ALBERT

Description: The Gioia Basin is a small trough located in the southeastern Tyrrhenian Sea between the Aeolian island arc and Sicily and Calabria. It is experiencing a post-rift margin evolution, while tectonic deformation and high rates of vertical movement are still affecting the Sicilian and Calabrian mainland. The analysis of the evolution of the post-rift depositional systems along the various sectors of the Gioia Basin margin has been carried out through the combined interpretation of multibeam bathymetry and seismic reflection data. Two seismic units have been identified and their component geomorphological elements ascertained through the analysis of seismic facies distribution. In general, the depositional architecture of the margin, the sedimentary environments and facies and related geomorphological elements that are active in the shaping of the margin appear to be mainly controlled by the physiography of the basin itself and by the geology of the hinterland that results from the structural evolution of the adjacent land areas. An evolution from a generalized slope bypass setting to a prograding offlapping slope architecture is recognized and explained as due to the transition from an out-of-grade to a graded profile progressing from the early post-rift stage to the later margin growth stage. Along the Sicilian margin, a constructional apron, mainly consisting of channel levee deposits, makes up much of the studied sedimentary package and reflects a high sediment supply related to the large size of river catchments on land. In contrast, the northeastern Sicilian basin sector is a destructional margin that flanks a region where small river drainage systems result in a low sediment supply to the basin and a continued high uplift rate promotes slope instability; as a consequence, the basin infill is here almost completely made up of mass-wasting deposits. In the Calabrian margin, a first phase of low sediment supply probably coinciding with the filling of the further inland Gioia Tauro half-graben was followed by the establishment of the Gioia-Mesima channel-canyon system that, furnishing an effective sediment flux to the margin, allows the formation of an intraslope depositional body consisting of channelized turbidite lobes.

Description: 〈span〉〈div〉ABSTRACT〈/div〉Through the seismo-stratigraphic analysis of new highresolution seismic data acquired along the southwestern offshore of the Hyblean Plateau, this work aims to improve the knowledge about the stratigraphic and structural setting in the marine area connecting the Hyblean Plateau Foreland to the Gela-Catania Foredeep.Two main goals have motivated the acquisition of new seismic profiles along the southern coastline of Sicily, in the Marina di Ragusa offshore: 〈ul〉 〈li〉(i) to obtain a better comprehension of the Cenozoic stratigraphic and structural setting of the area, with a particular attention to the characterization of the Pliocene-Holocene sedimentary deposits and their areal distribution;〈/li〉 〈li〉(ii) to identify, in the offshore area, the possible prolongation of the main structural lineaments outcropping in the hinterland (Scicli-Ragusa-Irminio Line), and verify the presence of structures, responsible for the tectonic activity affecting the area.〈/li〉 〈/ul〉Our model shows that an extensional fault system, characterized by a main NE-SW orientation, affects the highly deformed Oligo-Miocene, or older, substratum, originating structural highs and down-faulted sectors. These faults are inferred to record the early history of the Scicli Line and of the polyphase kinematic evolution of the N50° oriented regional fault systems.The Gessoso-Solfifera deposits (Messinian, Late Miocene) have been recognized in several sectors of the study area, showing a very peculiar seismic facies, and occupying deep erosional channels probably resting within down-faulted sectors. This feature is in good agreement with isolated onshore areas of the Hyblean Plateau (Licodia Eubea and south Vittoria villages) where the Gessoso-Solfifera deposits are associated to normal faults, thus documenting that Messinian evaporites are not restricted to compressive tectonic setting, such as the marginal sub-basins and the thrust top mini-basins of the Appennine-Maghrebian belt.A peculiar seismic facies has been associated to the Trubi Fm., unconformably lying upon the older succession.The undeformed seismic units, onlapping the older substratum, has been associated to the post-Trubi-Holocene deposits, arranged into seven seismic units that reflect the youngest depositional evolution of the nearby Catania-Gela Foredeep. These deposits, generally represented by plane-parallel seismic facies, are in turn separated by an unconformity highlighted by an onlap termination of the yougermost terms upon the older. In some cases they are interrupted by gas rising from the deeper succession that reaches, at times, also the seafloor.〈/span〉

