciclastic ramp. In the Mila C Member and carbonatic unit of Ilebeyk Formation, small cycles characterized by erosive surfaces and fining upward fossiliferous biomicrites suggest deposition in middle ramp setting, affected by storm events. On the other hand, the nodular limestone intervals at the top of the carbonatic units point to deposition below the SWB under a transgressional regime. The shale to heterolithic parasequences from the Ilbeyk Formation are interpreted as autocyclic fluctuations of the depositional system from lower to upper offshore environment. In the uppermost part, the sandstone-dominated interval is attributed to shoreface setting, marking an abrupt change in the bathymetric conditions after a forced regression. The sedimentological features of the studied area can be correlated with other coeval depositional events at both regional (Arabian plate) and global (Laurentia and Baltica) scales, providing new constraints for the lower Palaeozoic evolution of the northeastern Gondwanan margin.

SGI 2021

Facies analysis and depositional environment of a late Cambrian mixed carbonate-siliciclastic ramp from the Arabian Plate (Zagros Basin, Southwestern Iran)

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L'Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS e il Dipartimento di Matematica e Geoscienze dell'Università di Trieste sono orgogliosi di ospitare il 90° Congresso della Società Geologica Italiana a Trieste dal 14 al 16 settembre 2021. La modalità del congresso è interamente online.

Con il motto "Geologia senza frontiere" questo evento mira a promuovere le Scienze della Terra come disciplina scientifica proiettata nel futuro, oltre i confini geografici, politici e disciplinari, per comprendere meglio l'interno del Pianeta Terra e la struttura del sottosuolo, difendere la società da pericolosi eventi geologici, comprendere meglio la variabilità climatica, pianificare l'utilizzo delle georisorse in modo etico e nel rispetto dell'ambiente.


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The National Institute of Oceanography and Experimental Geophysics - OGS and the Department of Mathematics and Geosciences of the University of Trieste are proud to host the 90th Congress of the Italian Geological Society in Trieste on 14-16 September 2021.  The Congress will be held entirely online.

With the motto "Geology Without Borders" this event aims to promote Earth Sciences as a scientific discipline projected into the future, beyond geographical, political and disciplinary boundaries, to better understand the interior of Planet Earth and the structure of the subsurface, defend society from dangerous geological events, better understand climatic variability, plan the use of geo-resources in an ethical way and respecting the environment.


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Earth Sciences should be understood not only as necessary for a better understanding of the interior of the planet Earth, but also as a defense of society from dangerous geological events, for the understanding of climatic variations, for the planning and use of georesources in a ethical and respecting and protecting the environment.

technical paper

In the Northern Ionian Sea, the Calabrian Accretionary Wedge (CAW) is facing directly the subducting Apula plate, mainly made of Mesozoic to Tertiary Carbonate Platform (Del Ben et al., 2010; Volpi et al., 2017). This contribution illuminates the structures and stratigraphic relationships between the frontal part of the orogenic belt, the foredeep and adjacent Apulian foreland. A detailed seismic facies analysis of four multichannel seismic profiles has been carried out to define the tectonic-sedimentary evolution of the study area but without exploration wells not available for these deep offshore area. Seismic interpretation allows to identify four main structural domains: the highly tectonized CAW; the narrow foredeep basin filled by a Pliocene-Holocene subhorizontal succession laying above buried normal faults; the massive carbonate succession of the Apulian Platform showing reef and carbonate platform margin facies; the layered succession of the Apulian Platform characterized by ‘'intra-platform'’ facies in the easternmost portion of the area. Three main regional unconformities with characteristic relationships with structural trends were recognized: i) the Messinian unconformity, related to a regional and significant erosion associated to paleokarst processes on the exposed Mesozoic Apulian Platform, is cut by an array of normal faults in the Apulian foreland and by thrust in the accretionary wedge; ii) the angular and erosive middle Pliocene Unconformity truncates the Lower Pliocene reflectors and is affected by normal faults in the foreland and by compressive tectonics in the CAW; iii) a Jurassic/Cretaceous unconformity in the Apulian foreland is marked by Cretaceous reflectors onlapping the Jurassic carbonate platform. The CAW is characterized by compressive tectonics with several fore-thrusts forming a leading imbricate fan system nearby the orogenic front. The Mesozoic Apulian platform is affected by active extensional tectonics driven by flexural bending since Lower Pliocene (Volpi et al., 2017; Maesano et al., 2020), that probably reactivated old normal faults related to the Permian-Triassic rifting stage. The structural map shows that transpressive and positive inversion tectonics is a common deformational style in the central sector of the foreland, suggesting that the Apulia plate is already part of the Calabrian/Hellenic belt. According to these observations, the compressive tectonics affecting the Apula plate is interpreted as related to shortening processes of both the CAW and Hellenic wedge whose interference plays an important role in defining the tectonic-stratigraphic evolution of the Apula Plate in the Northern Ionian Sea.

