CIFICEN   24414
CENTRO DE INVESTIGACIONES EN FISICA E INGENIERIA DEL CENTRO DE LA PROVINCIA DE BUENOS AIRES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
HYDROGEOCHEMICAL AND ISOTOPIC CHARACTERIZATION OF THE TAPALQUÉ CREEK UPPER BASIN AND ITS ASSOCIATED KARST, BUENOS AIRES, ARGENTINA
Autor/es:
BARREDO CODESAL, S.P.; GLOK GALLI, M.; TREZZA, M.A.; MARTÍNEZ, D.E.
Lugar:
Sydney
Reunión:
Congreso; 17th International Congress of Speleology (17th ICS), Speleo 2017; 2017
Institución organizadora:
Australian Speleological Federation Inc (ASF)
Resumen:
In the center and southern regions of the Argentine Buenos Aires province, South America, isolated karst areas with cave systems exposed. In the central area, these are present in the Sierras Bayas town, located to the NE of the Tapalqué Creek Upper Basin (TCUB) that has a heterogeneous hydrogeological behavior and is mostly situated in the Olavarría district, one of the main mining sites of the country. Karst evolved in the epiclastic depositional sequences of the Sierras Bayas Group: the lowermost, Villa Mónica Formation (~800 Ma), with dolomites and stromatolites present; and the uppermost, Loma Negra Formation (~543-560 Ma), being composed of limestones. These rocks are presently exposed in quarries whose operations led to the discovery of well-developed caves, karstic terraces, collapse dolines and ancient karst features. Four isolated cavities were mapped but recent field work suggest that there are more caves present. The aim of the present work is to carry out speleological interpretation of the karst environment associated with the TCUB, together with a hydrogeological analysis and a hydrogeochemical and isotope (δ2H and δ18O) characterization of surface water and groundwater of the study site. This will improve the understanding of the TCUB hydrological system, considering that caves are aquifer analogues. The phreatic and topographic morphologies match and groundwater and surface water divides are approximately coincident. The regional flow has a NW-N-NE direction, originating in the S sector and receiving local groundwater contributions from the NW and NE zones (mountain ranges), this latter being where carbonate rocks are outcropping. Discharge occurs through the hydrographic network into the Tapalqué creek (gaining streams). Hydrogeochemical and stable isotopes analyses confirm this, with a groundwater and streamwater general classification mostly as sodium bicarbonate type and also as calcium and/or magnesium bicarbonate waters. Isotopic data show the source of the detritic aquifer (Pampeano aquifer) recharged from rainfall and a groundwater domain into the stream flow. It is proposed that ancient and new caves belong to a same regional system, being semiactive and follow the regional flow of groundwater and streamwater. The existence of tubular passages with elliptical cross sections and large scallops suggest initial phreatic origin although presently they are evolving under vadose conditions. Some unearthed galleries show steep entrances, smaller dissolution features and trickling water confirming the slow evolution in an epiphreatic environment though some inherited features suggest a probable polygenetic origin.