Sedimentological analysis of the Missão Velha Formation (Araripe Basin, northeast Brazil) is the aim of this paper through detailed facies analysis, architectural elements, depositional systems and paleocurrent data. The main facies recognized were: (i) coarse-grained conglomeratic sandstones, locally pebbly conglomerates, with abundant silicified fossil trunks and several large-to-medium trough cross-stratifications and predominantly lenticular geometry; (ii) lenticular coarse-to-medium sandstones with some granules, abundant silicified fossil wood, and large-to-medium trough cross-stratifications, cut-and fill features and mud drapes on the foresets of cross-strata, (iii) poorly sorted medium-grained sandstones with sparse pebbles and with horizontal stratification, (iv) fine to very fine silty sandstones, laminated, interlayered with (v) decimetric muddy layers with horizontal lamination and climbing-ripple cross-lamination. Nine architectural elements were recognized: CH: Channels, GB: Gravel bars and bed forms, SB: Sand bars and bedforms, SB (p): sand bedform with planar cross-stratification, OF: Overbank flow, DA: Downstream-accretion macroforms, LS: Laminated sandsheet, LA: Lateralaccretion macroforms and FF: Floodplain fines. The lithofacies types and facies associations were interpreted as having been generated by alluvial systems characterized by (i) high energy perennial braided river systems and (ii) ephemeral river systems. Aeolian sand dunes and sand sheets generated by the reworking of braided alluvial deposits can also occur. The paleocurrent measurements show a main dispersion pattern to S, SE and SW, and another to NE/E. These features imply a paleodrainage flowing into the basins of the Recôncavo-Tucano-Jatobá.

The Aptian Barbalha Formation records the beginning of the post-rift stage of the Araripe Basin. It consists predominantly of sandstones and mudstones interbedded with thin layers of bituminous black shales and conglomerates. The depositional and architectural features of the alluvial succession of the Barbalha Formation were characterized by detailed study and descriptions of the selected outcrops and analysis of well core data. In this study, two main depositional sequences were identified. The lower depositional sequence is more than 100 m thick and comprises a vertical facies succession composed of amalgamated, multistorey, braided fluvial channel sandstone bodies overlain by a widespread lacustrine black shale up to 10 m thick. The lacustrine black shales–carbonate mixed interval is known as the Batateira Beds and constitutes a regionally important stratigraphic correlation marker in the basin. This interval records the establishment of a large lake that experienced severe water-level fluctuations and anoxic events. The upper depositional sequence is 60–95 m thick, and mainly consists of thin, yellowish, medium- to fine-grained sandstones and variegated shales. The upper sequence rests unconformably on the lacustrine black shales of the Batateira Beds. Thin and discontinuous conglomerate beds at the base of the upper sequence laterally grade into coarse-grained sandstones. These coarse-grained sandstones are overlain by interbedded sandstones and mudstones organized in fluvial cycles. The upper and lower sequences of the Barbalha Formation are separated by an erosive unconformity, traceable throughout the study area, formed during a period of stratigraphic base-level lowering. This surface marks a change in the lower sequence from a dominantly fluvial depositional style, with amalgamated multistorey braided fluvial channel sand bodies, to a lacustrine system in the top to an eminently fluvial sedimentation, which in the basal section comprises amalgamated, multistorey, braided fluvial channel sand bodies, and in the superior section the amalgamated fluvial channels are overlain by floodplain and overbank sandstone bodies with fixed fluvial channel deposits, interpreted as a suspended-load-dominated fluvial system in the upper sequence. This change in the depositional style is accompanied by a reduction in grain size and a change in the fluvial regime, suggesting that the drainage system was restructured due to tectonic movements in the basin and climatic variations. In addition to the restructuring of the drainage basin, the characteristics of the discharge of the river system have changed, probably because of the more humid climatic conditions that dominated during the deposition of the upper sequence. The fluvial deposition in the lower sequence is associated with more ephemeral river systems, while the facies architecture of the upper sequence is associated with perennial systems and is suggestive of a suspended-load-dominated fluvial system. This fluvial system is capped by lacustrine deposits of the Crato Formation. The upper sequence grades upwards into the Crato Formation. The boundary between these two units is delineated by the presence of greenish calciferous shales that are covered by lacustrine laminated limestones and shales of Neoaptian age. Palaeocurrent readings from the fluvial deposits of both sequences display a consistent palaeoflow to the SE. Sedimentological and palaeontological evidence indicates a tectonic control on sedimentation and humid to subhumid climate conditions.

Este trabalho objetivou a caracterização tectonossedimentar das fases início de rifte e clímax de rifte da Bacia do Araripe. As principais estruturas identificadas foram falhas normais, transcorrentes e inversas em ordem de importância. Esse grupo de falhas coloca lateralmente diferentes unidades litoestratigráficas como rochas de unidades início de rifte e clímax de rifte. Exemplo é o contato lateral das formações Missão Velho e Brejo Santo ao longo de falhas normais NNE. É de grande importância a integração entre análise geométrica e cinemática dessas falhas com a evolução estratigráfica para uma evolução global da evolução geológica da Bacia do Araripe. Principais afloramentos de campo utilizados neste trabalho consistem em exposições formadas durante as obras de construção da ferrovia Transnordestina e da transposição do Rio São Francisco. A análise tectônica realizada para este trabalho identificou dois conjuntos principais de falhas: falhas orientadas segundo a direção NE-SW (mais antigas) e falhas orientadas na direção NW-SE e WNW-ESE (mais jovens). Além disso, foram também analisadas falhas transcorrentes e inversas. A tectônica rifte que afetou a Bacia do Araripe (extensional) reativou falhas antigas do embasamento Pré-Cambriano e, por sua vez, forneceu falhas normais de direção NE-SW e também gerou falhas de orientação E-W e NW-SE.

A Bacia de Jatobá pertence ao denominado Rifte Recôncavo-Tucano-Jatobá, estrutura geotectônica constituída por extenso rifte abortado no Cretáceo durante as fases de fragmentação do Supercontinente Gondwana. Este trabalho enfoca inédita análise de facies e sistemas deposicionais da Formação São Sebastião (Eocretáceo). As facies foram identificadas segundo a litologia predominante, geometria dos corpos, estruturas sedimentares e padrão de paleocorrentes. As principais litofacies reconhecidas foram: (i) conglomerados sustentados pela matriz e arenitos grossos a médios, conglomeráticos com estratificações cruzadas acanaladas de pequeno porte, ou maciços; (ii) arenitos grossos a médios com estratificações cruzadas acanaladas de médio e grande porte; (iii) arenitos médios com boa seleção e estratificação plano-paralela e (iv) arenitos médios com estratificação cruzada tabular de médio porte, bem selecionados. As facies (i) foram interpretadas como geradas por sistemas fluviais entrelaçados efêmeros. O conjunto de facies (ii), (iii) e (iv) foi interpretado como originado em campo de dunas eólicas, lenções de areia eólica e interduna. A Formação São Sebastião representa a interação de dois sistemas deposicionais: eólico e fluvial. As características sedimentológicas dos arenitos da Formação São Sebastião indicam ambiente de sedimentação inicialmente fluvial, com posterior retrabalhamento por vento, e a superior, um ambiente desértico, tipicamente eólico, com interações fluviais.