- Ryo Matsumoto, Toshihiko Sugai, José Maria Landim Dominguezedit
Empty elliptical vesicles are observed in outcrops of Barremian very fine clayey sandstone to siltstone lacustrine slurry deposits of the Pitanga Member (Maracangalha Forma‑ tion), exposed in the Maré Island, Southern Recôncavo Basin,... more
Empty elliptical vesicles are observed in outcrops of Barremian very fine clayey sandstone to siltstone lacustrine slurry deposits of the Pitanga Member (Maracangalha Forma‑ tion), exposed in the Maré Island, Southern Recôncavo Basin, Brazil. These sedimentary features have been traditionally in‑ terpreted as water escape structures triggered by the diapirism of the underlying shales of the Candeias Formation. This work proposes that vesicles were generated during massive gas hydrate dissociation as a result of tectonic activity in a paleolake system. Tectonic uplift would have triggered both the reduction of the confining pressure as well as an increase in lake bottom tem‑ perature, resulting in the instability of gas hydrate and causing intense release of both methane — or carbon dioxide (CO 2) — and water. On one hand, this proposal has a strong impact on pa‑ leoenvironmental interpretations, giving support to the current hypothesis that rocks related to the Pitanga Member would have been deposited under water columns deep enough for gas hydrate formation and subsequent dissociation. On the other hand, it provides new insights on the genesis of fluid escape structures in sedimentary rocks, both lacustrine and marine, providing a paleobathymetric indicator. RESUMO: Vesículas elípticas ocas são observadas em afloramentos de areni-tos argilosos muito finos e siltitos lacustrinos do Membro Pitanga da Formação Maracangalha, expostos na Ilha de Maré, sudeste da Bacia do Recôncavo, Es-tado da Bahia, Brasil. Essas rochas foram depositadas em condições subaquo-sas e são consideradas depósitos gravitacionais do tipo slurry. Essas feições têm sido tradicionalmente interpretadas como sendo estruturas de escape de água, resultado da ação do diapismo de folhelhos sotopostos da Formação Candeias. Este trabalho propõe que as vesículas foram geradas durante uma intensa dis-sociação de hidratos de gás em resposta à atividade tectônica existente naquele sistema lacustre. O soerguimento tectônico do fundo do lago teria propiciado a redução da pressão confinante nos poros sedimentares, bem como o aumento de temperatura nas águas de fundo, resultando na instabilidade dos hidratos de gás contidos nas porções rasas dos sedimentos e causando uma violenta libera-ção de metano — ou gás carbônico (CO 2) — e água. Se correta, esta proposta tem um grande impacto na interpretação paleoambiental da Bacia do Recôn-cavo, uma vez que corroborará com a hipótese corrente de que as rochas do Membro Pitanga teriam sido depositadas em ambientes profundos, suficientes para a formação de hidratos de gás e a consequente dissociação em período de soerguimento. Por outro lado, permite uma interpretação adicional acerca da gênese de estruturas de escape de fluidos em rochas sedimentares, lacustres ou marinhas, servindo como um potencial indicador de paleobatimetria.
Research Interests:
A quantidade de trabalhos que abordam aspectos tectônicos, magmáticos e deposicionais das bacias sedimentares brasileiras é vasto e abrangente. Entretanto, muitos destes trabalhos são localizados e não abordam, de forma integrada, a... more
A quantidade de trabalhos que abordam aspectos tectônicos, magmáticos e deposicionais das bacias sedimentares brasileiras é vasto e abrangente. Entretanto, muitos destes trabalhos são localizados e não abordam, de forma integrada, a evolução do continente Sul-Americano como um todo. A última grande tentativa de integração dos dados evolutivos foi a atualização das Cartas Estratigráficas das
Bacias Sedimentares Brasileiras, publicada no Boletim de Geociências da Petrobras (v.15, n.2) em 2007. O presente trabalho visa integrar e condensar as informações contidas naquela publicação, bem como compilar o máximo de informações já publicadas. A correlação entre as bacias sedimentares e os principais eventos geológicos, durante
a evolução do continente, teve como amarração a Carta Estratigráfica Internacional, tornando possível a correlação destes eventos ao longo do tempo geológico. Além disto, foi feita uma criteriosa compilação de dados sobre os substratos
destas bacias, evidenciando os diversos ambientes geotectônicos envolvidos antes e durante a evolução polifásica do continente Sul-Americano. A principal intenção deste trabalho, no entanto, é resumir o estado-da-arte do conhecimento geológico sobre as bacias sedimentares brasileiras através de um painel, no qual estas informações foram integradas.
