Made available in DSpace on 2015-02-24T19:48:38Z (GMT). No. of bitstreams: 1 LilianeRC_Capa_ate_Cap3.pdf: 3239359 bytes, checksum: 5d036616594887894c2008efe8619990 (MD5) Previous issue date: 2008-09-26 / This thesis deals with the tectonic-stratigraphic evolution of the Transitional Sequence in the Sergipe Sub-basin (the southern segment of the Sergipe-Alagoas Basin, Northeast Brazil), deposited in the time interval of the upper Alagoas/Aptian stage. Sequence boundaries and higher order internal sequences were identified, as well as the structures that affect or control its deposition. This integrated approach aimed to characterize the geodynamic setting and processes active during deposition of the Transitional Sequence, and its relations with the evolutionary tectonic stages recognized in the East Brazilian Margin basins. This subject addresses more general questions discussed in the literature, regarding the evolution from the Rift to the Drift stages, the expression and significance of the breakup unconformity, the relationships between sedimentation and tectonics at extensional settings, as well as the control on subsidence processes during this time interval. The tectonic-stratigraphic analysis of the Transitional Sequence was based on seismic sections and well logs, distributed along the Sergipe Sub-basin (SBSE). Geoseismic sections and seismic facies analysis, stratigraphic profiles and sections, were compiled through the main structural blocks of this sub-basin. These products support the depositional and tectonic-stratigraphic evolutionary models built for this sequence. The structural analysis highlighted similarities in deformation styles and kinematics during deposition of the Rift and Transitional sequences, pointing to continuing lithospheric extensional processes along a NW trend (X strain axis) until the end of deposition of the latter sequence was finished by the end of late Aptian. The late stage of extension/rifting was marked by (i) continuous (or as pulses) fault activity along the basin, controling subsidence and creation of depositional space, thereby characterizing upper crustal thinning and (ii) sagstyle deposition of the Transitional Sequence at a larger scale, reflecting the ductile stretching and thinnning of lower and sub crustal layers combined with an increasing importance of the thermal subsidence regime. Besides the late increments of rift tectonics, the Transitional Sequence is also affected by reactivation of the border faults of SBSE, during and after deposition of the Riachuelo Formation (lower section of the Transgressive Marine Sequence, of Albian age). It is possible that this reactivation reflects (through stress propagation along the newlycreated continental margin) the rifting processes still active further north, between the Alagoas Sub-basin and the Pernambuco-Para?ba Basin. The evaporitic beds of the Transitional Sequence contributed to the development of post-rift structures related to halokinesis and the continental margin collapse, affecting strata of the overlying marine sequences during the Middle Albian to the Maastrichtian, or even the Paleogene time interval. The stratigraphic analysis evidenced 5 depositional sequences of higher order, whose vertical succession indicates an upward increase of the base level, marked by deposition of continental siliciclastic systems overlain by lagunar-evaporitic and restricted marine systems, indicating that the Transitional Sequence was deposited during relative increase of the eustatic sea level. At a 2nd order cycle, the Transitional Sequence may represent the initial deposition of a Transgressive Systems Tract, whose passage to a Marine Transgressive Sequence would also be marked by the drowning of the depositional systems. At a 3rd order cycle, the sequence boundary corresponds to a local unconformity that laterally grades to a widespread correlative conformity. This boundary surface corresponds to a breakup unconformity , being equivalent to the Pre-Albian Unconformity at the SBSE and contrasting with the outstanding Pre-upper Alagoas Unconformity at the base of the Transitional Sequence; the latter is