Estratigrafia da série eoceno no Baixo do Mosqueiro, bacia de Sergipe-Alagoas
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Data
2017-08-08
Autores
Rancan, Cristiano Camelo [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As rochas do Grupo Piaçabuçu foram alvo de poços exploratórios nos últimos dez anos, nas águas profundas a ultra-profundas da Bacia de Sergipe-Alagoas, que lograram êxito na prospecção de hidrocarbonetos. São também um clássico na história do petróleo no Brasil, pois nelas estão os primeiros campos de produção em águas oceânicas, em reservatórios paleogenos do compartimento estrutural Baixo do Mosqueiro. O estudo estratigráfico da Série Eoceno, com base em perfis elétricos e biozoneamento de poços situados no Baixo do Mosqueiro, exigiu o zoneamento do Grupo Piaçabuçu como um todo, dividido nos intervalos Senoniano, Paleoceno, Eoceno e Oligo-Neogeno. O depocentro senoniano situa-se na Depressão de Areia Branca e os demais na Depressão de Vaza-Barris, deslocados ao longo de cada intervalo, com migração gradual para S e W. A Série Eoceno foi dividida nos intervalos Inferior, Médio e Superior. O primeiro tem depocentro na Depressão de Dourado e os demais na Depressão de Vaza-Barris, condicionados por halocinese e deformação no embasamento. A deposição do Eoceno Inferior ocorreu como uma continuidade do evento de afogamento que se estendia desde o Neopaleoceno (pontuado por deposição progradacional de mar baixo), com superfície de máxima inundação ao nível da biozona N-420. Esta seção possivelmente aflora em superfície na Depressão da Ilha de Mem de Sá. A discordância que define a base do Eoceno Médio (Discordância Pré-luteciana) representa o principal evento erosivo de toda a série e a partir dela os sistemas progradaram no Meso e Neoeoceno, com recuo de depocentro no último. No Mesoeoceno o limite entre o Baixo do Mosqueiro e a Plataforma de Estância foi colmatado pela sedimentação e as sub-bacias de Sergipe e Jacuípe passaram a atuar como um único compartimento estrutural. Na Depressão de Vaza-Barris predominaram associações de fácies de fluxos gravitacionais de sedimentos e nas depressões menores e degraus a leste associações do tipo lobos arenosos de frente deltáica. Ambos os zoneamentos, para o Grupo Piaçabuçu e Eoceno, permitiram propor uma compartimentação estrutural interna do Baixo do Mosqueiro e sua variação ao longo do tempo. Há indícios de deformação direcional transpressiva pós-eocênica. A partir do Oligoceno a fisiografia do Baixo do Mosqueiro assumiu geometria homoclinal, dominado por sedimentação arenosa e carbonática plataformal.
Piaçabuçu Group rocks were exploratory targets of many wildcats along the last ten years, on deep to ultradeep water of Sergipe-Alagoas Basin, with sucess in petroleum search. This stratigraphic unit is a classic production zone on Brazil’s petroleum history, because the first offshore discovery where there, in Paleogene reservoirs of Mosqueiro Low Compartiment. A stratigraphic study in Eoceno Series, based on well logs and biostratigraphic data had the objective of understand depositional systems spacial distribution, response to accomodation space variation, controlled by eustasy and deformational history in time. In order to compreend this, Piaçabuçu Group was zoned in four intervals: Senonian, Paleocene, Eocene and Oligo-Neogen. Senonian Depocenter was in Areia Branca Trough and for the others in Vaza-Barris Trough, but gradually migrated along time to S and W. Eocene Series was shared in tree intervals: Lower, Middle and Upper. Lower Eocene has depocenter on Dourado Trough, while Middle and Upper Eocene are in Vaza-Barris Trough, controlled by halokinesys and basement deformation, respectively. Lower Eocene deposition was a continuity of Upper Palocene drowning interval (puncuated by progradational deposition on lowstand), with maximum flooding surface at N-420 biozone level. This interval probably outcrops at Ilha de Mem de Sá Trough, in western offshore sector. Middle Eocene basal unconformity is the main erosive event of the Series, and from it, depositional systems are strongly progradacional during Middle and Upper Eocene, with backstepping on the last one. During Lutetian and Bartonian, limits between Mosqueiro Low and Vaza-Barris Trough were buried ans Segipe and Jacuípe sub-basins turned to a single structural compartiment. In VazaBarris Trough, gravity sediments flow facies associations were more commom while in eastern troughs and steps, delta front sandstone lobe facies association were dominant. Piaçabuçu Group and Eocene Series zoning allow a Mosqueiro Low internal subdivisions and their variation along time. There are strong suggestions of post-Eocene transpressive deformation. Since Oligocene, basin has a marked homoclinal geometry, dominated by neritic sedimentation.
Piaçabuçu Group rocks were exploratory targets of many wildcats along the last ten years, on deep to ultradeep water of Sergipe-Alagoas Basin, with sucess in petroleum search. This stratigraphic unit is a classic production zone on Brazil’s petroleum history, because the first offshore discovery where there, in Paleogene reservoirs of Mosqueiro Low Compartiment. A stratigraphic study in Eoceno Series, based on well logs and biostratigraphic data had the objective of understand depositional systems spacial distribution, response to accomodation space variation, controlled by eustasy and deformational history in time. In order to compreend this, Piaçabuçu Group was zoned in four intervals: Senonian, Paleocene, Eocene and Oligo-Neogen. Senonian Depocenter was in Areia Branca Trough and for the others in Vaza-Barris Trough, but gradually migrated along time to S and W. Eocene Series was shared in tree intervals: Lower, Middle and Upper. Lower Eocene has depocenter on Dourado Trough, while Middle and Upper Eocene are in Vaza-Barris Trough, controlled by halokinesys and basement deformation, respectively. Lower Eocene deposition was a continuity of Upper Palocene drowning interval (puncuated by progradational deposition on lowstand), with maximum flooding surface at N-420 biozone level. This interval probably outcrops at Ilha de Mem de Sá Trough, in western offshore sector. Middle Eocene basal unconformity is the main erosive event of the Series, and from it, depositional systems are strongly progradacional during Middle and Upper Eocene, with backstepping on the last one. During Lutetian and Bartonian, limits between Mosqueiro Low and Vaza-Barris Trough were buried ans Segipe and Jacuípe sub-basins turned to a single structural compartiment. In VazaBarris Trough, gravity sediments flow facies associations were more commom while in eastern troughs and steps, delta front sandstone lobe facies association were dominant. Piaçabuçu Group and Eocene Series zoning allow a Mosqueiro Low internal subdivisions and their variation along time. There are strong suggestions of post-Eocene transpressive deformation. Since Oligocene, basin has a marked homoclinal geometry, dominated by neritic sedimentation.
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Palavras-chave
Eoceno, Estratigrafia, Depocentros, Baixo do Mosqueiro