Márcio de Morisson Valeriano

Palaeodrainage on Marajó Island, northern Brazil, in relation to Holocene relative sea-level dynamics

A large area in northeastern Marajó Island, northern Brazil, has been characterized geomorphologically, applying information acquired from Landsat imagery. This study was combined with detailed sedimentologic analysis of continuous cores, which provided a record of depositional settings developed in this area through the Holocene. The results revealed well-preserved, meandering to anastomosed drainage networks of wide palaeochannels that were superimposed by a narrower palaeochannel system. In both cases, the sedimentary record consists of sands, heterolithic deposits and muds, locally rich in plant debris. The strata are organized into fining upward successions that reach approximately 18 m thick in the wide channels and 4 m thick in the narrow channels. Sedimentary features suggestive of a coastal location for the wider palaeochannels and reworking of sediments by tidal currents include the prevalence of well to moderately sorted, rounded to sub-rounded, fine- to medium-grained sands displaying foreset packages separated by mud couplets, suggestive of tidal cycles. The data presented herein point to a rise in relative sea level reaching the Lake Arari area during the early to late/mid Holocene. This event was followed by a relative sea level drop. Tectonics seem to have contributed to an overall lowering in relative sea level in the study area since the mid-Holocene, which does not follow the same pattern recorded in other areas along the northern Brazilian coast.

Curvatura vertical de vertentes em microbacias pela análise de modelos digitais de elevação

Este trabalho objetiva desenvolver e avaliar um procedimento simples para mapear a curvatura vertical de vertentes, a partir de Modelos Digitais de Elevacao (MDE) com recursos basicos de Sistemas de Informacao Geografica (SIG). Este metodo se baseia em janelas moveis de 3x3 pixels e foi desenvolvido para fazer o calculo geometrico da segunda derivada atraves do perfil de vertente. Os testes envolveram MDE de seis microbacias de diferentes tipos de relevo, krigados a partir de curvas de nivel de diferentes especificacoes cartograficas. Para a programacao de procedimentos universalmente adaptaveis, o calculo de curvatura demandou a resolucao espacial como uma das entradas, de modo a resultar em valores absolutos comparaveis, com diferenca de declividade (em porcentagem) por distância horizontal (100 m) como unidade. A sobreposicao dos resultados de derivacao, calculada nas direcoes dos oito pixels vizinhos em cada posicao da janela, foi coordenada em octantes, pela classe de orientacao das vertentes. Guiada por interpretacao visual, a colocacao de limites de formas conhecidas de relevo subsidiou o estabelecimento de limiares arbitrarios de curvatura para a classificacao dos perfis de vertentes (concavo, convexo e retilineo).

Applying SRTM digital elevation model to unravel Quaternary drainage in forested areas of Northeastern Amazonia

There has been an increasing number of articles stressing the advantage of applying remote sensing products of synthetic aperture radar (SAR) and interferometric synthetic aperture radar (InSAR) for rapidly enhancing the volume of geological data in Amazonian areas, where forest cover is dense and high, clouds are abundant and accessibility is limited. The majority of these studies has emphasized geomorphology as a tool for both discussing tectonic reactivations during the Cenozoic and reconstructing Quaternary paleolandscapes. This work applies Digital Elevation Model (DEM) derived from the Shuttle Radar Topography Mission (SRTM) for delineating past morphological features under dense rainforest in an Amazonian lowland area. Previous use of this tool in southwestern Marajo Island (northern Brazil) helped to delineate, with exceptional precision, a paleochannel network hidden under the rainforest, which would be barely detected with other available remote sensing products. Fieldwork revealed that these paleochannels are related to palimpsest drainage systems developed mostly during the last 40,000 ^1^4C yrB.P. Measured altitudes acquired during topographic surveys attested that paleochannel areas are slightly higher than adjacent floodplains. This fact determined the successful application of SRTM-DEM for mapping paleochannels in Marajo Island. Integration of SRTM data with sedimentological information collected during fieldwork suggests paleoflows derived from continental areas located to south of the study area. This paleodrainage was active when the island was still connected to mainland. With island detachment due to reactivation of tectonic faults, the channels became abandoned and were progressively forested. The results obtained in the present study indicate that SRTM-DEM has high potential for unraveling similar morphological features from many other Amazonian areas with low topography and a dense forest cover.

