Litoestratigrafia e deformação cenzóica na região de Icapuí, Ceará, e implicações para a estruturação de campos de petróleo na borda ocidental da bacia Potiguar(NE do Brasil)

This thesis deals with the sedimentological/stratigraphic and structural evolution of the sedimentary rocks that occur in the NW continental border of the Potiguar Basin. These rocks are well exposed along coastal cliffs between the localities of Lagoa do Mato and Icapuí, Ceará State (NE Brazil). The sedimentological/stratigraphic study involved, at the outcrop scale, detailed facies descriptions, profile mapping of the vertical succession of different beds, and columnar sections displaying inferred lateral relationships. The approach was complemented by granulometric and petrographic analyses, including the characterization of heavy mineral assemblages. The data set allowed to recognize two kinds of lithological units, a carbonate one of very restricted occurrence at the base of the cliffs, and three younger, distinct siliciclastic units, that predominate along the cliffs, in vertical and lateral extent. The carbonate rocks were correlated to the late Cretaceous Jandaíra Formation, which is covered by the siliciclastic Barreiras Formation. The Barreiras Formation occurs in two distinct structural settings, the usual one with nondeformed, subhorizontal strata, or as tilted beds, affected by strong deformation. Two lithofacies were recognized, vertically arranged or in fault contacts. The lower facies is characterized by silty-argillaceous sandstones with low-angle cross bedding; the upper facies comprises medium to coarse grained sandstones, with conglomeratic layers. The Tibau Formation (medium to coarse-grained sandstones with argillite intercalations) occurs at the NW side of the studied area, laterally interlayered with the Barreiras Formation. Eolic sediments correlated to the Potengi Formation overly the former units, either displaying an angular unconformity, or simply an erosional contact (stratigraphic unconformity). Outstanding structural features, identified in the Barreiras Formation, led to characterize a neocenozoic stress field, which generated faults and folds and/or reactivated older structures in the subjacent late cretaceous (to paleogene, in the offshore basin) section. The structures recognized in the Barreiras Formation comprise two distinct assemblages, namely a main extensional deformation between the localities of Ponta Grossa and Redonda, and a contractional style (succeeded by oblique extensional structures) at Vila Nova. In the first case, the structural assemblage is dominated by N-S (N±20°Az) steep to gently-dipping extensional faults, displaying a domino-style or listric geometry with associated roll-over structures. This deformation pattern is explained by an E-W/WNW extension, contemporaneous with deposition of the upper facies of the Barreiras Formation, during the time interval Miocene to Pleistocene. Strong rotation of blocks and faults generated low-angle distensional faults and, locally, subvertical bedding, allowing to estimate very high strain states, with extension estimates varying between 40% up to 200%. Numerous detachment zones, parallel to bedding, help to acommodate this intense deformation. The detachment surfaces and a large number of faults display mesoscopic features analoguous to the ones of ductile shear zones, with development of S-C fabrics, shear bands, sigmoidal clasts and others, pointing to a hydroplastic deformation regime in these cases. Local occurrences of the Jandaíra limestone are controled by extensional faults that exhume the pre-Barreiras section, including an earlier event with N-S extension. Finally, WNWtrending extensional shear zones and faults are compatible with the Holocene stress field along the present continental margin. In the Vila Nova region, close to Icapuí, gentle normal folds with fold hinges shallowly pluging to SSW affect the lower facies of the Barreiras Formation, displaying an incipient dissolution cleavage associated with an extension lineation at high rake (a S>L fabric). Deposition of the upper facies siliciclastics is controlled by pull-apart graben structures, bordered by N-NE-trending sinistral-normal shear zones and faults, characterizing an structural inversion. Microstructures are compatible with tectonic deformation of the sedimentary pile, burried at shallow depths. The observed features point to high pore fluid pressures during deformation of the sediments, producing hydroplastic structures through mechanisms of granular flow. Such structures are overprinted by microfractures and microfaults (an essentially brittle regime), tracking the change to microfracturing and frictional shear mechanisms accompanying progressive dewatering and sediment lithification. Correlation of the structures observed at the surface with those present at depth was tested through geophysical data (Ground Penetrating Radar, seismics and a magnetic map). EW and NE-trending lineaments are observed in the magnetic map. The seismic sections display several examples of positive flower structures which affect the base of the cretaceous sediments; at higher stratigraphic levels, normal components/slips are compatible with the negative structural inversion characterized at the surface. Such correlations assisted in proposing a structural model compatible with the regional tectonic framework. The strong neogenepleistocene deformation is necessarily propagated in the subsurface, affecting the late cretaceous section (Açu and Jandaíra formations), wich host the hydrocarbon reservoirs in this portion of the Potiguar Basin. The proposed structural model is related to the dextral transcurrent/transform deformation along the Equatorial Margin, associated with transpressive terminations of E-W fault zones, or at their intersections with NE-trending lineaments, such as the Ponta Grossa-Fazenda Belém one (the LPGFB, itself controlled by a Brasiliano-age strike-slip shear zone). In a first step (and possibly during the late Cretaceous to Paleogene), this lineament was activated under a sinistral transpressional regime (antithetic to the main dextral deformation in the E-W zones), giving way to the folds in the lower facies of the Barreiras Formation, as well as the positive flower structures mapped through the seismic sections, at depth. This stage was succeeded (or was penecontemporaneous) by the extensional structures related to a (also sinistral) transtensional movement stage, associated to volcanism (Macau, Messejana) and thermal doming processes during the Neogene-Pleistocene time interval. This structural model has direct implications to hydrocarbon exploration and exploitation activities at this sector of the Potiguar Basin and its offshore continuation. The structure of the reservoirs at depth (Açu Formation sandstones of the post-rift section) may be controlled (or at least, strongly influenced) by the deformation geometry and kinematics characterized at the surface. In addition, the deformation event recognized in the Barreiras Formation has an age close to the one postulated for the oil maturation and migration in the basin, between the Oligocene to the Miocene. In this way, the described structural cenario represents a valid model to understand the conditions of hydrocarbon transport and acummulation through space openings, trap formation and destruction. This model is potentially applicable to the NW region of the Potiguar Basin and other sectors with a similar structural setting, along the brazilian Equatorial Atlantic Margin