Description: Widely used sequence stratigraphic models predict that specific facies assemblages alternate in the stratigraphy of deep-sea fans, depending on the cyclic nature of sea-level variations. Our work tests this assumption through facies reconstruction of submarine fans that are growing in a small basin along the tectonically active Sicilian margin. Connected canyons have heads close to the coastline; they can be river connected or littoral cell–connected, the first receiving sediment from hyperpycnal flows, the latter intercepting shelf sediment dispersal pathways. Hyperpycnal flows directly discharge river-born sediment into the head of the river-connected canyon and originate a large turbidite fan. A drift formed by the longshore redistribution of sediment of a nearby delta introduces sediment to the head of the littoral cell–connected canyon, forming turbidity currents that flow within the canyon to reach the basin plain. However, since sediment failure and landslide processes are common in the slope part of the system, a mixed fan, consisting of both turbidites and mass-transport deposits, is formed. Disconnected canyons, with heads at the shelf edge far from the coastline, are fed by canyon head and levee-wedge failures, resulting in mass-transport or mixed fan deposition, the latter developing when the seafloor gradient or the lithology of the failed sediment allows turbidity current formation. Connected canyons form in areas with high uplift rates, where the shelf is narrow and steep and the shelf edge is at a relatively shallow depth. Disconnected canyons develop where there are lower uplift rates or subsidence, where the shelf is large and relatively gentle with a deeper shelf edge. It is deduced that the relative vertical movements of fault-bound blocks control whether canyons are connected to the coast at the present day. The role of tectonics in controlling the canyon feeding processes and the facies of submarine fan growth during highstand periods is therefore highlighted. A further view that arises from our paper is that in active margins, the slope portion of fan systems, through seafloor instability and variations in channel gradient, is a key factor in determining the final deep-sea fan facies, regardless of the distance between the coast and the canyon. The concomitant growth of turbidites, mass-transport deposits, and mixed fans demonstrates that models that predict changes in submarine fan facies on the basis of sea-level cycles do not necessarily apply to systems developed along tectonically active margins.

Description: A bstract :  In deep-sea fans, fan lobes form from the stacking of the deposits of turbidity currents and other sediment gravity flows beyond the channel mouth. Slopes lateral or oblique to the main direction of turbidity currents exiting channel confinement can profoundly affect flow behavior and the distribution of facies and lithology in fan lobes. In this paper, we report on the analysis of multibeam and CHIRP subbottom data aimed at the study of the effects of a lateral slope on turbidity-current behavior and resultant geomorphology and stratigraphy of a modern fan lobe. The Villafranca fan lobe, the subject of this study, develops on the 0.5° dipping seafloor of the Gioia intraslope basin in the southeastern Tyrrhenian Sea. The Villafranca is a transient fan lobe that has its downslope limit coinciding with a 200-m-high bathymetric step formed by the erosional flank of the Stromboli slope valley, perpendicular to the fan-lobe trend. A "lobe complex" hierarchical level is assigned to the Villafranca fan lobe. The lobe complex develops beyond the mouth of the Villafranca leveed channel, which trends N and is oblique to the regional NW-dipping slope. The depositional topography created by an adjacent channel levee wedge to the west is the cause of the observed obliquity. The western and the eastern "lobes" constitute the Villafranca lobe complex. Both lobes have mainly NW-trending channels, and therefore they do not conform to the classical divergent pattern of channels observed in deep-sea fan lobes. The channel trend is a result of the inability of flows to freely spread sideways, due to the presence of the lateral slope and the dip of the seafloor at the channel mouth. The western lobe has an up-dip apex with respect to the eastern one and is characterized by channels that nucleate on the downslope side of a channel-mouth bar and that die out distally before reaching the flank of the Stromboli slope valley. The eastern lobe, in contrast, has channels that are depositional upslope but on approaching the flank of Stromboli slope valley become mainly erosional or bypass features. The two lobes develop concomitantly, therefore an evolution due to compensational stacking with the two lobes being in different stages of development is here disregarded. It is therefore feasible that turbidity currents, which due to different initiating mechanisms have distinct magnitude and efficiency, deposit their load either in the eastern or in the western lobe. Another possibility is that single turbidity currents exiting the Villafranca channel mouth form two separate flow portions with different properties, which independently but simultaneously feed the eastern and the western lobe. In both cases, the effect of the lateral slope and the obliquity between the dip of the slope and the trend of the channel mouth are here considered as the primary factors controlling the differences in depositional style of the two lobes.