An abandoned estuary within Marajó Island: Implications for late Quaternary paleogeography of northern Brazil

Several previous studies have recognized paleochannels as the most typical geomorphologic features imprinted in the modern landscape of Marajó Island, northern Brazil. A characterization of these paleochannels by detailed mapping has not yet been accomplished, despite their great potential for helping reconstructing the succession of events responsible for the origin and evolution of the drainage system at the mouth of the Amazon River during the Quaternary. The present study aims to provide a detailed mapping and characterization of these paleochannels using remote sensing (i.e., SRTM, Landsat 5-TM, and Landsat 7-ETM+), integrated with sedimentological and radiocarbon data obtained from outcrops and cores. The mapped paleochannels allowed for the first time correlation of the channel-like morphologies with fining-upward sedimentary successions, typical of channel deposits. The study focuses on the Lake Arari area located in the northeast of Marajó Island, where a complex fluvial network dominated by a funnel-shaped structure attributed to a Late Pleistocene paleoestuarine system was recognized. The inner estuary was connected to three fluvial channels that ran from the east-southeast throughout an area currently occupied by Marajó Bay, implying that this bay did not exist when the estuarine system was active. Separation of the eastern side of Marajó Island due to tectonic causes related to capture of Tocantins River by northeastward-orientated faults would have interrupted the fluvial inflow, ultimately causing the abandonment of the estuarine system. Today, the central part of the funnel-shaped structure related to the Late Pleistocene paleoestuary is occupied by Lake Arari, where sediments started to accumulate no earlier than the mid-Holocene. It is proposed that this lake might have developed from the Late Pleistocene estuary as the fluvial inflow was cut off during the detachment of Marajó Island. Marajó Island serves as an example of a very dynamic site of changing landscapes throughout the Quaternary as a result of tectonic activity.

Contribution to the stratigraphy of the onshore Paraíba Basin, Brazil

Several publications have contributed to improve the stratigraphy of the Paraiba Basin in northeastern Brazil. However, the characterization and distribution of sedimentary units in onshore areas of this basin are still incomplete, despite their significance for reconstructing the tectono-sedimentary evolution of the South American passive margin. This work provides new information to differentiate among lithologically similar strata, otherwise entirely unrelated in time. This approach included morphological, sedimentological and stratigraphic descriptions based on surface and sub-surface data integrated with remote sensing, optically stimulated luminescence dating, U+Th/He dating of weathered goethite, and heavy mineral analysis. Based on this study, it was possible to show that Cretaceous units are constrained to the eastern part of the onshore Paraiba Basin. Except for a few outcrops of carbonatic rocks nearby the modern coastline, deposits of this age are not exposed to the surface in the study area. Instead, the sedimentary cover throughout the basin is constituted by mineralogically and chronologically distinctive deposits, inserted in the Barreiras Formation and mostly in the Post-Barreiras Sediments, of early/middle Miocene and Late Pleistocene-Holocene ages, respectively. The data presented in this work support tectonic deformation as a factor of great relevance to the distribution of the sedimentary units of the Paraiba Basin.

Variáveis geomorfométricas locais e sua relação com a vegetação da região do interflúvio Madeira-Purus (AM-RO)

The objective of this work was to assess the potential of geomorphometric variables, derived from SRTM (Shuttle Radar Topographic Mission) data, to help identify vegetation types in the Amazonian Madeira-Purus interfluvio region. A RADAMBRASIL project vegetation map was used as a reference and the geomorphometric variables (elevation, slope, aspect and profile and plan curvatures) were compared to the mapped units. Analyses indicated vegetation types easily discriminated, depending on the topographic position. The variables of elevation, slope and aspect were the most important for their high discrimination power of the vegetation types. Although geomorphometric data are recognized as having strong potential for characterizing vegetation, this was not shown in the results, due to the mismatching of variability scales between the two sources of data; large units tend to exhibit similar distribution patterns of geomorphometry, and comprise classes with different responses for geomorphometric constraints. Discriminant analyses of geomorphometric variables permitted vegetation mapping up to the sub-physiognomy levels.

Mapeamento da declividade em microbacias com Sistemas de Informação Geográfica

The objective of this study was to establish optimal procedures for the calculation of watershed slope using Geographical Information Systems (GIS). The tests evaluated the geoprocessing methods according to regression analyses with a cartoghaphically hand-measured data set. Statistical and geostatistical analyses showed the high variability of slope values, turning cartographic generalization techniques inadequate. Field measured slopes showed low agreement with cartographic and GIS estimated values. It was concluded that slope angle calculations require high resolution of the Digital Terrain Model (DTM), interpolated through kriging. Smoothing the DTM decreased the slope determination accuracy, while increased correlation when applied to the slope image itself. Adjustment factors were calculated for different conditions of resolution and smoothing tested. The estimate errors in the developed method were evaluated by mapping the standardized residues.

