Produção Nacional
Hydrothermal bowls in the giant Cretaceous Botucatu paleoerg
2022; Sociedade Brasileira de Geologia; Volume: 52; Issue: 1 Linguagem: Inglês
10.1590/2317-4889202220210058
ISSN2317-4889
AutoresLéo Afrâneo Hartmann, Juliana Pertille, Marcos Müller Bicca, Cristiane Bahi dos Santos,
Tópico(s)Hydrocarbon exploration and reservoir analysis
ResumoFascinating circular hydrothermal bowls 0.5 m in diameter occur in paleodunes of the 1.2 million km2 Botucatu paleoerg in the Fronteira Oeste of Brazil, Rio Grande do Sul, and were exposed upon erosion of presumed 2,000 m of basalt and rhyodacite cover of the Paraná Volcanic Province (1 million km2) since the Cretaceous (135 Ma). The tops of the paleodunes display low-temperature (150-50°C) hydrothermal structures comparable to those in basalts and rhyodacites. The source beds of sand injectites display evidence of sequential fault-valve action. The bowls represent a new structure in continental paleodunes. They present circular rims sealed by quartz and a flat horizontal bottom with a central sealed vent. The inclined internal rims of the bowls exhibit a radial set of linear fractures filled with quartz, forming prominent, sharp, positive structures. Their origin is ascribed to the work of water vapor originated in the heated freshwater aquifer. The concave ceiling was lifted a few millimeters along circular fractures long enough for quartz to be deposited. Erosional exhumation of the buried Botucatu hyperdry sand sea has revealed the effects, including the new structures described here, of hydrothermalism associated with a major igneous province upon a giant paleoerg turned-aquifer.
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