Granulometric and compositional characterization of the Holocene formations in the northeastern sector of the Atlantic Ocean coast, Province of Buenos Aires, Argentina and its relation to hydrogeological aspects

CARRETERO S.; GARCÍA GALLUZZI A.; KRUSE E.

Advances in Geomorphology and Quaternary Studies of Argentina. 3. Selected papers of the Argentine Association on Geomorphology and Quaternary Studies Congress, Puerto Madryn, 2018

Springer

Año: 2021; p. 416 - 436

The evolutionof the coastal plain of the Province of Buenos Aires, Argentina, during the Pleistocene-Holocene is regarded as relevant in the regional hydrogeological behavior. The aim of this work was to undertake a detailed study from a granulometric and mineralogical perspective of the formations that compose the coastal aquifer system. Exploratory boreholes were drilled throughout the total thickness of the aquifer. Samples were sieved; the weight percentages of each grain-size fraction were determined and observed under a stereomicroscope. Thin sections were prepared for study by petrographic microscopy and X-ray diffractometry. The decrease in grain size with depth would indicate a decreasein effective porosity in the same direction, resulting in a lower flowvelocity. This was verified by means of the hydraulic conductivity (K) values obtained depending on the changes in grain size of the sediments in each formation. The mineralogy indicates the presence of abundant magnetic, opaque minerals (oxides and sulphides) and mafic minerals with Fe and Mg-Mn in their composition. This would explain the high concentrations of Fe and Mn in the groundwater, considering that it could be an environment in which the redox conditions allow the dissolution of such elements and their incorporation into groundwater.