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Master's Dissertation
DOI
https://doi.org/10.11606/D.21.2019.tde-05122019-155248
Document
Author
Full name
Raissa Basti Ramos
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2019
Supervisor
Committee
Mahiques, Michel Michaelovitch de (President)
Ayres Neto, Arthur
Souza, Luiz Antonio Pereira de
Title in Portuguese
O Papel dos Pockmarks nos processos sedimentares do Talude sul do Brasil
Keywords in Portuguese
pockmarks
armadilhas de sedimento
diapirismo
Abstract in Portuguese
Durante um cruzeiro oceanográfico, realizado em 2011, na região do Talude Sul do Brasil, foram contabilizadas 984 depressões, reconhecidas como pockmarks, distribuídas entre as isóbatas de 300 e 700 metros de profundidade. Um levantamento geofísico raso posterior, associado a dados de sísmica profunda, revelaram a associação dos pockmarks com diápiros de sal. Os dados geofísicos foram transformados para XYZ e, a partir deles, elaborados Modelos Digitais de Terreno. A partir dos registros sísmicos foram definidos locais de amostragem de sedimentos. Os sedimentos coletados foram submetidos a análises de Carbono Orgânico Total (%COT), Carbonato Biodetrítico (%CaCO3), razão isotópica de Carbono (δ13CPDB), Granulometria, Teor de Metais e Datação por radiocarbono. Foram encontrados pockmarks de tamanhos e formas variados e diápiros com distintos graus de exposição e extensão. Os registros sísmicos revelam sedimentação plano-paralela, estabelecida antes da formação dos pockmarks, posteriormente deformada nas zonas de pockmarks e diapirismo. Observaram-se, ainda, feições associadas à exsudação e acúmulo de gás, além de zonas de fratura associadas ao diapirismo. Juntamente à forçante halocinética, esta porção do talude tem sua morfologia moldada pela interação das correntes de fundo dominantes com os pockmarks e diápiros. Um modelo geomorfológico foi proposto a fim de caracterizar os diferentes estágios evolutivos desta porção de talude. A deposição de finos e a preservação do carbono orgânico dentro das depressões mostram a baixa interação das correntes de fundo com as zonas mais internas dos pockmarks, dando a esse tipo de feição o status de armadilha de sedimento. As análises geoquímicas mostram uma componente terrígena nos sedimentos depositados dentro dos pockmarks localizados numa zona de sedimentação carbonática e de tamanho de grão mais grosso.
Title in English
The Role of Pockmarks in the sedimentary processes of the Brazilian southern slope
Keywords in English
pockmarks
diapirism
sediment trap
Abstract in English
During an oceanographic survey, in 2011, on the Brazilian Southern Slope, 984 depressions were recorded, recognized as pockmarks, distributed between 300 and 700 m of water depth. A later shallow geophysical survey, associated with deep seismic data, revealed the association of pockmarks with salt diapirs. The geophysical data were transformed to XYZ and, from them, Digital Terrain Models were elaborated. Sediment sampling sites were defined from the seismic records. The collected sediments were submitted to analysis of Total Organic Carbon (% TOC), Biodetritic Carbonate (%CaCO3), Carbon Isotope Ratio (δ13CPDB), Grain Size, Metal Analyzes and Radiocarbon dating. pockmarks of varying sizes and shapes were found, as well as diapirs with varying degrees of exposure and extension. Seismic records reveal flat-parallel, deformed sedimentation in pockmarks and diapirism zones. There were also features associated with gas exudation and accumulation, as well as fracture zones associated with diapirism. Apart of the halokinetic forcing, this portion of the slope has its morphology shaped by the interaction of dominant bottom currents with pockmarks and diapirs. A geomorphological model was proposed in order to characterize the different evolutionary stages of this portion of the slope. The deposition of fine sediments and the preservation of organic carbon within the depressions show the low interaction of the bottom currents with the deeper zones of the pockmarks, giving this type of feature the status of a natural sediment trap. The geochemical analyzes show a terrigenous signature of sediments deposited within the pockmarks located on a zone of carbonatic sedimentation and coarse grain size.
 
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Publishing Date
2019-12-09
 
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