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The outer Fuegian fold and thrust belt is the deformed sector of the Austral-Magallanes Basin, which underwent a contractional phase since the Late Cretaceous and a strike-slip phase during the Neogene. The area hosts two Neogene basins (Yehuin and Chepelmut) which have been mainly developed by the influence of wrench deformation, and were subsequently modified by glacial activity of the Ewan and Fuego glacier lobes of the Fagnano palaeoglacier. Geophysical surveys using Electrical Resistivity Tomography, onland shallow seismic surveys, and magnetometry, have been combined with outcrop analysis and deep seismic lines to recognize both shallow and intermediate deep structures related to the lacustrine basins. Four sets of faults with different deformation history were involved in the basin genesis. Comparison with the Deseado Fault Zone indicates similarities of the structural features between the two zones. The stress field interpreted as responsible for the origin of the studied basins is analogous to the one in the Deseado valley, located in the western Tierra del Fuego. Therefore, a transcurrent fault zone, here named Yehuin–Chepelmut Fault Zone, is proposed as part of the diffuse boundary between South America and Scotia plates.

The geological and geophysical expedition duringcruise 52 of the R/V Akademik Ioffe was organized bythe Shirshov Institute of Oceanology, Russian Academyof Sciences, according to the expeditionary programof FASO Russia; it was combined with transit ofthe vessel after the end of the Arctic tourist season,from September 29 to November 8, 2016 (port of exit:Gdansk, Poland; port of entry: Ushuaia, Argentina).The objectives of the expedition were formulatedby scientific supervisor I.O. Murdmaa. The scientificparty included 12 persons. The expedition was led byE.V. Ivanova and her deputy D.G. Borisov. The tasksof the expedition were carried out by the geologicalteam (head E.A. Ovsepyan) and seismic profiling andmeteorology team (head N.V. Libina).The expedition was aimed at high-resolution seismicprofiling along the ship?s track and in the centralpart of the Ioffe Drift, with collection of sedimentcores and grab samples in order to investigate theimpact of bottom circulation on sedimentation.Geological works included sediment sampling tostudy contourites (sediments formed by contour currents)and other lateral sedimentation products (turbidites,gravitites). The studies were carried out intransform valleys of the Mid-Atlantic Ridge (MAR),on the Ioffe contourite drift in the southern BrazilBasin, and on contourite terraces of the southernArgentine continental slope. The stations of sedimentsampling by gravity corers (127 mm in diameter) andan Okean 0.25 grab sampler were selected on seismicprofiles with a high-resolution SES-2000 deep subbottomecho sounder (4?7 kHz). Positioning of thevessel at the scheduled sites was assisted by GPS. Themethods of preliminary onboard analyses during theexpedition, including 5487 NM of seismic profiling,were performed along the vessel track starting from theexit to the Atlantic, except for the economic zones ofEuropean countries and Argentina, and including194 miles in a survey area in the central Ioffe Drift.Twenty-seven geological sampling stations were made(Fig. 1) with the collection of 3 sediment cores and17 grab samples or minicores. Fil: Ivanova, E. V.. Russian Academy Of Sciences; Rusia Fil: Murdmaa, I. O.. Russian Academy Of Sciences; Rusia Fil: Borisov, D. G.. Russian Academy Of Sciences; Rusia Fil: Simagin, N. V.. Russian Academy Of Sciences; Rusia. Lomonosov Moscow State University; Rusia Fil: Ovsepyan, E. A.. Russian Academy Of Sciences; Rusia Fil: Libina, N. V.. Russian Academy Of Sciences; Rusia Fil: Isola, José Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Bulycheva, E. V.. Russian Academy Of Sciences; Rusia Fil: Shulga, N. A.. Russian Academy Of Sciences; Rusia Fil: Krek, A. V.. Russian Academy Of Sciences; Rusia Fil: Lobus, N. V.. Russian Academy Of Sciences; Rusia Fil: Lapidus, L. V.. Russian Academy Of Sciences; Rusia