alternatively referred, in the literature, as the breakup unconformity. This Thesis supports the Pre-Albian Unconformity as marker of a major change in the (Rift-Drift) depositional and tectonic setting at SBSE, with equivalent but also diachronous boundary surfaces in other basins of the Atlantic margin. The Pre-upper Alagoas Unconformity developed due to astenosphere uplift (heating under high lithospheric extension rates) and post-dates the last major fault pulse and subsequent extensive block erosion. Later on, the number and net slip of active faults significantly decrease. At deep to ultra deep water basin segments, seaward-dipping reflectors (SDRs) are unconformably overlain by the seismic horizons correlated to the Transitional Sequence. The SDRs volcanic rocks overly (at least in part) continental crust and are tentatively ascribed to melting by adiabatic decompression of the rising astenospheric mantle. Even though being a major feature of SBSE (and possibly of other basins), the Pre-upper Alagoas Unconformity do not correspond to the end of lithospheric extension processes and beginning of seafloor spreading, as shown by the crustal-scale extensional structures that post-date the Transitional Sequence. Based on this whole context, deposition of the Transitional Sequence is better placed at a late interval of the Rift Stage, with the advance of an epicontinental sea over a crustal segment still undergoing extension. Along this segment, sedimentation was controled by a combination of thermal and mechanical subsidence. In continuation, the creation of oceanic lithosphere led to a decline in the mechanical subsidence component, extension was transferred to the mesoceanic ridge and the newly-formed continental margin (and the corresponding Marine Sequence) began to be controlled exclusively by the thermal subsidence component. Classical concepts, multidisciplinary data and new architectural and evolutionary crustal models can be reconciled and better understood under these lines / Esta tese aborda a evolu??o tectono-estratigr?fica da Seq??ncia Transicional na Subbacia de Sergipe (por??o sul da Bacia Sergipe-Alagoas, Nordeste do Brasil), depositada no intervalo que abrange o Alagoas superior. Foram identificadas as suas superf?cies lim?trofes e seq??ncias internas, de maior ordem, bem como as estruturas que a afetaram ou controlaram a sua deposi??o. Essa abordagem integrada teve como objetivo caracterizar o contexto geodin?mico e os processos atuantes durante a deposi??o desta seq??ncia e sua rela??o com os est?gios tect?nicos reconhecidos na evolu??o das bacias da Margem Leste Brasileira. O tema da tese remete a uma problem?tica amplamente discutida na literatura, envolvendo a passagem entre os est?gios Rifte e Drifte, a express?o e o significado da discord?ncia de breakup, a rela??o entre a sedimenta??o e o tectonismo em ambientes distensionais, bem como os controles dos processos de subsid?ncia neste intervalo de tempo. A an?lise tectono-estratigr?fica da Seq??ncia Transicional foi realizada com base em se??es s?smicas e perfis de po?os, distribu?dos ao longo da Sub-bacia de Sergipe (SBSE). Foram executadas se??es geoss?smicas e an?lise de sismof?cies, perfis e se??es estratigr?ficas, que recobrem os principais compartimentos estruturais desta sub-bacia. A partir desses produtos, foram elaborados modelos deposicionais e da evolu??o tectonoestratigr?fica da Seq??ncia Transicional. A an?lise estrutural demonstra semelhan?as no estilo e cinem?tica da deforma??o atuante durante a deposi??o das seq??ncias Rifte e Transicional, que apontam para uma continua??o dos processos de distens?o litosf?rica ao longo da dire??o NW (eixo de strain X), at? o final do Neo-Aptiano, quando se encerrou a deposi??o desta ?ltima. Os est?gios tardios da distens?o/rifteamento estariam marcados pela (i) cont?nua (embora em pulsos) atividade de falhas ao longo da bacia, controlando a cria??o do espa?o de acomoda??o nas suas imedia??es e caracterizando o afinamento da crosta superior, e (ii) deposi??o em estilo sag, quando a Seq??ncia Transicional ? visualizada numa escala mais ampla, refletindo o componente de estiramento