The imprint of Late Holocene tectonic reactivation on a megafan landscape in the northern Amazonian wetlands

The imprint of Late Holocene tectonic reactivation on a megafan landscape in the northern Amazonian wetlands

Author Rossetti, Dilce de Fátima Google Scholar
Valeriano, Márcio de Morisson Google Scholar
Gribel, Rogério Google Scholar
Cohen, Marcelo Cancela Lisboa Google Scholar
Tatumi, Sonia Hatsue Autor UNIFESP Google Scholar
Yee, Márcio Autor UNIFESP Google Scholar
Abstract The modem Amazonian ecosystem outcomes from the complex interplay of different factors performed over the geological history, with tectonics being long speculated as perhaps a fundamental one. Nevertheless, areas where tectonic activity can be fully characterized are still scarce in view of the large dimension of this region. In this work, we investigate the signature of neotectonics in one megafan paleolandform that typifies a large sector of the Negro-Branco basin in northern Amazonia. The approach joined regional morphostructural descriptions of the Virua megafan surface and the acquisition of topographic, sedimentological, and chronological data focusing on the central sector of the megafan. The results revealed an abundance of rivers that form dendritic, sub-dendritic, and trellis patterns. These rivers also have numerous straight segments, orthogonal junctions, and orthogonal shifts in courses. Structural lineaments, defined by straight channels and also straight lake margins, are aligned along the NW-SE and NE-SW directions that are coincidental with the main regional structural pattern in Amazonia. This study also led to recognize two large areas of lower topography in the south-central part of the megafan that consist of rectangular depressions parallel to the morphostructural lineaments. A sedimentological survey indicated that cores extracted external to the largest depression have only distributary channel and overbank sand sheet megafan deposits. Optically stimulated luminescence (OSL) ages ranged from 17.5 +/- 2.0 to 46.9 +/- 3.4 ky and radiocarbon ages ranged from 5.9-5.7 to 20.1-19.6 cal ky BP. In contrast, cores extracted within the depression consisted of fluvial deposits younger than 2.1-1.9 cal ky BP that increased in thickness toward the central part of the depression. We propose that the studied megafan was affected by tectonic reactivation until at least a couple thousand years ago. Tectonics would have produced subsiding areas more prone to flooding than adjacent terrains, which constituted sites for renewed deposition of fluvial sediments reworked from the megafan surface following its abandonment. A comparison of our data with those from other Amazonian areas with similar records of late Holocene tectonics suggests a landscape imprinted by faulting, probably of strike-slip motion. This finding increases the record of neotectonic activity in the Amazonian wetlands and may be useful in studies aiming at discussing the origin and extension of late Holocene deformation in the South American intraplate. In addition, we present a megafan with an unusual development in a cratonic region under the combined effect of climate and tectonics.
Keywords Megafan paleolandorm
Northern Amazonia
Late Holocene
xmlui.dri2xhtml.METS-1.0.item-coverage Amsterdam
Language English
Sponsor Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Grant number FAPESP: 13/50475-5
Date 2017
Published in Geomorphology. Amsterdam, v. 295, p. 406-418, 2017.
ISSN 0169-555X (Sherpa/Romeo, impact factor)
Publisher Elsevier Science Bv
Extent 406-418
Access rights Closed access
Type Article
Web of Science ID WOS:000413175000029

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