Petrologia dos granitóides brasilianos associados à zona de cisalhamento Remígio-Pocinhos(PB)

The Brasiliano Cycle in the Seridó Belt (NE Brazil) is regarded mostly as a crustal reworking event, characterized by transcurrent or transpressional shear zones which operated under high temperature and low pressure conditions. In the eastern domain of this belt- the so-called São José de Campestre Massif (SJCM), a transtensional deformation regime is evidenced by extensional components or structures associated to the strikeslip shear zones. The emplacement of the Neoproterozoic Brasiliano granitoids is strongly controled by these discontinuities. Located in the southern border of the SJCM, the Remígio-Pocinhos shear zone (RPSZ) displays, in its northern half, top to the SW extensional movement which progressively grade, towards its southern half, to a dextral strike-slip kinematics, defining a negative semi-flower structure. This shear zone is overprinted upon allocthonous metasediments of the Seridó Group and an older gneiss-migmatite complex, both of which containing metamorphic parageneses from high amphibolite to granulite facies (the latter restricted to the strike-slip zone), defining the peak conditions of deformation. Several granitoid plutons are found along this structure, emplaced coeval with the shearing event. Individually, such bodies do not exceed 30 km2 in outcropping area and are essentially parallel to the trend of the shear zone. Petrographic, textural and geochemical data allow to recognize five different granitoid suites along the RPSZ: porphyritic granites (Serra da Boa Vista and Jandaíra), alkaline granites (Serra do Algodão and Serra do Boqueirão) and medium to coarse-grained granites (Olivedos) as major plutons, while microgranite and aluminous leucogranite sheets occur as minor intrusions. The porphyritic granites are surrounded by metasediments and present sigmoidal or en cornue shapes parallel to the trend of the RPSZ, corroborating the dextral kinematics. Basic to intermediate igneous enclaves are commonly associated to these bodies, frequently displaying mingling textures with the host granitoids. Compositionally these plutons are made up by titanite-biotite monzogranites bearing amphibole and magnetite; they are peraluminous and show affinities to the monzonitic, subalkaline series. Peraluminous, ilmenite-bearing biotite monzogranites and titanite-biotite monzogranites correspond, respectivally, to the Olivedos pluton and the microgranites. The Olivedos body is hosted by metasediments, while the microgranites intrude the gneiss-migmatite complex. Being highly evolved rocks, samples from these granites plot in the crustal melt fields in discrimination diagrams. Nevertheless, their subtle alignment also looks consistent with a monzonitic, subalkaline affinity. These chemical parameters make them closer to the I-type granites. Alkaline, clearly syntectonic granites are also recognized along the RPSZ. The Serra do Algodão and Serra do Boqueirão bodies display elongated shapes parallel to the mylonite belt which runs between the northern, extensional domain and the southern strike-slip zone. The Serra do Algodão pluton shows a characteristic isoclinal fold shape structure. Compositionally they encompass aegirine-augite alkali-feldspar granites and quartz-bearing alkaline syenite bearing garnet (andradite) and magnetite plus ilmenite as opaque phases. These rocks vary from meta to peraluminous, being correlated to the A-type granites. Aluminous leucogranites bearing biotite + muscovite ± sillimanite ± garnet (S-type granites) are frequent but not volumetrically important along the RPSZ. These sheet-like bodies may be folded or boudinaged, representing partial melts extracted from the metasediments during the shear zone development. Whole-rock Rb-Sr isotope studies point to a minimum 554��10 Ma age for the crystalization of the porphyritic granites. The alkaline granites and the Olivedos granite produced ca. 530 Ma isochrons which look too young; such values probably represent the closure of the Rb-Sr radiometric clock after crystallization and deformation of the plutons, at least 575 Ma ago (Souza et al. 1998). The porphyritic and the alkaline granites crystallized under high oxygen fugacity conditions, as shown by the presence of both magnetite and hematite in these rocks. The presence of ilmenite in the Olivedos pluton suggests less oxidizing conditions. Amphibole and amphibole-plagioclase thermobarometers point to minimum conditions, around 750°C and 6 Kbars, for the crystallization of the porphyritic granites. The zirconium geothermometer indicates higher temperatures, in the order of 800°C, for the porphyritic granites, and 780°C for the Olivedos pluton. Such values agree with the thermobarometric data optained for the country rocks (5,7 Kbar and 765°C; Souza et al. 1998). The geochemical and isotope data set point to a lower crustal source for the porphyritic and the alkaline granites. Granulite facies quartz diorite to tonalite gneisses, belonging or akin to the gneiss-migmatite complex, probably dominate in the source regions. In the case of the alkaline rocks, subordinate contributions of mantle material may be present either as a mixing magma or as a previously added component to the source region. Tonalite to granodiorite gneisses, with some metasedimentary contribution, may be envisaged for the Olivedos granite. The diversity of granitoid rocks along the RPSZ is explained by its lithospheric dimension, allowing magma extraction at different levels, from the middle to lower crust down to the mantle. The presence of basic to intermediate enclaves, associated to the porphyritic granites, confirm the participation of mantle components in the magma extraction system along the RPSZ. This mega-structure is part of the network of Brasiliano-age shear zones, activated by continental collision and terrane welding processes at the end of the Neoproterozoic

