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Teses em Geologia e Geoquímica (Doutorado) - PPGG/IG

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/6341

O Doutorado Acadêmico pertence ao Programa de Pós-Graduação em Geologia e Geoquímica (PPGG) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA).

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Aspectos litoestruturais e mineralizações Salobo 3A (Serra dos Carajás-PA)
(Universidade Federal do Pará, 1996-10-29) SIQUEIRA, José Batista; COSTA, João Batista Sena; http://lattes.cnpq.br/0141806217745286
The Salobo district is located at the Carajás Province in the Cinzento strike-slip system, and is formed of supracrustal rocks of the Salobo Group and gneisses of Xingu Complex, which were assembled by several generations of shear zones. The Salobo Group includes magnetite-fayalite schist, biotite-almandine-magnetite-fayalite-grϋnerite schist, biotite schist, anfibol schist, chlorite schist, banded iron formation and quartzite. The Xingu Complex includes banded tonalitic gneisses, trondhjemitc and granodiritic gneisses, partialy migmatized. The older shear zones correspond to ductile thrusts to which the generalized imbrication of the lithological units and the tectonic layering, defined by strips and lenses of supracrustais rocks alternated with gneisse is due. Their movements is synchronous to that of the Itacaiúnas belt; minerals transformations under thermal conditions of amphibolite facies, as well as important modifications in the stratigraphic relationships of several lithological units, are related to therm. The second generation of shear zones formed the transtensive Salobo-Mirim duplex. They are sinistral strike-slip shear zones, linked by normal shear zones along which minerals transformations of greenschist facies occurred. The development of the duplex was controled by the former tectonic layering, and its assymetric shape was influenced mainly by the presence of a basement gneiss megalense. The third generation of shear zones is of transcurrent type, with NW-SE and NNW-SSE trends, which modified the Salobo-Mirim duplex geometry, and are interpreted as X features linked to the sinistral moviments. The shear zones of the west corner of the area represent the propagation of a horse tail structure at the west end of the Carajás fault; in these case, they could be oblique thrust. The Salobo 3A deposit is situated in the central part of a normal oblique shear zone, which belongs to a release bend along the main strike-slip shear zone of the Salobo-Mirim duplex. The copper and gold mineralizations are hosted in extension structures, as single and composite pull-apart structures, transtensive sigmoide stringers, tension gashes, pressure shadows and star strucutures in the cross-cutting zones of descontinuities. The Salobo 3 A deposit is an example of concentracion/reconcentracion of cooper and gold mineralizations in s transtensive shear zone due to deformational, hydrothermal and metamorphic processes.
Acesso aberto (Open Access)
Braquiópodes devonianos da Bacia do Amazonas: novos dados taxonômicos, paleobiográficos e relações com as mudanças ambientais
(Universidade Federal do Pará, 2024-10-01) CORRÊA, Luiz Felipe Aquino; RAMOS, Maria Inês Feijó; http://lattes.cnpq.br/4546620118003936; https://orcid.org/0000-0003-0276-0575
The Devonian marked a significant phase in the evolutionary history of the Brachiopoda. During this period, the Phylum achieved its peak diversity (Emsian) and suffered one of its most significant declines (Frasnian–Famennian), ranking second only to the mass extinction event Permo-Triassic. Among the Brazilian sedimentary basins, the Amazonas Basin has the greater diversity of Devonian brachiopod genera, distributed among the following formations: Manacapuru (Lochkovian), Maecuru (early Eifelian), Ererê (Late Eifelian), and Barreirinha (early Frasnian). Studies of Devonian brachiopods from the Amazonas Basin began in the late 19th century with identifications of material collected during the Morgan Expeditions (1870–1871) and the Imperial Geological Commission of Brazil (1876). These expeditions focused primarily on the Maecuru and Ererê formations. The brachiopod fauna of the Manacapuru Formation (Lochkovian) was unknown until 2015, when during paleontological salvage at the Belo Monte hydroelectric plant in Vitória do Xingu, Pará, Brazil, a significant number of Rhynchonelliformes and Linguliformes samples were recovered. This work aims to carry out the taxonomic identification of brachiopods from the Manacapuru Formation, in addition to analyzing and discussing the possible factors that influenced the diversity of brachiopod genera among the sedimentary units of the Amazonas Basin (Mancapuru, Maecuru, Ererê, and Barreirinha formations). The taxonomic study of brachiopods from the upper part of the Manacapuru Formation (Lochkovian) has allowed, to date, the identification of two genera, Orbiculoidea d'Órbigny, 1847 and Schellwienella Thomas, 1910. Among the materials, Orbiculoidea has the greater diversity, totaling five species: Orbiculoidea baini Sharpe, 1856, Orbiculoidea bodenbenderi Clarke, 1913 and Orbiculoidea excentrica Lange, 1943 in addition to two new species: Orbiculoidea xinguensis Corrêa & Ramos, 2021 and Orbiculoidea katzeri Corrêa & Ramos, 2021. The species O. baini, O. bodenbenderi, and O. excentrica were recorded for the first time in the Manacapuru Formation and Northern Brazil, and they are also the oldest records (Lochkovian) from South America. The presence of Orbiculoidea in the region can be explained by two reasons: the proximity of the Amazonas Basin, located in the northwest of Gondwana during the Lower Devonian, with the paleocontinent Laurussia (where most occurrences of Orbiculoidea are recorded during the Silurian), favored the specific exchange between these two geographic regions; and the global rise in sea level during this period, which flooded much of northwest Gondwana, resulting in the presence of shallow seas in the Amazonas Basin, represented by marine sediments in the upper part of the Manacapuru Formation. These conditions favored the colonization of inarticulate brachiopods during the Early Devonian in northern Brazil. Furthermore, the new species Schellwienella amazonensis Corrêa et al. 2024, of the Pulsiidae Family Cooper and Grant, 1974, is proposed, this being the first record of the genus in the Amazonas Basin. Schellwienella amazonensis n. sp. and Schellwienella marcidula Amsden, 1958 from the Bois d’Arc Formation (Lochkovian), USA, are the oldest records of the genus. In the Devonian, Schellwienella occurred in all stages (Lochkovian, Pragian, Emsian, Eifelian, Givetian, Frasnian, and Famennian), mainly in the marine siliciclastic environments of Gondwana, transiting between temperate and polar latitudes. In the Carboniferous, its stratigraphic distribution was restricted to the Tournaisian-Visean interval, with a preference for warm water environments and carbonate platforms typical of low latitudes. We identified three distinct stages when analyzing the variation in Devonian brachiopod diversity in the Amazonas Basin. In stage 1, the peak of brachiopod diversity occurred in the early Eifelian (Maecuru Formation), when the Amazonas Basin was between subtropical latitudes 30°S and 60°S, under shallow and cold marine conditions, justified by the absence of carbonates, evaporites, and reefs in the region. In stage 2, the first decline in diversity occurred, recorded in the Ererê Formation (late Eifelian), attributed to a warmer climate and deeper waters than in the Maecuru Formation. Stage 3 occurred during the Frasnian when there was a second decline in brachiopod diversity in the Amazonas Basin (Barreirinha Formation). A major global transgression happened at the end of the Devonian. During this period, the Amazonas Basin experienced the deepest marine conditions in its history. Brachiopods of the Barreirinha Formation occur in black shale layers (offshore), attributed to a dysoxic to the anoxic environment of high stress, which explains the low diversity of brachiopods in this unit.