Bacias Sedimentares Brasileiras, publicada no Boletim de Geociências da Petrobras (v.15, n.2) em 2007. O presente trabalho visa integrar e condensar as informações contidas naquela publicação, bem como compilar o máximo de informações já publicadas. A correlação entre as bacias sedimentares e os principais eventos geológicos, durante
a evolução do continente, teve como amarração a Carta Estratigráfica Internacional, tornando possível a correlação destes eventos ao longo do tempo geológico. Além disto, foi feita uma criteriosa compilação de dados sobre os substratos
destas bacias, evidenciando os diversos ambientes geotectônicos envolvidos antes e durante a evolução polifásica do continente Sul-Americano. A principal intenção deste trabalho, no entanto, é resumir o estado-da-arte do conhecimento geológico sobre as bacias sedimentares brasileiras através de um painel, no qual estas informações foram integradas.
Research Interests:
A quantidade de trabalhos que abordam aspectos tectônicos, magmáticos e deposicionais das bacias sedimentares brasileiras é vasto e abrangente. Entretanto, muitos destes trabalhos são localizados e não abordam, de forma integrada, a... more
A quantidade de trabalhos que abordam aspectos tectônicos, magmáticos e deposicionais das bacias sedimentares brasileiras é vasto e abrangente. Entretanto, muitos destes trabalhos são localizados e não abordam, de forma integrada, a evolução do continente Sul-Americano como um todo. A última grande tentativa de integração dos dados evolutivos foi a atualização das Cartas Estratigráficas das
Bacias Sedimentares Brasileiras, publicada no Boletim de Geociências da Petrobras (v.15, n.2) em 2007. O presente trabalho visa integrar e condensar as informações contidas naquela publicação, bem como compilar o máximo de informações já publicadas. A correlação entre as bacias sedimentares e os principais eventos geológicos, durante
a evolução do continente, teve como amarração a Carta Estratigráfica Internacional, tornando possível a correlação destes eventos ao longo do tempo geológico. Além disto, foi feita uma criteriosa compilação de dados sobre os substratos
destas bacias, evidenciando os diversos ambientes geotectônicos envolvidos antes e durante a evolução polifásica do continente Sul-Americano. A principal intenção deste trabalho, no entanto, é resumir o estado-da-arte do conhecimento geológico sobre as bacias sedimentares brasileiras através de um painel, no qual estas informações foram integradas.
Bacias Sedimentares Brasileiras, publicada no Boletim de Geociências da Petrobras (v.15, n.2) em 2007. O presente trabalho visa integrar e condensar as informações contidas naquela publicação, bem como compilar o máximo de informações já publicadas. A correlação entre as bacias sedimentares e os principais eventos geológicos, durante
a evolução do continente, teve como amarração a Carta Estratigráfica Internacional, tornando possível a correlação destes eventos ao longo do tempo geológico. Além disto, foi feita uma criteriosa compilação de dados sobre os substratos
destas bacias, evidenciando os diversos ambientes geotectônicos envolvidos antes e durante a evolução polifásica do continente Sul-Americano. A principal intenção deste trabalho, no entanto, é resumir o estado-da-arte do conhecimento geológico sobre as bacias sedimentares brasileiras através de um painel, no qual estas informações foram integradas.
