IIMYC   23581
INSTITUTO DE INVESTIGACIONES MARINAS Y COSTERAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Tracing groundwater over the past one million years in deep aquifers of Argentina using noble gases and krypton-81
Autor/es:
BERTOLIN L.; LEXOW C.; MATSUMOTO T.; YANG G.; MARTINEZ D.E.; JIANG W.; LU Z.; QUIROZ LONDOÑO, M.; ALBOUY R.; KRUSE E.; MARBY J. ; ROMEO N.
Lugar:
San Francisco
Reunión:
Congreso; American Geophysical Union Fall Meeting 2020; 2020
Institución organizadora:
American Geophysical Union
Resumen:
The province of Buenos Aires, Argentina, hosts three deep sedimentary basins, from north to south, Salado, Claromecó and Colorado, with areas of 85,000 km , 3,100 km and 125,000 km , respectively. In these basins, a thick continental sequence of Neogene sediments contains confined thermal aquifers, at depths from several hundreds to more than 1 km. This study providesinsight into the Neogene aquifers by the application of He and Kr tracers for dating. 10 deep wells were sampled for noble gases using clamped copper tubes, and for Kr with a gas extractor. He analyses were performed at the IAEA laboratory by mass spectrometry, and Kr at the ATTA laboratory of USTC. H and C were sampled and determined at external laboratories.H contents were not detectable in all of the cases, thus no young water components exist. He were determined to be around 10 to 10 cm STP/g, several orders of magnitude above the atmospheric level, indicating very old groundwater. Samples are beyond the C range along the borders of the Salado Basin, one of them was found to be 640 ky old using Kr. Ages increase to 1,050 ky atthe basin axis. The large He concentrations, from 8 x 10 to 2 x 10 cm STP/g, reveal an external basal flux. The only well sampled in the Claromecó basin gives a Kr age of 630 ky. In the Colorado basin recharge takes place at the north, with C ages of 20 ky and Kr ages of 40 ky. Towards the south the maximum Kr ages of 920 ky were determined.The Neogene sedimentation is related to the tectonic evolution of the basins since the opening of the Atlantic. The Pliocene marine ingression deposited a thick clay layer, isolating it from the surface. Recharge occurs close to the mountain ranges where these clays disappear, but in most of the area they are confined, with a slow movement and mixing with connate waters, resulting in ages around one million years.