The response of the Apula plate to the advancing Calabrian and Hellenic wedges (Northern Ionian Sea): implications for subduction processes and tectono-stratigraphic evolution

The Tertiary Piedmont Basin (TPB) is an episutural basin located on top of the junction between the Western Alps and the Northern Apennines. This work combines geological mapping and interpretation of a seismic line provided by Eni S.p.A. aiming at investigating the sedimentary succession of the Arquata Scrivia-Carrosio area, a key sector separating the Alto Monferrato sector to the west from the Borbera-Curone sub-basin to the east. The seismo-stratigraphic analysis of a 33 km-long SE-NE striking seismic line extending from Carrosio to Alessandria and tied to a well, allowed recognizing seven key stratigraphic surfaces, which define six unconformity-bounded stratigraphic units. These could be tied to the outcrop by identifying component lithostratigraphic units at surface. This works contributes to better understanding of the tectono-sedimentary evolution of this sector of TPB, which can be summarized as follows: during the early Oligocene (Unit 1), coarse-grained deltas (Conglomerati di Savignone and Molare Fms.) established, which passed distally (i.e. to the NE) into turbidites and hyperpycnites (Monastero Fm). Following the swift late Oligocene transgression, these marginal fan deltas were onlapped SE-wards by hemipelagic marlstone, containing isolated channelized turbidites (Unit 2; Gremiasco Fm.). Coarse clastic supply was re-established during the Aquitanian-early Burdigalian, with deposition of confined turbidites, mass transport deposits, and channelized turbidites (Unit 3; Castagnola and Costa Montada Fms). In Unit 4 (Costa Areasa Fm., upper Burdigalian-lower Langhian) a basin plain environment established all over TPB, reflecting an increase of the accommodation space driven by southward tectonic tilting of the basin. A further event of basin inversion is that of the intra-Langhian sea level fall, driven by tectonic uplift to the south and recorded by Unit 5 (upper Langhian-lower Messinian), which comprises a range of shelfal systems (Marne di Cessole, Arenarie di Serravalle and Marne di S.Agata Fossili Fms.) making northward transition into turbidites (Cassinasco Fm.). Lastly, Unit 6 (upper Messinian-Pliocene) encompasses a basal package of conglomerates (Conglomerati di Cassano Spinola Fm.), followed upward by early Pliocene clays (Argille di Lugagnano Fm.), over which the shelf margin prograded depositing the Sabbie d’Asti Fm. In addition, the analysis of velocity data from four additional wells from other sectors of the TPB allowed defining a P-wave velocity and seismic wave propagation model. Besides the increase of velocity with depth, conglomeratic facies were found to show higher velocities (in the range 3500-4200 m/s at depths between 350 and 2800 m) than arenaceous and pelitic facies (in the range 2000-3370 m/s at depths between 350 and 3500 m below surface). Results will help time-depth conversion of seismic lines detailing the subsurface of TPB, contributing to accurate reconstruction of basin fill architecture.

Tectonics and sedimentation interplay in the eastern Tertiary Piedmont Basin (Arquata Scrivia, NW Italy): insights from new seismo-stratigraphic analysis