Research Interests:
The tephra which spreads and deposits in wide areas by volcanic eruption is one of the most important time makers for the paleoenvironmental researches in and around the Japanese Islands. However, the source and eruption age of many... more
The tephra which spreads and deposits in wide areas by volcanic eruption is one of the most important time makers for the paleoenvironmental researches in and around the Japanese Islands. However, the source and eruption age of many tephras is still unknown (Machida 2011). The study area, off Joetsu of the Japan Sea, has great advantage to establish tephrostratigraphy because the various tephras from the Japanese Islands and Ulreung-do Island are probably distributed and because sedimentation rate in the study area is high since the area is situated close to the continental shelf and Japan Alps. This report revealed the tephrastratigraphy off Joetsu based on the identification and correlation of the tephras layers collected from the long core samples obtained by MD 179 survey.
The tephra samples were collected from the six piston cores and two gravity cores collected at geomorphologically different places off Joetsu, and at the submarine valley off Sado Island. Each sample was listed in the mineral composition and the morphologic feature of volcanic glass shards, and the chemical composition of 20 shards of volcanic glass measured by microprobe analyzer (SEM-EDS). The total of 95 tephra samples were classified into 32 kinds of tephras based on the shape and the chemical composition of volcanic glass along with heavy-mineral combination. Then 12 kinds of them were identified and correlated with the well-established tephras, although the source and age of the other kinds of tephra were uncertain.
The tephra samples were collected from the six piston cores and two gravity cores collected at geomorphologically different places off Joetsu, and at the submarine valley off Sado Island. Each sample was listed in the mineral composition and the morphologic feature of volcanic glass shards, and the chemical composition of 20 shards of volcanic glass measured by microprobe analyzer (SEM-EDS). The total of 95 tephra samples were classified into 32 kinds of tephras based on the shape and the chemical composition of volcanic glass along with heavy-mineral combination. Then 12 kinds of them were identified and correlated with the well-established tephras, although the source and age of the other kinds of tephra were uncertain.
Research Interests:
This is a tentative to illustrate the tectonic-sedimentary evolution of Brazilian sedimentary basins during the geological time. This pannel was presented and distributed as a CD-ROM during the 46° Congresso Brasileiro de Geologia... more
This is a tentative to illustrate the tectonic-sedimentary evolution of Brazilian sedimentary basins during the geological time. This pannel was presented and distributed as a CD-ROM during the 46° Congresso Brasileiro de Geologia occurred in Santos city, São Paulo from Sep, 30th to Oct, 5th.
Research Interests:
The ratio of total organic carbon to total nitrogen (TOC:TN) and the stable carbon isotope ratio of organic matter (δ13Corg) are widely applied for inferring the origin of organic matter (OM) in Quaternary marine sediments. A plot of... more
The ratio of total organic carbon to total nitrogen (TOC:TN) and the stable carbon isotope ratio of organic matter (δ13Corg) are widely applied for inferring the origin of organic matter (OM) in Quaternary marine sediments. A plot of TOC:TN vs. δ13Corg is useful for such studies but is strongly based on qualitative constraints. This study is based on the qualitative characterization of the source of Quaternary OM via analysis of TOC:TN and δ13Corg signatures, but also proposes a probability parameter, which combines both signatures, to infer the amount of Terrestrial OM Input (TOMI). This index provides a method for quantifying the proportion of terrestrial OM vs. marine OM in a more comprehensive manner. The TOMI index concept was applied to a study area in the Joetsu Basin, eastern margin of the Japan Sea, where previous studies have characterized the OM from the Last Glacial Maximum (LGM) to the present. The upwards increase in TOC indicates that OM production during the Holocene was higher than during the LGM. The enriched δ13Corg signature upwards and decrease in TOC:TN suggest predominantly marine phytoplankton OM during the Holo-cene. Throughout the LGM, low OM production with depleted δ13Corg values and high TOC:TN values in the sediments suggest a predominantly C3 terrestrial plant source for the OM. Using these data, it was possible to calculate a proxy for a sea level variation curve during that period and to investigate the influence of the proximity of the coastal line to the continental slope on the input of terrestrial material to the basin. The proposal provides information for the application of sequence stratigraphic concepts. The TOMI index could confirm that the proximity to the shoreline and shelf break has a strong influence on the input of terrestrial material during lowstand periods.