This work analyzes the geometry and geodynamic development of the offshore sector (between 62° W and 67° W) of the south Magallanes and Malvinas basins wedge-top and foredeep, and associated orogenic wedge. It is based on the interpretation of more than 20,000 km of multichannel seismic profiles, along with bathymetric data. The fold-and-thrust belt front was mapped, and three structural domains were distinguished: western, transitional and eastern. A stepped foredeep characterizes the western domain with flower-structures that affect the basement, and by an intense erosion in the Miocene deposits. Towards the transitional domain, the erosion is less evident, and the wedge-top is more developed. This configuration is associated with the syn-deformational deposition and the generation of thrusts within an acoustically chaotic body in the transitional and eastern domains, deposited by processes of mass removal in the Oligocene. During the Oligocene/Miocene, the area was affected by compression/transpression, which generated an incipient tectonic inversion of the basement extensional faults, with the formation of anticlines associated with piggy-back basins in the wedge-top. The differences observed between the western and eastern domains would be related to the differential movement between the crustal blocks of Tierra del Fuego and Burdwood Bank, respectively, against the South American shelf since the Oligocene. Fil: Ormazabal, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Tassone, Alejandro Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Esteban, Federico Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Isola, José Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Cayo, Lubin Eric. Yacimientos Petrolíferos Fiscales; Argentina Fil: Lozano, Jorge Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Menichetti, Marco. Università Degli Studi Di Urbino Carlo Bo; Italia Fil: Lodolo, Emanuele. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; Italia

The Piedra Buena Terrace (PBT), situated in the Patagonian continental slope, is swept by the vigorous flow of Antarctic-sourced bottom water masses, and intersected by a considerable submarine canyon system. It thus represents a world-class natural laboratory to investigate the sedimentary dynamics of deep-ocean settings influenced by both, along-slope, and down-slope sedimentary processes. In the framework of the Pampa Azul project, the PBT was surveyed with swath bathymetry and a high-resolution parametric sub-bottom seismic profiler and sampled at several locations with a 7 m long gravity corer. Through the integration of the acoustic data, grain size results from a sediment core and two AMS 14C ages this work attempts to: (1) describe for the first time the detailed geomorphology of a poorly known region of the Patagonian continental slope; (2) depict the principal sub-surface seismic units, illustrating their internal structure, geometry, and distribution; (3) establish a correlation between sub-surface seismic facies and sediment deposits using the first age constraints for this region; (4) propose a model with the depositional history of the PBT, focusing on the interaction between along-slope and down-slope processes and seafloor morphology. The acquired bathymetric data imaged with unprecedent detail the geomorphology of the southern part of the PBT revealing the presence of a field of kilometric-sized, sub-circular, crater-like depressions, and a submarine canyon. The analyzed seismic sub-bottom profiles showed that the shallow sedimentary structure of the study area is represented by patchy-mounded deposits characterized by three distinctive features: cyclic stacks of two seismic facies (FA and FB), mounded shape, and preferential location northwards the morphological depressions and the submarine canyon. Integration of a seismic sub-bottom profile with one sediment core indicates that the alternation of seismic facies reflects variations in the hydrodynamic conditions. FA is related to a high to moderate energy medium with input of terrigenous material and FB is related to a low energy environment with a limited contribution of sediments from the continent. The patchy distribution, mounded shape and preferential location are associated with hydrodynamic processes occurring between the geomorphological features and the north-flowing Antarctic bottom currents, which result in the deposition of mounded contourites in the northern flank of depressions and hybrid along-slope down-slope deposits northwards a submarine canyon. The 14C ages constrain the chronological framework of these sediments to the Late-Pleistocene. This is in contrast with previous investigations that have suggested much older ages (Late Miocene) for the sub-surface sediments of PBT. Finally, a conceptual model is here proposed to illustrate the Late Quaternary sediment depositional history of the PBT where the interaction between north-flowing bottom contouritic currents and seafloor relief played an important role in the deposition and preservation of sediments in this area.

In this study, we examine the external part of the Magallanes-Malvinas Fold and Thrust Belt in offshore areas, including a portion in Tierra del Fuego onshore, in southern South America. Our investigations focus on the interaction between a thin-skinned fold and thrust belt and the basement in that deformation, considering pre-existing structures acting as stress risers and localizing a possible tectonic inversion. The data is composed of around 14,000 km of 2-D multichannel seismic lines and three exploratory wells, used to analyse the anticlines of the fold and thrust belt in the area. The strike of these folds progressively evolves from NW-SE trending in western onshore regions, to WSW-ENE trending in eastern offshore areas. The fold and thrust belt shows a buttressing effect against the Rio Chico Arch. The most shortening is seen in the apex of the Rio Chico Arch around 67° W, in the coast of Tierra del Fuego, and gradually decreases eastwards in offshore regions. A connection between basement-involved faults and folds offshore is inferred from the analysis of the Geminis and Ciclon anticlines, developed during the N–S last compressional stage of deformation in the late Oligocene/early Miocene. The Geminis anticline is a fault propagation fold with a total shortening of 205 m with a piggyback basin developed over its backlimb. The location and ENE-WSW strike-direction of the fold have been controlled by a basement-involved fault. The Ciclon anticline is a subtle fold trending WNW-ESE developed as a result of the slight tectonic inversion of a negative flower structure.

