Numerical simulation of drainage reversal of the Amazon River during\ud Andean orogeny

The uplift of Central and Northern Andes occurred concomitantly with an important reorganization of the drainage\ud pattern in Northern South America. During the Early Miocene, the fluvial systems that flowed from the Amazonian\ud Craton toward the sub-Andean basins and northward to the Caribbean were replaced by a megawetland, the Pebas\ud system, covering a large fraction of the Western Amazonia. In the Late Miocene the Pebas system progressively\ud disappeared and gave place to the transcontinental Amazon River, connecting the Andes and the equatorial Atlantic\ud margin. A previous work suggested that the reversal of the Amazon River and the disappearance of the Pebas\ud system were driven by dynamic topography promoted by mantle convection. Based on numerical models that\ud couple surface processes, flexural isostasy and crustal thickening due to orogeny, here I propose that the response\ud of the surface processes to the uplift of the Central and Northern Andes, along with the flexural isostasy of the\ud lithosphere, can explain the drainage reversal of the Amazon River during the Miocene without invoking dynamic\ud topography induced by mantle convection. In addition I observed that the existence, the permanence and the size of a megawetland in Northern South America is controlled by the rate of crustal thickening in the orogeny, the rate of\ud erosion and, mainly, the efficiency of the sediment transport through the drainage basins during the Andean upliftTrabalho publicado no periódico Geophysical Research Abstracts, Strasbourg, v. 16, EGU2014-11524, 201

Pirmspārņemšanas audita noteicošie faktori pārrobežu uzņēmumu pārņemšanas gadījumos: promocijas darbs

Pārrobežu pārņemšanai ir svarīga loma uzņēmumu stratēģiskajā attīstībā un starptautiskās darbības paplašināšanā. Promocijas darbā pētīti pirmspārņemšanas fāzē veicamā pirmspārņemšanas audita noteicošie faktori, to klāsts, izvirzītā hipotēze - pirmspārņemšanas fāzes kompleksais pirmspārņemšanas audits ir saistīts ar pārņemšanas panākumiem. Rezultāti atbalsta pieņēmumu, ka veiksmīgas pārņemšanas pirmspārņemšanas audita noteicošie faktori ir stratēģiskā partnera izvēle, uzņēmējdarbības potenciāls, cilvēkresursu zināšanas, finanšu faktori un pārņemšanas maksa, galvenā atziņa ir, ka uzņēmējdarbības potenciāls un cilvēkresursu zināšanas ir galvenie aktīvi, lai pārņemšanas fāzē varētu realizēt sinerģijas vērtības. Atslēgas vārdi: pirmspārņemšanas audits, informācijas asimetrija, organizāciju mācīšanās, apvienošana, pārņemšana, riska novērtējumusCross - border acquisitions play an important role in the corporate strategic development and international expansion. During the past decades, mergers and acquisitions were intensively researched through the lens of strategic management, corporate finance, behavioral finance etc. Despite the intense effort, the made progress is still fragmented and lacks unifying theories that approaches the whole acquisition process on the one side, and indepth research of critical factors on the other side. The dissertation topic intends to establish vital link between research and practice, deeply exploring infor mation asymmetry and role of exploratory learning in the pre - acquisition phase of cross - border acquisition. This thesis investigates the critical factors – and the scope of the due diligence, which is carried out in the pre - acquisition phase. Pre - acquisition due diligence theoretically conforms to the organizational learning theory, proposing that the more the acquiring firm learns about the acquisition target, the higher the probability of successful acquisition. The central hypothesis of the comprehensive model states that due diligence in the pre - acquisition phase is necessary for acquisition success. The empirical evidence is data sample of acquisitions made in the automotive manufacturing firms and their cross - border acquisitions in the European automot ive industry . The main results support the proposition that Choice of Strategic Partner, Business Capabilities and HR Knowledge and Financial Factors and Acquisition Premium are critical factors of due diligence needed for acquisition success. The main eff ort lies in pinpointing the specific area by which the business capabilities and knowledge transfer build the main asset in the realization of synergy values in the acquisition phase. In this context, the valuation of the business capabilities of the acqui sition targets is classified as the main challenge reflecting suitability of the acquisition price and establishing value generation from the combined firms in the post - acquisition phase. By studying acquisition risk and critical factors – both success and failure reasons – this research has tested and partially approved a theoretically sound assessment framework that can pre - determine the success or failure of planned acquisition efforts. From a practical standpoint, the research results provide acquisition management with proven method of performing the pre - acquisition evaluation of potential acquisition candidates. Such a reference offers critical factors evidence for firms with acquisition needs. Key words: due diligence, information asymmetry, organizational learning , risk assessment , mergers, acquisitions, cross - border acquisition

Climate changes and the formation of fluvial terraces in central Amazonia inferred from landscape evolution modeling

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

The influence of rifting on escarpment migration on high elevation passive continental margins

Using numerical models that couple surface processes, flexural isostasy, faulting and the thermal effects of rifting, we show that fault-bounded escarpments created at rift flanks by mechanical unloading and flexural rebound have little potential to "survive" as retreating escarpments if the lower crust under the rift flank is substantially stretched. In this configuration, a drainage divide that persists through time appears landward of the initial escarpment in a position close to a secondary bulge that is created during the rifting event at a distance that depends on the flexural rigidity of the upper crust. Moreover, the migration of the escarpment to the secondary bulge occurs when the pre-rift topography dips landward, otherwise the evolution of the escarpment is guided by the pre-existing inland drainage divide. To illustrate this new mechanism for the evolution of passive margins, we study the examples of Southeastern Australia and Southeastern Brazil. We propose that a pre-existing inland drainage divide with rift related flank uplift can produce the double drainage divide observed in Southeastern Australia. On the other hand, we conclude that it is possible that the Serra do Mar escarpments on the Southeastern Brazilian margin originated as a secondary flexural bulge during rifting that persisted through time. In both cases, the retreating escarpment scenario is unlikely and the present-day margin morphology can be explained as resulting from rift-related vertical motions alone, without requiring significant post-rift "rejuvenation".FAPESP [2006/06881-5, 2009/50493-8

Andean Tectonics and Mantle Dynamics as a Pervasive Influence on Amazonian Ecosystem

The Amazonian landscape evolution is the result of the combined effect of Andean tectonism, climate and the Earth’s interior dynamics. To reconstruct the landscape evolution and its influence on paleoenvironmental variations within Amazonia since the Oligocene, we conducted numerical experiments that incorporate different surface and geodynamic processes, reproducing many paleogeographic features as inferred from the sedimentary record. We show that the evolution of the drainage pattern gradually reduced the area of sedimentation derived from the Guiana and Brazilian shields while expanded the Andean derived deposits during the Miocene, affecting the nutrient availability. First order biotic habitats were inferred from these paleogeographical reconstructions, showing an eastward expansion of várzea and terra firme forests and consequent retraction of igapó forests, with a millennial-scale reconfiguration of a mosaic of habitats in the lowlands. We conclude that this dynamism probably guided the observed patterns of speciation in the most biodiverse biome on Earth. © 2019, The Author(s)

Spatial and temporal uplift history of South America from calibrated drainage analysis

A multidisciplinary approach is used to analyze the Cenozoic uplift history of South America. Residual depth anomalies of oceanic crust abutting this continent help to determine the pattern of present-day dynamic topography. Admittance analysis and crustal thickness measurements indicate that the elastic thickness of the Borborema and Altiplano regions is ≤₁₀ km with evidence for sub-plate support at longer wavelengths. A drainage inventory of 1827 river profiles is assembled and used to investigate landscape development. Linear inverse modeling enables river profiles to be fitted as a function of the spatial and temporal history of regional uplift. Erosional parameters are calibrated using observations from the Borborema Plateau and tested against continent-wide stratigraphic and thermochronologic constraints. Our results predict that two phases of regional uplift of the Altiplano plateau occurred in Neogene times. Regional uplift of the southern Patagonian Andes also appears to have occurred in Early Miocene times. The consistency between observed and predicted histories for the Borborema, Altiplano, and Patagonian plateaux implies that drainage networks record coherent signals that are amenable to simple modeling strategies. Finally, the predicted pattern of incision across the Amazon catchment constrains solid sedimentary flux at the Foz do Amazonas. Observed and calculated flux estimates match, suggesting that erosion and deposition were triggered by regional Andean uplift during Miocene times

Conceptual and empirical advances in Neotropical biodiversity research

The unparalleled biodiversity found in the American tropics (the Neotropics) has attracted the attention of naturalists for centuries. Despite major advances in recent years in our understanding of the origin and diversification of many Neotropical taxa and biotic regions, many questions remain to be answered. Additional biological and geological data are still needed, as well as methodological advances that are capable of bridging these research fields. In this review, aimed primarily at advanced students and early-career scientists, we introduce the concept of "trans-disciplinary biogeography," which refers to the integration of data from multiple areas of research in biology (e.g., community ecology, phylogeography, systematics, historical biogeography) and Earth and the physical sciences (e.g., geology, climatology, palaeontology), as a means to reconstruct the giant puzzle of Neotropical biodiversity and evolution in space and time. We caution against extrapolating results derived from the study of one or a few taxa to convey general scenarios of Neotropical evolution and landscape formation. We urge more coordination and integration of data and ideas among disciplines, transcending their traditional boundaries, as a basis for advancing tomorrow\u27s ground-breaking research. Our review highlights the great opportunities for studying the Neotropical biota to understand the evolution of life

Joint numerical modeling of sedimentary and tectonic processes in sedimentary basins

O principal objetivo deste trabalho é prever a evolução de margens divergentes desde o início da extensão litosférica, levando-se em consideração a interação entre processos superficiais e tectônicos. Para isto, foi desenvolvido um modelo numérico que acopla isostasia flexural, efeitos térmicos, estiramento litosférico e processos superficiais. A isostasia flexural é simulada através de uma placa elástica fina sobre um fluido invíscido, representando o comportamento flexural da litosfera flutuando sobre a astenosfera. Durante a simulação, a estrutura térmica da litosfera evolui como um resultado da advecção e difusão do calor no interior da Terra. Considera-se que o estiramento da litosfera é acomodado por falhas planas na crosta superior e deformação dúctil na crosta inferior e manto. O modelo de processos superficiais descreve como a paisagem é erodida e como os sedimentos são transportados e depositados nas bacias sedimentares. Através desse modelo numérico, é mostrado que o estiramento litosférico tem uma profunda influência na evolução da migração de escarpas em margens divergentes. Os resultados sugerem que escarpas limitadas por falhas criadas em flancos de rifts por descarregamento mecânico e resposta flexural têm pouca chance de \"sobreviver\" através de recuo erosivo se a crosta inferior sob o flanco do rift foi substancialmente estirada. Nessa configuração, o divisor de drenagem que persiste através do tempo é criado em direção ao continente em uma posição que depende da rigidez flexural da crosta superior. Esse cenário ocorre quando a topografia pré-rift mergulha para o continente, caso contrário a evolução da escarpa é guiada pelo divisor de águas interior pré-existente. Esses conceitos são aplicados no estudo das margens do sudeste da Australia e do sudeste do Brasil, onde o cenário de retração de escarpas através de recuo erosivo mostrou-se improvável. O mesmo modelo numérico foi utilizado para estudar como a passagem de uma anomalia térmica sob a litosfera pode afetar a evolução pós-rift de bacias sedimentares em margens divergentes. Os resultados numéricos mostram que a velocidade da litosfera em relação à anomalia térmica e a rigidez flexural da litosfera oceânica e continental afetam a evolução de bacias sedimentares devido ao soerguimento da superfície relacionado com a expansão térmica da litosfera. Como exemplo, é estudada a possível influência de uma anomalia térmica (Pluma de Trindade?) na evolução das bacias de Campos e Espírito Santo, na margem sudeste brasileira.The purpose of this work is to predict the evolution of divergent margins since the onset of lithospheric extension, taking into account the interaction between surface and tectonic processes. For this, a numerical model was developed to study the coupling of flexural isostasy, thermal effects, stretching of the lithosphere and surface processes. The flexural isostasy is simulated through a thin elastic plate overlying an inviscid fluid, representing the flexural behavior of the lithosphere floating on the asthenosphere. During the simulation, the thermal structure of the lithosphere evolves as a result of advection and diffusion of heat in the Earths interior. The stretching of the lithosphere is assumed to be accommodated by planar faults in the upper crust and ductile flow in the lower crust and mantle. The surface processes model describes how the landscape is eroded and how the sediments are transported and deposited in the sedimentary basins. The results from this numerical model show that the amount of lithospheric stretching has a profound influence on the evolution of escarpment migration in divergent margins. These results suggest that fault-bounded escarpments created at rift flanks by mechanical unloading and flexural rebound have little potential to survive as retreating escarpments if the lower crust under the rift flank is substantially stretched. In this configuration, a drainage divide that persists through time is created landward in a position that depends on the flexural rigidity of the upper crust. This scenario occurs when the pre-rift topography dips landward, otherwise the evolution of the escarpment is guided by the pre-existing inland drainage divide. These concepts are applied to study the margins of Southeastern Australia and Southeastern Brazil, where the retreating escarpment scenario showed to be unlikely. The same numerical model is used to study how the passage of a thermal anomaly under the lithosphere can affect the post-rift evolution of sedimentary basins in divergent margins. The numerical results show that the velocity of the lithosphere relative to the thermal anomaly and the flexural rigidity of the continental and oceanic lithospheres affect the evolution of sedimentary basins due to surface uplift related to thermal expansion of the lithosphere. As an example, the model is applied to assess the possible influence of a thermal anomaly (Trindade Plume?) on the evolution of the Campos and Esp rito Santo Basins, in Southeastern Brazilian margin

Joint numerical modeling of sedimentary and tectonic processes in sedimentary basins

O principal objetivo deste trabalho é prever a evolução de margens divergentes desde o início da extensão litosférica, levando-se em consideração a interação entre processos superficiais e tectônicos. Para isto, foi desenvolvido um modelo numérico que acopla isostasia flexural, efeitos térmicos, estiramento litosférico e processos superficiais. A isostasia flexural é simulada através de uma placa elástica fina sobre um fluido invíscido, representando o comportamento flexural da litosfera flutuando sobre a astenosfera. Durante a simulação, a estrutura térmica da litosfera evolui como um resultado da advecção e difusão do calor no interior da Terra. Considera-se que o estiramento da litosfera é acomodado por falhas planas na crosta superior e deformação dúctil na crosta inferior e manto. O modelo de processos superficiais descreve como a paisagem é erodida e como os sedimentos são transportados e depositados nas bacias sedimentares. Através desse modelo numérico, é mostrado que o estiramento litosférico tem uma profunda influência na evolução da migração de escarpas em margens divergentes. Os resultados sugerem que escarpas limitadas por falhas criadas em flancos de rifts por descarregamento mecânico e resposta flexural têm pouca chance de \"sobreviver\" através de recuo erosivo se a crosta inferior sob o flanco do rift foi substancialmente estirada. Nessa configuração, o divisor de drenagem que persiste através do tempo é criado em direção ao continente em uma posição que depende da rigidez flexural da crosta superior. Esse cenário ocorre quando a topografia pré-rift mergulha para o continente, caso contrário a evolução da escarpa é guiada pelo divisor de águas interior pré-existente. Esses conceitos são aplicados no estudo das margens do sudeste da Australia e do sudeste do Brasil, onde o cenário de retração de escarpas através de recuo erosivo mostrou-se improvável. O mesmo modelo numérico foi utilizado para estudar como a passagem de uma anomalia térmica sob a litosfera pode afetar a evolução pós-rift de bacias sedimentares em margens divergentes. Os resultados numéricos mostram que a velocidade da litosfera em relação à anomalia térmica e a rigidez flexural da litosfera oceânica e continental afetam a evolução de bacias sedimentares devido ao soerguimento da superfície relacionado com a expansão térmica da litosfera. Como exemplo, é estudada a possível influência de uma anomalia térmica (Pluma de Trindade?) na evolução das bacias de Campos e Espírito Santo, na margem sudeste brasileira.The purpose of this work is to predict the evolution of divergent margins since the onset of lithospheric extension, taking into account the interaction between surface and tectonic processes. For this, a numerical model was developed to study the coupling of flexural isostasy, thermal effects, stretching of the lithosphere and surface processes. The flexural isostasy is simulated through a thin elastic plate overlying an inviscid fluid, representing the flexural behavior of the lithosphere floating on the asthenosphere. During the simulation, the thermal structure of the lithosphere evolves as a result of advection and diffusion of heat in the Earths interior. The stretching of the lithosphere is assumed to be accommodated by planar faults in the upper crust and ductile flow in the lower crust and mantle. The surface processes model describes how the landscape is eroded and how the sediments are transported and deposited in the sedimentary basins. The results from this numerical model show that the amount of lithospheric stretching has a profound influence on the evolution of escarpment migration in divergent margins. These results suggest that fault-bounded escarpments created at rift flanks by mechanical unloading and flexural rebound have little potential to survive as retreating escarpments if the lower crust under the rift flank is substantially stretched. In this configuration, a drainage divide that persists through time is created landward in a position that depends on the flexural rigidity of the upper crust. This scenario occurs when the pre-rift topography dips landward, otherwise the evolution of the escarpment is guided by the pre-existing inland drainage divide. These concepts are applied to study the margins of Southeastern Australia and Southeastern Brazil, where the retreating escarpment scenario showed to be unlikely. The same numerical model is used to study how the passage of a thermal anomaly under the lithosphere can affect the post-rift evolution of sedimentary basins in divergent margins. The numerical results show that the velocity of the lithosphere relative to the thermal anomaly and the flexural rigidity of the continental and oceanic lithospheres affect the evolution of sedimentary basins due to surface uplift related to thermal expansion of the lithosphere. As an example, the model is applied to assess the possible influence of a thermal anomaly (Trindade Plume?) on the evolution of the Campos and Esp rito Santo Basins, in Southeastern Brazilian margin

Reappraisal of the effective elastic thickness for the sub-Andes using 3-D finite element flexural modelling, gravity and geological constraints

P>Estimates of effective elastic thickness (T(e)) for the western portion of the South American Plate using, independently, forward flexural modelling and coherence analysis, suggest different thermomechanical properties for the same continental lithosphere. We present a review of these T(e) estimates and carry out a critical reappraisal using a common methodology of 3-D finite element method to solve a differential equation for the bending of a thin elastic plate. The finite element flexural model incorporates lateral variations of T(e) and the Andes topography as the load. Three T(e) maps for the entire Andes were analysed: Stewart & Watts (1997), Tassara et al. (2007) and Perez-Gussinye et al. (2007). The predicted flexural deformation obtained for each T(e) map was compared with the depth to the base of the foreland basin sequence. Likewise, the gravity effect of flexurally induced crust-mantle deformation was compared with the observed Bouguer gravity. T(e) estimates using forward flexural modelling by Stewart & Watts (1997) better predict the geological and gravity data for most of the Andean system, particularly in the Central Andes, where T(e) ranges from greater than 70 km in the sub-Andes to less than 15 km under the Andes Cordillera. The misfit between the calculated and observed foreland basin subsidence and the gravity anomaly for the Maranon basin in Peru and the Bermejo basin in Argentina, regardless of the assumed T(e) map, may be due to a dynamic topography component associated with the shallow subduction of the Nazca Plate beneath the Andes at these latitudes.ANPFAPESP[06/01211-1]CNPq[300736/2005-3