Acesso aberto (Open Access)
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 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)
Caracterização geomorfológica estratigráfica e geoquímica da Planície Costeira do município de Itarema-CE.
(Universidade Federal do Pará, 2011-09-01) PEREIRA, Lamarka Lopes; FREIRE, Geoerge Satander Sá; http://lattes.cnpq.br/6803944360256138; 6803944360256138; EL-ROBRINI, Maâmar; http://lattes.cnpq.br/5707365981163429; 5707365981163429
The Itarema coastal plain, situated at the western coast of Ceará, in the area dominated by the Cenozoic sedimentary cover. This thesis shows the geomorphological, sedimentological and geochemical features of this coastal plain. The Itarema coastal plain is subdivided in two major morpho-structural units: pre-coastal ¨plateaus¨ and coastal plain, that is subdivided into lithostratigraphic units, lagoon plain, tidal plain with and without mangroves, marine and fluvial plain, mobile and fixed dunes, beach ridges, tidal channels, sand bars and beaches. The supply and sediment transport in the area are closely linked to the climatic, meteorological and oceanographic conditions. The sedimentary, stratigraphy, geomorphological and geochemical data have been defined: (1) five lithological units: Lagoon Deposits, dune deposits, eolianits deposits, beach deposits and alluvial deposits and (2) seven lithofacies: mud sandy, mud, Sand mud, fine sand, medium sand, thick sand, conglomeratic sand-clay with different characteristics which have been drawn through the lateral and vertical correlations, thus allowing the interpretation of depositional paleoenvironments related to the evolution of the Itarema Coastal Plain. The analysis of the lithological units allowed the reconstruction of the processes indicative of a transgressive sucession prograded during which the lagoon-barrier system was installed on the system of alluvial fans, the bus of small streams, forming the lagoon plain, it was also noted that the lagoon has undergone changes in their size both by progradation of the barrier and subsequently by the deposition of sediments within the same wind. The Itarema coastal plain presents physiographic features of an coastal promontory or embaiments of central nuclei as a spiral, that would have provided the evolution to the current environment and the current model of coastline with beaches of the barrier beach-type and suggests that is occurring repetition in the construction of comparative morphology morphogenetic active in the region's past.
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)
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.
Acesso aberto (Open Access)
A fragmentação do Gondwana na região meio-norte do Brasil durante o mesozóico
(Universidade Federal do Pará, 2007-08-09) SOARES JÚNIOR, Adilson Viana; COSTA, João Batista Sena; http://lattes.cnpq.br/0141806217745286; 0141806217745286
South America, Africa, India, Antarctic and Australia continents formed a great and complex supercontinent called Gondwana at the end of the Precambrian. From the Mesozoic this mega-continent underwent extension and regional uplift with volcanism associated, resulting in triple junctions which evolved to rift systems. These events are related to the Wealdenian Reactivation or South-Atlantic event witch took place in the interior and the boundary of the South America plate, been followed by intense basic magmatism and extensional systems formation, with listric and planar faults. Some basin architecture are controlled by ancient shear zones reactivations. From Triassic the extension gave rise to uplifts associates to the magmatism in the weakness areas of the basement, including the Paleozoic basins in the northern Brazil. This event responds to the Pangaea break-up, the formation of the Central Atlantic Ocean and the individualization of the Laurasia and Gondwana supercontinents. The arm of the Central Atlantic in the South America evolved to rift system in the Foz do Amazonas basin and volcanism in the Parnaíba Basin during the Triassic and Jurassic. This rifting event died out towards the south and propagated to the Caribbean region, resulting in North America plate formation. From the early Cretaceous (end of Barremian and beginning of the Aptian), new phase of rifting is registred in the region, without linkage to the Central Atlantic. This had been increased the Foz do Amazonas basin and Marajó basin formation and a new phase of uplifting followed by volcanism and rifting concentrated at the Ferrer-Urbano Santos Arc, Parnaíba Basin, and the formation of the Gurupi Graben System (Bragança-Viseu, São Luís and Ilha Nova basins) and Grajaú Basin. This event includes two distinct phases: early rifting resulting in the formation of the Bragança-Viseu and Ilha Nova basins; and thermal subsidence with the formation of the São Luís and Grajaú basins, separate by short time span. These basins underwent rapid evolution, with sedimentary environment records since fluvial and lacustrine until transgressions. In the Lower Cretaceous continued the evolution of the Foz do Amazonas Basin witch the fragmentation propagating towards the SE, resulting in the formation of the Pará-Maranhão Basin and Barreirinhas Basin at the beginning of the Albian. This event is resposible for the Equatorial Atlantic Ocean individualization, with associated transgression in the Pará-Maranhão and Barreirinhas basins, as well in the São Luís, Ilha Nova and Grajaú Basins, controled by NE-SW fractures and faults in the São Marcos Bay and by partial collapse of the Ferrer-Urbano Santos Arc. During the Late Cretaceous it had reducted the extension at the Marajó Basin, stopped the fragmentation in the Gurupi Graben System and the South America and African continents were completely pulled apart, with formation of oceanic crust and passive margins in the Foz do Amazonas, Pará-Maranhão and Barreirinhas Basins. From the Upper Cretaceous, the east margin of the South America and the west margin of Africa had assumed its current configuration, withchanges related to drifting and to the Neotectonic.
