Integração de métodos potenciais (gravimetria e magnetometria) na caracterização do embasamento da região sudoeste da bacia de pelotas, Sul do Brasil

Abstract

ABSTRACT. Through the integrated application of gravity and magnetic methods, it was intended to contribute to structural and compositional characterization of Pelotas Basin basement. The study area is the south region of Rio Grande do Sul Coastal Province, located between latitudes 31 • 45 and 34 • S and longitudes 52 • and 53 • 30 W. The interpretation of potential methods maps into a Geographic Information System (GIS) allowed verifying a complex structuration and a compositional heterogeneity of the bedrock. These structures are related to the Uruguaio-Sul-Rio-Grandense Shield evolution and with South Atlantic Ocean opening. A negative gravity anomaly in Banhado do Taim area was interpreted as a topographic low in the basin basement. In this region, previous works identified a segmentation in the Pleistocene depositional systems of the Rio Grande do Sul Coastal Plain. The presence of a basement low in the same position of the identified segmentation indicates that the stratigraphic record of the region was controlled by the basin basement. Therefore a control of geologic inheritance in the area is suggested, probable related to fault reactivation and differential subsidence associated with the bedrock compositional heterogeneity. Future studies with data acquisition in not covered areas (lagoons and swamps) and their integration with other methods could be able to improve and to test the present interpretations.Keywords: geologic inheritance, gravity method, magnetic method, Rio Grande do Sul Coastal Plain. RESUMO.Por meio da aplicação integrada dos métodos potenciais de gravimetria e magnetometria, visou-se contribuir com a caracterização do arcabouço estrutural e composicional do embasamento da Bacia de Pelotas. Aárea selecionada para este estudoé a região sul da Província Costeira do Rio Grande do Sul, entre as latitudes 31 • 45 e 34 • S e as longitudes 52 • e 53 • 30 W. A interpretação integrada dos mapas gerados através dos métodos potenciais, em um Sistema de Informações Geográficas (SIG), permitiu verificar uma complexa estruturação e a heterogeneidade composicional do embasamento. Essa estruturação está relacionada com a evolução do Escudo Uruguaio-Sul-Rio-Grandense e com a abertura do Oceano Atlântico Sul. Uma anomalia gravimétrica negativa, na região do Banhado do Taim, foi interpretada como uma calha no embasamento. Nessa região, trabalhos anteriores identificaram uma segmentação nos sistemas deposicionais pleistocênicos da Planície Costeira do Rio Grande do Sul. A presença desta calha na mesma posição da segmentação identificada indica que o registro estratigráfico da região foi condicionado pelo embasamento, sugerindo a existência de um controle da herança geológica naárea. Esse controleé possivelmente relacionado com a reativação de falhas e com a subsidência diferencial devidoà heterogeneidade das litologias presentes no embasamento. Estudos futuros com a aquisição de novos dados em regiões onde não foram realizadas medidas (lagoas e banhados) e a integração com outros métodos possibilitarão m...

Holocene Sea-Level Changes in Southern Brazil Based on High-Resolution Radar Stratigraphy

“…Curumim gives name to the prograded (or regressive) barrier that was formed in a very gentle embayment between Tramandaí and Torres [15] (Figure 1). The coastal plain where the Curumim barrier occurs is characterized by coastal sandy barriers and lagoons formed during the Quaternary [16], and its location in an intra-plate position suggests a tectonically stable condition [17]. There is no indication that basin subsidence and sediment compaction were relevant during the Holocene [18].…”

Developing an initial 3D hydrostratigraphical model of the emerged part of the Pelotas Basin along the northern coast of Rio Grande do Sul state, Brazil

“…The Pelotas Basin was formed during the fragmentation of the Gondwana continent and the opening of the South Atlantic, and is described in detail in (Rosa et al, 2017) . The coastal plain of Rio Grande do Sul state, where the AOI is located, is a physiographic feature of the upper, onshore part of the Pelotas Basin (Rosa et al, 2009) , and is divided into an alluvial fan system and four barrier-lagoon systems (Tomazelli & Villwock, 2000) . The alluvial fan system is of Tertiary age, and developed adjacent to the outcropping rocks of the São Bento Group as a result of the erosion and transport of its sediments.…”

U-Pb zircon xenocrysts dating as a proxy to assess volcanic assimilation and the underlying crust, Cretaceous Jaguarão Formation, RS, Brazil

“…Geophysical studies describe positive gravimetric and residual magnetic field anomalies for the Jaguarão region (Rosa et al 2009), with a complex structure and significant compositional heterogeneity. The rifting that led to the opening of the Atlantic Ocean is associated with magmatism, and the E-W Jaguarão Lineament is continuous to the east, associated with positive gravimetric anomalies (Rosa et al 2009), probably indicating that the Jaguarão magmatism is represented by a larger unit not exposed.…”