Estratigrafia de seqüências aplicada à caracterização de aqüíferos: um estudo de caso na área de Candiota, Rio Grande do Sul

Abstract

Detailed stratigraphic analysis of the Early Permian (Artinskian/Kungurian) succession of the intracratonic Paraná Basin in southernmost Brazil has been applied focusing stratigraphic characterization of potential aquifers. In the study area, the counties of Candiota and Hulha Negra, in the southwestern region of Rio Grande do Sul state, the sedimentary succession (Itararé, Rio Bonito and Palermo units) is interpreted to have been formed in a shallow, wave-dominated sea, originated mainly in a mixed (tide and wave) influenced estuary setting. Four main depositional systems have been recognized: alluvial fan, fluvial-dominated delta, lagoonal estuary and barrier/shoreface. The regional correlation of the lithofacies within the different depositional systems has led to a high-resolution stratigraphic framework, with three third-order depositional sequences (i.e., unconformity-bounded depositional packages formed during a complete cycle of falling and rising base level). The main sandbodies occur within sequence 2 which is formed by seven fouthorder parasequences, and at the base of the third sequence. Under the viewpoint of groundwater prospecting, the best sandbodies occur within parasequences 1,2 4 and 7. Based upon the stratigraphic characterization, optimal borehole locations are given, as well as estimatives on productive dephs and water volume.