Acesso aberto (Open Access)
Gestão Integrada das Águas em Rondônia
(Universidade Federal do Pará, 2010-10-30) ZUFFO, Cátia Eliza; ABREU, Francisco de Assis Matos de; http://lattes.cnpq.br/9626349043103626; 9626349043103626
The situation of waters in Rondônia, the challenges for their management and, notably, for the social mobilization in their defense are the main focus of this thesis which was presented to the Geology and Geochemistry Post Graduation Program, of the Federal University of Pará, PPGG/UFPA. In tune with the Research Line in “ Hydric Resources Management”, from PPGG, the main objectives of the research were meant to: follow, register and analyze the process the policies implementation process and the system of management of hydric resources of Rondônia; contribute for the advance of this process through the accomplishment of studies on hydrogeology, underground and superficial water quality; put into practice some of the main pressupositions in water management in Brazil, at present time, which are the planning for hydrographic basin and the environmental education. The research was carried through based on the following hypothesis: the integrated water management in Rondônia, just like other states in the Amazon, is in a deficient or nonexisting situation idue to structural problems in the federative units administrative arrangement; the lack of management tools foreseen by Hydric Resource National Policies; the abundance and wastefulness culture; and, still, the execution of anthropic actions without the necessary research endorsement or consistent Waters data analysis, in their varied occurrence forms. Among the ways to go through the current situation are: management tool application by hydrographic basins, basin plan formulation and social mobilization valuation, getting to the constitution of collegiates, such as the hydrographic basin committees, important fori for debates in order to provide conditions to support sustainable regional development, what make it evident that integrated waters management depends on technical-scientific knowledge, administrative structure, compatible legislation and society mobilization to take good care of them. The employed methodology embodied studies and action focusing the physical environment, socioeconomic aspect of land use, underground and superficial waters, allied to the hidrographic basin planning application experience – hydric resource management unit – and GESTÃO INTEGRADA DAS ÁGUAS EM RONDÔNIA 5 Catia Eliza Zuffo -2010- Tese de Doutorado (PPGG-UFPA) environmental education as na instrument of social mobilization, through the Alive Acqua Viva Rede UNIR - for Waters of Rondônia, searching to contribute for the integrated management of Rondonian waters. The development of this work allowed the balance on the current state of knowledge on distinct subjects, even theough they are complementary among themselves. The format chosen to present the thesis studies, actions and results was the preparation and submission of articles to recognized technical-scientific diffusion means, according to the following arrangement: In articles 1 and 2, aspects linked to underground waters are approached: 1) RONDÔNIA’S HYDROGEOLOGIC NATURE AND ITS RELATIONS WITH SIAGAS DATA BASE (Zuffo et al. submitted to the on-line magazine Pesquisas em Geociências from UFRGS); 2) UNDERGROUND WATERS QUALITY CHARACTERIZATION IN RONDÔNIA (Zuffo et al. submitted to the on-line magazine of the Institute Geológico - SP); In articles 3 and 4 aspects linked to superficial waters are presented: 3) SUPERFICIAL WATERS QUALITY CHARACTERIZATION IN RONDÔNIA (Zuffo et al. submitted to the on-line magazine Yearbook of the Institute of Geociências of UFRJ); 4) PLANNING AND ENVIRONMENTAL ZONING OF THE TAPADO IGARAPÉ BASIN - RONDÔNIA: a contribution to its management (Catia Eliza Zuffo & Francisco de Assis Matos de Abreu - scientific article accepted for publication in a book of the Master’s Degree Program in Geography at UNIR). Waters management and environmental education are the focus of articles 5 and 6: 5) SHARED WATERS MANAGEMENT RONDÔNIA: action and proposals for the formation of the Hydrographic Basin Committees (Catia Eliza Zuffo & Francisco de Assis Matos de Abreu - submitted to Formação – Electronic, magazine of the Post-Graduation Program in Geography of the FCT-UNESP Presidente Prudente). 6) NEVIRONMENTAL DUCATION AND WATERS MANAGEMENT IN RONDÔNIA: performance of ACQUA VIVA REDE UNIR (Catia Eliza Zuffo & Francisco de Assis Matos de Abreu - Submitted the Remea - Electronic magazine of the Mater’sw degree em Environmental Education of FURG). So, these articles compose an integrated whole, each one of them, individually, is presented in a complete form, comprising materials and methods which were used, as well as the results, discussions and bibliographical references. Thus, the constant results in these articles bring subsidies meant to improve the Waters management in Rondônia and to promote development in effectively sustainable bases.
Acesso aberto (Open Access)
lndicadores de estabilidade da matéria orgânica em terras pretas nos sítios arqueológicos Jabuti e Jacarequara (Pará)
(Universidade Federal do Pará, 2015-09-02) SENA, Luciana Freitas de; KERN, Dirse Clara; http://lattes.cnpq.br/8351785832221386; 8351785832221386; LEMOS, Vanda Porpino; http://lattes.cnpq.br/1829861620854008; 1829861620854008
Environmental conditions in the Amazon region favor the weathering and decomposition of soil organic matter, making it depleted in nutrients and difficult agricultural use. But in the same region, areas that have been modified by human action preterit, known as Terra Preta Archaeological (TPA), have different properties, among which stands out the high stability of soil organic matter (SOM) that in some research it is attributed to interactions between the MOS and other soil constituents such as pyrogenic carbon and minerals from the soil. In this study were selected two archaeological sites in the state of Pará, the Jabuti, the cemetery housing type, located in the city of Bragança, and the Jacarequara, the sambaqui type, located in Barcarena, in order to assess the stability of organic matter TPA from soil extracted solutions (depths 30 and 80 cm) and own soil (collected during the implementation of extractors in December 2013) in areas of TPA and vicinity. The characterization of soil solutions was conducted in the period between March and June 2013, based on the macroscopic properties and the chemical indicators: dissolved carbon concentrations (organic, inorganic and total), determined by the combustion method; pH, Eh and conductivity. The SOM stability assessments in the solid phases of the TPA and surrounding areas (ADJ) were based on textural verification of soil chemical indicators (pH, organic carbon concentrations and Ca, K, P, Na, and Mg) and biological represented by the microbial biomass, determined by the method of irradiation / extraction and expressed in terms of carbon (Cbm) and nitrogen (Nbm). The results of the soil solutions showed that two sites in the pH values are higher in depth (80 cm), and at the site Jacarequara values were determined for this parameter up to 7.2, while the site Jabuti pH results do not exceed the value 6. The maximum values of Eh (mV), conductivity (μs) and dissolved organic carbon (mg L-1) in place Jacarequara, 30 cm deep were respectively +201 mV, 427 µs e 13 mg L-1 and in the area adjacent to this site, at the same depth the highest values were +128 mV, 72 µs e 23 mg L-1 for the same parameters. At the Jabuti site and its ADJ, in 30 cm deep, the respective maximum values of the same areas were Eh +108 mV and +96 mV; conductivity 138.87µs and 59.85µs, dissolved organic carbon 12 mg L-1 and 21.08 mg L-1. Comparing the areas of TPA and their ADJ, the data Eh and dissolved organic carbon refer to more stable components in soil areas of solutions of TPA, owing to the more oxidizing values and smaller dissolved organic carbon concentrations, the results conductivity, which is an indicator of the concentration of ions is higher in the TPA reporting the increased availability of nutrients. In both sites, soils presented sandy texture, both in the areas of TPA as the ADJ, the latter being more sandy. In the soil Jacarequara site and its ADJ in the range of 20 to 30 cm deep, the following values were obtained respectively: 119.82 g kg-1 and 20.34 g kg-1 for SOM; pHH2O equal to 6.8 and 4.9; 183 mg/dm3 and 5 mg/dm3 P (available); 39 mg/dm3 and 29 mg/dm3 K (exchangeable); 14.8 cmolc/dm3 and 0.7 cmolc/dm3 Ca (exchangeable); 0.1 cmolc/dm3 and 1.7 cmolc/dm3 Al (exchangeable), 181.26 μg g-1 and 88.74 μg g-1 of Cbm and 3.27 mg kg-1 and 1.91 mg kg-1 Nbm. In the soil of Jabuti site, the determined values were: 83.66 g kg-1 of MOS, pHH2O equal to 4.4; 55 mg/dm3 P (available); 59 mg/dm3 K (exchangeable); 0.3 cmolc/dm3 Ca (exchangeable); 4 cmolc/dm3 of Al (exchangeable); 92.56 mg kg-1 of Cbm and 1.41 mg kg-1 Nbm; in the area adjacent to this site, the values were: 13.13 g kg-1 of MOS, pHH2O equal to 4.6; 4 mg/dm3 P (available); 29 mg dm3 K (exchangeable); 0.3 cmolc/dm3 Ca (exchangeable); 1 cmolc/dm3 Al (exchangeable), 27.54 mg kg-1 of Cbm and 0.96 mg kg-1 Nbm. As well as other archaeological sites with TPA, Jacarequara and the Jabuti had significantly higher levels of nutrients compared to surrounding areas, with the exception of Ca element in Jabuti. In the sites, carbonaceous particles were investigated, showing no intrinsic results pyrogenic carbon. In areas of TPA, the results obtained from the soil analysis indicated positive correlation between the microbial biomass, organic matter and nutrients, which can be associated with better quality of the soil in these areas compared their ADJ, consistently with the data highlighted in the soil solutions. Comparing the two sites, the results indicate that the SOM in Jacarequara site shows more stable constituents.