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Integrated geological, geochemical, and geophysical exploration since 2004 has identified massive accumulation of gas hydrate associated with active methane seeps on the Umitaka Spur, located in the Joetsu Basin on the eastern margin of... more
Integrated geological, geochemical, and geophysical exploration since 2004 has identified massive
accumulation of gas hydrate associated with active methane seeps on the Umitaka Spur, located in the
Joetsu Basin on the eastern margin of Japan Sea. Umitaka Spur is an asymmetric anticline formed along
an incipient subduction zone that extends throughout the western side of the Japanese island-arc
system. Seismic surveys recognized chimney structures that seem strongly controlled by a complex
anticlinal axial fault system, and exhibit high seismic amplitudes with apparent pull-up structures,
probably due to massive and dense accumulation of gas hydrate. Bottom simulating reflectors are widely
developed, in particular within gas chimneys and in the gently dipping eastern flank of the anticline,
where debris can store gas hydrates that may represent a potential natural gas resource. The axial fault
system, the shape of the anticline, and the carrier beds induce thermogenic gas migration to the top of
the structure, and supply gas to the gas hydrate stability zone. Gas reaching the seafloor produces strong
seepages and giant plumes in the sea water column.
accumulation of gas hydrate associated with active methane seeps on the Umitaka Spur, located in the
Joetsu Basin on the eastern margin of Japan Sea. Umitaka Spur is an asymmetric anticline formed along
an incipient subduction zone that extends throughout the western side of the Japanese island-arc
system. Seismic surveys recognized chimney structures that seem strongly controlled by a complex
anticlinal axial fault system, and exhibit high seismic amplitudes with apparent pull-up structures,
probably due to massive and dense accumulation of gas hydrate. Bottom simulating reflectors are widely
developed, in particular within gas chimneys and in the gently dipping eastern flank of the anticline,
where debris can store gas hydrates that may represent a potential natural gas resource. The axial fault
system, the shape of the anticline, and the carrier beds induce thermogenic gas migration to the top of
the structure, and supply gas to the gas hydrate stability zone. Gas reaching the seafloor produces strong
seepages and giant plumes in the sea water column.
Research Interests:
The Holocene sediments of the eastern margin of the Japan Sea are characterized by high total organic carbon (TOC) and total nitrogen (TN) contents, low TOC/TN and TS/TOC values with enriched 13Corg signatures, as a result of high marine... more
The Holocene sediments of the eastern margin of the Japan Sea are characterized by high total organic carbon (TOC) and total nitrogen (TN) contents, low TOC/TN and TS/TOC values with enriched 13Corg signatures, as a result of high marine productivity during present oxic highstand. On the other hand, the LGM sediments are characterized by low TOC and TN contents, high TOC/TN and TS/TOC values with depleted 13Corg signatures, characteristic of C3-derived terrestrial organic matter input during that anoxic lowstand. However, at the top of mounds at the seafloor, where gas hydrate and authigenic carbonate nodules occur, the host sediments have geochemical signatures similar to those of the LGM. Both gas hydrate and authigenic carbonate, formed by the anaerobic oxidation of methane, increased the sedimentary volume and caused an uplift of older sediments, inducing mound formation. The thickness of the Holocene sediments over mounds is very small or absent exposing the LGM sediments to the seafloor. The uplift of the LGM sediments within mounds is estimated to be of ca. 2 to 3 meters. We conducted geochemical analysis to detect such sediment movement, using samples collected by shallow cores in the Joetsu Basin, eastern margin of the Japan Sea.