Mecanismos de alojamento de magmas granitóides :exemplo do plúton de Japi(RN)

This dissertation describes the igneous suites of the Japi granitoid pluton, intrusive in the Paleoproterozoic gneiss-migmatite complex of the eastern domain of the Seridó Belt, northeastern Brazil. Field relations show that the pluton is affected by strong deformation associated to the Brasiliano orogeny (known as the D3 phase) , with a NW-trending extensionalleft-hand senestral shear zone (the Japi Shear Zone, JSZ) bordering the intrusive body to the west. Four plutonic suites are found in the main pluton and as satellyte intrusions, besides Iate pegmatite and pink leucogranites. An alkaline granitoid suite, dominated by syenogranites bearing sodic augite (and subordinate hornblende), define a main elliptical intrusion. In its northern part, this intrusion is made up by concentric sheets, contrasting with a smaller rounded stock to the south. These granites display a pervasive solid-state S>L fabric developed under high T conditions, characterized by plastic deformation of quartz and feldspar. It is especially, developed along the border of the pluton, with inward dips. A regular magmatic layering is present sometimes, parallel to the tectonic foliation. The syntectonic emplacement as regards to the Brasiliano (D3) event is indicated by the common occurrence of dykes and sheets along transtensional or extensional sites of the major structure. Field relations attest to the early emplacement of the alkaline granites as regards to the other suites. A basic-to-intermediate suite occurs as a western satellyte body and occupying the southern tail of the main alkaline pluton. It comprises a wide variety of compositional terms, including primitive gabbros and gabbro-norites, differentiated to monzonitic intermediate facies containing amphibole and biotite as their main mafic phases. These rocks display transitional high-K calc-alkaline to shoshonitic affinities. Porphyritic monzogranite suítes commonly occur as dykes and minor intrusives, isolated or associated with the basic-tointermediate rocks. In the latter case, magma mingling and mixing features attest that these are contemporaneous igneous suites. These granites show K-feldspar phenocrysts and a hornblende+biotite+titanite assemblage, displaying subalkaline/monzonitic geochemical affinities. Both suites exhibit SL magmatic fabrics overprinting or transitional to solid-state D3 deformation related to the JSI. Chemical data clearly show that they are related to different parental magmas. Finally, a microgranite suite occurs along a few topographic ridges paralell to the JSI. It comprises dominantly granodiorites with a mineralogy similar to the one of the porphyritic granitoids. However, discriminant diagrams show their distinct calc-alkaline affinity. The granodiorites display an essencially magmatic fabric, even though an incipient D3 solid-state structure may be developed along the JSI. Intrusion relationships with the previous suites, as well as regards to the D3 structures, point to their Iate emplacement. All these suites are intrusive in a Paleoproterozoic, high-grade gneiss-migmatite complex affected by two previous deformation phases (D1, D2). The fabrics associated with these earlier events are folded and overprinted by the younger D3 structures along the JSZ. The younger deformation is characterized by NE-dipping foliations and N/NE-plunging stretching lineations. In the JSZ northern termination the foliation acquires an ENE orientation, containing a stretching lineation plunging to the south. Symmetric kinematic cri teria developed at this site confirms the transpressional termination of the JSZ, as also shown by orthorrombic quartz c-axis patterns. E-W-trending d extra I shear zones developed in the central part of the JSZ are interpreted as antithetic structures associated to the transtensional deformation along the JSZ. This is consistent with its extensional-transcurrent kinematics and a flat-and-ramp geometry at depth, as shown by gravimetric data. The lateral displacement of the negative residual Bouguer anomalies, as regards to the main outcropping alkaline pluton, may be modelized by other deeper-seated granite bodies. Based on numerical modelling it was possible to infer two distinct intrusion styles for the alkaline pluton. The calculated model values are consistent with an emplacement by sheeting for the northern body, as already suggested by satellyte imagery and field mapping. On the other hand, the results point to a transition towards a diapir-related style associated to the smaller. southern stock. This difference in intrusion styles may relate to intensity variations and transtensional sites of the shear deformation along the JSZ. Trace element and Sr and Nd isotopes of the alkaline granites are compatible with their derivation trom a more basic crustal source, as compared to the presently outcropping highgrade gneisses, with participation (or alternatively dominated by) of an enriched lithospheric mantle component. Like other igneous suites in the Seridó Belt, the high LlL contents and fractionated REE patterns of the basic rocks also point to an enriched mantle as the source for this kind of magmatism. Geochemical and isotope data are compatible with a lower crustal origin for the porphyritic granites. On the basis of the strong control of the JSZ on the emplacement of lower crustal (porphyritic and alkaline granites) or lithospheric mantle (basic rocks, alkaline granites or a component of them) magmas, one may infer a deep root for this structure, bearing an important role in magma extraction, transport and emplacement in the Japi region, eastern domain of the Seridó Belt