Acesso aberto (Open Access)
O mar epicontinental Itaituba na região central da Bacia do Amazonas: paleoambiente e correlação com os eventos paleoclimáticos e paleoceanográficos do carbonífero
(Universidade Federal do Pará, 2019-03-14) SILVA, Pedro Augusto Santos da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Carboniferous paleogeography of the West Gondwana was dominated by epicontinental seas connected with the Panthalassa Ocean to the west. 50m-thick Pennsylvanian mixed siliciclastic-carbonate transgressive succession of the Amazonas Basin, Northern Brazil, were studied in outcrops and cores using facies and stratigraphic analysis in combination with O- and C-isotopic stratigraphy. Thirty-four facies, representative of coastal to shelf depositional systems grouped in three facies associations (FA): FA1) coastal desertic deposits, consisting of fine to medium-grained sandstone, mudstone and fine-grained dolostone that corresponds to a complex association of aeolian dunes, sand sheets, interdunes, fluvial channels and lagoon deposits bioturbated by Palaeophycus, Lockeia, Thalassinoides and Rosselia trace fossils; FA2) mixed tidal flat setting, constituted by fine to medium-grained sandstone, mudstone, shale, siltstone, lime mudstone and fine dolostone interpreted as supratidal, tidal channel, tidal delta and lagoon deposits with some brachiopod and echinoderm body fossils; and FA3) carbonate shelf deposits, consisting of lime mudstone, wackestone, packstone and grainstone with allochems (ooids and peloids), terrigenous grains and abundant and diversified open shallow marine benthic organisms, including, fish remains, foraminifers, brachiopods, echinoderms, gastropods, bryozoans, trilobites, corals, ostracodes, and conodonts, interpreted as bioclastic bars and carbonate shelf deposits. The conodonts species Neognathodus symmetricus, Streptognathodus sp. and Ellisonia sp. in the FA3 indicate the Baskirian-Moscovian age. The dolomitization affected the limestone and sandstone of AF1 and AF2 replacing the micritic matrix and occur as saddle dolomite indicating mixed of meteoric and marine waters and late burial. The neomorphism of opaque micritic matrix and bivalve shells are indicated by the growing of xenotopic mosaic of calcite crystals. In contrast, the secondary calcite cement is equant, fiber, bladed and espatic. Micritization is found in the bioclast shells exhibiting micritic coatings. The autigenesis of quartz and biogenic pyrite is commonly found in FA2 and FA3. The mechanic and chemical compaction in limestone caused the porosity reduction, cementation, fractures and development of dissolution seams and stylolite. The sandstones were cemented by quartz, calcite and iron hydroxides/oxides and show concave-convex and sutured contacts between quartz grains. The predominance of eodiagenetic and subordinate mesodiagenetic features in the Monte Alegre-Itaituba succession indicated less modified framework by the diagenesis corroborating the pristine signature of δ13C values ranging from ~ -2 to ~+5.28‰. This enriched trend upsection coadunate with high organic productivity triggered by massive flourishment of euphotic-controlled benthic organisms mainly in the FA3. Five types of shallowing upward asymmetric cycles characterize the Monte Alegre-Itaituba succession. Peritidal cycles in coastal desertic (Cycle I) were formed by alternance of dolostone and sandstone with δ13C values ranging from -1.5 to +0.3‰. Cycles II consist in interbedded of sandstone-mudstone and sandstone-mudstone-floatstone rhythmites and the Cycle III constitute dolostone interbedded with sandstone. These cycles II and III were interpreted as tidal flat and lagoon deposits with δ13C values ranging from +3,98%₀ to +4, 62%₀. The Cycle IV is a rhythmite formed by wackestones/mudstones couplets while the Cycle V consists of alternance of grainstones, wackestones and lime mudstone (ABC cyclicity) passing upsection for cycles composed by wackestones and lime mudstone (AB cyclicity). The cycles IV and V are shelf deposits with δ13C values ranging from +3,65%₀ a +5,28%₀. The stacking of 53 cycles with average thickness of 1,1 m, combined with Fisher plot diagram, indicated an aggradational to retrogradational stacking pattern inserted in the lowstand to early transgressive system tract (Cycles I-III) and late transgressive system tract (Cycles IV and V). The succession was deposited in ~13 Ma and individual cycles accumulated in an approximately 0.25 my typical of fourth order cycles related to high-frequency fluctuations of relative sea level. These data were correlated to the global δ13C and sea-level curves that positioned the Monte Alegre-Itaituba succession in the Late Serpukhovian to Early Moscovian age. The influence of Late Misssipian glaciation was negligible in these deposits but the post-glacial transgression combined with slow subsidence of the Amazonas basin caused the generation of allogenic cycles I, IV and V. The cycles II and III were formed by autochthonous processes during a period of equilibrium between supply and glacioeustasy. The Monte Alegre-Itaituba succession is the record of a large Amazonia epicontinental sea that was directly connected with the Panthalassa Ocean during Pennsylvanian.
Acesso aberto (Open Access)
Paleoambiente e isótopos de C e O da capa carbonática de Tangará da Serra (MT), margem Sul do Cráton Amazônico.
