Fossil megafans evidenced by remote sensing in the Amazonian wetlands

Rossetti, Dilce de Fátima; Zani, Hiran; Cremon, Édipo Henrique

doi:10.1127/0372-8854/2013/0118

Cited by 24 publications

(15 citation statements)

References 36 publications

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“…This feature has a maximum length and width corresponding to 107 km and 60 km, respectively, and it shows a regional inclination of 0.008° in the main southward direction. Such data were analyzed in a recent work that discussed the regional topography in the northern Amazonia megafans [19]. In addition, its axis points to the NNW, i.e., into the Guiana Shield, and the fringe spreads out to the SSE.…”

Section: Resultsmentioning

confidence: 99%

“…This is because the grassland and shrubland open vegetation classes are not randomly distributed, but they highlight previously recognized residual megafan landform in the Demini area [19]. Such morphology reflects the accumulation of a large volume of sediment transported from highland basement rocks into the sedimentary basin represented by the Pantanal Setentrional wetland.…”

Section: Relationship Between Vegetation and The Megafan Landformmentioning

confidence: 99%

“…It is intriguing that such occurrences are not randomly distributed, but they are confined to several large-scale, triangular-shaped morphologies related to residual megafan depositional systems [19] due to their resemblance to many megafans described in the literature [20][21][22][23][24]. This is because megafans are characterized by extensive (i.e., >10 3 km 2 ) sedimentary deposits with triangular and/or conical geometry in plain view.…”

Section: Introductionmentioning

confidence: 99%

“…This was made possible mainly considering the geometry defined by the distribution of vegetation classes, such as shape, elongation, sinuosity, size, as well as pre-knowledge of the geomorphology from previous works undertaken in this region [19,28,29].…”

Section: Validation Of the Phytophysiognomic Mapmentioning

confidence: 99%

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Classification of Vegetation over a Residual Megafan Landform in the Amazonian Lowland Based on Optical and SAR Imagery

2014

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Abstract:The origin of large areas dominated by pristine open vegetation that is in sharp contrast with surrounding dense forest within the Amazonian lowland has generally been related to past arid climates, but this is still an issue open for debate. In this paper, we characterize a large open vegetation patch over a residual megafan located in the northern Amazonia. The main goal was to investigate the relationship between this paleolandform and vegetation classes mapped based on the integration of optical and SAR data using the decision tree. Our remote sensing dataset includes PALSAR and TM/Landsat images. Five classes were identified: rainforest; flooded forest; wooded open vegetation; grassy-shrubby open vegetation; and water body. The output map resulting from the integration of PALSAR and TM/Landsat images showed an overall accuracy of 94%. Narrow, elongated and sinuous belts of forest within the open vegetation areas progressively bifurcate into others revealing paleochannels arranged into distributary pattern. Such characteristics, integrated with pre-existing geological information, led us to propose that the distribution of vegetation classes highlight a morphology attributed to a Quaternary megafan developed previous to the modern fluvial tributary system. The characterization of such megafan is important for reconstructing landscape changes associated with the evolution of the Amazon drainage basin.

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Section: Resultsmentioning

confidence: 99%

Section: Relationship Between Vegetation and The Megafan Landformmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Validation Of the Phytophysiognomic Mapmentioning

confidence: 99%

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Classification of Vegetation over a Residual Megafan Landform in the Amazonian Lowland Based on Optical and SAR Imagery

2014

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“…For instance, Bertani, Rossetti, and Albuquerque (2013) applied OBIA on SRTM−DEM for separating savanna from low and high forest canopies in a southwestern area of the Amazonian lowland. SRTM−DEM was recurrently used to separate classes of campinaranas from classes of ombrophilous forest associated with the studied megafan palaeoform Rossetti, Bertani, et al 2012;Rossetti, Bertani, et al 2012;Rossetti et al 2014). This is probably due to the capability of the use of SRTM−DEM in different methods for detecting even small topographic gradients (Rennó et al 2008;Rossetti et al 2012a;b, 2014).…”

Section: Attribute Influence In Class Separationmentioning

confidence: 95%

Mapping vegetation in a late Quaternary landform of the Amazonian wetlands using object-based image analysis and decision tree classification

