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Climate changes have been considered an essential factor controlling the shaping of the recent alluvial landscapes in central Amazonia, with implications for explaining the biogeographic patterns in the region. This landscape is characterized by wide floodplains and various terrace levels at different elevations. A set of older terraces with ages between 50 and >200 ka occupy the higher portions of central Amazonia, whereas multiple terraces next to floodplains occur at lower elevations and display ages of a few thousand years. These lower terraces, referred to as middle–lower terraces, reveal what can be perceived as a stochastic pattern both in space and time. Despite the widespread occurrence of these geomorphic features, no process-oriented analysis has been conducted to explain their formation. Here, we develop a landscape evolution model referred to as SPASE (Sedimentary Processes and Alluvial Systems Evolution) to explicitly account for fluvial erosion and deposition in combination with lateral channel migration to explore the controls on terrace development. The model results show that the higher terraces were deposited under the condition of a higher base level for the basins upstream of the confluence between the Solimões and Negro rivers. The subsequent decrease in the base level initiated a phase of gradual incision, thereby resulting in the current fluvial configuration. The model also predicts that high-frequency climate changes resulted in the construction of middle–lower terraces at various elevations which, however, are all situated at lower elevation than the higher terrace levels. Our model shows that dry-to-wet shifts in climate, in relation to the modern situation, yield a landscape architecture where middle–lower terrace levels are better preserved than wet-to-dry changes in climate, again if the current situation is considered as reference. Finally, our results show that fast and widespread landscape changes possibly occurred in response to high-frequency climate changes in central Amazonia, at least since the Late Pleistocene, with great implications for the distribution and connectivity of different biotic environments in the region. Because of this short timescale of response to external perturbations, we suggest that the streams in central Amazonia possibly also respond in rapid and sensitive ways to human perturbations.

Made available in DSpace on 2022-04-28T19:47:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-12-01 Global Neoproterozoic glaciations are related to extreme environmental changes and the reprise of iron formation in the rock record. However, the lack of narrow age constraints on Cryogenian successions bearing iron-formation deposits prevents correlation and understanding of these deposits on a global scale. Our new multiproxy data reveal a long Cryogenian record for the Jacadigo Group (Urucum District, Brazil) spanning the Sturtian and Marinoan ice ages. Deposition of the basal sequence of the Urucum Formation was influenced by Sturtian continental glaciation and was followed by a transgressive interglacial record of >600 m of carbonates that terminates in a glacioeustatic unconformity. Overlying this, there are up to 500 m of shale and sandstone interpreted as coeval to global Marinoan glacial advance. Glacial outwash delta deposits at the top of the formation correlate with diamictite-filled pa-leovalleys and are covered by massive Fe and Mn deposits of the Santa Cruz Formation and local carbonate. This second transgression is related to Marinoan deglaciation. Detrital zircon provenance supports glaciostatic control on Cryogenian sedimentary yield at the margins of the Amazon craton. These findings reveal the sedimentary response to two marked events of glacioeustatic incision and transgression, culminating in massive banded iron deposition during the Marinoan cryochron. Faculdade de Tecnologia Universidade de Campinas Departamento de Geología Universidade Federal de Ouro Preto Instituto de Geociências Instituto de Astronomía Geofísica e Ciências Atmosféricas Universidade de São Paulo Departamento de Geologia Universidade Estadual Paulista Departamento de Geologia Universidade Estadual Paulista

Made available in DSpace on 2021-06-25T10:57:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Although virtual outcrops or digital outcrop model applications in geological studies are becoming increasingly common, virtually no attention has been given to acquisition of palaeocurrent data from cross-strata. Palaeocurrent indicators are abundant in the sedimentary record, mainly as cross-strata, and present compelling implications for basin analysis, plate tectonics and palaeoenvironmental reconstructions, as well as for sediment transport systems. Palaeocurrents from cross-strata also comprise a quantifiable parameter in sedimentary successions that can be used in quantitative modelling of depositional architecture with implications for reservoir characterization through outcrop analogue studies. A common obstacle in obtaining large cross-strata orientation datasets is the limited access to steep and high outcrop faces, as well as financial and time restrictions on field work. To overcome these issues, the simplest workflow for drone-based acquisition, photogrammetric processing and analysis of virtual outcrops aiming at the attainment of palaeocurrent data from cross-strata is appraised here. The results show that orientations of cross-beds measured on virtual outcrops, with and without ground control points, and using two different levels of resolution downsampling, are comparable to field measurements using analogue and electronic devices. Time and financial resources can thus be saved by using the straightforward method presented here to supplement palaeocurrent mapping across wide areas and distinct stratigraphic intervals. Geology Lab School of Technology University of Campinas, Rua Paschoal Marmo, 1888, Jardim Nova Itália Institute of Geosciences University of São Paulo, Rua do Lago, 562, Cidade Universitária Institute of Marine Science São Paulo Federal University, Rua Carvalho de Mendonça, 144, Encruzilhada Departamento de Geologia (DGEOL) / Programa de Pós-graduação em Geociências e Análise de Bacias Universidade Federal de Sergipe, Marechal Rondon Ave., Geology Bldg., Multi-user Complex, Rosa Elze Departamento de Geologia Aplicada Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista/UNESP, Avenida 24-A, Bela Vista, 178 Departamento de Geologia Aplicada Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista/UNESP, Avenida 24-A, Bela Vista, 178