e afinamento d?ctil de n?veis infra e subcrustais, combinado ? crescente import?ncia do regime de subsid?ncia t?rmica. Al?m da tect?nica rifte nos seus incrementos tardios, a Seq??ncia Transicional tamb?m se encontra afetada pela reativa??o das falhas de borda na SBSE, durante e ap?s a deposi??o da Forma??o Riachuelo (por??o inferior da Seq??ncia Marinha Transgressiva, de idade albiana). ? poss?vel que essa reativa??o constitua o reflexo (transmiss?o de tens?es ao longo da margem continental em forma??o) dos processos de rifteamento ainda ativos mais a norte, entre a Sub-bacia de Alagoas e a Bacia Pernambuco-Para?ba. As camadas evapor?ticas da Seq??ncia Transicional contribu?ram para o desenvolvimento de estruturas p?s-rifte, relacionadas ? halocinese e ao colapso da margem, as quais perturbam os estratos das seq??ncias marinhas sobrepostas num intervalo que se estende do Mesoalbiano ao Maastrichtiano, ou mesmo at? o Pale?geno. A an?lise estratigr?fica demonstrou a ocorr?ncia de 5 seq??ncias deposicionais de maior ordem, cuja sucess?o vertical indica um aumento progressivo do n?vel de base, marcado pela deposi??o dos sistemas silicicl?sticos continentais, que passam para sistemas lagunares-evapor?ticos e marinhos restritos, indicando que a Seq??ncia Transicional foi depositada num flanco de subida relativa do n?vel eust?tico. Num ciclo de 2? ordem, essa seq??ncia pode representar a deposi??o inicial de um Trato de Sistemas Transgressivo, cuja passagem para a Seq??ncia Marinha Transgressiva tamb?m estaria marcada por um afogamento dos sistemas deposicionais. Num ciclo de 3? ordem, a passagem entre estas seq??ncias ? balizada por uma discord?ncia restrita que lateralmente passa a uma concord?ncia correlativa, mais abrangente. Esta passagem corresponde ? discord?ncia de breakup , equivalente ? Discord?ncia Pr?-Albiano na SBSE, e contrasta com a maior express?o da Discord?ncia Pr?-Alagoas superior, esta ?ltima na base da Seq??ncia Transicional e alternativamente referida, na literatura, como a discord?ncia de breakup. Nesta Tese, ? adotado o conceito de que a Discord?ncia Pr?-Albiano seria o marco da mudan?a de contexto deposicional e do ambiente tect?nico (Rifte-Drifte) na SBSE, com superf?cies equivalentes mas tamb?m di?cronas, em outras bacias da Margem Atl?ntica. A Discord?ncia Pr?-Alagoas superior teria se formado em resposta ? subida da astenosfera (aquecimento sob altas taxas de distens?o litosf?rica) e p?s-data o ?ltimo pulso importante de falhamentos (a ela sotopostos) e eros?o de blocos. Acima dela, o n?mero de falhas ativas e o seu rejeito decresceram significativamente. Em ?guas profundas a ultraprofundas, os seaward-dipping reflectors (SDRs) s?o capeados em discord?ncia pelos horizontes s?smicos correlatos ? Seq??ncia Transicional. Essas rochas vulc?nicas foram (pelo menos parcialmente) alojadas sobre crosta continental, sendo tentativamente atribu?das ? fus?o do manto astenosf?rico em processo de subida e descompress?o adiab?tica. Embora seja uma fei??o muito importante na SBSE (e possivelmente, em outras bacias), a Discord?ncia Pr?-Alagoas superior n?o delimita o final do processo de distens?o litosf?rica e o in?cio de cria??o de assoalho oce?nico, haja vista as evid?ncias de estruturas distensionais de escala (pelo menos) crustal, que afetam a Seq??ncia Transicional. Considerando todo esse contexto, a deposi??o da Seq??ncia Transicional ? melhor posicionada no intervalo tardio do Est?gio Rifte, com a entrada de um mar epicontinental sobre o segmento de crosta ainda em processo de distens?o. Ao longo deste segmento, a sedimenta??o estaria ent?o controlada pela combina??o de subsid?ncia t?rmica e mec?nica. Em seq??ncia, o in?cio de cria??o de litosfera oce?nica conduziu ao decl?nio do componente de subsid?ncia mec?nica, a distens?o foi transferida para a cadeia mesoce?nica e a margem continental em forma??o (e a correspondente Seq??ncia Marinha) passou a ser controlada exclusivamente pelo componente de subsid?ncia t?rmica. Conceitos cl?ssicos, dados multidisciplinares e novos modelos arquiteturais e de evolu??o da crosta podem ser reconciliados e melhor compreendidos sob as linhas discutidas