(Universidade Federal do Pará, 2012-12-03) SOARES, Joelson Lima; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; 8867836268820998
The paleoclimatic and paleoceanographic conditions during the formation of Neoproterozoic post-glacial carbonates have been intensely debated in the last decades. During the end of the Proterozoic, these conditions influenced the biological evolution of the planet, which was punctuated with global glacial events extensive to the low latitudes. The post-glacial geological record comprises carbonate layers with diagnostic structures overlying glacial diamictites. These cap carbonate were intensely studied in cratons worldwide, using geochemical, sedimentological, petrographical and isotopical (C and O) analysis. Similar studies were carried out in newly discovered 50 m thick cap carbonate in the Southern Amazon Craton, in the regions of Tangará da Serra and Mirassol d’Oeste, 200 km away from each other and comparable to the other cap carbonate occurrences around the world. The Tangará da Serra cap carbonate includes two lithostratigraphic units belonging to the Araras Group: the Mirassol d’Oeste Formation characterized by microcrystalline dolomites overlaid by interbedded limestones and shales of the Guia Formation. The peloidal dolograinstones and pink dolomudstones/dolopackstones of the Mirassol d’Oeste display even parallel and quasi-planar lamination with low-angle truncation, often truncated by tubestone and changing vertically into symmetric megaripple bedding with wavy corrugated and internal asymmetric laminations interpreted as deposits of shallow to moderately deep platform influenced by wave. The Guia Formation comprises marls and fine grained limestones with megaripple bedding, sandy limestones with asymmetric wavy laminations interbedded with dark mudstones with hydrocarbon interpreted to have formed in moderately deep mixed platform dominated by current and wave deposits. Upwards in the Guia Formation were observed fine grained, terrigenous-rich limestones interbedded with laminated shales forming tabular layers, tens of meters long with ripple marks, crystal fans (calcite after aragonite pseudomorphs), neptunian dykes, slump structures, convolutions, faults and intraformational breccias (clasts of limestones and dolomites). These features were interpreted as related to CaCO3 supersaturated, deep water platform deposits. δ13C values are depleted (-8‰) at the contact between the Mirassol d’Oeste and Guia formations relatively to the other parts of the succession (5‰ in dolomites and limestones). The isotopic ratios at the base of the Guia Formation can be affected by dolomitization and neomorfism processes. Petrography data indicates that: 1) diagenetic alteration was stronger in limestones than in dolomites, also supported by C (-6‰ a -5‰) and O (-6‰ a -4‰) isotopic rations; 2) the good preservation of depositional features, including lamination, porosity and macropeloids is indicative of primary origin for the dolomite in the Mirasson d’Oeste Formation; 3) The source of Mg and the mechanism of dolomite precipitation were the seawater and the action of sulphatereducing bacteria; 4) hydrocarbons are scarce in the low permeability dolomitic limestones compared to the upper portions of the sequence. Shales and limestones of the Guia Formation were the source rocks of the hydrocarbons. Five successive deformational events of synsedimentary nature were recognized in the two occurrences of Neoproterozoic cap carbonate: 1) large to small-scale load cast structures in the contact zone between the dolostones and glaciogene sediments; 2) tubestones crosscutting stromatolitic lamination; 3) generation of vertical to subvertical fractures and faults and large-scale syncline and anticlines with subordinated chevron folds; 4) vertical to subvertical fractures and faults infilled with conglomerate and breccia, forming neptunian dykes enclosed by undeformed beds; and 5) formation of slump and sliding deposits in the top of the cap limestone. The event layers 1, 2 and 5 are genetically related to the depositional environment, whilst the preferred orientation of the deformational structures in the event layers 3 and 4 are compatible with regional scale tectonics that produced seismically active extensional structures where earthquakes triggered the deformation of sediments associated with fault slip and large scale mass movement. Slump deposits were formed by gravity flows along a ramp, caused by high productivity carbonate. The cap carbonate exposed in the Tangará da Serra region registers a ramp platform environment with a steep slope at the edge of the platform (distally steepened ramp) eventually disturbed by seismic shocks.
Acesso aberto (Open Access)
Paleoambiente e paleoclima da Formação Pedra de Fogo da Bacia do Parnaíba e sua correlação com os eventos globais de silicificação.
(Universidade Federal do Pará, 2019-09-02) ANDRADE, Luiz Saturnino de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Pedra de Fogo Formation of the Parnaíba Basin, Northern Brasil is a sedimentary unit that has one of the most important sedimentary records of the early Permian (Cisuralian), characterized mainly by intense silicification. Although previous works have contributed to the understanding of its paleoenvironment, important gaps regarding the sedimentary and paleoclimatic conditions that favored the great concentration and preservation of silica, due to the global changes occurred at the beginning and along of the Permian, still remain inconclusive. Problems as to which sources of silica contributed most to the expressive chert content were never satisfactorily explained. There is no reference to the organic and/or inorganic origins, nor is little known about the conditions and processes that led to the preservation of silica deposits and concretions, as well as the genesis of the known occurrence of carbonates. In order to fill these gaps and/or contribute to a better understanding of the depositional processes in the Pedra de Fogo Formation. This study made facies and stratigraphic analysis, and petrography, complemented by cathodoluminescence image, XRD and SEM-EDS analysis of the permian deposits exposed in the east and southeast portions of the Parnaíba Basin. The main sedimentary facies were grouped into facies associations representative of braided fluvial-aeolian systems from the top Piauí Formation (Carboniferous). This deposits are overlain by lacustrine-sabkha system, wave-dominated nearshore-lacustrine and ephemeral streamsdeposits of the Permian Pedra de Fogo Formation. In general, this unit was deposited in an arid, endorheic lacustrine system, often affected by storm regimes and fed by unconfined flows. Although the arid climate was predominant, this system keeps seasonally, relatively high levels of moisture sufficient to maintain and proliferate its thriving taphoflora, formed mainly by Ferns and Gymnosperms tree. This flora colonized the lakeshore, both in relatively wet and dry periods, as a way to compensate for the low humidity in macroenvironmental. Cyclic variations between the records of organosedimentary structures (microbial mats and stratiform stromatolites) and gymnosperm stem in life position were interpreted as the recurrent migration of the lacustrine shoreline, in response to the expansion and contraction phases of these lakes, triggered by climatic seasonality in the southwestern portion of Pangea. Probably, the flora of the Pedra de Fogo Formation was an important catalyst for the expressive silicification that characterizes this predominantly syndepositional / eodiagenetic unit. This silicification is formed largely by microquartz, under conditions of supersaturation in silica, high enough to preserve the delicate cyanobacteria filaments, as well as pinnules ferns and gymnosperm stems in life position. The occlusion of fractures and dissolution voids (secondary pores), by mosaic megaquartz mosaic, chalcedony spherulites and two generations of chalcedonic overlays, in addition to large crystals (mm) in coarse mosaic calcspar are indicative of polycyclic silicification and circulation of carbonate fluids to mesogenetic zones. The presence of gridwork microtexture indicates that the genesis of silicification is similar to the Magadi chert-type (Rift Valley of Kenya), but from distinct sources, given the absence of volcanic sources associated with Pedra de Fogo deposits.