Integration of Polarimetric PALSAR Attributes and Local Geomorphometric Variables Derived from SRTM for Forest Biomass Modeling in Central Amazonia

Abstract. The objective of this work is to generate a predictive model for biomass estimation in a forested area of central Amazonia based on the integration of incoherent target scattering decomposition polarimetric attributes extracted from Phased Array type L-band Synthetic Aperture Radar (PALSAR) data and geomorphometric variables derived from Shuttle Radar Topography Mission (SRTM). In addition to their incorporation as variables of ecophysiological nature in biomass modeling, the geomorphometrics variables were also evaluated with regard to the possibility of minimization of topographic effects that affect the acquisition of PALSAR data. Based on the processed data, three biomass models were generated. The first model involves independent parameters extracted from polarimetric PALSAR data, the second includes the same polarimetric variables, which are additionally adjusted for the cosine factor effect. The third model integrates both the polarimetric parameters extracted from PALSAR and the geomorphometric variables derived from SRTM. The latter model showed the best results of biomass estimation among the models generated. Our results confirm the importance of geomorphometric variables as additional input in prognostic biomass models that use radar remote sensing, in this case L band, because of their causal relationship with ecophysiological aspects that condition the growth of forest communities and because of minimization of the terrain effects on the radar signal. Résumé L’objectif de cette étude est de créer un modèle prédictif pour l’estimation de la biomasse d’unerégion forestière de l’Amazonie centrale. Le modèle est basé sur l’intégration d’attributs issus de la décomposition polarimétrique incohérente de données PALSAR et de variables géomorphométriques dérivées du SRTM. En plus de leur intégration comme variables de nature écophysiologique dans la modélisation de la biomasse, nous avons évalué le potentiel des variables géomorphométriques à minimiser les effets topographiques qui influencent l’acquisition de données PALSAR. Basés sur les données traitées, trois modèles de biomasse ont été développés. Le premier modèle utilise les données polarimétriques originales SAR comme variables indépendantes. Le second modèle prend en compte les variables indépendantes du premier modèle ainsi que l’effet du facteur de cosinus. Le troisième modèle est composé des variables originales polarimétriques et des variables géomorphométriques. Ce dernier modèle a produit les résultats les plus cohérents d’estimation de la biomasse. Les résultats des modèles confirment l’importance des variables géomorphométriques en tant que données d’entrée dans les modèles prédictifs de biomasse qui utilisent la télédétection radar, dans ce cas, la bande L. Ces résultats sont dus, d’une part, à la relation causale avec entre les variables geomorphométriques et les aspects écophysiologiques qui conditionnent la croissance des communautés forestières et, d’autre part, à la minimisation des effets de la topographie sur le signal radar.

Digital elevation model validation with no ground control: application to the topodata dem in Brazil

Digital Elevation Model (DEM) validation is often carried out by comparing the data with a set of ground control points. However, the quality of a DEM can also be considered in terms of shape realism. Beyond visual analysis, it can be verified that physical and statistical properties of the terrestrial relief are fulfilled. This approach is applied to an extract of Topodata, a DEM obtained by resampling the SRTM DEM over the Brazilian territory with a geostatistical approach. Several statistical indicators are computed, and they show that the quality of Topodata in terms of shape rendering is improved with regards to SRTM.

Relação entre as variáveis morfométricas extraídas de dados SRTM (Shuttle Radar Topography Mission) e a vegetação do Parque Nacional de Brasília

Este trabalho visa ao estudo da relacao entre a distribuicao de fitofisionomias do Parque Nacional de Brasilia (PNB) e variaveis topograficas, para avaliar o potencial de dados SRTM isoladamente, como complemento aos dados tradicionalmente aplicados no sensoriamento remoto da vegetacao. Esta relacao foi verificada atraves de analises discriminantes entre o mapa de vegetacao referencia do PNB e as seguintes variaveis morfometricas: elevacao, declividade, orientacao de vertente, curvatura vertical e curvatura horizontal. Tais analises indicaram as classes de vegetacao que podem ser separadas com base nas condicoes topograficas do terreno. As variaveis morfometricas mais importantes na distincao entre os tipos vegetacionais foram a elevacao, a declividade e a orientacao de vertente. Apesar de os dados morfometricos mostrarem potencial indicativo das classes de vegetacao, as analises resultaram em discriminacao em um nivel aquem do detalhamento tematico do mapa referencia. Tal desempenho pode ser explicado pela incompatibilidade das escalas de variacao exibidas entre os dados morfometricos em relacao ao tamanho das unidades de mapeamento da vegetacao. Alem disso, a variacao de tipos de vegetacao do cerrado pode ser explicada por uma serie de outros fatores alem da topografia. Com base nas analises discriminantes das variaveis morfometricas, foi possivel o mapeamento experimental da vegetacao ao nivel de subfisionomias.