Description: The 350-m-thick succession of the Po River lowstand wedge (Italy) associated with the Last Glacial Maximum (deposited over ~17 k.y) contains stratal architecture at a physical scale commonly attributed to much longer time scales, with complex, systematically varying internal clinothem characteristics. This study investigated clinothem stacking patterns and controls through the integration of seismic reflection data with sediment attributes, micropaleontology, regional climate, eustacy, and high-resolution age control possible only in Quaternary sequences. Three clinothem types are differentiated based on topset geometry, shelf-edge and onlap-point trajectory, internal seismic facies, and interpreted bottomset deposits: type A has moderate topset aggradation, ascending shelf-edge trajectory, and mass-transport bottomset deposits; type B has eroded topset, descending shelf-edge trajectory, and bottomset distributary channel-lobe complexes; and type C has maximal topset aggradation, ascending shelf-edge trajectory, and concordant bottomsets. Type A and C clinothems exhibit reduced sediment bypass and delivery to the basin, whereas type B clinothems are associated with short intervals of increased sediment export from the shelf to deeper water. Clinothems individually span a range of 0.4–4.7 k.y., contemporaneous with significant eustatic and climate changes, but their stacking patterns resemble those found in ancient successions and ascribed to significantly longer durations, indicating that (1) the response time of ancient continental margin–scale systems to high-frequency variations in accommodation and sediment supply could be as short as centuries, (2) even millennial- to centennial-scale stratal units can record substantial influence of allogenic controls, and (3) sandy deposits can be compartmentalized even in a short-duration lowstand systems tract.

Description: 〈span〉〈div〉ABSTRACT〈/div〉Lampedusa Island represents a key-area due to its central position within the Sicily Channel and the whole Mediterranean region. The acquisition and interpretation of sixteen “sparker-system” seismic lines allowed a refined reconstruction of the sedimentary architecture of the Lampedusa continental shelf and the detailed timing of its tectonic evolution, providing a contribution to the geodynamic processes affecting this sector of the Sicily Channel.The offshore profiles show five seismic facies, which have been compared with the onshore succession. The older seismic unit (S1) was correlated with the pre-rift Cala Pisana Mb. of the Lampedusa Fm., separated by the overlain Capo Grecale Mb. (=S2) by an erosional surface, identified with the offshore TU (=Tortonian Unconformity) horizon, passing upward to the Vallone della Forbice Mb. (=S3) through a gradual, concordant boundary (Upper Tortonian Boundary=UTB). Capo Grecale and Vallone della Forbice Mbs., and thus the S2 and S3 units, represent the syn-rift deposits, recording the Late Miocene extensional tectonic activity. The effects of the strong erosional phase connected with the Mediterranean Salinity Crisis of Messinian age, are visible in all the seismic lines coinciding with a high impedance irregular surface (MH=Messinian Horizon), above which a further seismic unit (S4) develops. This latter, constituted by reflections onlapping the substratum, in the lower part, and prograding in the upper one, does not find an onshore correspondence, but has been attributed to the post-Messinian (Zanclean) transgression, followed by the subsequent regressive phase (Piacenzian-Gelasian). The uppermost seismic unit (S5), unconformably covering the older substratum, through the Early Pleistocene Unconformity (=EPU horizon) corresponds to the Pleistocene-Holocene onshore deposits. The seabed (top of S5) shows regular morphologies in the southern sector, while in the northern sector it is cut by erosive channels connected to strong streams on the bottom.From a structural point of view, the southern sector recorded an extensional tectonic phase, giving rise to normal faults involving units from S1 to S3, sutured by the MH and the overlain deposits. In the northern sector, the tectonic phase continued until the Pliocene, also involving the S4 unit.The reconstructed tectonic setting well fits the more general setting of the Sicily Channel Rift Zone, where main WNW-ESE faults were active during the Late Miocene and until the Pliocene age, generating small depositional areas, bounded by second-order NNW-SSE normal faults.〈/span〉

Description: 〈span〉〈div〉ABSTRACT〈/div〉Tectonic activity can affect every single segment of a sedimentary system and the various environments within a basin react in specific ways to tectonic forcing. However, the outcomes of tectonic activity on one environment have important consequences on the sedimentary processes in adjacent ones. In this paper, I evaluate the relationships between tectonic activity and sedimentary processes in several distinct environments, and in different times within the last sea-level cycle, in the submarine part of a single sedimentary system: the Capo d’Orlando Basin. The study area is located in the southeastern Tyrrhenian Sea along the northern Sicilian margin and is affected by active tectonics. A multibeam bathymetric coverage, chirp and regional sparker profiles are available over the study area. In the shelf, the Caronia Horst controls the thickness of the high stand systems tract and the character and the preservation potential of the coastal deposits of the transgressive systems tract. Coastal physiography, due to differential vertical movements, affects offshore current strength and pattern of sediment transport, causing the sand-mud line to move offshore. In the upper slope, tilting increases sediment instability and the accumulation of landslide deposits. Uplift, responsible for the local shallower depth of the shelf edge, favoured the connection between canyon heads and river mouths during the last sea-level low stand. More importantly, some of the canyon heads are still close to the coast and can receive sediment from rivers or offshore currents even during the present-day high stand. The Naso and the Calavà Channels have fault-controlled courses and an asymmetric profile, which controls the location of overbank flows, sediment failures and landslide deposition. In the basin plain, the continued activity of the major faults has created subtle topography and the turbidite lobes do not present a compensational stacking pattern but remain fixed in fault-controlled lows; differential compaction in the separate fault blocks also contribute to differences in turbidite thickness. Landslides are present at the base of the fault-controlled basin-bounding escarpments and punctuate the otherwise turbidite-dominated succession. The analysis of the Capo d’Orlando Basin illustrates the range of effects that tectonic structures have on sedimentary processes going from the continental shelf to the basin plain. More importantly, although in a qualitative way, this research shows how the tectonic influence on up-dip processes is also responsible for the nature of the depositional record in the deeper part of the basin.〈/span〉

Description: 〈span〉〈div〉ABSTRACT〈/div〉Continental margins are often characterised by wide slope sectors with complex topography due to seafloor deformation linked with mobile shale or salt, or local tectonics. Within the resulting slope environments, sedimentary systems can be complex and often structured in variously connected, separate intraslope basins. In this paper, we investigate how the diverse arrangement of sedimentary systems on topographically complex slopes relate to regional differences in extensional tectonic setting. Our study is carried out through the analysis of bathymetric data in the central and southeastern portion of the Tyrrhenian Sea, a back-arc basin that displays wide slope sectors, surrounding the deep Marsili and Vavilov basin plains. A “connected tortuous corridor” forms in the Latium-Campanian slope, where extensional faults are parallel to the margin. Here, tectonic structures are important in controlling the relative extent of dip and strike sectors as well as depositional and erosional segments of submarine drainage networks. Confined, margin-parallel troughs, such as the Capo d’Orlando and the Paola Basins, form respectively landward from volcanic edifices and mud remobilisation ridges. Their depositional setting is mainly the result of the relationships between the basin dip and the site of major sediment input. An unconfined trough parallel to the margin forms when its edge coincides with down-to the basin extensional faults, such as in the case of the Gioia Basin. Its axis is the site of a longitudinal slope valley that shows morphologic variations controlled by tectonic structures. Transverse troughs cutting the entire slope form when tectonic structures are perpendicular to the margin, such as in the Cilento slope. Here, the pattern of extensional faulting is the major control on the degree of connection of successive basins and the eventual development of a drainage system. Throughgoing slope valleys form in graded slope, where sedimentary packages are thick enough to heal the relief associated with tectonic structures. They have planforms, relief and erosional or depositional attitude that is controlled by slope steps connected with faults. As a general outcome, our research provide a valid framework that illustrates the range of possible architectures of sedimentary systems and of their constituents in extensional continental margins.〈/span〉

Description: Although spreading rate is commonly taken as a proxy for decompression mantle melting at mid-ocean ridges (MORs), magmatism at back-arc spreading centers (BASCs) is further influenced by the subduction-related flux melting of the mantle. These regions consequently show a diversity of crustal structures, lava compositions, and morphologies not typically found in MORs. Here we investigate the crustal plumbing system of the small-scale, Marsili back-arc spreading center of the Southern Tyrrhenian Sea using plagioclase data from a wide spectrum of lavas (basalts to andesites) dredged from its summit and flanks. We employ petrological modeling to identify the plagioclase populations carried in the individual lavas, allocate them to plausible magmatic components present within the plumbing system, and trace the processes occurring during magma ascent to the surface. The properties of the system, such as mush porosity and abundance of the melt bodies, vary from one magma extraction zone to another along the BASC, evidencing the local variability of melt supply conditions. The plagioclase crystals document a range of relationships with the host lavas, indicating magma extraction from a composite, vertically extensive mush and melt-lens system resembling that of MORs. At the same time, however, in small BASCs, such as in the case of the Marsili Basin, crustal accretion and resulting morphology are significantly influenced by the three-dimensional setting of the basin margins. This is an important deviation from the conventional model based on the linear continuity and essentially two-dimensional framework of MORs. © 2017. American Geophysical Union. All Rights Reserved.