Estudos sedimentológicos e o contexto estrutural da formação Serra do Martins, nos platôs de Portalegre, Martins e Santana/RN

This dissertation deals with sedimentological and structural framework of the siliciclastic rock of the Serra do Martins Formation (FSM) in the Portalegre, Martins and Santana plateau, located to the south of Potiguar Basin, in the southwest and central Rio Grande do Norte state. This formation, regarded as of Oligo-Miocene age based on intrusive relations of the Miocene Macau volcanics, has a still disputable age due to the lack of appropriate bio and/or chronostratigraphic markers. The FSSM deposits crop out along 650 to 750 m high plateau, as a remanescent sedimentary cover directly overlying topographically uplifted pre-cambrian crystalline rocks. During the last decades, these deposits were interpreted according to a Tertiary paleoclimatic evolutionary model, associated to pedogenetic processes. The sedimentological characterization of the FSM was done through a detailed study of its facies, petrography and diagenetic features. The facies study was based on description of field relations, textures and structures, the piling up of the strata and their lateral variations. The FSM was deposited by an anastomosing to coarse-meandering fluvial system, including deposits of lag, cannel-fill, ouver-bank and flood plain. The petrographic composition of the sediments, coupled to their facies and paleocurrent directions, suggest a rather distal sourcearea, to the south of the present plateau. The diagenetic study identified an incipient grain mechanical compaction, pronounced dissolution of the framework, matrix and/or cement components, intense precipitation of kaolinite, silic and, eventually, iron oxides, besides mechanical infiltration of the clays. Most of these events, regarded in the literature as associated to near-surface conditions (eo or telodiagenesis), indicate the FSM sediments were never deeply buried. Topographic relations along longitudinal and transversal sections reaching the Potiguar Basin to the north identified regional dips that allow to discuss stratigraphic correlations between the FSM and the basin formations. The sedimentological features of the different units and the intrusive relations of the Macau volcanics were also considered in these correlations,which support the Oligo-Miocene age previously accepted for the FSM. Concerning the tectonic framework of the FSM, this work investigated the pre-cambrian to cretaceous heritage and the cenozoic deformation, allowing the recognition of pre-, sin and post-FSM structures. The crystalline basement, belonging to the Seridó Belt, displays NE and WNW foliation trends related to the Brasiliano-age ductile shear zones. In this terrain, brittle-ductile and brittle NE- and NW-trending structures, associated with extensional joints filled with pegmatites and quartz veins, are related to an E-W compression by the end of Brasiliano Cycle. The E-W joints and NE-trending fractures were reactivated by N-S to N-S to NW extension during late Jurassic to Cretaceous times, controlling the emplacement of the Rio Ceará-Mirim basic dyke swarm and the opening of the Potiguar rift basin

Tectônica rúptil e sismicidade na área de inundação do açude do Castamhão (CE): implicações para o risco sísmico

This study describes brittle deformation and seismicity in the Castanhão Dam region, Ceará State, Brazil. This reservoir will include a hidroeletric power plant and will store about 6,7 billions m3 of water. Five main litostratigraphic unit were identified in the region: gneissic-migmatitic basement, metavolcanosedimentary sequence, granitoid plutons of Brasiliano age, Mesozoic basaltic dike swarm, and Cenozoic fluvial terraces of the Jaguaribe river. The region has experienced several faulting events that occurred at different crustal levels. Faults formed at depths less than about 12 km present left-lateral movement and are associated with epidote and quartz infillings. Faults formed at depths less than 7 km are mainly strike-slip present cataclastic rocks, fault breccia and gouge. Both fault groups form mainly NE-trendind lineaments and represent reactivation of ductile shear zones or new formed faults that cut across existing structures. Seismically-induced liquefaction fractures take place in Cenozoic terraces and indicate paleoearthquakes that may have reached at leat 6,8 MS. In short, this work indicate that the level of paleoseismicity is much greater than one observed in the instrumental record. Several faults are favourably oriented for reactivation and induced seismicity should be expected after the Castanhão Dam impoudment