High-resolution seismic surveys have been successfully applied in the study of active sedimentary environments in shallow submerged settings, particularly improving the interpretation of sedimentary facies and architectural elements that characterize fluvial rock records. Nevertheless, specific data processing workflows to emphasize sedimentary structures have not been proposed or tested, so that interpretation currently relies on the subjective opinion of individual interpreters, which might lead to biased conclusions. Aiming at the construction of a less biased data processing workflow, we developed a software that analyzes seismic data and performs standardized interpretation by linking individual seismic traces to generate interpreted reflector lines. A dataset acquired with boomer continuous seismic profiler in the sedimentary bed of the Amazonas river in Brazil was processed with a typical sequence of filter and gain (using Seismic UNIX software), as well as a routine of trace interpolation written in GNU Octave. The application of the Standardized Interpreter at different stages of processing enabled the comparison of the resulting interpretation scenarios in terms of the representation of geometries related to internal sedimentary structures, thus leading to the proposition of a workflow adapted to the specific needs of sedimentary structure interpretation from seismic data.

Palinspastic reconstructions suggest that the late Proterozoic–Cambrian Brasiliano/Pan-African orogenic belt in southeast Brazil and west Congo terminated northwards into an embayment within the São Francisco-Congo cratonic unit. The orogenic shortening that created the Araçuaí-West Congo orogen in this embayment has been explained by tightening of the horseshoe-shaped São Francisco-Congo craton in a fashion referred to as “nutcracker tectonics”. We show that this model is incompatible with the general orogenic evolution proposed in recent literature, which involves (1) ∼50 m.y. of subduction of oceanic crust and associated arc formation, followed by (2) collisional orogeny and crustal thickening. Quantitative considerations show that the original nutcracker model is too rigid to explain even the second, crustal thickening part, let alone any long pre-collisional history. To soften the model, we suggest that the so-called São Francisco – Congo bridge was broken by a ∼150 km wide orogenic corridor along the current African Atlantic margin. This corridor adds sufficient mobility to the system to explain the orogenic thickening of the crust to 60–65 km. However, even with this additional softening the confined nature of this orogen is incompatible with prolonged arc development. We therefore suggest that oceanic crust was nonexistent or very limited in the Macaúbas basin, and reject the widely published model involving ∼50 m.y. of subduction of oceanic crust and related arc development. Instead, we find strong support for a hot intracontinental orogen model in the currently available P-T, geochronologic, petrographic and structural data. In this model, extensive melting and flow of the middle crust is likely to have caused spreading of the upper crust in an orogenic setting that was created by collisions along the N, W and S margins of the São Francisco craton from ∼630 Ma. acceptedVersion