Acesso aberto (Open Access)
Paleoambiente e quimioestratigrafia da porção superior do Grupo Araras, neoproterozoico da faixa Paraguai Norte, estado do Mato Grosso.
(Universidade Federal do Pará, 2015-06-22) RUDNITZKI, Isaac Daniel; ADER, Magali; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; 8867836268820998
In the central portion of the South-America Platform occurs the carbonate succession of the Araras Group, that register an extensive carbonate platforms of the Neoproterozoic, developed along a passive margin at S-SW portion of the Amazon Craton. These sedimentary basins were submitted to a compressional collisional event at Ediacaran-Cambrian transition, resulting in the origin of the Paraguay Belt. While the lower Araras Group are recognized as a post-glacial record of the Marinoan event (~635 Ma), the final paleoceanographic and sedimentary events that led the end of carbonate deposition are discussed, for the first time, in this thesis. The upper Araras Group, represented by Serra do Quilombo and Nobres formations, are the last stage of Araras carbonate platform sedimentation. These units are covered by siliciclastic deposits of Alto Paraguay Group, Middle Ediacaran, which the basal deposits are related to the glacial Gaskiers event (~580 Ma), reported only on the eastern portion of the Belt. Stratigraphy, sedimentology and carbon isotope studies were performed on carbonate rocks exposition in Cáceres and Nobres regions, respectively the western and eastern portion of the belt, Mato Grosso state, Brazil. The Serra do Quilombo and Nobres formations are a unique carbonate ramp in a homoclinal system composed by: i) deep ramp with massive thin dolostone of offshore. ii) Middle ramp with massive thin dolostone, intraclastic and sandy dolostone with hummocky and swaley cross stratification, planar and wave lamination, oncolitic dolostone with wavy bedding and massive oolitic dolostone, from shoreface, oolitic bar complex, and foreshore/shallow subtidal zones; and iii) inner ramp comprising in massive thin dolostone, intraclastic dolostone and dolomitic sandstone with megaripple bedding, microbialites, chert, evaporite molds, laminated sandstone mudstone, deposited in tidal flats. These deposits were developed during highstand conditions after the Marinoan transgressive event , and preceding the implantation of siliciclastic platform from Alto Paraguay Group during the Ediacaran-Cambrian transition. The palinomorphs assemblages from Nobres Formation are represented by spheroidal forms, such as Leiospharidia, rare filamentous and acanthomorphous acritarchs represented mostly by Tanarium correlated to biozone ECAP (Ediacaran Complex Acantomorph Palynoflora) that suggest an age between 600-550 Ma. The High frequency stratigraphy appoint to orbital force as the principal mechanism responsible to accommodation space generation and peritidal cycles composition, and secondarily influenced by tectonic. The patters of carbon isotopes from carbonate (δ13Ccarb), organic matter (δ13Corg) and the coupling of carbon isotope composition (Δ13Ccarb-org = δ13Ccarb - δ13Corg) associated with low TOC suggests an oxidant ocean in equilibrium with atmosphere, with minimal redox variation on sediment/water interface, that includes: i) anoxic layer with δ13Ccarb around ~0‰ and δ13Corg <-28‰, restrict to the distal zone of deep ramp with early organic diagenesis conduct by chemosynthetic organism; ii) oxic layer with δ13Ccarb around ~0‰ and δ13Corg between -28 a -25‰ in open sea system of deep and middle ramp, with primary photosynthetic activities; iii) oxic layer with low pCO2 associates to positives signal of δ13Ccarb (+3‰) and δ13Corg (>-25‰) in shallow middle ramp associated with high ration of inorganic carbonate precipitation; and iv) oxic layer restrict features by negative δ13Ccarb (-2‰) and δ13Corg between -31 to -25‰, exclusive to inner ramp, related to primary photosynthetic production and effective organic early diagenesis drive by sea level changes. These data define the upper Araras Group as the record of a carbonate ramp with restrict coastal environments, on an oxidant ocean, tropical zones with warm waters, high evaporation rate and photosynthetic biomass, during the Middle Ediacaran. The pre-glacial influence indicated by carbon cycles anomalies or glacioeustasy they were not documented to the upper Araras Group. The final sedimentation stage of Araras carbonate platform was influenced by initial continental uplift source areas responsible for the siliciclastic input on carbonate coastal zone, preceding a progradation of continental-coast systems from Alto Paraguay Group at Middle Ediacaran.
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O Pensilvaniano da Bacia do Parnaíba, norte do Brasil: implicações paleoambientais, paleogeográficas e evolutivas para o Gondwana Ocidental
(Universidade Federal do Pará, 2019-02-21) MEDEIROS, Renato Sol Paiva de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The end of the Paleozoic Age was marked by landmasses tectonic movements that were forming the supercontinent Gondwana, which stretched mainly in the southern hemisphere, surrounded by the Panthalassa oceans to the west and Tetis to the east. During the Carboniferous period, there were several cycles of climatic variations in the earth's history, evidenced in glaciogenic icehouse and greenhouse carbonate deposits, both in the paleocontinent Gondwana and in Laurasia. These global cycles of eustatic variation were recorded in the epicontinental seas, as they represent the thawing phase and eustatic level increase in a greenhouse period, which together with a favorable paleogeography form extensive marine transgressions over the continental blocks, with cyclic stacking patterns, called cyclothems (eg., terrestrial; terrestrialmarine mixed; marine and restricted marine / evaporitic pattern). Records of these events in northern Brazil are found in the intracratonic basins, particularly in the Balsas Group of Parnaíba Basin, where the exhibits allow us to assess the Pennsylvanian sedimentary history. The sedimentary succession studied belongs to the Piauí Formation Upper Member, described among the cities of José de Freitas, União, Miguel Alves and Lagoa Alegre, and exhibits richly fossiliferous carbonate deposits overlapped by thick pelitic packages and progradant clinoforms. Seventeen sedimentary facies were grouped into four facies associations (FA), representative of a shallow carbonate platform, adjacent to a coastal dune field, later replaced by lacustrine-delta deposits. The FA 1- coastal dune field/interdune comprises well selected, intensely bioturbed, fine to medium sandstones with plane-parallel stratification, tabular crossbedding and climbing translatent lamination. The shallow-sea deposits FA 2 consists of a succession of fossiliferous carbonate rocks, laterally continuous for hundreds of meters, interspersed with bituminous shale. These carbonates were dolomitized and have negative δ13Ccarb values covariate with positive values of δ18Ocarb, suggesting that the supersaturated fluid volume was sufficient to change not only δ18O but also δ13C. The FA 3- suspension lobes/mouth bar and FA 4- lacustre prodelta consist respectively of sigmoidal cross-stratification and planeparallel stratification sandstones and intercalated fine sandstones and pelites. The thick politic layers of prodelta in contact with FA 2 feature quartz grains with morphology texture of windorigin sediments, with textures such as bulbous and smooth edges, upturned plates, irregular depressions, and percussion marks. Subarea exposure surfaces in carbonate marked by shrinkage cracks and dissolution features indicate the end of carbonate sedimentation (eg., Marine Sequence - Highstand System Tract) with the Pennsylvanian Sea Retreat and Confinement in an extensive lacustrine system. (eg., Continental Sequence – High Accommodation System Tract) in the central portion of Gondwana. The FA 4 mineral clay assembly confirms the aridest climatic pattern to the top of the studied succession, presenting mainly smectites and illite. This marine retraction was concomitant with the Appalachian orogeny (300 Ma) that caused the uplift in western Gondwana and definitively disconnected the Itaituba-Piaui epeiric sea from the Panthalassa ocean to the west. Restricted seas or lakes were progressively beset by prograding hipopycnal flows with the establishment of the most extreme arid conditions triggered during Pennsylvanian.