Estruturação do grupo Serra Grande região de Santana do Acaraú- CE e a reativação do lineamento Sobral Pedro II, integração com dados geofísicos

The study area is located in the NW portion of the Ceará state nearby the city of Santana do Acaraú. Geologically it lies along the Sobral-Pedro II lineament which limits the domains of Ceará Central and Noroeste do Ceará, both belonging to the Borborema Province.The object of study was a NE trending 30km long siliciclastic body (sandstone and conglomerate) bounded by transcurrent dextral faults. The sediments are correlated to the Ipú Formation (Serra Grande Group) from the Parnaiba basin, which age is thought to be Siluro-Devonian. Existing structural data shown that bedding has higher but variable dips (70-45) near the borders faults and much lower to subhorizontal inward the body. The brittle deformation was related to a reactivation, in lower crustal level, of the Sobral-Pedro II lineament (Destro (1987, 1999; Galvão, 2002).The study presented here was focused in applying geophysicals methods (gravimetry and seismic) to determine the geometry of the sandstone/conglomeratic body and together with the structural data, to propose a model to explain its deformation. The residual anomalies maps indicate the presence of two main graben-like structures. The sedimentary pile width was estimated from 2D gravimetric models to be about 500-600 meters. The 3D gravimetric model stressed the two maximum width regions where a good correlation is observed between the isopach geometry and the centripetal strike/dip pattern displayed by the sediments bedding. Two main directions (N-S and E-W) of block moving are interpreted from the distribution pattern of the maximum width regions of the sedimentary rock

Caracterização macro, meso e microscópica das estruturas frágeis do corpo arenítico conglomerático da região de Santana do Acaraú (CE) e seu embasamento circundante

The structural framework of the sedimentary basins usually plays an important role in oil prospects and reservoirs. Geometry, interconectivity and density of the brittle features developed during basin evolution could change the permo-porous character of the rocks involved in generation, migration and entrapment of fluid flow. Once the structural characterization of the reservois using only sub-surface data is not an easy task, many studies are focused in analogous outcrops trying to understand the main processes by which brittle tectonic is archieved. In the Santana do Acaraú region (Ceará state, NE Brazil) a pack of conglomeratic sandstone (here named CAC) has its geometry controlled mainly by NE trending faults, interpreted as related to reactivation of a precambrian Sobral Pedro II Lineament (LSP-II). Geological mapping of the CAC showed a major NE-SW trending synform developed before its complete lithification during a dextral transpression. This region was then selected to be studied in details in order of constrain the cretaceous deformation and so help the understanding the deformation of the basins along the brazilian equatorial margin. In order to characterize the brittle deformation in different scales, I study some attributes of the fractures and faults such as orientation, density, kinematic, opening, etc., through scanlines in satellite images, outcrops and thin sections. The study of the satellite images showed three main directions of the macrostructures, N-S, NE-SW and E-W. Two of theses features (N-S and E-W) are in aggreement with previous geophysical data. A bimodal pattern of the lineaments in the CAC´s basement rocks has been evidenciated by the NE and NW sets of structures obtained in the meso and microscale data. Besides the main dextral transpression two others later events, developed when the sediments were complety lithified, were recognized in the area. The interplay among theses events is responsible for the compartimentation of the CAC in several blocks along within some structural elements display diferents orientations. Based on the variation in the S0 orientation, the CAC can be subdivided in several domains. Dispite of the variations in orientations of the fractures/faults in the diferents domains, theses features, in the meso and microscopic scale, are concentrated in two sets (based on their trend) in all domains which show similar orientation of the S0 surface. Thus the S0 orientation was used to group the domains in three major sets: i) The first one is that where S0 is E-W oriented: the fractures are oriented mainly NE with the development of a secondary NW trending; ii) S0 trending NE: the fractures are concentrated mainly along the trend NW with a secondary concentration along the NE trend; iii) The third set, where S0 is NS the main fractures are NE and the secondary concentration is NW. Another analized parameter was the fault/fracture length. This attribute was studied in diferent scales trying to detect the upscale relationship. A terrain digital model (TDM) was built with the brittlel elements supperposed. This model enhanced a 3D visualization of the area as well as the spatial distribution of the fault/fractures. Finally, I believe that a better undertanding of the brittle tectonic affecting both CAC and its nearby basement will help the future interpretations of the tectonic envolved in the development of the sedimentary basins of the brazilian equatorial margin and their oil reservoirs and prospects, as for instance the Xaréu field in the Ceará basin, which subsurface data could be correlated with the surface ones

Arquitetura, litofácies e evolução tectonoestratigráfica da bacia do rio do peixe, nordeste do Brasil