A Sub-bacia Camaquã Oriental compreende exposições da borda leste da Bacia do Camaquã, como o Vale do Piquiri, pertencentes ao Grupo Santa Bárbara (Ediacarano). Estudos estratigráficos de fácies, sistemas deposicionais, proveniência e paleocorrentes conduziram à subdivisão do Grupo Santa Bárbara na Sub-bacia Camaquã Oriental em duas unidades: (i) Formação Passo da Capela, formada por turbiditos de leques subaquosos; e (ii) Formação Rincão dos Mouras, constituída por arenitos e conglomerados de leques aluviais e sistemas fluviais entrelaçados. Este artigo propõe formular um modelo de evolução de altos estruturais durante o preenchimento de uma bacia rifte. Conglomerados de leques subaquosos da Formação Passo da Capela apresentam composição do arcabouço derivada da própria bacia (arenitos), indicando autofagia, além de rochas do embasamento (quartzitos, xistos, metarriolitos). Análises de paleocorrentes indicam dispersão dos sedimentos segundo NNE, compatível com litotipos do Complexo Porongos (quartzitos, metarriolitos, milonitos). A norte, análises de proveniência dos conglomerados indicam derivação principalmente do Sienito Piquiri, e também de outras litologias. Esse fato sugere que a proveniência reflete contribuição do embasamento adjacente (clastos do Sienito Piquiri), com pouco ou nenhum transporte. Conglomerados aluviais da Formação Rincão dos Mouras contam com proveniência diversificada. Na base ocorrem clastos metamórficos do Complexo Porongos (metarriolitos) e da própria bacia (arenitos). Análises de proveniência sugerem denudação do Complexo Porongos (altos de embasamento) e da bacia. A porção intermediária apresenta clastos de granitos róseos/muscovita leucogranitos correlacionáveis ao Batólito Pelotas, e litologias do Complexo Porongos. Sienitos e traquitos aparecem em pequena proporção, assim como arenitos. Análises de proveniência, aliadas às de paleocorrentes, indicam que áreas a leste estavam sendo soerguidas e erodidas, como Batólito Pelotas e Complexo Porongos, comportando-se como altos de embasamento fornecedores de sedimentos para a bacia. No topo predominam fragmentos do Complexo Porongos (mármores). Análises de paleocorrentes realizadas na Formação Rincão dos Mouras sugerem controle tectônico importante durante o preenchimento da unidade, com mudanças de fontes de detritos para a bacia e soerguimento de altos internos. As análises de proveniência levadas a efeito em todas as unidades (i) indicaram sempre fonte adjacente aos depósitos sedimentares; (ii) demonstraram as fontes de detritos; e (iii) auxiliaram na diferenciação entre as formações Passo da Capela e Rincão dos Mouras. A ocorrência na Formação Rincão dos Mouras de fragmentos de mármore e o aumento considerável da proporção de clastos do Granito Encruzilhada do Sul, situado a ENE da região do Vale do Piquiri, foi mais um dos critérios utilizados na separação das unidades, sobretudo quando conglomerados estratificados de ambas se acham contíguos.

The interpretation of large river deposits from the rock record is hampered by the scarcity of direct observations of active large river systems. That is particularly true for deep-channel environments, where tens of meters deep flows dominate. These conditions are extremely different from what is found in smaller systems, from which current facies models were derived. MBES and shallow seismic surveys in a selected area of the Upper Amazonas River in Northern Brazil revealed the presence of large compound barchanoid dunes along the channel thalweg. The dunes are characterized by V-shaped, concave-downstream crest lines and convex-up longitudinal profiles, hundreds of meters wide, up to 300 m in wavelength and several meters high. Based on the morphology of compound dunes, expected preserved sedimentary structures are broad, large-scale, low-angle, concave up and downstream cross-strata, passing laterally and downstream to inclined cosets. Examples of such structures from large river deposits in the rock record are described in the Silurian Serra Grande Group and the Cretaceous Sao Sebastiao and Marizal formations in Northeastern Brazil, as well as in Triassic Hawkesburry Sandstone in Southeastern Australia and the Plio–Pleistocene Ica Formation in the western Amazon. All these sedimentary structures are found near channel base surfaces and are somewhat coarser than the overlying fluvial deposits, favoring the interpretation of thalweg depositional settings. The recognition of large barchanoid dunes as bedforms restricted to river thalwegs and probably to large river systems brings the possibility of establishing new criteria for the interpretation of fluvial system scale in the rock record. Sedimentary structures compatible with the morphological characteristics of these bedforms seem to be relatively common in large river deposits, given their initial recognition in five different fluvial successions in Brazil and Australia, potentially enabling substantial improvements in facies models for large rivers.