The Northern Apennines are a seismically active accretionary wedge formed in response to the Late Cretaceous-Eocene closure of the Ligurian-Piedmont Ocean and the Oligocene-Miocene collision between Adria and Europe. The wedge is shaped by WNW-ESE-striking, SW-dipping thrusts accommodating bulk top-to-the NE tectonic transport. Since the Late Miocene, thrusting in the belt external domains acted coevally with extension in the western hinterland domain, where crustal thinning is still being accommodated by NW-SE-striking normal faults. The focal mechanism solutions of earthquakes between 8 and 35 km constrain NE-SW shortening in the frontal part of the wedge, whereas extensional tectonics controls the seismicity along the belt’s axial portion and in the hinterland. Atop the deformed accretionary wedge occur the Epiligurian Units, which consist of middle Eocene-upper Miocene bathyal to shallow-water siliciclastic deposits infilling wedge-top basins. A regional unconformity separates pre- and post-Burdigalian sequences within the Epiligurian succession, with sedimentary facies changing from deep marine-to platform environment. Our mesoscale structural analysis shows compressional, extensional, and strike-slip fault arrays affecting extensively all the Epiligurian Units, with distinct structural features. Top-to-the NE, WNW-ESE-striking reverse faults are defined by commonly slickensided planar surfaces decorated by thin damage zones. Top-to-the SE, WSW-ENE-striking reverse faults are, instead, generally devoid of well-developed damage zones. NW-SE and NE-SW-striking normal and oblique faults systematically cut across the reverse faults and accommodate centimetric to metric throws. Common cataclastic and disaggregation deformation bands are associated with NE-SW striking normal faults cutting through Upper Eocene-Lower Oligocene siliciclastic units. On the other hand, calcite veins and fibres locally decorate NW-SE and NE-SW-striking normal and oblique faults in marly post-Burdigalian sequences, attesting to fluid-rock interaction within dilatant rock volumes during faulting. A remote sensing analysis has been performed on tectonic structures mapped at the regional scale and confirms a variable trend distribution and density for both normal and reverse faults within both the pre- and post-Burdigalian sequences. Our results suggest that these wedge-top basins probably evolved independently, influenced by lateral thickness variations of the stratigraphic sequences, erosion, subsidence rates and tectonics in response to regional and local variations of the stress regime within the underlying orogenic prism. We propose that the present-day framework of the Epiligurian Units can be used as a powerful structural-stratigraphic gauge to track down the variation, through time and space, of the tectonic regime and state of stress of the Apennines wedge, with noteworthy implications on its current seismotectonic setting.

Unveiling the structural architecture of the wedge-top Epiligurian Units in the Northern Apennines

Diagnostic morphological features (e.g. rectilinear seafloor scarps) and lateral offsets of the Upper Quaternary deposits are typically used to infer offshore active faults. These structures are not necessarily capable of producing large earthquakes as they could be shallow and formed in response to local stresses. We present a multiscale approach to reconstruct the structural pattern in offshore areas and distinguish between shallow, non-seismogenic, active faults, and deep blind faults, potentially associated with large seismic release. The approach is based on the interpretation of seismic reflection profiles with different resolution/penetration and the quantitative morphometric analysis of multibeam bathymetry. The site chosen for testing the method is the Sant’Eufemia Gulf (south-eastern Tyrrhenian Sea) because it is a natural laboratory to investigate the relationships between regional and local processes associated with a slab tear fault (e.g. Rosenbaum et al., 2008) and crustal structures controlling the Plio-Quaternary tectonic evolution (e.g. Brutto et al., 2016). Data highlights the occurrence of three major tectonic events since the Late Miocene. The first extensional or transtensional phase occurred during the Late Miocene. Since the Early Pliocene, a right-lateral transpressional event caused the positive inversion of deep (> 3 km) tectonic features, and the formation of NE-SW faults in the central part of the gulf. Also, NNE-SSW to NE-SW trending anticlines (e.g. Maida Ridge) developed in the eastern sector. Since the Early Pleistocene (Calabrian), shallow (< 1.5 km) NNE-SSW oriented structures formed in a left-lateral transtensional regime. The results of this work integrated with literature data indicate that the transpressional/transtensional structures developed in an ~E-W oriented principal displacement zone extending from the Sant’Eufemia Gulf to the Ionian offshore. The strike-slip zone likely represents the upper plate response to the development of a slab tear fault.  The quantitative morphometric and bathymetric analyses indicate that NNE-SSW to NE-SW trending anticlines were negatively reactivated during the last tectonic phase. We suggest that the deep structure below the Maida Ridge may correspond to the seismogenic source of the large magnitude earthquake that struck the Calabrian region in 1905. The multiscale approach contributes to understanding the tectonic imprint of active faults with different hierarchical order developed in a strike-slip zone orthogonal to the Calabrian Arc.

Geometry and kinematics of offshore active faults revealed by an integrated multiscale method

The role of sea-bottom topography in the dispersal of shallow water-derived calciturbidites across a submarine rift, as determined by the local extensional architecture, is under-investigated, namely with pelagic settings along ancient passive continental margins. A comparison with modern carbonate platform/basin analogues, or with siliciclastic systems, is not always feasible, as ancient carbonate systems were commonly home to anachronistic environments (e.g. the Western Tethyan Mesozoic). Geological mapping of the Jurassic rift basin exposed in the Apennines of Central Italy revealed a complex pattern of intrabasinal highs (pelagic carbonate platforms) and intervening basins, controlled by the high density, and oddly variable trends, of faults rooted in a shallow detachment layer corresponding to thick Triassic salt. A map pairing the occurrences of resedimented beds in pelagic successions with an updated palaeogeography becomes therefore the natural descriptor of the itineraries followed by sediment gravity flows. This qualitative method represents a companion, or even alternative, approach to the one strictly based on physical stratigraphy, and it greatly improves our knowledge of regional geology and rift-basin analysis. Our study focuses on: i) a reconstruction of the palaeotectonic architecture of the Umbria-Marche Basin in the Jurassic, and on ii) how this architecture produced a submarine topography which governed the dispersal of sediment, shed by the neighbouring Lazio-Abruzzo Carbonate Platform, for >40 million years. Geological mapping, coupled with the measurement and correlation of stratigraphic sections, shows that the marginal palaeoescarpments of pelagic carbonate platforms formed obstacles to the gravity flows as sediment load was discharged in confined basins at their toes and/or flows were deflected and forced along alternative itineraries. While turbidity currents were locally vigorous enough to climb the escarpments, leaving graded and laminated overbank deposits on the pelagic carbonate platform-tops, a “shelter” effect is evidenced by the resediment-free nature of those basins lying downflow, which were shielded by the highs. Our case study potentially represents the analogue of hydrocarbon fields both inland and in the offshore.

Role of Early Jurassic rift architecture in the dispersal of calciturbidites, as revealed by geological mapping in Central and Northern Apennines

A 2D and 3D re-interpretation of vintage seismic profiles acquired during the 1970s in the area of the Northern Tyrrhenian Sea between the Elba Island and the Argentario promontory was performend to build a 3D models of the main structures characterizing the Tuscan shelf. Stratigraphic information were extracted by the Pianosa island surface geology along with the Martina-1 and Mimosa-1 exploration wells. We identified eight seismostratigraphic units separated by eight unconformities. Among these seismostratigraphic units, two represent the pre-Neogenic foundation while six post-orogenic units represent the Neogenic succession covering the Tuscan shelf. The main shallow structures of the area are the narrow, mostly N-S and NE-SW trending Neogenic basins of Montecristo, Punta Ala and Uccellina, where the post-orogenic seismostratigraphic units deposited. Effort has been done to unravel the relationship between the position and evolution of the basins with previous compressive structures, mostly consisting in deep East-verging thrusts belonging to a previous compressional phase. Intringuingly, and partially in contrast with the literature works in the area, no evidence of listric and low angle fault systems were observed. A new evolutionary model of the Tuscany shelf was then proposed. In this view the formation of the Neogenic basins began in the upper Burdigalian initially as intermontane basins developed along the flanks of the antiforms formed during the compressive tectonics. The position of the basins, usually recovered at the forelimb vs. the backlimb of the thrust antiforms, influenced the  asymmetrical or symmetrical shape during their evolution. Starting from the Messinian, we observe a general collapse of the platform, which leads to the deepening of the basins driven by the normal high-angle bordering faults. This process continues up to the lower Pliocene, when the deactivation of all normal faults is recorded, and conditions of widespread subsidence are clear throughout the platform, together with the deposition of the two more post-orogenic units. In this contribution we reviewed the tectonic evolution of the northern Tyrrhenian Sea posing new questions both on the mechanisms responsible for the extensional processes and on the structures which impacted on such arrangement, also establishing a new starting point for a full unravelling of the Tuscan Shelf evolution.A 2D and 3D re-interpretation of vintage seismic profiles acquired during the 1970s in the area of the Northern Tyrrhenian Sea between the Elba Island and the Argentario promontory was performend to build a 3D models of the main structures characterizing the Tuscan shelf. Stratigraphic information were extracted by the Pianosa island surface geology along with the Martina-1 and Mimosa-1 exploration wells. We identified eight seismostratigraphic units separated by eight unconformities. Among these seismostratigraphic units, two represent the pre-Neogenic foundation while six post-orogenic units represent the Neogenic succession covering the Tuscan shelf. The main shallow structures of the area are the narrow, mostly N-S and NE-SW trending Neogenic basins of Montecristo, Punta Ala and Uccellina, where the post-orogenic seismostratigraphic units deposited. Effort has been done to unravel the relationship between the position and evolution of the basins with previous compressive structures, mostly consisting in deep East-verging thrusts belonging to a previous compressional phase. Intringuingly, and partially in contrast with the literature works in the area, no evidence of listric and low angle fault systems were observed. A new evolutionary model of the Tuscany shelf was then proposed. In this view the formation of the Neogenic basins began in the upper Burdigalian initially as intermontane basins developed along the flanks of the antiforms formed during the compressive tectonics. The position of the basins, usually recovered at the forelimb vs. the backlimb of the thrust antiforms, influenced the  asymmetrical or symmetrical shape during their evolution. Starting from the Messinian, we observe a general collapse of the platform, which leads to the deepening of the basins driven by the normal high-angle bordering faults. This process continues up to the lower Pliocene, when the deactivation of all normal faults is recorded, and conditions of widespread subsidence are clear throughout the platform, together with the deposition of the two more post-orogenic units. In this contribution we reviewed the tectonic evolution of the northern Tyrrhenian Sea posing new questions both on the mechanisms responsible for the extensional processes and on the structures which impacted on such arrangement, also establishing a new starting point for a full unravelling of the Tuscan Shelf evolution.