The Rio do Peixe Basin is located in the border of Paraíba and Ceará states, immediately to the north of the Patos shear zone, encompassing an area of 1,315 km2. This is one of the main basins of eocretaceous age in Northeast Brazil, associated to the rifting event that shaped the present continental margin. The basin can be divided into four sub-basins, corresponding to Pombal, Sousa, Brejo das Freiras and Icozinho half-grabens. This dissertation was based on the analysis and interpretation of remote sensing products, field stratigraphic and structural data, and seismic sections and gravity data. Field work detailed the lithofacies characterization of the three formations previously recognised in the basin, Antenor Navarro, Sousa and Rio Piranhas. Unlike the classical vertical stacking, field relations and seismostratigraphic analysis highlighted the interdigitation and lateral equivalency between these units. On bio/chrono-stratigraphic and tectonic grounds, they correlate with the Rift Tectonosequence of neocomian age. The Antenor Navarro Formation rests overlies the crystalline basement in non conformity. It comprises lithofacies originated by a braided fluvial system system, dominated by immature, coarse and conglomeratic sandstones, and polymict conglomerates at the base. Its exposures occur in the different halfgrabens, along its flexural margins. Paleocurrent data indicate source areas in the basement to the north/NW, or input along strike ramps. The Sousa Formation is composed by fine-grained sandstones, siltites and reddish, locally grey-greenish to reddish laminated shales presenting wavy marks, mudcracks and, sometimes, carbonate beds. This formation shows major influence of a fluvial, floodplain system, with seismostratigraphic evidence of lacustrine facies at subsurface. Its distribution occupies the central part of the Sousa and Brejo das Freiras half-grabens, which constitute the main depocenters of the basin. Paleocurrent analysis shows that sediment transport was also from north/NW to south/SE

Desenvolvimento de dobras e falhas em ambiente distensional: Aplicação da modelagem física

The geological modeling allows, at laboratory scaling, the simulation of the geometric and kinematic evolution of geological structures. The importance of the knowledge of these structures grows when we consider their role in the creation of traps or conduits to oil and water. In the present work we simulated the formation of folds and faults in extensional environment, through physical and numerical modeling, using a sandbox apparatus and MOVE2010 software. The physical modeling of structures developed in the hangingwall of a listric fault, showed the formation of active and inactive axial zones. In consonance with the literature, we verified the formation of a rollover between these two axial zones. The crestal collapse of the anticline formed grabens, limited by secondary faults, perpendicular to the extension, with a curvilinear aspect. Adjacent to these faults we registered the formation of transversal folds, parallel to the extension, characterized by a syncline in the fault hangingwall. We also observed drag folds near the faults surfaces, these faults are parallel to the fault surface and presented an anticline in the footwall and a syncline hangingwall. To observe the influence of geometrical variations (dip and width) in the flat of a flat-ramp fault, we made two experimental series, being the first with the flat varying in dip and width and the second maintaining the flat variation in width but horizontal. These experiments developed secondary faults, perpendicular to the extension, that were grouped in three sets: i) antithetic faults with a curvilinear geometry and synthetic faults, with a more rectilinear geometry, both nucleated in the base of sedimentary pile. The normal antithetic faults can rotate, during the extension, presenting a pseudo-inverse kinematics. ii) Faults nucleated at the top of the sedimentary pile. The propagation of these faults is made through coalescence of segments, originating, sometimes, the formation of relay ramps. iii) Reverse faults, are nucleated in the flat-ramp interface. Comparing the two models we verified that the dip of the flat favors a differentiated nucleation of the faults at the two extremities of the mater fault. V These two flat-ramp models also generated an anticline-syncline pair, drag and transversal folds. The anticline was formed above the flat being sub-parallel to the master fault plane, while the syncline was formed in more distal areas of the fault. Due the geometrical variation of these two folds we can define three structural domains. Using the physical experiments as a template, we also made numerical modeling experiments, with flat-ramp faults presenting variation in the flat. Secondary antithetic, synthetic and reverse faults were generated in both models. The numerical modeling formed two folds, and anticline above the flat and a syncline further away of the master fault. The geometric variation of these two folds allowed the definition of three structural domains parallel to the extension. These data reinforce the physical models. The comparisons between natural data of a flat-ramp fault in the Potiguar basin with the data of physical and numerical simulations, showed that, in both cases, the variation of the geometry of the flat produces, variation in the hangingwall geometry

