The modern 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 Viruá 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, subdendritic, 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±3.4ky and radiocarbon ages ranged from 5.9–5.7 to 20.1–19.6calky BP. In contrast, cores extracted within the depression consisted of fluvial deposits younger than 2.1–1.9calky 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.
Geomorphology – Elsevier
Published: Oct 15, 2017
It’s your single place to instantly
discover and read the research
that matters to you.
Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.
All for just $49/month
Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly
Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.
Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.
Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.
All the latest content is available, no embargo periods.
“Hi guys, I cannot tell you how much I love this resource. Incredible. I really believe you've hit the nail on the head with this site in regards to solving the research-purchase issue.”Daniel C.
“Whoa! It’s like Spotify but for academic articles.”@Phil_Robichaud
“I must say, @deepdyve is a fabulous solution to the independent researcher's problem of #access to #information.”@deepthiw
“My last article couldn't be possible without the platform @deepdyve that makes journal papers cheaper.”@JoseServera