Eduardo A. Gómez

Radiocarbon Reservoir Ages and Hardwater Effect for the Northeastern Coastal Waters of Argentina

Accelerator mass spectrometry (AMS) radiocarbon dates were obtained for 18 mollusk shells collected alive along the Buenos Aires province coast, Argentina, over the period AD 1914-1935. Reservoir ages were estimated for all samples on the basis of the tree-ring calibration curve for the Southern Hemisphere (SHCal04, McCormac et al. 2004) and the marine Δ R values calculated as the difference between the conventional 14C age and the age deduced from the marine, mixed-layer model calculation (Marine04, Hughen et al. 2004). For most coastal locations, a great Δ R scatter was observed, ranging from 191 to 2482 yr, which is explained by the input of varying content of dissolved carbonate by rivers and groundwater (hardwater effect) and indicates a serious limitation for shell-based 14C chronologies. Within the interior of Baha Blanca estuary, Δ R values ranged from 40 to 50 46 as a consequence of the local geological particularities of the environment. This suggests that, with some restrictions, the marine calibration curve with standard parameters ( Δ R = 0) could be used at this location.

Total mercury in marine sediments near a sewage outfall. Relation with organic matter.

Abstract Total mercury content of sediments affected by a sewage outfall was determined. The results as obtained were correlated with other parameters (humic substances, protein content, % silt‐clay); a marked positive correlation was found to exist between total mercury and humic substance contents of these sediments. Mercury distribution seems to be influenced not only by certain physical processes (ebb and flow, adsorption, etc.) but also by biological and chemical ones.

Depredación de ostrácodos del Cuaternario del sur de la provincia de Buenos Aires, Argentina

Depredation of Quaternary ostracods from southern Buenos Aires province, Argentina. The presence of fossil traces in ostracods valves from different quaternary palaeoenvironments in southern Buenos Aires province, Argentina, are studied in this paper. A number of 12500 specimens were analyzed and a total of 33 bored valves were separated. Two types of depredation fossil traces were determined: Oichnus simplex Bromley and Oichnus paraboloides Bromley, which comprised more than 60% of the total boreholes. The highest percentage of valves with evidence of predation (3.33%) was registered in sediments of a continental permanent lagoon with favourable trophic conditions and high density of ostracods. There was not relationship between the borehole diameter and the size of the predated valves. Evidences of depredation were registered in species with smooth valves as well as in species with adorned valves.

Morfodinámica de un campo de dunas submarinas en una entrada de marea: San Blas, Argentina

The morphology of a submarine dune field developed in a tidal inlet that connects the Argen- tinean continental shelf with Anegada Bay (southern Buenos Aires province) was studied. The sediment circu- lation was inferred from the differential displacements of the bedforms evaluated by comparing consecutive surveys. An echosounder and a Phase Measuring Bathymetric System (PMBS) called GeoSwath were used to obtain a detailed submarine morphology. Large dunes, with heights between 4.5 and 5.0 m and from 100 to 120 m separating them, were present near the southern limit of the dune field at 24 m depth. These dunes move towards the outer part of the channel at a speed of 18 to 75 m year -1 . At the northern end of the dune field, at 21 m depth, the dunes are smaller, being 2.0 to 2.5 m in height and separated by 40 to 80 m. The smaller dunes move towards the interior of Anegada Bay at 18 to 36 m year -1 . The distribution of the water flow in the entire water column was obtained through a perpendicular profile of the channel by means of an ADCP. Maximum current speeds were 2 m s -1 , and were found during flood tide. The results obtained indicate a circulatory transport model of sedimentary sands, with the formation of ebb and flood deltas at both ends of the deep inlet throat, which lacks of unconsolidated sediments.

Asociaciones de ostrácodos bentónicos actuales y del Holoceno del estuario de Bahía Blanca (Buenos Aires, Argentina): interpretaciones paleoambientales

Fil: Kihn, Romina Gisela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina

Subaequeous landslides analysis in lacustrine deltas (Nahuel Huapi lake, Argentina) through high-resolution bathymetry

Las localidades asentadas en las costas de los grandes lagos de Norpatagonia Andina estan expuestas a frecuente actividad sismica y volcanica regional y a fenomenos tsunamigenicos asociados. Olas extraordinarias como el tsunami de 1960 en el lago Nahuel Huapi, que afecto las costas de la ciudad de Bariloche, pueden ser inducidas por deslizamientos subaereos o subacuaticos desencadenados durante un sismo de magnitud (Villarosa et al., 2009). Este trabajo aborda el estudio de los procesos de remocion en masa que se desarrollan en la porcion sumergida de deltas lacustres ubicados en las costas de las localidades de Bariloche y Dina Huapi, con el fin de aportar informacion relevante que sirva de base a futuras evaluaciones de peligrosidad en estas costas. Se registro la morfologia subacuatica mediante un Sonar Batimetrico por Medicion de Fase y se confeccionaron Modelos Digitales de Elevacion y mapas derivados utilizando ArcGIS. Los resultados indican que se trata de deltas tipo Gilbert: frentes deltaicos de pendientes pronunciadas donde el sustrato se moviliza mediante procesos gravitacionales (deslizamientos, flujos de detritos y/o corrientes de turbidez). La abundancia y magnitud de los deslizamientos (con escarpas de cabecera de unos 10 m de altura y hasta 200 m de longitud y escarpas laterales que se extienden hasta el limite del area estudiada, superando los 600 m de longitud) indican que periodicamente se desarrollan fenomenos de remocion que involucran grandes volumenes de sedimento. Estos eventos son potenciales generadores de ondas en la superficie del lago. La cercania entre estos ambientes y las localidades costeras implica que un evento de este tipo desencadenado por un terremoto de magnitud considerable en la region podria afectar a las costas mas vulnerables.