Análise da deformação pós-Rifte na Bacia do Araripe, Nordeste do Brasil

The Araripe Basin is located over Precambrian terrains of the Borborema Province, being part of Northeast Brazil inner basins. Its origin is related to the fragmentation of the Gondwana supercontinent and consequently opening of South Atlantic during early Cretaceous. The basin has a sedimentary infill encompassing four distinct evolution stages, comprising Paleozoic syneclisis, pre-rift, rift and post-rift. The target of this study comprises the post-rift section of the basin focusing deformational styles which affect evaporates from Ipubi Member of the Santana Formation, which is composed by gypsum and anidrite layers interbedded with shales. These units occur widespread across the basin. In the central part of the basin, near Nova Olinda-Santana do Cariri, evaporites are affected by an essentialy brittle deformation tipified by fibrous gypsum filled fractures, cutting massive layers of gypsum and anidrite. Veins with variable orientations and dips are observed in the region distributed over three main populations: i) a dominant NWSE with shallow to moderate NE dipping population, consisting of gypsum filled veins in which fibers are normal to vein walls; i) NE-SW veins with moderate SE dips containing subhorizontal growth fibers; and iii) N-S veins with shallow E-W dips with fibers oblique to vein walls. In the west portion of the basin, near Trindade-Ipubi-Araripina towns, evaporate layers are dominantly constituted by gypsum/anidrite finely stratified, showing a minor density of veins. These layers are affected by a unique style of deformation, more ductile, typified by gentle to open horizontal normal folding with several tens of meters length and with double plunging NW-SE or NE-SW hinges, configuring domic features. In detail, gypsum/anidrite laminae are affected by metre to decimeter scale close to tight folding, usually kinked, with broken hinges, locally turning into box folds. Veins show NE-SW main directions with shallow NE dips, growth fibers are parallel to vein walls, constituting slickenfibers. This region is marked by faults that affect Araripina Formation with NW-SE, NE-SW and E-W directions. The main structural styles and general orientations of structures which affected the post-rift section of Araripe Basin yielded important kinematic information analysis which led us to infer a E-W to NE-SW extension direction to the northeastern part of the Basin, whereas in the southeastern part, extension occurred in N-S direction. Thus, it was possible to determine a regional kinematic setting, through this analysis, characterizing a NE-SW to ENE-WSW system for the post-rift section, which is compatible with the tension settings for the Sout American Plate since Albian. Local variations at the fluid pressure linked (or not) to sedimentary overload variation define local tension settings. This way, at the northeastern portion of the basin, the post-rift deformation was governed by a setting which σ 1 is sub-horizontal trending NE-SW and, σ 3 is sub-vertical, emphasizing a reverse fault situation. At the southwestern portion however there was characterized a strike slip fault setting, featuring σ 1 trending ENEWSW and σ3 trending NNW-SSE

Análise estrutural da deformação cenozóica na Bacia de Cumuruxatiba (BA)

The Cumuruxatiba basin is located at the southern coast State of Bahia in northeastern of Brazil. This basin was formed in distensional context, with rifting and subsequent thermal phase during Neocomian to late Cretaceous. At Cenozoic ages, the Abrolhos magmatism occurs in the basin with peaks during the Paleocene and Eocene. In this period, there was a kinematic inversion in the basin represented by folds related to reverse faults. Structural restoration of regional 2D seismic sections revealed that most of the deformation was concentrated at the beginning of the Cenozoic time with the peak at the Lower Eocene. The post-Eocene is marked by a decrease of strain rate to the present. The 3D structural modeling revealed a fold belt (trending EW to NE-SW) accommodating the deformation between the Royal Charlotte and Sulphur Minerva volcanic highs. The volcanic eruptions have caused a differential overburden on the borders of the basin. This acted as the trigger for halokinesis, as demonstrated by physical modeling in literature. Consequently, the deformation tends to be higher in the edges of the basin. The volcanic rocks occur mainly as concordant structures (sills) in the syn-tectonic sediment deposition showing a concomitant deformation. The isopach maps and diagrams of axis orientation of deformation revealed that most of the folds were activated and reactivated at different times during the Cenozoic. The folds exhibit diverse kinematic patterns over time as response to behavior of adjacent volcanic highs. These interpretations allied with information on the petroleum system of the basin are important in mapping the prospects for hydrocarbons

Expressão em superfície do sistema de falhas Poço Verde-caraúbas, Bacia Potiguar

The structural knowledge of the western portion of the Potiguar Basin is still in its infancy, especially these related to NW-trending fault systems. This paper analyzes the Poço Verde-Caraúbas Fault System, which was initially recognized in subsurface. The activities involved in this study correspond to remote-sensing analysis and, in particular, to the geometric and kinematic analysis of post-rift sequences of the basin. In addition, the study aimed to determine the stress fields operating in the area. The studies were carried out in an area of 1,000 km², located in the western portion of Potiguar Basin along the Poço Verde-Caraúbas Fault System, Rio Grande do Norte State. The remote sensing imagery indicates a predominance of NW-SE-trending lineaments, consistent with the fault system under study, followed by the NE-SW, N-S and E-W directions. The tectonic structures mapped were analyzed only in outcrops of the Jandaíra Formantion. They are joints (filled or not) in all directions, but with predominance of the NW-trending joints. Faults are usually N-S-trending normal faults and NW-SE and NE-SW-trending strike-slip faults. Geodynamic analysis identified two tectonic stress fields: the first field, "Field 1" is represented by an N-S-trending horizontal compression and E-W-trending horizontal extension. This field affected the Potiguar Basin at least until the Miocene. The second field, "Field 2", is represented by an E-W-trending horizontal compression and N-S-trending horizontal extension. This is the present-day stress field and has affected the Potiguar basin since the Pliocene

Caracterização multi-escalar de bandas de deformação nas tectonossequências paleozóica, pré- e sin-rifte da Bacia do Araripe, Nordeste do Brasil