One key factor for the advance in the study of fluvial deposits is the application of geophysical methods, being the Ground Penetrating Radar one of special value. Although applied to active rivers, the method is not extensively tested on the rock record, bearing interest for hydrocarbon reservoir analogue models. The São Sebastião and Marizal formations were the subject of previous studies, which made possible the comparison of Ground Penetrating Radar survey to previous stratigraphic studies in order to identify the best combination of resolution, penetration and antenna frequency for the studied subject. Eight radar facies were identified, being six of them related to fluvial sedimentary environments, one related to eolian sedimentary environment and one radar facies interpreted as coastal sedimentary environment. The Ground Penetrating Radar data showed compatibility to sedimentary structures in the outcrops, like planar and trough cross-stratified beds. It is noted that the obtained resolution was efficient in the identification of structures up to 0.3 m using a 100 MHz antenna. In this way, the Ground Penetrating Radar survey in outcrops bears great potential for further works on fluvial depositional architecture. RESUMO: Um fator-chave para o avanço no estudo de depósitos fluviais é a aplicação de métodos geofísicos, e o Radar de Penetração no Solo é um método de especial valor. Embora amplamente aplicado em ambientes de rios ativos, em ambientes fluviais consolidados esse tipo de estudo é mais escasso, em contrapartida há uma grande importância em mais estudos de modelos análogos de hidrocarboneto. Por essa motivação, o presente trabalho aplicou o Radar de Penetração no Solo em afloramentos já estudados estratigraficamente nas Formações São Sebastião e Marizal e comparou ambos os resultados, além de definir se a resolução, a penetração e a frequência da antena foram adequadas na área de estudo. Por meio dos resultados, é possível identificar oito radar fácies diferentes, dos quais seis estão relacionadas a ambientes fluviais, uma a ambiente eólico, e a última a ambiente costeiro. Observou-se que houve compatibilidade entre os refletores encontrados nas seções Radar de Penetração no Solo e as estruturas sedimentares observadas em afloramento, como conjuntos de estratos cruzados preenchidos por estruturas planares ou acanaladas. Nota-se que a resolução do método foi muito eficiente e identificou estruturas decimétricas de até 0,3 m com uma antena de 100 MHz, porém com menor penetração de sinal em comparação com trabalhos de rios ativos. Dessa forma, o Radar de Penetração no Solo mostrou-se de grande potencial para estudos futuros sobre a arquitetura deposicional das unidades investigadas.

This article presents the scientific rationale for an ambitious ICDP drilling project to continuously sample Late Cretaceous to modern sediment in four different sedimentary basins that transect the equatorial Amazon of Brazil, from the Andean foreland to the Atlantic Ocean. The goals of this project are to document the evolution of plant biodiversity in the Amazon forests and to relate biotic diversification to changes in the physical environment, including climate, tectonism, and the surface landscape. These goals require long sedimentary records from each of the major sedimentary basins across the heart of the Brazilian Amazon, which can only be obtained by drilling because of the scarcity of Cenozoic outcrops. The proposed drilling will provide the first long, nearly continuous regional records of the Cenozoic history of the forests, their plant diversity, and the associated changes in climate and environment. It also will address fundamental questions about landscape evolution, including the history of Andean uplift and erosion as recorded in Andean foreland basins and the development of west-to-east hydrologic continuity between the Andes, the Amazon lowlands, and the equatorial Atlantic. Because many modern rivers of the Amazon basin flow along the major axes of the old sedimentary basins, we plan to locate drill sites on the margin of large rivers and to access the targeted drill sites by navigation along these rivers.

In Eastern South America, a series of fault-bounded sedimentary basins that crop out from Southern Uruguay to Southeastern Brazil were formed after the main collisional deformation of the Brasiliano Orogeny and record the tectonic events that affected the region from the Middle Ediacaran onwards. We address the problem of discerning the basin-forming tectonics from the later deformational events through paleostress analysis of more than 600 fault-slip data, mainly from the Camaquã Basin (Southern Brazil), sorted by stratigraphic level and cross-cutting relationships of superposed striations, and integrated with available stratigraphic and geochronological data. Our results show that the Camaquã Basin was formed by at least two distinct extensional events, and that rapid paleostress changes took place in the region a few tens of million years after the major collision (c.a. 630 Ma), probably due to the interplay between local active extensional tectonics and the distal effects of the continued amalgamation of plates and terranes at the margins of the still-forming Gondwana Plate. Preliminary paleostress data from the Castro Basin and published data from the Itajaí Basin suggest that these events had a regional nature.No Leste da América do Sul, um conjunto de bacias sedimentares que afloram do sul do Uruguai ao sudeste do Brasil formou-se após os eventos colisionais da Orogenia Brasiliana, registrando os eventos tectônicos que afetaram a região a partir do Mesoediacarano. O problema da distinção entre a tectônica formadora das bacias e os eventos deformacionais posteriores é aqui abordado através da análise de paleotensões de mais de 600 dados de falhas com estrias, obtidos principalmente na Bacia Camaquã (Sul do Brasil), que foram classificados por nível estratigráfico e relações de corte entre estrias sobrepostas, e intergrados a dados estratigráficos e geocronológicos disponíveis. Nossos resultados revelam que a Bacia Camaquã teve origem em ao menos dois eventos distensivos, e que modificações rápidas no campos de tensões ocorreram na região alguns poucos milhões de anos após a colisão principal (c.a. 630 Ma), provavelmente em decorrência da interação entre esforços distensivos locais e os efeitos distais da contínua amalgamação de placas e terrenos nas margens da placa Gondwana, ainda em formação. Dados preliminares de paleotensões da Bacia de Castro e dados publicados da Bacia Itajaí sugerem que esses eventos tiveram um caráter regional.