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Planos de sistemas aqüíferos como fundamento legal para a gestão de recursos hídricos
(Universidade Federal do Pará, 2010-07-14) GUTIERREZ, Lucy Anne Cardoso Lobão; ABREU, Francisco de Assis Matos de; http://lattes.cnpq.br/9626349043103626; 9626349043103626
The evaluation of self supply conditions in RMB, especially in 25 districts, which present consolidated and available information, bespoke the need of improving the management of groundwater resources in the state. In order to achieve that, the elaboration of the Water Systems Plans as a legal fundament for the management of water resources in the State of Pará, especially in RMB. The information and data gathered showed that the public water supply system presents some deficit, mostly due to absence of the public water supply network in many areas; inefficiency or absence of plans to extend this network; need of improvement and adequacy for the existing network; low availability of goods acquisition to the general improvement of the system; the high index of loss verified; and so on. Because of this the number of users has increased, particularly in the residential sector, which uses the tubular wells for self supply, almost ever completed in the water systems Pós-Barreiras and Barreiras. This scenario is observed, mainly in the districts having the most of buildings, such as Nazaré, Reduto, Umarizal and São Braz, which respectively present (62,9%), (49,2%), (31,8%), and (33,3%) of the residential economies provided by private wells for self supply. These aquifers demonstrate moderate to high vulnerability, whereas the available data of their water quality reveal high nitrate indexes probably caused by almost entire absence of sewage collection and treatment systems. A survey and an analysis about federal and state laws which are relevant to the water resources were also made for planning the model, observing that this law is much more advanced for superficial water. The settlement of future scenarios, from the methodology described by Michel Goodet, brought the linkage between management and planning of superficial and ground water, in view of the fact that in the national model, the territory for the management of the water is the drainage basin. To allow that planning groundwater does not occur in a disintegrated way in the scope of drainage basins nor is totally attached to the start of superficial water management, a model of groundwater planning and management is proposed to the State of Pará. According to this model, the aquifer systems planning could be done through Aquifer Systems Plans, under the responsibility and coordination of the State. To the definition of elaboration and approval of these Plans, it is suggested the creation of Aquifer Systems Committees to be coordinated by the organ of the State for Water Resources, which will incorporate the imperative participation of users, representatives of the counties that are surrounded by overlying drainage basins to these aquifer systems, as well as the civil society organized, a new paradigm of operation for a contemporaneous society.
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Reconstituição Paleoambiental e Potencial Petrolífero da Sucessão Siliciclástica-Carbonática Permiana da Bacia do Paraná
(Universidade Federal do Pará, 2022-02-15) BRITO, Ailton da Silva; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Permian age was marked by extreme paleogeographic and paleoclimatic changes with predominances of arid conditions across the globe as a consequence of the eustatic sea-level fall from the end of the Carboniferous glaciation to the beginning of the Permian. The final phases of continental agglutination of the Pangea supercontinent caused uplifts accompanied by successive regressions of the epicontinental seas, culminating with the installation of desert systems at the end of the Permian. During the marine regressive phase, Western Pangea was the depositional site of a 50m thick mixed siliciclastic-carbonatic succession under restricted and shallow paleoenvironmental conditions, widely distributed in the Paraná Basin, SE of South America. The studied succession includes the top of the Palermo, Irati, and the base of the Serra Alta Formation, comprising a total of 120 m-thick. The Irati succession is essentially composed of dolomite intercalated with organic matter gray to black shale rich, which is considered an important source rock for hydrocarbons. This unit covers the heterolithic deposits from the Palermo Formation and is overlaid by shales from the Serra Alta Formation. The high content and good quality of organic matter present in Irati shales aroused economic interest since the 19th century. Although many works have contributed to the knowledge of the depositional paleoenvironment and generating potential of this unit, mainly from organic geochemical data, gaps remain regarding the paleoenvironmental understanding, previously interpreted as restricted sea or lacustrine. This research was carried out from 125 drill cores distributed in the center-north, center-south, and extreme south of the basin, provided by the company Irati Petróleo LTDA. complemented by outcrops from the northern region. Twenty-three drill cores were selected for sedimentological and stratigraphic study from facies/microfacies analyses, aided by XRD, SEM-EDS, and cathodoluminescence images. Total organic carbon (TOC), Rock-Eval pyrolysis, and biomarker analysis were performed on 102 cores. The integration of data allowed: the lateral correlation of the Irati Formation for more than 2,000 km in the SSW-NNE direction of the basin; the paleoenvironmental reconstitution; and lateral and vertical characterization of the generating potential. Twenty-one facies/microfacies were identified and organized into about 300 siliciclastic-carbonate couplet that are grouped into 59 high-frequency cycles representative of mid-outer ramp and offshore environments dominated by distal turbidity systems. The succession consists of four third-order sequences (S1, S2, S3, and S4). Sequence boundaries are type 2, with no evidence of subaerial erosion, marked by overlapping transgressive offshore deposits. Transgressive Systems Tracts are succeeded by Highstand Systems Tracts defined by the appearance of dolomite levels with a thickening upwards tendency, which indicates high carbonate productivity under normal to hypersaline conditions, evidenced by the presence of gammaceran, halite crystals. and pseudomorphs of gypsum. The transgressive deposits of sequences S3 and S4 (Assistance Member) form the two intervals (oil-shale) with the greatest generating potential in the Paraná Basin. Oil-shale S3 has the highest values of organic carbon and generating potential. The highest TOC peaks were 19.40% for the extreme south region, 22.23% for the center north, and 27.12% for the center-south of the basin. Kerogen predominates types I and II, which also presents an increased contribution, mainly from type I converging to the center-south. Oil-shale S4 presents lower TOC values for the extreme south region (8.82%), south-central (21.7%), and north-central (14.61%). The kerogen type is similar to oil-shale S3, it predominates type II, with a high contribution of type I in the south-central region and smaller proportions of type III. The organic matter of the Irati Formation is predominantly immature, however, occurrences of maximum pyrolysis temperature (Tmax) equal to or greater than 440 ºC in samples close to diabase sills show that there was localized maturation of organic matter, which corroborates the occurrence of a non-conventional petroleum system for mixed deposits of black shales (generators) - carbonates (reservoirs) of the Irati Formation. Regarding the quantity and quality of the source rock present in the Irati Formation, the center-south portion presents the highest values of organic carbon as well as the potential for hydrocarbon generation. The analysis of the stacking patterns associated with the previous ages of SHRIMP U-Pb from volcanic ash allowed the correlation of the succession with the global sea-level curve, allowing to estimate an age of 8.0 Ma for the Irati Sea and of 2 .7 Ma for 3rd order depositional sequences. Likewise, ages of 26.6 ka were calculated for the carbonate-siliciclastic couplets, 135.5 ka and 400 ka for the high-frequency cycles, whose origin is here attributed to the climatic cyclicity induced by the terrestrial orbital oscillation, compatible with the Milankovitch cyclicity. The characterization of the cycles based on faciological and organic geochemical data also demonstrates a strong climate control in the generation of intervals rich in organic matter.
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Sedimentação siliciclástica e proveniência do grupo Alto Paraguai (neoproterozóico-cambriano), borda Sul do Cráton Amazônico e faixa Paraguai Norte, estado do Mato Grosso.
(Universidade Federal do Pará, 2011-09-02) SILVA JÚNIOR, José Bandeira Cavalcante da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; 8867836268820998
The Neoproterozoic-Cambrian Alto Paraguai Group exposed in the southern Amazon Craton and the northern Paraguay Belt, western-central Brazil, represents a 2,400m thick siliciclastic succession that succeed the carbonate platform sedimentation deposited after the last Cryogenian glaciation (635 Ma). The Alto Paraguai Group consists of Raizama (fine to coarse grained sandstones, conglomerates, mudstones, pebbly mudstones and secondary chert), Sepotuba (dolomites, stromatolites, mudstones and fine to medium grained sandstones) and Diamantino (mudstones and fine to medium grained sandstones) formations. Outcropbased facies and stratigraphic analysis in combination with provenance studies using detrital zircon U-Pb dating, allowed understanding the lithostratigraphy and the depositional history of the Alto Paraguai Basin. The depositional model include the progradation of a fluvialwave-tide- and storm-dominated coastal region (upper member of the Raizama Formation) onto a shallow to moderately deep storm-influenced marine platform, locally influenced by debris flow (lower member of the Raizama Formation). Afterwards, the last transgressive event in the Paraguai Basin generated tidal flat-sabkha setting in the shallower portions of the basin to the west (lower member of the Sepotuba Formation) and a storm-dominated marine platform in the central and eastern portion of the basin (upper member of the Sepotuba Formation). The progression of the Pan-African-Brasilian orogenesis resulted in the confinement of the Sepotuba Sea as a foredeep sub-basin, against the edge of the Amazon Craton. These restricted lake/sea was filled with turbidites deposits (lower member of Diamantino Formation), lacustrine sediments (middle member of the Diamantino Formation) and progradational deltaic front deposits (upper member of the Diamantino Formation). This sedimentation was supplied by source areas of 600 to 500 Ma, located in the southeast and east of the basin, related to the Brasilia Belt and the Paraguay orogen. This stage represents the final amalgamation of Western Gondwana, marked by the closure of the Neoproterozoic Clymene Ocean between the Amazon Craton and Central Gondwana, generating the northern Paraguay Belt.
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O sistema fluvial Solimões-Amazonas durante o Quaternário
(Universidade Federal do Pará, 2012-09-03) GONZÁLEZ ROZO, José Max; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; 8867836268820998
The Amazon River has been considered as having a predominantly anastomosing pattern with increasing stability from upstream to downstream. Meandering and even straight patterns have been recognized in the upper Amazon as well as meandering reaches identified in the Solimões River in Brazil. Additionally, meandering features in the form of scroll bars and oxbow lakes have been also identified in different anastomosing reaches of the Amazon. Theses meandering features have been considered rare or absent in anastomosing rivers. In this context, it is clear that the Amazon, with its meandering features, is different from many other anastomosing rivers that have laterally stable, non-meandering channels. The limited information on the Amazon River provided mainly by remote sensing data and the lack of field data make difficult to understand the characteristics of this fluvial system, to establish a clear relationship between the meandering and anastomosing features and also to determine to what extend in time and space the anastomosing pattern is developed. The lack of information increases respect to the channel pattern characteristics of the Amazon River prior to present-day conditions. Channel pattern features during Pleistocene have been scarcely described, with a few studies that suggest a main single-channel meandering pattern during that time. In contrast, a broad discussion about the origin of the Amazon River as a transcontinental eastward flow has been developed in recent years with no agreement on the exact time this event took place and very scarce sedimentologic data on the deposits of central Amazonia. To our knowledge, no research has yet been undertaken to understand: 1) the origin of the Amazon’s anastomosing pattern and the development of its meandering features; 2) the behavior of the upper reaches of the Amazon, and specifically whether this reaches develop only meandering features, or whether they share the characteristic main anastomosing pattern with meandering secondary channels of the Amazon River in Brazil; 3) the characteristics of the Amazon River during Pleistocene and whether the river was different from the present-day pattern. To reach these goals, the current channel pattern of the Amazon River was studied between Manaus and the mouth of the Madeira River. Sedimentary processes were studied using field data, channel changes were analyzed trough a temporal analysis using remote sensing data, morphology was studied and optically stimulated luminescence (OSL) dates were obtained. The river in this area was found to be anastomosing with extensively distributed scroll bars. These scroll bars are mainly formed by sinuous secondary channels and related to subrecent and present-day migration. Avulsion, midchannel bar formation and chute cut-offs are the formative mechanisms of anastomosis in this system. The main anastomosing pattern and the meandering secondary channels have coexisted at least since 7.5 ± 0.85 ka. A reach of the Colombian Amazon River (upper Amazon River) was studied to more precisely define differences with the middle Amazon River with respect to channel pattern, and also to identify the triggers for its channel pattern development. Channel changes were analyzed trough a temporal analysis using remote sensing data, morphology studied and discharge data was analyzed over three different periods. The river in this area was found to be a multichannel meandering pattern that corresponds to a laterally active anabranching river. Mid-channel bar formation and chute cutoffs are the formative mechanisms of the multichannel pattern in this system. Variations in discharge seem to be responsible for the deposition and erosion dynamics found from remote sensing analysis. To determine for how long the current channel pattern of the Amazon River has existed, and to understand the paleogeographic conditions prior to the Holocene, Pleistocene deposition was studied. Pleistocene deposition (Iça Formation) is very restricted between the upper and the middle reaches of the Amazon River, with the Coari area having the best outcrops. Sedimentary processes were studied using field data, clay and heavy minerals analyzed and optically stimulated luminescence (OSL) dates were obtained. A mainly meandering system was found in this area, developing at least since 133.8± 20.9 ka. This system seems to be characterized as a multichannel meandering pattern similar to present-day conditions of the Colombian Amazon River.