Deformation bands are structures, developed in porous sandstones, that has small offsets and they are not shown on seismic section. The deformation bands of the pre and synrift sandstones of Araripe Basin were studied in outcrop, macroscopic and microscopic scales. The hierarchical, cinematic and spatial-geometric characteristics, and also the deformational mechanisms acting during its structural evolution were established too. In general, the mesoscopic scale observation allowed to discriminate deformation bands as singles or clusters in three main sets: NNE-SSW dextral; NE-SW normal (sometimes with strike-slip offset); and E-W sinistral; further a bed-parallel deformation bands as a local set. The microscopic characterization allowed to recognize the shearing and cataclastic character of such structures. Through the multi-scale study done in this work we verified that deformation bands analyzed were preferentially developed when sandstones under advanced stage of lithification. We also infer that the geometrical-spatial complexity of these bands, together with the presence of cataclastic matrix, can difficult the migration of fluids in reservoir rocks, resulting on their compartmentalization. Therefore, the study of deformation bands can aid researches about the structural evolution of sedimentary basin, as well as collaborate to understand the hydrodynamic behavior of reservoirs compartmented by these deformational structures

Parâmetros cinemáticos da marcha com obstáculos em idosos com Doença de Parkinson, com e sem efeito da levodopa: um estudo piloto

CONTEXTO: Os efeitos da levodopa na marcha de pacientes com Doença de Parkinson (DP) em terrenos desobstruídos são conhecidos, mas pouco se conhece sobre seus efeitos na marcha com obstáculos. OBJETIVO: Este estudo objetivou descrever, por meio de ferramenta cinemática, o comportamento locomotor de pacientes com DP e verificar as estratégias locomotoras, sem e sob o efeito da levodopa, durante a ultrapassagem de obstáculos de diferentes alturas. MÉTODO: Cinco pacientes com DP (Hoehn e Yahr= 2±0; idade= 68,4±5,7 anos) percorreram, andando, 10m e ultrapassaram um de dois obstáculos (alto= metade da altura do joelho e baixo= altura do tornozelo) posicionado no meio da passarela em duas sessões (em jejum e no pico de ação do medicamento). As seguintes variáveis foram coletadas e analisadas: distância horizontal pé-obstáculo (DHPO), distância vertical pé-obstáculo (DVPO); distância horizontal obstáculo-pé (DHOP) e velocidades médias, horizontais e verticais, nas fases de abordagem e aterrissagem (respectivamente, VHAO,VVAO; VHDO,VVDO). RESULTADOS: A ANOVA, por tentativa, revelou efeito principal de obstáculo para DVPO (F1,49=15,33; p< 0,001), para VVAO (F1,49= 82,184; p< 0,001), para VHDO (F1,49= 15,33; p< 0,001) e para VVDO (F1,49= 31,30; p< 0,001); e efeito principal de medicamento para DVPO (F1,49= 6,66; p< 0,013) e para VVAO (F1,49= 10,174; p< 0,002). CONCLUSÕES: Pacientes foram mais perturbados pelo obstáculo alto. Os sintomas da DP (bradicinesia e hipocinesia) foram diminuídos com o medicamento, evidenciando aumento geral da velocidade da perna de abordagem e da margem de segurança sobre os obstáculos. Pacientes com DP, independente da condição de medicamento, apresentaram um comportamento que garantiu segurança e estabilidade na marcha.

Parâmetros na marcha na paralisia supranuclear progressiva: um estudo de caso

INTRODUÇÃO: Comprometimentos na marcha de pacientes com paralisia supranuclear progressiva (PSP) podem aumentar o risco de quedas durante o andar, especialmente em ambientes complexos. OBJETIVO: Descrever o comportamento locomotor de uma paciente com PSP, nas condições de marcha livre e marcha adaptativa. MATERIAIS E MÉTODOS: Estudo de caso de uma paciente com PSP (71 anos). Para análise cinemática, nas condições de marcha livre, com obstáculo baixo e alto, uma câmera digital registrou uma passada completa da paciente. RESULTADOS: Com o aumento da complexidade do ambiente (marcha livre, obstáculo baixo e alto, respectivamente), foi observada diminuição do comprimento do passo (0,37 ± 0,07; 0,30 ± 0,07; 0,26 ± 0,06 m), do comprimento da passada (0,71 ± 0,11; 0,58 ± 0,15; 0,47 ± 0,07 m) e da velocidade da passada (0,55 ± 0,14; 0,43 ± 0,11; 0,36 ± 0,11 m/s). Aumento progressivo ocorreu na duração do duplo suporte da passada livre (29,47%) para a passada antes do obstáculo alto (41,11%). Observou-se, ainda, ligeira diminuição na distância vertical pé/obstáculo alto (membro/abordagem: 7,18 ± 1,88; e membro/suporte: 8,84 ± 2,57 cm) em relação ao obstáculo baixo (membro de abordagem: 8,86 ± 1,88; e membro de suporte: 11,67 ± 2,09 cm). CONCLUSÃO: A PSP afetou de forma evidente a marcha da paciente. Inflexibilidade para a adaptação da marcha às demandas do ambiente foi observada durante a aproximação e a transposição dos obstáculos, o que pode aumentar o risco de tropeços e quedas.