This work presents a study of selected outcrops from the Pedra das Torrinhas Formation of the Guaritas Group (Cambrian, Camaquã Basin), near the basin bordering Encantadas Fault Zone. The studied succession includes alluvial fan deposits that pass laterally into eolian deposits. Sedimentary facies and architectural element analysis were performed, followed by sedimentary petrography and microscopic porosity analysis, aiming to characterize the porosity of the deposits and its spatial distribution. The main objective was to contribute to a better understanding of the porosity spatial distribution in depositional systems characterized by the interaction between alluvial and eolian processes, with special reference to deposits formed prior to the development of terrestrial plants. Porosity values are related to depositional processes, with higher porosities associated to eolian dune deposits (mean of 8.4%), and lower porosity related to interdunes (mean of 3.4%) and alluvial fans (mean of 4.3%). Architectural elements analysis revealed the spatial relationships of these deposits, a response to the interplay of the eolian and alluvial processes. The integration of porosity data reveals that the interaction of alluvial and eolian processes results in heterogeneous distribution of porosity at the facies association scale. Eolian reworking of alluvial facies increases porosity whereas sheet-flood and other alluvial processes in the interdune areas reduce porosity.O presente trabalho consiste no estudo de afloramentos da Formação Pedra das Torrinhas do Grupo Guaritas (Cambriano, Bacia Camaquã), próximo à Zona de Falha das Encantadas. As sucessões estudadas incluem depósitos de leques aluviais que passam lateralmente para depósitos eólicos. Foram realizadas análises de fácies e de elementos arquiteturais, seguidos de petrografia sedimentar e análise microscópica de porosidade, com o objetivo de caracterizar a porosidade da unidade e sua distribuição espacial. o principal objetivo foi contribuir para uma melhor compreensão da distribuição espacial de porosidade em sistemas deposicionais caracterizados pela interação aluvial-eólica, com atenção especial à sistemas deposicionais pré-vegetação. A porosidade é controlada principalmente pelos processos deposicionais, com os valores maiores associados a depósitos de dunas eólicas (média de 8,4%) e os menores a facies de interdunas (média de 3,4%) e de leques aluviais (média de 4,3%). A análise dos elementos arquiteturais mostra a relação espacial destes depósitos, provocada por interações entre sistemas deposicionais aluviais e eólicos. A integração de dados revela que a interação de processos aluviais e eólicos resultou em uma complexa heterogeneidades na escala de associação de facies. o retrabalhamento eólico de fácies aluviais provocou aumento de porosidade enquanto que a ocorrência de enchentes-em-lençol em áreas de interduna e o aporte de sedimentos aluviais em interdunas inundadas formaram corpos sedimentares com porosidade reduzida.