Tectonic-Sedimentary evolution of the Tuscan shelf: seismic-stratigraphic analysis of Neogenic succession in the norther Tyrrhenian sea (Elba Island - Argentario)

The Turkana depression (Ethiopia-Kenya) is a tectonic basin related to the Cretaceous-Early Cenozoic development of the South Sudan and the Anza grabens filled with a thick sequence of Cretaceous-Paleogene sediments reaching up to a thickness of 6–8 km. These two NW-SE trending depressions, which likely resulted from NE-SW extension, were later affected by W-E extension related to the Cenozoic East African Rift System. The influence of crustal thinning related to these NW-SE grabens on later W-E-related extension is testified by the marked change in style of deformation from the narrow rift valleys in Kenya and Ethiopia, to a distributed, basin-and-range-style faulting in the Turkana depression. Despite some local scale reactivation is visible, large scale reactivation of pre-existing NW-SE structures in the Turkana depression is not obvious, as it is extensively masked by the sedimentary and volcanic cover; consequently, contrasting hypothesis on the possible role exerted by discrete pre-existing fabrics have been proposed in the literature. To address this controversy, we performed analogue models to investigate whether inherited structures, largely obscured by sediments in the Turkana depression, might have been reactivated during subsequent tectonic phases. We run 2-layer, brittle-ductile models deformed in two successive phases: a first phase of NE-SW extension, followed by W-E extension. Different models were subjected to different amount of bulk extension during the first phase to investigate the influence of this parameter (and the importance of first-phase structures) on later reactivation. Our models indicate that the amount of deformation in the initial tectonic phase is key for structure reactivation in subsequent tectonic phases: the larger the deformation in the first phase, the higher the probability of reactivation. Comparison of the experimental results with nature suggest that, despite some local fault reactivation, large-scale structures were likely not reactivated in the Turkana depression. These outcomes represent a useful tool to decipher fault reactivation, not only in the Turkana depression but also in tectonic basins worldwide, especially where thick sedimentary covers may mask tectonic structures.

Reactivation or non-reactivation? Analogue models of multiphase rifting and applications to the Turkana depression, East Africa

We present PALEOSTRIPv1.0, a MATLAB open-source software designed to perform 1D, 2D and 3D backtracking of paleo-bathymetries. PALEOSTRIP comes with a Graphical User Interface (GUI) to facilitate computation of sensitivity tests and to allow the users to switch on and off all the different processes and thus separate the various aspects of backtracking. As such, all physical parameters can be modified from the GUI. It includes 3D flexural isostasy, 1D thermal subsidence and possibilities to correct for prescribed sea level and dynamical topography changes. In the following we detail the physics embedded within PALEOSTRIP and we show a few applications on a drilling site (1D), a transect (2D) and a map (3D), taking the Ross Sea (Antarctica) as a case study. PALEOSTRIP has been designed to be modular and to allow users to insert their own implementations.