Analysis of high-resolution multi-beam bathymetry, 2D multi-channel seismic, and high-resolution seismic sub-bottom profiles revealed the presence of widespread fluid escape features in the middle slope of the Patagonian Continental Margin. On the sea-bottom, these features correspond to pockmarks and mud volcanoes, whereas in the sub-surface they are represented in the seismic records by several acoustic anomalies such as chimneys, acoustic blanking, enhanced reflectors, and reverse-phase enhanced reflectors among others. Some of these acoustic signatures can be traced to syn-rift deposits that fill a deep re-activated and inverted graben. Analysis of pockmarks elongation and pockmarks alignments show a good correlation with inverted normal faults, suggesting that faults and fractures have influenced the pockmark's shape and might have acted as pathways for upward fluid migration. Some of the acoustic anomalies associated with pockmarks are interpreted as evidence of gas. The gas observed in the seismic data seems to be thermogenic, and the seismic data suggests a deep origin associated with over-pressured syn-rift deposits. Two morphometrically different sets of pockmarks were identified: an older set hosted by Miocene aged rocks, and a younger set hosted by Quaternary deposits. Different potential triggers are discussed for the genesis of the Miocene pockmarks in relation to the seismostratigraphy, structural geology and regional tectonics. It is concluded that, tectonic activity associated with the Neogene inversion of the graben faults, due to Andean compression, is the most likely cause for the formation these pockmarks. The presence of gas charged sediment and young pockmarks also suggest that after the Middle Miocene tectonic climax, a more recent pulse of release of fluids occurred., Sí

The South American-Scotia plate boundary is a left-lateral fault system which runs roughly E-Wfor m o reth an 3000 km across the SW Atlantic Ocean and the Tierra del Fuego Island, reaching to the west thesouthern Chile Trench. Analyses of a large dataset of single- and multi-channel seismic reflection profiles acquired offshore has allowed to map the trace of the plate boundary from Tierra del Fuego to the Malvinas Trough, a tectonic depression located in the eastern part of the fault system, and to reconstructt he shape and geometry of the basins formed along the principal displacement zone of the fault system.Three main Neogene pull-apart basins that range from 70 to 100 km in length, and from 12 to 22 km inwidth, have been identified along this segment of the plate boundary. These basins have elongated shapes with their major axes parallel to the ENE-WSW direction of the fault zone. The sedimentary architecture and the infill geometry of the basins suggest that they represent mostly strike-slip dominated transtension basins which propagated from E to W. The basins imaged by seismic data show in some cases geometrical and structural features linked to the possible reactivation of previous wedge-top basins and inherited structures pertaining to the external front of the Magallanes fold-and-thrustcompression belt, along which the South American-Scotia fault system has been superimposed. It is sugge sted that the sequence of the elongated basins occur symmetrically to a thorough going strike-slip fault, in a left-stepping geometrical arrangement, in a manner similar to those basins seen in other transcurrent environments. Fil: Esteban, Federico Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Tassone, Alejandro Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Isola, José Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Lodolo, Emanuele. Istituto Nazionale Di Oceanografia E Di Geofisica; Italia Fil: Menichetti, Marco. Luniversita Degli Studi Di Urbino Carlo Bo; Italia

Lago Chepelmut is a relatively small lake in size, of ellipsoidal shape, located in the outer fold-and-thrust belt of the Fuegian Andes (southernmost South America). High-resolution single-channel seismic profiles, integrated with geological information in the surrounding area, have allowed to reconstruct for the first time a bathymetric map of the lake and the architecture, distribution and thickness of the sedimentary cover. Two main seismic units were identified in the seismic records: (i) a Lower Unit of glacial nature, likely associated to the Last Glacial Maximum (LGM), and irregularly distributed through the basin, and (ii) an Upper Unit of lacustrine origin which drapes the entire basin. Submerged moraine deposits within the lake were also found from seismic data, and correlated with moraine arcs widespread distributed in the surroundings of the basin. These morphologies represent the recessional deposits left by the Ewan glacier lobe, one of the easternmost fronts of the Tierra del Fuego glaciers during the LGM. The lacustrine sedimentary record shows that the lake level was not constant through the recent history of the lake. Moreover, data analysis has shown that there is also an important structural component that has conditioned the evolution of the basin, in addition to that linked to glacial activity. Fil: Lozano, Jorge Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Tassone, Alejandro Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Bran, Donaldo Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Lodolo, Emanuele. Istituto Nazionale Di Oceanografia E Di Geofisica Sperimentale; Fil: Menichetti, Marco. Università di Urbino; Italia Fil: Cerredo, Maria Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Esteban, Federico Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Ormazabal, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Isola, José Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Baradello, Luca. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; Italia Fil: Vilas, Juan Francisco A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina