Navegando por Orientadores "NOGUEIRA, Afonso César Rodrigues"

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O Cambriano no Sudeste do Cráton Amazônico: paleoambiente, proveniência e implicações evolutivas para o Gondwana Oeste
(Universidade Federal do Pará, 2018-06-15) SANTOS, Hudson Pereira; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Transgressive events recorded in many cratonic regions marked the Cambrian period, hypothetically related to the glacioeustasy and/or the progressive opening of the Iapetus ocean (~600 Ma). Such events influenced the paleoceanography of this period, including the progressive biota evolution – the ‘Cambrian Revolution’. Although the Gondwana Supercontinent margins, entirely amalgamated in the Lower Cambrian (540 Ma), were flooded, the inner part of this supercontinent was emergent, probably triggered by postcollisional epirogenic uplifts. Epeiric seas covered subsiding areas with projections towards the interior of the Western Gondwana, developing shallow platforms that covered ancient colisional suture zones. In the southeastern Amazon Craton, the recurrence of platform environments dates from Upper Cryogenian (~635 Ma) until the Cambrian with the installation of glacial deposits, overlaid by carbonatic and siliciclastic successions. Despite the previous insertion in the context of a foreland type basin related to the evolution of North Paraguai Belt (650-640 Ma), these deposits have been included in an inverted intracratonic basin in the Ordovician. The bottommost deposits of the Cambrian sequences, here presented, are comprised dominantly by siliciclastic rocks. These consist in the Upper and Lower members of the Raizama Formation and the base of Lower Member of the Sepotuba Formation, Alto Paraguai Group, exposed in the central and northeast portions of the inverted intracratonic basin, Mato Grosso state. Two depositional sequences (DS1 and DS2) characterize the Cambrian successions of the base of Alto Paraguai Group. The DS1 presents as a sequence boundary (SB1) an erosional hiatus previously interpreted in the southwestern basin. This stratigraphic surface becomes a correlative conformity towards the central and northern portions, where this covers the Araras carbonates and Cryogenian glacial deposits from Puga diamictites. The SB1 represents an erosional or non-depositional period of approximately 80 Ma developed over the carbonates of the Lower Ediacaran Araras Group, related to the epeirogenic uplifts of the basin. A second thermal subsidence phase would have led to the installation of a siliciclastic platform during the Cambrian, characterized by DS1 composed by two facies associations denominated FA1 and FA2. FA1 consists of subarkoses, quartz-wackes and pelites dominated by wave and storm processes, inserted in the offshoretransition, lower-middle shoreface and upper shoreface zones. The presence of infaunal vertical trace fossils belonging to the Skolithos Ichnofacies (Skolithos linearis; Diplocraterion parallelum; and Arenicolites isp.) at the base of the lower-middle shoreface deposits indicated a Lower Cambrian age, or younger, to the Raizama Formation, previously considered as Ediacaran. The FA2 comprehends subarkoses, quartzarenites, sublitarenites, quartz-wackes and sandstone/pelite rhythmites interpreted as complex tidal plain deposits, unconformably overlaid (SB2) by braided fluvial channel deposits of (FA3), which belong to the DS2. The DS1 would have been deposited during lowstand to transgressive system tract, organized in progradational parasequences. This stacking pattern is not compatible with the traditional stratigraphy sequence for TST, which is attributed to a slow subsidence rate concomitantly to a high sediment supply indicated by the Skolithos Ichnofacies. Subsequently, a less expressive drop in the sea level promoted a progradation of distal braided deposits (FA3) over the DS1, related to the lowstand system tract (LST) characterized by an abrupt change of the tidal heterolitic deposits to medium and coarse-grained quartzarenites from fluvial deposits. Paleoflow data oriented preferentially to NE and SE obtained in coastal beds from FA2 and FA3 allied to the Paleo- to Mesoproterozoic U-Pb detrital zircon ages have indicated provenance exclusively from SW and NW sources from Amazon Craton. Besides that, the detrital quartz grains analysis of sandstones of the bottommost Cambrian deposits indicate mainly igneous and metamorphic sources. Previous works indicated that the fluvial deposits of DS2 were succeeded by a transgressive system tract, marking this as the last transgressive event that influenced the Cambrian deposits of the intracratonic basin. Slowly, the ocean connection was interrupted as a consequence of the closing of Iapetus Ocean (~500 Ma) as a result of basin uplift. In this way, Cambrian epeiric seas were confined and consequently started the lacustrine phase of the basin in the Ordoviacian, represented by the Diamatino Formation deposits. Posteriorly, the intracratonic basin of the southeast Amazon Craton would have been inverted by the transtensional tectonics which propitiated the implantation of post-Cambrian intracontinental basins of the Western Gondwana.
Acesso aberto (Open Access)
O Camp nas bacias dos Solimões, Amazonas, Parnaíba e Parecis, Norte do Brasil: implicações geotectônicas e deposicionais para o jurássico do Gondwana Ocidental.
(Universidade Federal do Pará, 2024-08-23) REZENDE, Gabriel Leal; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Geological studies in conjunction with applications of geophysical techniques are being widely used to highlight and characterize CAMP gravimetric anomalies throughout Northern Brazil, including the Solimões, Parecis, Amazonas and Parnaíba basins. Interpretations of a residual gravimetric anomaly from these basins were used to expand the understanding of the distribution of CAMP throughout the subsurface. This study was carried out through qualitative and quantitative interpretations of gravimetric data, supported by surface geological information, mainly stratigraphic data based on outcrops. From direct gravimetric modeling, based on available crustal gravitational structure models to separate a residual gravity signal from observed gravity data, realistically detailed geological and tectonic features were interpreted, providing useful information for a geophysical interpretation of geological sources. With the residual gravity anomaly, a map of the elastic thickness (Te) of the basins was obtained, using a new procedure, presumably allowing some gaps presented in the current literature on the CAMP to be filled. For each Te value, the residual gravimetric signal was calculated, considering the surfaces described by topography and Moho for a regional model with standard density and discretized into prisms. The cross-correlation between the observed gravity signal and calculated gravity signal made it possible to obtain a map of the elastic thickness of the studied areas. The highest correlation value is directly related to the best value of elastic thickness and Moho depth associated with crustal deformation. Our study used a combination of these techniques to presumably define the possible extent of Jurassic magmatism, the basin rheology of igneous body intrusion and history of thermal subsidence that largely controlled depositional control during and after the CAMP. The presence of low gravity values is closely related to the less dense lithological units of the upper crust, while the high gravity values are related to high-density rocks correlated to the continental tholeiitic flood basalts of the CAMP. The use of residual gravity anomaly based on crustal modeling combined with previous geological data was effective in identifying the CAMP record in these Amazonian sedimentary basins. Furthermore, some gravimetric signatures correlate well with the main structural discontinuities, particularly with the Monte Alegre Dome and Xambioá, Serra Formosa and Vilhena arches, respectively, in the Amazon, Parnaíba and Parecis basins. This interpretation provides a reasonable explanation for understanding structural lineaments without exclusively tectonic connotations, assuming a new interpretation for the gravitational field related to intracrustal density contrast or residual gravity field for these basins. Eastern Gondwana was gradually uplifted by subvolcanic bodies of the Penatecaua magmatism in the Amazon and Solimões basins. In contrast, extrusive volcanism characterizes Mosquito magmatism in the Parnaíba basin interspersed with intertrap sediments. Information obtained from the elastic thickness map, Moho depth and residual gravity signal indicate a thinner crust in the Parnaíba basin favoring the magmatic eruption induced by a hot spot installed on the western edge of the basin. On the other hand, in basins with denser and thicker crust, magma accumulates mainly as sills, providing greater resistance to rupture due to the swelling of the CAMP. The Parnaíba Basin experienced three magmatic pulses at intervals of approximately 1 Myr, alternating with the development of aeolian-fluvial-lacustrine systems (intertrap sediments) during non-magmatic periods, indicating short intervals of magmatic resump-tion and cooling in the CAMP, contrasting with the longer and continuous magmatism in the Amazon and Solimões basins, which lack intertrap deposits. These results are important for a new disposition of the tectonomagmatic, structural and stratigraphic history for these basins, since from a new context or geological evolution for the area it will allow a better understanding of the studied basins in lava-sediment interaction, preserved from the Jurassic and related to the CAMP events, which preceded the main continental rupture in northwestern Pangea.
Acesso aberto (Open Access)
A capa carbonática do sudoeste do cráton amazônico, estado de Rondônia: nova ocorrência e extensão dos eventos pós-glaciação marinoana (635 Ma)
(Universidade Federal do Pará, 2014-11-27) GAIA, Valber do Carmo de Souza; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
In the Western Amazon Craton, specifically in Western Parecis Basin, Rondônia State, carbonate rocks exposed on border of Pimenta Bueno and Colorado Grábens are considered to be part of the eopaleozoic basin fill. The facies and microfacies analysis together with chemostratigraphy of theses rocks in Chupinguaia and Pimenta Bueno Region, confirmed the occurrence of pinkish dolostone that overlie glaciogenic diamictite, previously interpreted as alluvial fan. Previous works reported δ13C negative excursions, confirmed in this work as well, ranging from -4.6 e -3,8‰VPDB in Chupinguaia, and average of -3,15‰VPDB in Pimenta Bueno. This sedimentation and chemostratigraphic pattern, uncommon in paleozoic rocks, is widely found in the anomalous neoproterozoic carbonates. In the Southern Amazon Craton, Mato Grosso State, rocks with the same features were described as cap carbonates related to the Marinoan Glaciation (635 Ma). Therefore this work considers this dolostones at the same context of the cap carbonate in Mato Grosso. Additionally we stand out the sharp and loaded contact between dolostone and diamictite, which happens in both occurrences, and is seemingly a typical feature of cap carbonates in the Amazon Craton. This paradoxal relationship has been interpreted as rapid change from icehouse to greenhouse conditions, and the loaded contact is attributed to isostatic rebound. The Rondônia cap carbonate presents two facies associations (FA2 and FA3) that overlie glaciomarine deposits (FA1) subdivided in two facies: Polymitic paraconglomerates (Pp) and laminated pebbly sandstone (Asl). The FA2 consists into: peloidal dolomudstone/dolopackstone with planar to quasi-planar laminations and low-angle truncations (Dp), megarriple bedding (Dm) and wave truncated laminations. This association is interpreted as shallow platform deposits wave influenced. This coastal succession is overlaid by FA3, which comprises the facies: dolomudstone/dolopackstone and dolomudstone/ dolograinstone with shale partition (Df) and laminated shaly siltstone (Sl). Df comprises 6m-thick of dolomite with parting shale, showing laterally continuous laminations of fibrous calcite (pseudomorph of gypsum) and dolomite with current wavy lamination. The Sl comprises 5m-thick of planar-laminated shaly siltstone. This association is interpreted as shallow platform deposits tide influenced. Finally, this inner platform succession is overlaid unconformably, in angular contact, by eopaleozoic glaciogenic diamictite. The isotopic values of C and O are negative and reflect the primary signal of C, however it can be considered a slight influence of meteoric diagenesis in the signal. The main shifts in negative signals are associated with meteoric influences, expressed by replacement and pores filling by calcite, and also by its proximity of stratigraphic surfaces, which reflect some patterns of diagenetic alteration, represented by the most negative signals. Differently from Mato Grosso cap carbonate, the Rondônia occurrence presents levels of pseudomorph of evaporites and dolomite with parting shale (rhythmites), order in succession of shallow marine facies, where the dolomites of wavy influenced shallow platform pass up-section to rhythmites and shaly siltstone of tide influenced shallow platform, setting up a retrogradational succession. This new occurrence of cap carbonate has strong implications to the stratigraphy of the base of Parecis Basin, since it excludes these carbonate rocks from the eopaleozoic sequence. Moreover, it provides information that allows reconstruct the coastal paleogeography of neoproterozoic basin that accumulated deposits of Araras Platform, as well extends the postmarinoan events of the Snowball/Slushball Earth hypothesis to the southwesternmost Amazon Craton, exposed in the Rondônia State.
Acesso aberto (Open Access)
A capa carbonática marinoana do Sul do Cráton Amazônico: multiproxies aplicados na reconstituição paleoceanográfica e geobiológica do início do Ediacarano.
(Universidade Federal do Pará, 2024-08-30) SANTOS, Renan Fernandes dos; SANSJOFRE, Pierre; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The post-Marinoan glaciation (~650-635 Ma) was the most severe event from the late Cryogenian period of the planet. The snowball Earth conditions induced a climate anomaly, triggering major changes in the paleoenvironmental and ocean chemistry recorded in the carbonate cap sequences. The dramatic effects on the global sea level were caused by glacial-isostatic adjustment (GIA) and ice gravity on the coastal zones associated with the ocean thermal expansion under greenhouse conditions. The fast input of meltwaters contributed to a stable density ocean stratification formed by hypersaline deep waters and meltwater surface layers. The ocean destratification occurred in a timescale ranging from tens of thousands to thousands of years. The Puga cap carbonate (~635 Ma), the basal deposits of the Araras-Alto Paraguai basin from the southern Amazon Craton, is revisited in the classical sections from the Tangará da Serra and Mirassol d'Oeste, Mato Grosso State. This succession is one of the best records for evaluating the supersaturation events under GIA and transgression conditions that controlled the accommodation space in the southern Amazon Craton. Sedimentological and stratigraphic data were integrated with new paleoceanographic, and paleo-redox data combined with diagenetic, crystallographic, geochemical (primarily rare earth elements and trace metals), and isotopic (whole rock 87Sr/86Sr, εNd(t), δ 13C, δ 18 O, Sm/Nd) results providing further insights to understand the post-Marinoan conditions. The Puga cap carbonate sequence spans approximately 90 meters, with the first 10 meters composed of glaciomarine deposits, diamictites, and dropstones from the Puga Formation. The basal contact with diamictites is plastically deformed, indicating rapid carbonate precipitation. The cap dolostone consists of stratiform doloboundstones with gypsum pseudomorphs and domal doloboundstones with tubestone, which were deposited in a shallow platform with intense microbial activity. Peloidal dolomudstone/dolopackstone with laminations parallel to bedding planes and peloidal dolograinstones/dolomudstone with quasi-planar laminations and low-angle truncation were formed in a wave-influenced shallow platform. The cap limestone conformably overlies the cap dolostone deposits, marked by dolomitic marlstone with calcite crystal fans (aragonite pseudomorphs) interbedded with mega-rippled limestone. The facies association of the cap limestone indicates moderately deep-water conditions dominated by waves and storms transitioning to a deep platform supersaturated with CaCO3. The main diagenetic process is dolomitization during syn-depositional and shallow burial stages. Rare earth element + yttrium patterns have been analyzed in these deposits. Low Y/Ho ratios (<36) in the cap dolostone suggest a mixture of meltwater and seawater, while the base records superchondritic Y/Ho values up to 70 and high Eu/Eu* values up to 3, indicating upwelling of hypersaline seawater with hydrothermal fluid interaction, suggesting dolomite precipitation during ocean destratification. The radiogenic isotopic compositions of Nd, combined with other proxies such as δ 13C and 87Sr/86Sr, indicate the influence of continental and marine contributions. The Nd isotopic system, less susceptible to diagenetic exchanges, revealed distinct signatures of water masses and enhanced weathering of the Amazon Craton during deglaciation. This process is indicated by geochemical trends (e.g., Y/Ho) and 87Sr/86Sr, εNd(t), δ 13C values. 87Sr/86Sr data in the cap dolostone range from 0.7264 to 0.7084, higher than pre- and postglacial seawater values. More radiogenic 87Sr/86Sr values associated with less radiogenic εNd(t) values, similar to those found in diamictites, reinforce coastal weathering contribution to meltwaters. This multiproxies approach is a reconciliation with the previous rapid cap carbonate precipitation model following the short-term timescale for ocean destratification. Redox-sensitive trace metal data, U, Mo, V, Ni, Cu, P, and δ13C isotopes, indicated paleo-redox states and paleoproductivity during the post-glacial transgression. The cap dolostone precipitated under oxygenated conditions with extensive microbial community contributions, transitioning to predominantly dysoxic conditions with wave action in the last deposition phase. The abrupt sea-level rise altered the biogeochemical cycle, indicating a direct relationship between oxygen production and rapid microbial community colonization. The rapid sea-level rise and continental weathering reduced seawater Mg/Ca ratios with substantial Ca2+ input, also demonstrated by εNd(t) values, causing the change of dolomitic platform to CaCO3 -supersaturated seas in the Amazon Craton margin. Additionally, low siliciclastic content in the cap dolostone is consistent with the siliciclastic starvation model, and the abrupt increase caused the decline of microbial communities coincident with the predominance of dysoxic conditions and longterm transgression. During specific Cryogenian-Ediacaran deglaciation scenarios, anomalous sedimentary and geochemical processes generated one of the most complex paleoenvironmental disturbances in the biogeochemical cycle. They strongly influenced the rapid primary productivity, directly impacting microbial life. The analysis of Precambrian scenarios in the Amazon Craton unraveling the extreme climates sheds critical light on extremophile life proliferation and has strong implications for understanding other planetary surfaces.
Acesso aberto (Open Access)
O cenozoico superior do centro-oeste da Bacia do Amazonas: paleobotânica do embasamento cretáceo e evolução do Rio Amazonas
(Universidade Federal do Pará, 2018-11-08) BEZERRA, Isaac Salém Alves Azevedo; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
At the end of the Neogene and during the Quaternary, the development of the Amazon River caused significant paleoenvironmental and geomorphological changes that generated current ladscape at Amazonia. Previous models elaborated on a continental scale were based on data obtained from a drill core carried out on the Atlantic continental shelf, distant 200 km of the Amazon River mouth, suggesting the establishment of this drainage with Andean provenance from the Middle to Upper Miocene. In contrast, studies based on outcrops in the western and central portions of the Amazon have indicated younger ages for this ecosystem, from Pliocene to Quaternary. The sedimentological-stratigraphic study of the fluvial terraces of the Amazon River, exposed in the center-west portion of the Amazon Basin, assisted by luminescence geochronology, allowed to sequence the sedimentation events and discuss the paleoenvironmental and paleogeographic since Late Neogene. The studied Neogene- Quaternary deposits overlies Cretaceous rocks whose sedimentological and paleobotanical study revealed the preservation of impressions and counter-impressions of leaves and other macro-plant remains in pelites interpreted as flood plain and abandoned channel deposits of meandering rivers. The first record of angiosperms in this unit with possible affinities to the families Moraceae, Fagaceae, Malvaceae, Sapindaceae and Anarcadiaceae with appearance from Late Cretaceous, and the family Euphorbiaceae with record starting in the Mid- Cretaceous confirm the Cretaceous age for these rocks. The terraces of the Amazon River informally subdivided into lower and upper units are composed of sand, gravel and clay, organized in finning upward cycles representative of channel filling and overbank deposits. The lower unit was interpreted as a record of the proto-Amazonas, with migration to the east and deposition around 2 Ma. During this stage, the alluvial plain was restricted, preferentially following weakness zones coincident with fractures in the Paleozoic and Cretaceous basement. The climatic oscillations during the Quaternary and the increase of the volume of orographic rains in the headwaters region of the fluvial systems, in the eastern flank of the Andean ridge modified the hydrological regime, amplifying the escarpment erosion. The gradual expansion of the alluvial plain formed a large area of 120 km around 1 Ma to 140 ka, recorded by the upper unit deposits. At this stage, the eastern portion of the Amazon Basin topographically higher restricted the Pleistocene sedimentation in minimum accommodation space. The lower unit deposits are correlate in part to the Miocene-Pliocene deposits of the Amazon Basin, while the upper units are correlate with the Pleistocene deposits of the Solimões and Amazon basins. The dynamics of the construction of the Amazon River valley during the end of the Neogene and Quaternary was influenced by neotectonics (106 yr) and climatic oscillations (104-105 yr). The landscape of the central-eastern portion of the Amazon dominated no Pleistoceno by terra firme in elevated areas was governed by the dynamics of expansion and contraction of the alluvial plain. At the end of the Quaternary, the várzea formed by floodplains within the alluvial plain, which used to occupy a wide area, became increasingly restricted by the continuous processes of fluvial incision during the glacial maximum (18 to 22 ka). The continuous lateral migration of the meandering channel to the north led to the confinement of the channel by the fluvial scarps developed in the Cretaceous basement, which culminated in the current landscape in the Center-East of the Amazon. Testing the reliability and accuracy of some Pleistocene and older OSL ages for Amazon River deposits revealed that are much more minimum ages than buried ages for pre- Quaternary deposits.
Acesso aberto (Open Access)
Depósitos carbonáticos-siliciclásticos da porção superior da Formação Piauí, carbonífero da bacia do Parnaíba, região de José de Freitas-PI
(Universidade Federal do Pará, 2015-07-22) MEDEIROS, Renato Sol Paiva de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The northwestern margin of the Gondwana, in the Neocarboniferous period, was influenced by a large transgressive-regressive event, depositing thin carbonate sequences from Andean basins to center-southern portions of the paleocontinent, such as the stratigraphic boundaries of the Parnaíba Basin. The Higher Member of the Piauí Formation in the Parnaíba Basin, studied in the region of José de Freitas, displays richly fossiliferous carbonate deposits overlapped by prograding clinoforms, defining the transition from a transgressive system tract to an highstand system tract. The facies and stratigraphic analysis of this succession allowed the individualization of 17 sedimentary facies and microfacies grouped in four facies associations (FA): the FA1 – Campo de Dunas – is below to the further FA and is composed by thin and average sandstone, with well selected and rounded grains, displaying plane parallel stratification with high level of bioturbation, cross-tubular stratification and translatant subcritically climbing ripple cross-lamination. The FA2 - Shallow sea deposits – is composed by a carbonate plain with tubular and continuous layers of solid carbonate and fossiliferous peloids interspersed with thin lenses of bituminous shale. The FA3 – Frente Deltaica and FA4 – Prodelta consist of pelitic layers and thin and average sandstones, arcosians and quartz sandstones, marked by surfaces of subaerial exposure with shrinkage cracks, cemented by carbonate, arranged in continuous tabular layers or in the form of sigmoidal lobes, as well as liquefaction structures of the types load cast and flame, and fluidization of the type disruption of layers, which distort the strata. The facies data corroborate the idea that the sea in the Pennsylvanian retrograded up to the border of the Parnaíba Basin, and later with the Appalachian orogeny (300 Ma) the top of the Parnaíba River arched and stepped back the marine incursion, followed by a progradational event on marine deposits.
Acesso aberto (Open Access)
Depósitos de rampa carbonática ediacarana do Grupo Corumbá, região de Corumbá, Mato Grosso do Sul
(Universidade Federal do Pará, 2019-02-12) OLIVEIRA, Rick Souza de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Depositional events which occurred after Late Cryogenian global glaciations (850 - 635 Ma) were marked by the implantation of extensive carbonate platforms and ramps developed in several cratons worldwide. In this period, one of the bioevolutive innovations was the appearance of calcified skeleton animals, like the genus Cloudina (~548 Ma). In South America, one of the best records of Ediacaran carbonate deposits with these macrofossil is the Corumbá Group, exposed in the southern Amazon craton. These deposits were deformed by Brazilian/Pan-African tectonics which led to the establishment of the Paraguay belt in the Neoproterozoic-Cambrian transition. Outcrop-based facies and stratigraphic analysis, assisted with C, O and N isotope data of the Bocaina and Tamengo formations, belonging to the upper Corumbá Group, were carried out in the Corumbá and Porto Morrinhos regions, State of Mato Grosso do Sul, Brazil, and allowed the reconstitution of the Ediacaran carbonate ramp and the habitat of Cloudina. The Bocaina Formation consists of small-scale shallowing upward cycles grouped into two facies associations: 1) intertidal plain, consisting of well sorted and rounded fine-grained quartz-sandstones cemented by dolomite and fine dolomite with stratiform and columnar stromatolites, fenestral/bird´s eyes porosity and mud cracks; and 2) subtidal shoals, formed mainly by intraclastic dolomites (intraclasts of dolomicrite and peloidal dolomite) and subordinated fine-grained sandstones and shales. Deformation structures occur in both associations and are related to liquefaction and fluidization processes, possibly triggered by seismicity. The Tamengo Formation consists of the associations: 1) shoreface with oolithic bars, composed of intraclastic and oolithic packstones, lime mudstone/ bituminous shale rythmithes with Cloudina; and 2) storm-influenced offshore, consisting of crystalline limestone with rare terrigenous grains, massive bedding, hummocky/swaley cross stratification, low-angle cross lamination and Cloudina shell fragments. Mudrocks and shales separate discrete tempestite beds. Cloudina lived in protected environments in the shoreface zone, periodically reworked by storms that accumulated coquinas in the offshore zone. The high carbon concentration (TOC up to 0.41%), the enriched values of δ13C (1.5 ‰ to 5.4‰) and δ15N (between 3.5 and 4.5‰) found in the carbonate rocks with Cloudina, indicate high organic productivity and oxygen concentration for the Terminal Neoproterozoic, similar to those of the current atmosphere/ocean interface.
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Depósitos lacustres rasos da Formação Pedra de Fogo, Permiano da bacia do Parnaíba, Brasil
(Universidade Federal do Pará, 2015-04-15) ARAÚJO, Raphael Neto; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Permian Pedra de Fogo Formation, exposed in the east and west borders of Parnaíba Basin, northern Brazil, represent one of the most important terminal Paleozoic sedimentary record of the Western Gondwana. The main lithotypes of this unit are sandstones, shales, carbonate rocks, evaporites. The unit is famous for its large amounts of chert and presence of well-preserved Permian flora. In the last decades of the 20 th century, previous works interpreted the paleoenvironment of the Pedra de Fogo Formation as transitional fluvial-deltaic deposits, storm influenced-shallow neritic (marine) to coastal sabkha plain, lacustrine and fluvial deposits with contribution of marine-aeolian sediments and shallow to restrict sea or epicontinental type. Facies analysis focused principally on outcrops of the base and upper part of this unit, involving approximately 100 m thick of the siliciclastic succession. Eleven sedimentary facies were recognized and grouped into three facies associations (FA), representative of a shallow lacustrine depositional system associated with mudflat and ephemeral rivers. FA1 is interpreted as mudflat deposits, consisting of laminated claystone/siltstone, sandstones/pelites with mud cracks and sandstones with cross-lamination, massive and megaripple beddings. Silicified nodules and molds like popcorn indicate evaporites deposits. Other common features are silica concretions, silicified teppes and silcretes. FA2 represents deposits of nearshore and consists of fine-grained sandstones with even parallel lamination, climbing ripple cross-lamination, massive and megaripple beddings, as well as, laminated mudstone/siltstone. FA3 refers to wadi/inundite deposits, generally organized in fining upward meter-scale cycles, consisting of conglomerates and medium-grained pebbly sandstones with massive bedding and cross-stratification, and claystone/siltstone with even parallel to wavy lamination. Tabular beds are frequent in FA3 while scour-and-fill geometry is rare. The alternation of pelites and fine to medium-grained sandstones with even parallel to wavy lamination are the main framework of the Pedra de Fogo Formation. Bioturbations, shrinkage cracks and different types of siliceous concretions, as well as, teeth of fish, ostracods, bryozoans and scolecodontes are common in the studied succession. Silicified plant remains, preliminarily classified to the genus Psaronius, are found in situ, concentrated near the upper contact with Motuca Formation, considered here as excellent biostratigraphic markers for the upper Pedra de Fogo Formation. Mudflats deposits occur in the basal Pedra de Fogo succession suggesting arid and hot climates for the early Permian. The midlle Permian was predominated semiarid allowing the proliferation of fauna and flora in humid regions adjacent and into the lake margin. The ephemeral fluvial inflow or wadis carried plant remains and terrigenous to the lake generating inundites. Retreat and expansion phases characterized the Pedra de Fogo lake, induced by extreme climatic changes influencing not only the sedimentation pattern as also the fossilization of the best well-preserved Permian fauna and flora. In the late Permian, the climate again became hot and arid due to the complete aggregation of Pangea supercontinent, favoring the deposition of Motuca red beds and establishment of Sambaíba erg, near in the Permian-Triassic boundary.
Acesso aberto (Open Access)
Depósitos pleistocenos da formação Itaubal: paleoambiente e implicações na evolução da planície costeira do Amapá
(Universidade Federal do Pará, 2014-03-28) BEZERRA, Isaac Salém Alves Azevedo; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
In the Late Pleistocene of northern coast of South America, sea level fluctuations, related to climate variations and the sedimentary discharge of the Amazon River, have modified the landscape of this region. Terraces of the Itaubal Formation previously considered as Miocene Barreiras Formation, are part of the Amapá Coastal Plain, which covers the rocks of the Guianas Shield. The geochronological analysis by Optically Stimulated Luminescence / single and multiple aliquote regeneration (OSL/SAR-MAR) provided age around 120.600 (± 12.000) to 58.150 (±6.800) yrs BP and integrated with facies and stratigraphic analysis allowed the identification of coastal deposits and put the Tartarugazliznho Formation in the Upper Pleistocene. These up to 10 m thick, reddish tabular sediments have been divided into two units separated by unconformity. The Lower Unit consists of subtidal plain deposits (FA1), tidally influenced meandering stream deposits (FA2) and tidal plain deposits (FA3), whereas the Upper Unit, containing a higher clay content tham the lower one, is composed of braided stream deposits (FA4). The strata pattern of these units is progadational and takes part in the regressive system tract. The Tartarugazinho Formation onlaps the basement of Guianas Shield, weathered during Miocene-Pliocene and was exposed during the Last Glacial Maximum, about 22.000 – 18.000 yrs BP. Finally fine graided deposits derived from the Amazon River covered the Itaubal Formation and are responsible for the present shape of the northern coastline of South America. For the first time, the Itaubal Formation defines the Pleistocene sedimentary evolution of the Amapá coastal plain and the correlation with similar sediments in Suriname and northeastern Pará expands the discussion about the evolution of the coastal line in Northern South America during Pleistocene.
Acesso aberto (Open Access)
Diagênese da formação guia, Ediacarano da Bacia Araras -Alto Paraguai, sul do Cráton amazônico
(Universidade Federal do Pará, 2022-10-31) SANTOS, Caio Silva dos; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Guia Formation is a limestone unit of the Araras Group, exposed in central region of South America. They correspond to Ediacaran (622-614Ma) carbonate platform deposits, developed in an epicontinental sea. This deposits unconformably overlies diamictite of Puga Formation related to 635Ma Marinoan glaciation, also distributed over the metamorphic basement. The Guia Formation, aim of study, is composed of limestones interbedded with thin layers of black shales. The data were obtained from an analysis of a 350m stratigraphic profile in one of the best exposition of Guia Formation in a COPACEL mine open pit in Nobres town, State of Mato Grosso. The unit consist in six lithofacies, grouped in one facies association that records a deep carbonate platform: bituminous lime-mudstone, massive lime-mudstone and lime-mudstone rich in terrigenous grains, carbonate shale, carbonate breccias and deformed breccias. These rocks were intensive affected by diagenetic process such as aggrading neomorphism, organic matter maturation, physical compaction, spar calcite cement, dolomitization, chemical compaction and hydrocarbon migration. Aggrading neomorphism affect the matrix, turn it to microspar and pseudospar with hipidiotopic mosaic. The micrite rich in organic matter is partially dissolved by fluids capable of dissolving the matrix, generating the vug pores. That pores are cemented by spar calcite. This cement has coarse granulation, subhedral crystals, when it fills fractures it presents crystals with rhombohedral cleavage, with two directions. In cathodoluminescence, the cement has orange to red bright when it fills vug fracture, and it has zoned pink bright luminescence filling pore vug. The stylolites form serrated surfaces of low amplitude, insoluble material, composed by clays, quartz, and organic matter compound its. Dolomitization affects the rocks in three moments: the first one is the replacement of spar calcite filling fractures with subeuhedral dolomites in hipidiotopic mosaic and opaques minerals inclusions, the second on is the filling by the matrix replacement with anehedral dolomites; the third one is the formation of saddle dolomite associated with hydrocarbon. Spot analysis with SEM/EDS, shows a large amount of Ca, ang low range of Mg, Si, S, Ca, Mn, Fe, Ni, Zn, Sr, Cd, Ba and Pb. Reasserting that carbonate are scant changed by diagenetic/dolomitizing fluids. These rocks are part of the Araras Petroleum System, the Total Organic Content Analysis (TOC) indicated values between 0.04 and 0.50%, classified as a low to medium potential. The association among the petrographic and geochemistry data suggest that the bitumen migration occurred at 610 Ma, during thermal uplift of the Araras Intracratonic Basin, before the deposition of the Alto Paraguai Group, which led to exposure of the Araras Group and oxidation of the hydrocarbon, allowing the identification of type IV kerogen. Rock Eval pyrolysis, Hydrogen Index and Oxygen Index data of these rocks, do not have the potential to generate oil or gas, and are constituted by oxidized organic matter, with immature thermal evolution.
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Estratigrafia e eventos da transição Neoarqueano-Paleoproterozoico da Bacia de Carajás, sudeste do Cráton Amazônico
(Universidade Federal do Pará, 2020-09-18) ARAÚJO, Raphael Neto; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Neoarchean-Paleoproterozoic transition is marked by a series of paleoenvironmental, paleoclimatic and tectonic changes that resulted in dramatic events, which imposed to the Earth novel conditions, some of them with irreversible characteristics. On the paleoenvironmental aspect, it is highlighted the rise of oxygen in the hydrosphere-atmosphere system, onset the Great Oxidation Event (GOE) at around ca. 2.45 Ga. The rise of this gas caused consequently the decrease of the greenhouse gases such as CH4, which promoted the emergence of glacial episodes at around ca. 2.45–2.22 Ga, generically termed the Huronian Glacial Event (HGE). Although several studies support the hypothesis that these glacial episodes represent the first global glaciation of the Earth's history (Paleoproterozoic snowball Earth), stratigraphic and geochronological contradictions impose doubt as to its global extension. Strangely, although this set of events is widely recognized in several cratonic areas around the globe, these events are still poorly understood and/or not yet reported in the Amazonian Craton. In this study, the stratigraphic, sedimentological and geochronological investigation of the volcano-sedimentary succession (ca. 5-km-thick) of the Carajás Basin, situated in the southeastern Amazonian Craton, northern Brazil, allowed the recognition and sequencing of some of these events in this basin. Two new units are being formally proposed to this basin: the Serra Sul and Azul formations. Glacial diamictite intervals of the Siderian–Rhyacian (ca. 2.58–2.06 Ga) occur stacked within the Serra Sul Formation, and are the first reported occurrence of glacial deposits of that age in South America. In paleogeographic terms, the occurrence of Paleoproterozoic glacial deposits in this part of the globe, expands the reach of these glaciations to the Amazonian Craton for the first time, although the Serra Sul diamictite may be correlated with any of the know Paleoproterozoic glaciations, or none of them. Well-preserved textures, such as glacial foliation and dropstone features, indicate that the deposition of the Serra Sul Formation occurred in a coastal subglacial setting, in which glaciogenic sediments were resedimented in submarine fan system, and through ice rafting process in distal waters of the marine environment. The Serra Sul glacial system was developed immediately above of pre-glacial strata represented by the Neoarchean banded iron formation and volcanic rock units, which not was the main substrate, but also was the main source of sediments to this glacial system. Additionally, the stratigraphic results indicate that the immediately above of the Serra Sul diamictite, rhythmite deposits of the Azul Formation, locally enriched in manganese, were deposited in a shallow marine environment (offshore and offshore transition/shoreface zones), as a result of the sea level rise during the deglaciation phase. The manganese-bearing strata were possibly deposited in association with black shale deposits—which allowed the formation of rhodochrosite during diagenesis—in deep zones of the marine basin. Petrographic and mineralogical evidences, supported by field observation, indicate that manganese oxides were secondarily remobilized through faults to zones with low strain and high permo-porosity within red bed strata of the Azul Formation, similarly to that observed in hydrocarbon migration. In stratigraphic terms, the Azul Formation represents the same interval previously arranged in the lower member of the Águas Claras Formation. This formation was redefined to designate exclusively sandstone, conglomerate and jasper conglomerate strata, deposited in a braided fluvial system, which occur in unconformably immediately above of the Azul Formation. Moreover, it is suggested that the Azul and Águas Claras formations are the stratigraphic record associated with a transgressive-regressive sequence (T-R). The dating (U-Pb) of detrital zircon grains separated from the Azul and Águas Claras formations indicate that Meso- to Neoarchean rocks, possibly of the Rio Maria and Carajás domains, were the main source of sediments. The 207Pb/206Pb Age distribution of the 76 concordant analysis of the Azul Formation indicate a youngest population at ca. 2.27 Ga, interpreted as the maximum deposition age of this unit. The occurrence of Rhyacian to Siderian zircon grains in this unit strongly suggest that the Bacajá Domain may have been a subordinated source of sediments, and in paleogeographic terms, suggest a possible connection between this domain and the Carajás Domain at that time period. The integration of the results obtained from this study, supported by previous data on the regional geology, allowed the proposition of a tectono-sedimentary evolutive model to the Paleoproterozoic succession of the Carajás Basin. It is envisaged that this basin evolved during the greater part of the Paleoproterozoic in a foreland style, as result of the collision of the Bacajá and the Carajás domains during the Transamazonian orogenetic cycle at ca. 2.2–2.0 Ga. The convergent movement of these blocks caused the gradual uplift of the Carajás protocontinent; the closure of the Azul Sea, and installation of a wide fluvial-alluvial system, in which the Águas Claras and Gorotire formations were deposited. This scenario of profound changes is directly related to the Columbia supercontinent assembly at the end of the Paleoproterozoic, that promoted the continentalization and amalgamation of the ancient landmasses that later formed the proto-Amazonian Craton at the end of Paleoproterozoic.
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Estratigrafia e paleoambiente da Formação Pastos Bons, Jurássico-Cretáceo da Bacia do Parnaíba.
(Universidade Federal do Pará, 2019-03-06) CARDOSO, Alexandre Ribeiro; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Jurassic-Cretaceous transition was marked by the fragmentation of the West Gondwana supercontinent and consequent opening of the Atlantic Ocean. The pre-rupture stages were characterized by epeirogenic uplifts associated with voluminous magmatic accumulation in the infracrust. Additionally, expressive volcanic flows occurred in the central portion of the West Gondwana, composing the Central Atlantic Magmatic Province (CAMP). A post-CAMP thermal subsidence stage allowed the installation of massive lakes coincidently with the depocenters of the Parnaíba Basin, which is recorded in the Jurassic-Cretaceous Pastos Bons Formation (PBF). The PBF is a predominantly constituted of thick reddish mudstones interbedded to tabular sandstones. The basal portion is composed of fossiliferous black shales, the Muzinho Shale. Due to discontinuous exposures and fault displacements, the stratigraphy of the Mesozoic of the Parnaíba Basin keeps poorly understood and the is a necessity for more detailed faciological and sedimentological studies. In this sense, this research performed a sedimentological lecture of these deposits in order to elucidate the paleoenvitonment and Paleogeography of the PBF in the context of the West Gondwana, through outcrop-based facies analysis and cyclostratigraphy. The provenance of this succession was investigated through compositional sandstones diagram, quartz hot cathodoluminescence and heavy minerals analyses. The Muzinho Shale beds were evaluated through petrography, XRD and SEM/EDS. The PBF is composed of four facies associations, interpreted as central lake (FA1), sheet-like delta front (FA2), lakeshore (AF3) and ephemeral fluvial channels (FA4). FA1 is composed of drying/shallowing upward cycles, defined by millimeter-scale black shales interlayered with limestones, that grade to reddish shales and laminated/stratified sandstones. Shales are composed by quartz, illite, smectite and calcite. The fossiliferous levels include young and adult macroforms in the same horizon, sandwiched by crinkly laminations with organic rich Fe-smectites. FA1 indicate sedimentation in the center of the lakes, in eutrophic and anoxic conditions. Mass mortality events were probably induced by contamination of the ater column due to H2S release by cyanobacteria. The transition to mudstones and sandstones reflects the evolution of underfilled to overfilled lakes, as the sediment and water supply were increased. FA2 is composed of tabular sandstones in thickening upward cycles, which record unconfined flows and progressive lake filling, with consequent reworking of the top of the beds by wave action. FA3 is constituted of shallowing upward cycles, marked by wave marks, adhesion structures or mud cracks. FA4 is defined by fining upward cycles developed by ephemeral fluvial channels, with conglomerates and sandstones grading to mudstones. This succession defines open and stratified lakes, dominated by settling and unconfined flows, in hyperpycnal regime. The stratigraphic framework of the PBF is composed of four depositional cycles, constituted of centimeter to millimeter-scale cycles, bounded by flooding surfaces and unconformities. These cycles define a retrogradational-progradational-retrogradational stacking pattern, with increasing accommodation space upward conditioned by post-CAMP thermal subsidence pulses and variations in sediment supply. The Mesozoic succession suggests migration of the West Gondwana toward Equatorial regions during Jurassic-Cretaceous, with aridity attenuation relatively to the Permian-Triassic. The sandstones of the PBF indicate provenance from recycled orogens and craton interior, whereas cathodoluminescence data indicate predominantly volcanic sources. In order to test possible correlations with adjacent units, we verified the heavy minerals assemblage of the PBF is very similar to the Corda Formation, and both differ from the fluvial deposits of the Grajaú Formation. The ZTR, GZi and RZi indexes are higher for sandstones of the PBF and Corda Formation, and lower for the Grajaú Formation. The fluvial deposits distinguish mainly by sillimanite and high hornblende content (>50%). These data indicate polycyclic minerals and mixed sources for sandstones of the Parnaíba Basin. The Mearim Group exhibits volcanic contribution supplied by CAMP basalts and low to medium grade metapelitic sources. This last was possibly supplied by Neoproterozoic rocks of the Médio Coreaú Domain, Borborema Province. Differently, the Grajaú Formation was supplied by type-I Brazilian granites. This geological evolution indicates change in provenance areas or exhumation of common source areas during the Mesozoic of the Parnaíba Basin.
Acesso aberto (Open Access)
Estratigrafia e tectônica da Faixa Paraguai Norte: implicações evolutivas neoproterozóicas no Sudeste do Cráton Amazônico
(Universidade Federal do Pará, 2016-11-11) SANTOS, Iara Maria dos; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Northern Paraguay Belt, located at Southeast of Amazonian Craton, was established during the final stages of Brasiliano Cycle (940-620 My.) marked by the collisions among Amazonian, San Francisco and Rio de La Plata cratons to assembly the Gondwana West Supercontinent. The Northern Paraguay Belt consists mainly of metasedimentary rocks of the Cuiabá Group (720 My.), assigned to passive margins basins in an extensional context during the break-up of Supercontinent Rodinia (1.0 Gy.). These basins were affected by tectonic inversion by Brasiliano Orogeny, causing regional metamorphism and ductile crustal level deformation. Subsequently, the orogen had been uplifted, exposed to erosion and subjected to extensional episodes, developing intracratonic basin where sedimentary rocks of the Puga Formation (635 My.), Araras Group (627 ± 32 My.), Raizama Formation (645 ± 15 My.) and Diamantino Formation (541 ± 7 Ma.) were unconformably deposited in moderately deep to shallow storm influenced plataformal environment, tidal affected transitional environment and, lacustrine deltaic environment, respectively. These rocks are classically assigned to a Foreland Basin, however, ancient suture zones usually exposes the orogen roots, and these basins are currently not well preserved. These intracratonic or plataformal basin sedimentary rocks show considerable thicknesses and outcrop in Northeast-Southwest aligned trending mountain ranges. The São Vicente Granite (518 My.) and the Tapirapuã Formation basalts (197 My.) occur as intrusive rocks in the studied area along the Northern Paraguay Belt. The geological contacts between the metasedimentary rocks of the Cuiabá Group with sedimentary rocks of Puga Formation, Araras Group and Alto Paraguay Group, is interpreted as non-conformity. The Cuiabá Group rocks (720 My.) are mainly composed by quartz, plagioclase, muscovite, biotite and phengite and correspondent to greenschist facies affecting a low grade pelitic protolith. These rocks were deformed by ductile shear zone trending Northeast-Southwest, with strain partitioning, described as Transpressional Structural Domain D1, which was divided into two deformation facies: (1) D1-A and (2) D1-B. (1) The D1-A features a fine continuous foliation and stretching mineral lineation, with a rake of 40º, moderately inclined to recumbent, “S” type asymmetrical flexural folds; ductile-brittle thrustfaults and late strike-slip dextral ductile-brittle shear bands; (2) The D1-B is marked by a mylonitic foliation, with its stretching mineral lineation, with a 15º rake. These deformational facies comprises a mainly transpressional sinistral flow mostly dominated by simple shear and influenced by the strain partitioning. All structures indicate tectonic vergence from Northwest toward Southeast, as a result of the collisional setting of the Brasiliano Orogeny (620 Ma.). The sedimentary rocks were deformed under brittle crustal level conditions. Consequently they show inclined to subvertical, asymmetric "Z" type drag folds indicating dextral movement, besides normal faults and cataclastic foliation. The drag folds in the sedimentary rocks indicate tectonic vergence toward both Southeast and Southwest, therefore they were not generated under directed tectonic effort. Normal faults which deform sedimentary rocks are related to later transtensional reactivation episodes of ancient structures forming drag folds and Post-Paleozoic grabens affecting both the Parecis and Parana sedimentary basins. Late quartz veins occur emplaced only in the Cuiabá Group rocks. In conclusion, the Northern Paraguay Belt rocks were affected for at least two main tectonic episodes: (1) The Brasiliano Orogeny, only represented by Cuiabá Group rocks which show metamorphism and ductile deformation; (2) and transtensional reactivation that had been responsible for the establishment of the sedimentary basins followed by brittle deformation of Puga Formation, Araras Group, Raizama and Diamantino Formation.
Acesso aberto (Open Access)
Eventos diagenéticos e hidrotermais do sul do Cráton Amazônico: desvendando a origem das brechas carbonáticas e os processos de dolomitização da Formação Serra do Quilombo do Ediacarano, sudeste do Estado de Mato Grosso
(Universidade Federal do Pará, 2024-04-01) SILVA, Leandro Freitas Sepeda da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; https://orcid.org/0000-0002-5225-9255
The Ediacaran period was characterized by the establishment of extensive platforms during CaCO3 supersaturation events, and by the exceptional creation of accommodation space associated with the aftermath of the Marinoan glaciation (~635 Ma). The carbonate deposits in the Araras Group recorded sedimentation from the beginning of the Ediacaran period, stage 1, in the Amazon Craton. The Serra do Quilombo Formation is a distinct unit characterized by the occurrence of strongly fractured dolomites and faults, along with the presence of dolomitecemented breccias (BC) overlying thick packages of limestone associated with diagenetic and hydrothermal modifications. This evidence introduces complexity to these scenarios. The origin of this deposit is still uncertain, as work has mainly focused on paleoenvironmental issues. This study aims to unravel the origin of cemented breccias and diagenetic/burial processes within the unit, focusing on dolomitization processes. The dolomite samples were analyzed using petrography, scanning electron microscopy, microprobe, Raman microscopy, cathodoluminescence, and isotopic analyses (δ13C, δ18O, 87Sr/86Sr) to unravel their burial history. BCs occur as subvertical to subhorizontal bodies with complex geometries, generally cutting through bedding at a high angle, indicative of hydrofracturing processes related to vertical flows of hydrothermal fluids (hydraulic breccia), in addition to exhibiting the typical cockade texture of expansion breccias in dilatational faults. The paragenetic assemblage of these rocks includes dolomite, quartz, calcite, alkali-feldspar, apatite, pyrite, chlorite, bitumen, and iron oxide, with the replacement features (RD) and dolomite cementation (DC) being the main targets of analysis. The almost micritic substitutive matrix (RD1/RD2) is the primary constituent of the Serra Quilombo Formation, with its low correlation between the values of δ13C and δ18O (R²=0.009), well-preserved fabric, and similarity to the isotopic values (C and Sr) documented for Ediacaran carbonates, suggesting syndepositional dolomitization of this constituent under conditions of shallow burial, possibly involving seawater. The first generation of dolomite cement (DC1) and the last phase of dolomite cementation (saddle dolomite - DC3) occur by filling pores, BCs, and fractures. The cockade texture of the breccias highlights a low precipitation rate or a pause in precipitation between DC1 and DC3. Concomitantly, DC1 has isotopic signals of δ18O = -4.34 ± 1.32‰ (n=18) and 87Sr/86Sr = 0.708831 (n=2), while DC3 has values of δ18O = -9.57 ± 2.51‰ (n=15) and 87Sr/86Sr = 0.711464 (n=3). The significant isotopic difference between the two cementation phases indicates distinct dolomitizing fluids. This relationship shows an increase in 87Sr in the fluid as the temperature increases. Furthermore, the enrichment of 87Sr in the fluid can be explained by its interaction with crystalline basement rocks. Thus, faults with deep roots spatially close to tectonically active zones are likely the main conduits for the ascent of this radiogenic fluid. The occurrence of BCs, essentially in the Serra do Quilombo Formation, is attributed to the limestone-dolomite contact and was interpreted as facilitating the development of fracture corridors, which assist in the percolation of hydrothermal fluids. Finally, it is understood that the conduits with carbonate breccia are subsequent to the silicification event of the evaporites of the Nobres Formation, which acted as a sealing rock for hydrothermal fluids. The presence of tectonic stylolites cutting the cemented breccias and the subverticalized zebra-like stratified structures indicates that the BCs were already formed during the installation of post-Ordovician transtensional structures, preceding the installation of the Paleozoic Basins on the South American Platform.
Acesso aberto (Open Access)
Evidências geofísicas e geológicas da CAMP nas bacias sedimentares do Pré-Cambriano e Fanerozoico do sul do Cráton Amazônico.
(Universidade Federal do Pará, 2019-03-16) REZENDE, Gabriel Leal; MARTINS, Cristiano Mendel; http://lattes.cnpq.br/8303640454649778; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The sedimentary basins in the Southwestern Tocantins and Southern Tapajós provinces were affected by the emplacement of large Triassic-Jurassic basaltic rocks volumes termed as Central atlantic Magmatic Province (CAMP), result of the Pangea break up and opening of the Central Atlantic Ocean. Two basins, object of this study, were implanted over Tonian metamorphic rock of the Northern Paraguay Belt and Paleo to Mesoproterozoic rocks of the Amazonian Craton: 1) the Paleozoic Parecis Basin; and 2) the Late Cryogenian-Ordovician Intracratonic Basin or Araras-Paraguay Basin, afterwards inverted during the Ordovician. The mapped basalt exposed locally in these basins reach 5 % in volume, being the most ocurrences at the Chupinguaia and Tangará da Serra regions, states of Mato Grosso and Rondônia, respectively. These exposed basalts are not compatible with the great volume and magnitude related to the CAMP, which have motivated the research in subsurface of other occurrences. The reinterpretation of previous geophysical and geological methods combinated with a crustal modelling allowed a new interpretation to the gravity field related to the intracrustal density contrast or residual gravimetric field for this part of Amazonia Craton. The anomaly in this field allowed to identify higher density bodies within the Paleozoic Parecis and Araras-Paraguai basins, interpreted as continental tholeiitic flood basalts associated to the CAMP, reaching a volume 3 million of km3. The study of the residual gravimetric anomaly based on crustal modelling applied here can be effective to guide future works in the mapping in subsurface of highly density rocks associated to the basalts, allowing to obtain the probable distribuition in area and contributing for a better understanding about the magmatic events of the CAMP in sedimentary basins.
Acesso aberto (Open Access)
Evolução da paisagem da porção centro-oriental da Amazônia do Cretáceo ao Paleógeno.
(Universidade Federal do Pará, 2024-06-23) MOURA, Matheus Ramos de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
This study presents a new perspective for the evolution of the relief in Central and Eastern Amazonia based in geomorphologic and stratigraphic analysis of two areas: the first one at the surroundings of Paragominas and the second includes territories from Juruti, Belterra and Santarém counties, both at the state of Pará. The results of the relief analysis demonstrate a diversity of morphological modellings that indicate a polycyclic evolution involving periods of development of flat plateaus, associated with the development of lateritic profiles, alternated with intervals that tend to erosional activity from unstable and collapsing slopes, being the planation reliefs representative of the Paleocene-Eocene and Early-Middle Miocene, while the dissection modellings mark ages from the Neoeocene-Neooligocene and Neomiocene-Pliocene. The ages of the planation modellings are confirmed by age estimations of Cenozoic paleosurfaces that occur along the Amazon region (with which they are correlatable) and by global eustatic and climatic tendencies. The sedimentological and stratigraphic analysis identified two typical profiles for these study areas – PWH (profiles with well-defined horizons) and PMC (profiles with massive conglomerates), distinguished by their in situ/reworking characteristics. Regarding to the PMC profiles, there were observed two facies associations: FA1: an association of conglomerates of diverse supportings and arenites assumed to be formed by proximal fan deposits generated through debris flows; and FA2: packs of clay displaying mostly a massive framework, interpreted as distal fan deposits generated through sheet flow and mudflow. Both associations have subaerial exposure evidence and erosive surfaces in their bases, that allow to conclude a deposition at embedded valleys through rapid pulses of detritus, and hence were interpreted as colluvial and alluvial fan deposits, that formed along the most erosive periods of the regions, having been initiated in the vicinities of the main drainages of the analyzed areas (Capim and Amazonas rivers). The results of this study demonstrate a more intense sedimentary and tectonic activity than that generally accepted for the Amazon region during the Cenozoic Era, showing that this region’s landscape was more affected than it was believed to be by another tectonic remarkable events in the South America continent, such as: the Andes Uplift, the deposition of the Amazonas and Marajó basins and Bragantina Platform neogene formations, the Tortonian Regression and the install and evolution of the Amazonas River.
Acesso aberto (Open Access)
Fácies e estratigrafia da parte superior da Formação Pedra de Fogo, Permiano da Bacia do Parnaíba, região de Filadélfia-TO
(Universidade Federal do Pará, 2012-05-02) ANDRADE, Luiz Saturnino de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Permian Pedra de Fogo Formation, which belongs to the Balsas Group of the Parnaíba Basin, northern Brazil, is characterized a siliciclastic-carbonate succession with expressive chert content, rare stromatolites and fossils of animals and plants, especially silicified trunks, mainly of the Psaronius genus. In order to emprove the stratigraphic and paleoenvironmental knowledgement of the upper portion of the Pedra de Fogo Formation, outcrop-basedm facies analysis was carried out in the Filadélfia region, State of Tocantins, Southwestern Parnaíba Basin. This study allowed the definition of a 100 m thick siliciclastic succession with subordinate occurrences of carbonate and evaporites. Twenty-five sedimentary facies grouped into six facies associations (FA) were identified: FA1-Lacustrine with ephemeral river deposits; FA2- Storm wave-influenced lake deposits; FA3-Continental sabkha deposits; FA4- Central lake deposits; FA5-Dune field deposits; and AF6-Lake/oasis deposits with inunditos. These associations indicate that during Permian, an extensive lacustrine system developed with adjacent dune fields and continental sabkha, as well as with contributions from ephemeral rivers. Which when debauching into the lakes provide the formation of suspension lobes and sheet flows (FA1). Sabkha plains (FA3) were formed in the marginal portions of the lake, eventually influenced by storm waves (FA2), while the central zone was site of intense pelitic deposition (FA4). The low supply of wind-blocon sand led to the formation of restricted dune fields (FA5) with development of interdune lakes (oasis), where giant ferns, sporadically flooded by ephemeral rivers (FA6). The predominanc of smectite and the lack of kaolinite as well as the ocorrence of evaporites in the Association AF3 support the facies data that the apper part of the Pedra de Fogo Formation was laid during a hot and arid climate.
Acesso aberto (Open Access)
Fácies e isótopos de carbono e oxigênio da Formação Nobres, Neoproterozóico da Faixa Paraguai Norte, Mato Grosso.
(Universidade Federal do Pará, 2011-06-16) RUDNITZKI, Isaac Daniel; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The lastest stages of orogenic evolution of the Northern Paraguay Belt, south of the Amazon Craton, are related to a closure of a passive margin in the Neoproterozoic-Cambrian transition. In this basin, the predominant carbonate sedimentation of the Araras Group was succeeded by siliciclastic deposits of the Alto Paraguay Group. Events that led to the inhibition of carbonate sedimentation were partially recorded in the Nobres Formation, uppermost unit of the Araras Group. In the southern part of the Northern Paraguay Belt, in the Cáceres region, state of Mato Grosso, Central Brazil, the Nobres Formation overlies in unconformity the dolostones of the Serra do Quilombo Formation, and is overlain unconformably by coastal siliciclastic deposits of the Raizama Formation of the Alto Paraguai Group. The Nobres Formation consists of shallowing / brining upward small-scale arid peritidal cycles subdivided into two members: (i) lower member, composed of massive dolostone, intraclastic dolopackstones with enterolithic and megaripple bedding, wavy lamination with mud drapes, dolostone with silicified evaporite molds and domic to stratiform stromatolites, interpreted as tidal flat/sabkha deposits; and (ii) upper member, consisting of massive dolostone, dolomitic sandstone with megaripple bedding, wavy lamination with mud drapes, domic to stratiform and wrinkled stromatolites, dolostones with silicified evaporates molds, sandstones with low angle and climbing ripple cross lamination and mudstones with even parallel and wavy lamination, interpreted as mixed tidal flat deposits. The chemostratigraphic framework of Nobre Formation includes values of 13C and 18O between -2.19 and 0, 27‰VPDB and -7.42 and -4.25‰VPDB, respectively. The δ13C values are primary and representative of the original composition of Neoproterozoic seawater. The analysis of the δ13C stratigraphic curve in combination with the facies interpretation and following the Ediacaran stratified ocean model, allowed the identification of four isotopic patterns of the studied succession: type I, related to the storm wave to storm influenced shallow platform of Serra do Quilombo, with δ13C values near zero ranging from -0.27 to 0.4 ‰VPDB interpreted as a mixing of stratified waters of the ocean; type II, which refers to the transition between Serra do Quilombo and Nobres formations, with δ13C values ranging from -0.12 to 0.41 ‰VPDB, whose positive trend is interpreted as the fixation of 12C by biological activity; type III, defined as the typical isotopic signal of the Nobres Formation, trending and ranging from uniform values δ13C from -1.80 to -0.13‰VPDB related to changes in sea level; and type IV, that consist of crinkled pattern with δ13C values from -2.19 to -0.73‰VPDB indicative of isotopic reequilibrium of peritidal waters. The stacking of peritidal cycles, up to 200 m thick, suggests continuous and recurrent generation of accommodation with probably linked to tectonic subsidence. The siliciclastic inflow in the end of the deposition of the Nobres Formation, hindered the carbonate sedimentation, and it is attributed to uplift of source areas linked to the initial phase of the closure of Clymente Ocean, during the Pampean-Araguaia orogeny at the Neoproterozoic-Cambrian limit.
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Fácies e proveniência de depósitos costeiros da Formação Raizama: evidências do registro Ediacarano-cambriano na faixa Paraguai, região de Nobres, Mato Grosso
(Universidade Federal do Pará, 2014-03-10) SANTOS, Hudson Pereira; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Siliciclastic rocks from the Raizama Formation, a basal unit of the Alto Paraguai Group, from the Ediacaran-Cambrian interval (635-541 Ma), is discontinuously occur distributed along the southern margin of the Amazonian Craton within the Paraguay Fold Belt northern segment, west-central of Brazil, Mato Grosso state. This Group unconformably overlies carbonate shelf deposits of the Araras Group, where evidence of Marinoan glacial event (635 Ma) was recorded. The Alto Paraguai Group represents the final stages of the collision between the Paranapanema and Amazonian blocks, leading to the closure of the Clymene Ocean (540-520 Ma). The Raizama Formation is approximately 570 m of thickness and is composed by mudstone, fine to coarse sandstones, and sandstones with dolomitic cement previously interpreted as fluvial-coastal deposits distributed in the lower member (270 m) and upper member (300 m). The facies and stratigraphic studies of this unit in the Nobres region, Mato Grosso state, were mainly focused on the outcropping section of 600 m in the bed of Rio Serragem II, which includes the Serra do Tombador waterfall. In this stratigraphic section, 17 sedimentary facies were described and grouped into five facies association (AF), representative of a progradational coastal sequence beginning with lower shoreface deposits, overlying in correlative conformity the shelf carbonate deposits of the Serra do Quilombo Formation (Araras Group). The AF1 facies consists of sandstones with planar lamination and wave-ripple cross-lamination (microhummocky), individualized by layers of laminated pelite interpreted as lower shoreface deposits. It stands out in the AF1 the first occurrence of centimetric bioturbed levels of Skolithos in Neoproterozoic-Cambrian deposits in the Paraguay Belt. The AF2 facies is composed by sandstones with swaley cross-stratification and plane bedding interpreted as upper shoreface deposits. The AF3 facies is composed by sandstones with tangential and trough cross-stratification with drapes of siltstone/very fine sandstone representative of channel and subtidal bars deposits. The AF4 facies is characterized by sandstones with tangential and sigmoidal cross-stratification, planar to low angle cross-lamination, rhythmites very fine sandstone/siltstone with flaser bedding and mudcracks, organized in metric tidal flat shallowing upward cycles. The AF5 facies is comprised of sandstone with trough cross-bedding characterized by common lags at the base of the association, sandstone with planar to low-angle cross-stratification, interpreted as distal braided rivers, in part reworked by waves. Detrital zircon grains were obtained from AF3 and dated by U-Pb method, resulting in an age 1001±9 Ma interpreted as the age of the maximum deposition of Raizama Formation. Combined with this analysis, the NE-SE paleocurrents show that source area of these sediments would be the Sunsas Fold Belt, SW of the Amazonian Craton not being discarded contributions coming from the NW part of this Craton. The obtained Mesoproterozoic age has predominantly served to unravel the provenance of Raizama Formation. Whereas dating from the base of Araras Group, around 627-622 Ma, associated with the clear presence of the ichnogenus Skolithos, suggests that the age of this unit is closer to the limit with the Lower Cambrian. Trace fossils from the Proterozoic are characterized almost exclusively by horizontal traces, while vertical bioturbation are virtually absent throughout the Neoproterozoic. This inference is confirmed by the maximum age of 541 Ma obtained for Diamantino Formation, which overlies the studied unit. The radiometric data combined with paleoenvironmental interpretation, including the record of the first burrowing activities in Paraguai Fold Belt, opens up perspectives to understand in greater detail the sequence of events that typify the Ediacaran-Cambriam boundary strata of Brazil, still poorly known.
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Fácies e proveniência de depósitos siliciclásticos cretáceos e neógenos da bacia do Amazonas: implicações para a história evolutiva do proto-amazonas.
(Universidade Federal do Pará, 2015-06-23) MENDES, Anderson Conceição; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Siliciclastic deposits exposed near the channel of the modern Amazon River and overlaid by Neogene units have been attributed to the Cretaceous, formally named as Alter do Chão Formation. Integrated studies based on sedimentology, stratigraphy, trace fossils, petrography of sandstones and heavy minerals, as well as, U-Pb dating of zircon grains allowed reconstitute the depositional paleoenvironment and infer the probable source areas of these Cretaceous deposits in the Amazon Basin. Despite its wide geographical distribution throughout the Amazonas Basin, stratigraphic and sedimentological studies of Alter do Chão Formation were located in areas where there was not allowed a better paleoenvironmental and paleogeographic reconstruction. These deposits record the evolution of a large-scale fluvial system or “Big River”, with meandering pattern in the central-eastern Amazonas Basin, while in the western portion of the basin, predominate an anastomosed configuration with large overbank zones colonized by animals and plants. The recorded of this biologic activity are traces fossil of Taenidium, Planolites, Diplocraterion, Beaconites, Thalassinoides, adhesive meniscate burrows and excavations of insects and vertebrates, as well as, root marks. The fluvial succession consists of kaolinitized and locally silicified conglomerates, sandstones and pelites, grouped in eight architectural elements, Gravel Bar, Sand edforms, Lateral Accretion Bar, Levee, Channels, Crevasse Splay Lobes, Abandoned Channel Fills and Overbank Fines. The expressive terrigenous supply probably came of uplifted areas related to Gurupá Arch, eastern limit of the basin, and zircon grains ages range from 1.8 to 2.9 Ga, indicate the Maroni-Itacaiúnas and Central Amazon provinces as main cratonic sources of sediments. The massive sediment input reflected in the hundreds of meters thick of cretaceous deposits, extense for thousands of kilometres, suggests expressives drainages from the craton, feeding an approximate E-W-oriented "Big River”. Probably, the Late Cretaceous paleogegraphy will be similar to current configuration of the modern Amazon River, but with opposite migration, directioned to the Pacific Ocean. The unconformity between Alter do Chão Formation and Neogene deposits attests long period of subarial exposure in the Amazon Basin during the Paleogene, coincident with the development of lateritic-bauxitic profiles. Paleocurrent measures confirms the flow reversion to the east, in direction of Atlantic, during the Neogene. Additionally, the spectrum of zircon grains ages, ranging from 0.5 to 2.7 Ga, comparable to obtained for Quaternary deposits, indicates cratonic and mainly Andean sources, recording the beginning of the Amazon River. The results obtained here allowed, by first time, to propose a transcontinental drainage model for the Late Cretaceous, as weel as, to record the initial sedimentation of proto-Amazon river during the Neogene.