The study of the mechanisms which shape the central Amazonia alluvial landscapes in the long term is of great relevance for the reconstruction of the past drainage systems and biogeographical patterns in the region. Current conceptual models for the Quaternary are based on paleogeographic interpretations of the vast alluvial terrace systems found in the region and on the role of external forcings, such as climate change, eustatic variation and neotectonics. In that context, evaluating, from a quantitative perspective, the interactions between alluvial dynamics and those external controls is key to constraint the interpretation of the morphological elements and sedimentary deposits. Therefore, the aim of this dissertation is to present a new numerical model capable of quantitatively testing hypotheses and conceptual models concerning the evolution of the great alluvial plains in Central Amazonia during the Quaternary. The model operates at a spatial of 10 5 km 2 and a temporal scale of 10 5 years, and presents a novel approach to simulate the lateral erosion of channel banks, coupled with a conventional model of erosion and deposition of sediments on channel beds. Scenarios were tested which simulate the modern configuration of the region containing the Solimões river and its tributary Japurá River, but with altered rainfall rates, rates of lateral erosion, base-level variation, sediment input and subsidence of specific areas in the grid to simulate the development of grabens. The results reveal that lateral erosion in an essential mechanism not only for the formation of alluvial plains and widening of valleys but also for the shape of the river long profiles, thus significantly altering the landscape evolution. In-valley incisional and aggradational processes resulted from three different mechanisms: base-level variation, changes in rainfall rate and shifts in the trunk river position, which modified the local base level for the tributaries. In the case of in-valley aggradation due to base-level rise of a drop in the rainfall rate, the trunk river, with great sediment flux, is capable of infilling the new accommodation space. Smaller tributaries, on their turn, cannot respond to the elevation of the trunk river alluvial plain and develop ria lakes. An important effect recognized in the model is an increase in the rate of valley widening by lateral erosion during deposition and aggradation, since the augmented avulsion rates at that stage result in a higher probability of valley margin erosion. The graben formation scenario reveals that when these tectonic features occur in the trunk river valley, they are rapidly filled and their margins are reworked by erosion, thus leaving no evidence of their presence in the landscape surface. Grabens developed on higher terraces, on the other hand, result in preserved morphological elements. As a whole, these results reveal processes and relations that have not been considered in current conceptual models, while enabling quantitative testing of the hypotheses concerning the paleogeography and the role of external forcings in the evolution of large alluvial plains. O estudo dos mecanismos que, a longo prazo, moldam a paisagem aluvial na Amazônia Central é de grande relevância para a reconstrução da evolução dos sistemas de drenagem e dos padrões biogeográficos dessa região. Modelos conceituais vigentes para o Quaternário baseiam-se em interpretações paleogeográficas dos amplos sistemas de terraços aluviais encontrados na região e na atuação de controles externos como mudanças climáticas, variações eustáticas e neotectônica. Nesse contexto, a avaliação quantitativa da interação entre a dinâmica aluvial e tais controles externos é necessária para uma interpretação mais consistente dos elementos morfológicos e depósitos sedimentares. Assim, o objetivo deste trabalho é apresentar um novo modelo numérico que é capaz de testar quantitativamente hipóteses e modelos conceituais sobre a evolução das grandes planícies aluviais da Amazônia Central no Quaternário. Esse modelo, que trabalha em uma escala espacial de 10 5 km 2 e em uma escala temporal de 10 5 anos, apresenta uma nova abordagem simplificada, capaz reproduzir a erosão lateral de bancos por canais, acoplada a um modelo de erosão de fundo de canal, deposição e transporte de sedimentos. Foram testados cenários que simulam a situação atual da região do Rio Solimões e seu afluente Juruá, com diferentes condições de taxas pluviométricas, taxas de erosão lateral, variações no nível de base, aporte externo de sedimentos e subsidência em áreas específicas para simular a formação de grabens. Os resultados mostraram que a erosão lateral é um mecanismo essencial não apenas para a formação de planícies de inundação e abertura de vales, mas também para a determinação dos perfis longitudinais de equilíbrio dos rios, alterando significativamente a evolução da paisagem. Processos de incisão e agradação em vales resultaram de três diferentes mecanismos: variações do nível de base, alterações na precipitação pluviométrica e modificações na posição do rio tronco, alterando o nível de base local de tributários. No caso da agradação sedimentar nos vales por subida do nível de base ou redução da precipitação, o rio tronco, devido ao seu alto fluxo sedimentar, é capaz de preencher o novo espaço de acomodação enquanto que pequenos tributários não conseguem responder rapidamente a elevação do rio tronco e formam rias fluviais. Um importante efeito reconhecido no modelo é o aumento da taxa de alargamento de vales por erosão lateral durante a agradação, já que taxas aumentadas de avulsão resultam em maior probabilidade de erosão das margens dos vales. O cenário com formação de grabens mostrou que quando estes ocorrem dentro dos vales do rio tronco são rapidamente preenchidos e suas margens retrabalhadas por erosão, não deixando evidências se sua existência na superfície, já quando ocorrem nos terraços têm suas formas preservadas. O conjunto destes resultados revelam processos e inter relações não consideradas nos modelos conceituais vigentes e permitem testes quantitativos de hipóteses sobre a paleogeografia e o papel de controles externos na evolução de grandes planícies aluviais.