Cordeiro

Rossetti

2015

International Journal of Remote Sensing

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Fan-shaped morphologies related to late Quaternary residual megafan depositional systems are common features over wide areas in northern Amazonia. These features were formed by ancient distributary drainage systems that are in great contrast to tributary drainage networks that typify the modern Amazon basin. The surfaces of the Amazonian megafans constitute vegetacional mosaic wetlands with different campinarana types. A fine-scale-resolution investigation is required to provide detailed classification maps for the various campinarana and surrounding forest types associated with the Amazonian megafans. This approach remains to be presented, despite its relevance for analysing the relationship between stages of plant succession and sedimentary dynamics associated with the evolution of megafans. In this work, we develop a methodology for classifying vegetation over a fan-shaped megafan palaeoform from a northern Amazonian wetland. The approach included object-based image analysis (OBIA) and data-mining (DM) techniques combining Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images, land-cover fractions derived by the linear spectral mixing model, synthetic aperture radar (SAR) images, and the digital elevation model (DEM) acquired during the Shuttle Radar Topography Mission (SRTM). The DEM, vegetation fraction, and ASTER band 3 were the most useful parameters for defining the forest classes. The normalized difference vegetation index (NDVI), ASTER band 1, vegetation fraction, and the Advanced Land Observing Satellite (ALOS)/Phased Array type L-band Synthetic Aperture Radar (PALSAR) transmitting and receiving horizontal polarization (HH) and transmitting horizontal and receiving vertical polarization (HV) were all effective in distinguishing the wetland classes campinarana and Mauritia. Tests of statistical significance indicated the overall accuracies and kappa coefficients (κ) of 88% and 0.86 for the final map, respectively. The allocation disagreement coefficient of 5% and a quantity disagreement value of 7% further attested the statistical significance of the classification results. Hence, in addition to water, exposed soil, and deforestation areas, OBIA and DM were successful for differentiating a large number of open (forest, wood, shrub, and grass campinaranas), forest (terra firme, várzea, igapó, and alluvial), as well as Mauritia wetland classes in the inner and outer areas of the studied megafan.

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The influence of late Quaternary sedimentation on vegetation in an Amazonian lowland megafan

Rossetti

Gribel

Tuomisto

et al. 2018

Earth Surf Processes Landf

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The largest areas of white‐sand vegetation in northern Amazonia are confined to Late Pleistocene–Holocene megafan depositional systems, which suggest a relationship between the two. The aim of this work is to determine: (i) the relative role of sedimentary history and recent ecological processes to explaining the mosaic of white‐sand forest patches, grasslands and shrublands in a wetland area of northern Amazonia; and (ii) the long‐term successional trajectory that led to the establishment of the white‐sand forest patches. Facies analysis was used to reconstruct the megafan paleoenvironment; δ13C, total organic carbon and carbon/nitrogen from sedimentary organic matter to reconstruct the past vegetation; and floristic inventories to characterize the modern vegetation. The results revealed that the Viruá megafan consists of various sandy sub‐environments, including aeolian sand dunes and sheets developed mostly in the Holocene after the megafan turned inactive as a depositional site. Dune margins and tops are colonized by white‐sand trees mixed with a few generalist rain‐forest species, whereas adjacent lower‐lying areas, which are affected by seasonal flooding, are covered by graminoid plants and/or shrubs. The latter initiated their development over the megafan surface in different times of the Holocene due to hydrological gradients imposed by the topography of the various megafan depositional environments, while the white‐sand forest became dominant only on sand dunes over the last few centuries. We suggest that the late Quaternary sedimentary history was crucial in creating morphologies that now determine topographic gradients responsible for different vegetation physiognomies over the Amazonian lowlands. Copyright © 2017 John Wiley & Sons, Ltd.

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Fossil megafans evidenced by remote sensing in the Amazonian wetlands

Cited by 24 publications

References 36 publications

Classification of Vegetation over a Residual Megafan Landform in the Amazonian Lowland Based on Optical and SAR Imagery

Classification of Vegetation over a Residual Megafan Landform in the Amazonian Lowland Based on Optical and SAR Imagery

Mapping vegetation in a late Quaternary landform of the Amazonian wetlands using object-based image analysis and decision tree classification

The influence of late Quaternary sedimentation on vegetation in an Amazonian lowland megafan

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