Modelo geológico conceitual do paleocânion de Regência, região onshore da Bacia do Espírito Santo, Cretáceo ao Eoceno
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Data
2018-10-22
Autores
Batiston, Denis Antonio [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O paleocânion de Regência é reconhecido em subsuperfície da bacia do Espírito Santo, localizado nas proximidades da foz do Rio Doce (ES), originado no Cretáceo e preenchido até meados do Eoceno. Dados de 31 seções sísmicas, 29 poços e marcadores bioestratigráficos (definidos por nanofósseis calcários) substanciaram a elaboração de modelos geológicos que aprimoram o conhecimento sobre a evolução do paleocânion. Os resultados incluem correlações estratigráficas, interpretações de feições estruturais e das principais superfícies estratigráficas no âmbito das formações Mariricu, São Mateus, Regência e Urucutuca, assim como seções esquemáticas transversais e longitudinais do paleocânion, mapas de contorno estrutural dos topos litoestratigráficos e de contorno morfológico do paleocânion. Estas informações foram integradas em detalhe para discutir sua origem, o preenchimento e os fatores de controle. Desde o início, o paleocânion foi estruturado por falhas no embasamento. Próximo ao topo da Formação Mariricu, de idade aptiana, já há indícios de uma extensa calha rasa. O paleocânion é dividido pela Zona de Charneira Cedro-Rio Doce (ZCCRD), que é um sistema de falhas normais de direção praticamente N-S. A morfologia e a largura do paleocânion também foram controladas por diversas falhas normais menores nos blocos proximal e distal à ZCCRD, originadas no embasamento, ainda ativas quase até o final do preenchimento do paleocânion, com direção principalmente SO-NE. Falhas normais também tiveram papel determinante na origem de um canal secundário de grande porte a sudoeste, assim como outros menores ao longo da margem norte do paleocânion. Na porção proximal, depósitos neocretácicos podem ter sido preservados devido a abatimento e rotação de blocos por falhas normais. Faltam sedimentos paleocênicos no depocentro do paleocânion em razão de processos erosivos provavelmente controlados por abaixamento relativo do nível do mar. Pode- se inferir que o preenchimento proximal eo-eocênico foi por sedimentos da mesma fonte que aqueles acumulados no depocentro do paleocânion em fase de nível relativo do mar baixo. Refletores sísmicos sugerem a presença de canais empilhados e gradação ascendente para canais dispersos. Na parte proximal basal há padrões de refletores sísmicos atribuíveis a fluxos gravitacionais subaquosos e, mais comumente, associados à borda do paleocânion. Notam-se também feições causadas por compactação diferencial. O conjunto de interpretações é sintetizado esquematicamente através de um modelo geológico evolutivo e deposicional.
Santo Basin, located near to the mouth of the Doce River (State of Espírito Santo, Southeast Brazil), carved from the Cretaceous and filled up to the mid Eocene. Data of 31 seismic sections, 29 wells and biostratigraphic markers (of calcareous nannofossils) have substantiated the conception of geological models that improve the awareness concerning the paleocanyon evolution. The results include stratigraphic correlations, structural geology interpretations and stratigraphic surfaces determination within the Mariricu, São Mateus, Regência and Urucutuca formations, as well as schematic transversal and longitudinal sections of the paleocanyon, structural contour maps of the lithostratigraphic tops and morphologic contour map of the paleocanyon. These information were integrated in detail to promote discussion about the origin, the filling and the controls of the paleocanyon development. Since the beginning, the structure was related to faults in the basement. The first long shallow channel is evidenced near the top of the Aptian Mariricu Formation. The paleocanyon is divided into a proximal block and a distal one by an almost N-S system of normal faults designated as Cedro-Rio Doce Fault Zone (CRDFZ). In both blocks, the morphology and width of the paleocanyon were also controlled by several smaller normal faults with main SW-NE direction, originated in the basement, still moving until the almost complete fill of the paleocanyon, with main direction SW-NE. Normal faults were also determinant in the carving of an secondary large channel in the southwestern region, as well as other smaller channels along the northern margin of the canyon. In the proximal region, Late Cretaceous deposits may have been preserved because of a block sinking and rotation by normal faults. Paleocene sediments are missing in the paleocanyon depocenter due to erosive processes probably controlled by a fall of the relative sea level. It can be inferred that during relative low sea level in early Eocene, both the proximal and the distal depocenters of the paleocanyon were filled by sediments from the same source. Seismic reflectors evidence the occurrence of stacked channels and upward gradation to scattered channels. In the proximal basal part, the seismic patterns may be ascribed to aquatic gravitational flows, which most commonly were related to the paleocanyon borders. Differential compactation features are observed as well. The set of interpretations is schematically synthesized through an evolutionary and depositional geological model.
Santo Basin, located near to the mouth of the Doce River (State of Espírito Santo, Southeast Brazil), carved from the Cretaceous and filled up to the mid Eocene. Data of 31 seismic sections, 29 wells and biostratigraphic markers (of calcareous nannofossils) have substantiated the conception of geological models that improve the awareness concerning the paleocanyon evolution. The results include stratigraphic correlations, structural geology interpretations and stratigraphic surfaces determination within the Mariricu, São Mateus, Regência and Urucutuca formations, as well as schematic transversal and longitudinal sections of the paleocanyon, structural contour maps of the lithostratigraphic tops and morphologic contour map of the paleocanyon. These information were integrated in detail to promote discussion about the origin, the filling and the controls of the paleocanyon development. Since the beginning, the structure was related to faults in the basement. The first long shallow channel is evidenced near the top of the Aptian Mariricu Formation. The paleocanyon is divided into a proximal block and a distal one by an almost N-S system of normal faults designated as Cedro-Rio Doce Fault Zone (CRDFZ). In both blocks, the morphology and width of the paleocanyon were also controlled by several smaller normal faults with main SW-NE direction, originated in the basement, still moving until the almost complete fill of the paleocanyon, with main direction SW-NE. Normal faults were also determinant in the carving of an secondary large channel in the southwestern region, as well as other smaller channels along the northern margin of the canyon. In the proximal region, Late Cretaceous deposits may have been preserved because of a block sinking and rotation by normal faults. Paleocene sediments are missing in the paleocanyon depocenter due to erosive processes probably controlled by a fall of the relative sea level. It can be inferred that during relative low sea level in early Eocene, both the proximal and the distal depocenters of the paleocanyon were filled by sediments from the same source. Seismic reflectors evidence the occurrence of stacked channels and upward gradation to scattered channels. In the proximal basal part, the seismic patterns may be ascribed to aquatic gravitational flows, which most commonly were related to the paleocanyon borders. Differential compactation features are observed as well. The set of interpretations is schematically synthesized through an evolutionary and depositional geological model.
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Palavras-chave
Cretáceo, Eoceno, Grupo Barra Nova, Formação Urucutuca, Bacia marginal, Fase drifte, Cretaceous, Eocene, Barra Nova Group, Urucutuca Formation, Marginal basin, Drift phase