Grupo de de Prospección Geológica y Geofísica Marina y Lacustre (GeofLaMa)
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Grupo de de Prospección Geológica y Geofísica Marina y Lacustre (GeofLaMa)
Featured research (11)
The management of invasive species in large, little-known, nature reserves is difficult. Weighing the risk of invasion against the conservation value of each sector in nature reserves would help design viable management strategies. We evaluated the invasion risk of the Pacific oyster (Crassostrea gigas) in nature reserves in the Bahía Blanca estuary (Argentina). We tested the hypothesis that there were areas of high conservation value in the nature reserves that are susceptible to invasion by C. gigas. We measured its spatial expansion and increase in density on the north coast of the estuary from 2010 to 2015. This allows establishing its preferences of substrate type and tide level in the intertidal zone, hereafter geo-environmental units. We mapped these geo-environmental units within nature reserves using GIS analysis. We found high risk of invasion in 246 hectares of high priority sectors in nature reserves, which minimized the need of management efforts to 13.5% of the total area of nature reserves. We highlight the sectors where C. gigas would generate the strongest impact, as well as where management efforts would be more cost-effective. Our approach provides a framework that can be used to assess risk in nature reserves and help identify management priorities.
Shallow biogenic gas deposits located in the surface of the seabed may affect abundance, diversity, biomass and structure of benthic communities. Nevertheless, the magnitude and responsible variables of this effect still not clear. For this, the current study applies sedimentological metrics to the different community patterns associated with gas presence detected by acoustic methods across two seasons (spring and winter). Gas-bearing sediments showed higher organic matter content, lower shear strength and greater textural homogeneity across the column. Gas trapped in sediments was found associated with changes in the structure of benthic community, in species composition as well as in relative abundance and biomass of each taxa. Also, lower total abundance, species richness and diversity and higher total biomass was found in gas site. Higher organic matter content of sediments in gas site explained benthic community patterns across seasons. Gas bubbles trapped in surface of seabed sediments changed physical and chemical properties of sediments affecting benthic communities in ways that seems comparable with shallow water gas seeps and reducing environment. Unlike the latter, gas bubbles trapped have the advantage of having been widely mapped in coastal systems by geophysicists and marine geologists, with high resolution seismic (3.5 kHz) which according to our results seems to affect benthic communities.
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 Río Chico Arch. The most shortening is seen in the apex of the Río 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 Géminis and Ciclón anticlines, developed during the N–S last compressional stage of deformation in the late Oligocene/early Miocene. The Géminis 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 Ciclón 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.
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.