A user-friendly 3D backtracking software to reconstruct paleo-bathymetries

We present a brand new multi-proxy dataset of thermal maturity indicators, which derive from the application of several analytical techniques on surface and subsurface sedimentary successions. The study area spans from the Greater Caucasus to the Adjara-Trialeti fold-and-thrust belt (FTB), comprising the intervening western Kura Basin, in Georgia, and represents a region of continental deformation in the hinterland of the Arabia-Eurasia collision zone. Original and published clay mineralogy, Raman spectroscopy and petrography on dispersed organic matter, and pyrolysis data are integrated for the first time in a coherent tectono-sedimentary scenario. Thermal maturity spans from the low diagenetic realm (60-80°C) in the Upper Miocene section of the Kura sedimentary fill, to the oil window in the Cretaceous to Lower Miocene successions of Adjara-Trialeti FTB, Kakheti ridge and Kura Basin (70-120°C), up to about 400°C in the Greater Caucasus core. Integration of different indicators, besides allowing the estimation of maximum burial temperatures acquired through time, enabled to draw the tectonic evolution of the area. Different maturity trends and thermal histories, coupled with structural and stratigraphic data, highlight that the study area comprises two domains derived from positive tectonic inversion: the E-W Adjara-Trialeti doubly-verging FTB from an Eocene back-arc rift basin and the SSW-verging Georgian Greater Caucasus from a Mesozoic rift basin. Between the two, thin-skinned south-verging thrusts deform the Kura Basin and the Kakheti ridge successions, originally deposited on an extensional structural high which was later flexured during compression. The similar thermal maturity degree in the Adjara-Trialeti FTB and the Kakheti ridge/Kura Basin areas has been acquired in different time spans: during Paleogene extension and during Miocene thin-skinned shortening, respectively. The results indicate that thermal maturation of the sedimentary successions in the Adjara-Trialeti FTB can be ascribed to burial during rift evolution. The same conclusion can be drawn for the axial zone of the Greater Caucasus, whereas tectonic overburden may have contributed to the thermal maturity of the rocks in the southern foothills of the Greater Caucasus: this area needs further work to assess its tectonic evolution.

Using multi-proxy thermal maturity datasets to validate deformation styles from the Adjara-Trialeti fold-and-thrust belt to the Greater Caucasus (Georgia)A

The tide-dominated Messina Strait (southern Italy) is a 3 km wide marine passageway, whose block-faulted borders form steep subaqueous zones incised by canyons and gullies. These erosional features retreat towards the shorelines and are often in direct connection with subaerial valley-bounded river deltas. High-energy density-flows generated by river floods periodically enter the canyon heads, attaining supercritical-flow regime and accreting large, upslope-migrating bedforms. Although these bedforms have been documented in recent studies, little attention has been paid to the definition of the type of delta entering canyon heads, the internal features of river-influenced deposits accumulated in the nearshore zone, and their interplay with tidal currents flowing axially to the strait. This study focuses on a Lower Pleistocene coarse-grained succession exposed along the north-eastern margin of the modern Messina Strait, investigated using conventional facies analysis and sedimentological logging, integrated with photogrammetric techniques and interpretation of drone-acquired imagery. Facies confinement between basement blocks suggests a subaqueous delta complex shed from the tectonically controlled margin of the ancient strait and entering shallowly submerged canyon heads. Basal breccias, conglomerates and pebbly sandstones exhibiting channel-form discontinuities and upslope dipping backsets are interpreted as cyclic-step and antidune deposits. Units composed of these facies are comprised between master erosional surfaces and tidal ravinement surfaces. The tidal ravinements suggest that canyon infill occurred during a major phase of sea-level rise, punctuated by minor falls and stillstands. These surfaces are overlain by mixed bioclastic–siliciclastic, arenitic, trough and planar cross-strata, representing dunes migrating roughly parallel to the palaeo-coastline and originated by tidal currents amplified by the narrowing of the ancient Messina Strait. Tidal-influenced sedimentation dominated over the fluvial-influenced processes during the late transgression, overfilling the canyon relief. The exceptionally good exposure of depositional architectures and facies characteristics is key to outline the general features of a specific type of delta system, fed by valley-bounded rivers and entering canyon heads in the nearshore of tectonically-controlled, tide-influenced steep strait margins. The pre-existing subaqueous incised topography forced the delta front to be split into lobe branches during the canyon infilling, hampering clinoform architectures and preserving large supercritical-flow sedimentary structures. This study suggests these as possible criteria for the recognition of similar systems in outcrop or subsurface.

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