Synthesis of the hydrogeological studies in the sedimentary basins Amazon and Solimões: the Aquifers Systems Içá-Solimões and Alter do Chão

Abstract

Geological maps and stratigraphic charts of the Amazon and Solimões sedimentary basins were reviewed, emphasizing the formations Alter do Chão, Içá and Solimões, the largest reserves of fresh groundwater in these basins. The lack of information on these formations was minimized by sample probe and stratigraphic profiles of construction, lithological and geophysical water and oil wells, obtained in the Base Operacional Geólogo Pedro de Moura, Urucu region, about 650 km southwest of Manaus (AM). In the Amazon Basin, the Aquifer System Alter do Chão is characterized by unconfined and confined aquifers, with transmissivity between 1.5 and 9.1 x 10-3 m²/s, indicated for public supply. In the Solimões Basin, this system is confined by Aquiclude Solimões, recovered by the Içá-Solimões Aquifers. The reserve is estimated as 33,000 km³. The Aquifer System Içá-Solimões, in Urucu, is unconfined-confined, with two aquifers hydraulically connected: the superficial, with top and bottom at depths near 20 and 70 m, respectively; and the deeper, between 50 and 120 m. With an outcrop area of 948,600 km² in the Solimões Basin, the reservation of this system was estimated as 7,200 km³, less expressive than the Aquifer System Alter do Chão. The average hydrodynamic parameters were: T = 3 x 10-3 m²/s, S = 5 x 10-4 and K = 1 x 10-4 m/s, orders of magnitudes similar to those found in the aquifer Alter do Chão. Assessing the interrelationships and potential of these two regional aquifers sought to contribute to the hydrogeological knowledge in the Amazon Basin region, where researches on groundwater are still incipient.