SEDIMENTOLOGY AND EVOLUTION OF A LATE
PLEISTOCENE-HOLOCENE HUMID MEGAFAN IN
NORTHERN BRAZIL
Dilce F. Rossetti
Hiran Zani
Marcelo C. L. Cohen
Édipo H. Cremon
MEGAFAN MODEL
Nichols & Fisher 2007
Okavango Megafan (Gumbricht & McCarthy, 2001)
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Taquari
(Assine, 2005)
Tectono and climatic setting for the formation
of megafans (Nichols & Fisher, 2007)
Kosi (Chakraborty et al. 2010)
Fan-shaped deposits of the Pantanal Setentrional Basin
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Escudo das Guianas
Viruá
Morphology of the Viruá megafan
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Morphology of the Viruá megafan
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Chronology of the Viruá megafan
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Viruá megafan
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Viruá megafan
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Viruá megafan
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MODEL FOR A MEGAFAN IN A HUMID TROPICAL REGION
AMAZONIAN REGION
-Modern tributaries
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- Tropical areas with high
temperature and high
precipitation
MEGAFANS IN THE PANTANAL SENTENTRIONAL BASIN
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TECTONIC INFLUENCE IN THE PANTANAL SENTENTRIONAL BASIN
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ORIGIN OF THE VIRUÁ MEGAFAN
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VIRUÁ MEGAFAN- TECTONIC INFLUENCE
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VIRUÁ MEGAFAN: TECTONICS + MONSOONAL-LIKE CLIMATE
Assine 2005
CONCLUSIONS
- Late Pleistocene-Holocene deposits are much more widespread in
the Amazonian wetlands than previously recognized;
-They occur as numerous, large, fan-like morphologies in the PSB, with
the Viruá fan in Roraima being one of them;
-This feature displays morphological (i.e., large-scale fan geometry,
divergent drainage networks, gently-dipping slopes, concave-up and
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convex-up longitudinal and transversal
(dominantly sandy lithologies and fining and coarsening upward units
related to active channels, overbank sand/sheets and terminal fan lobe,
abandoned channel, floodplain, debris flow deposits and lake/pond muds)
characteristics compatible with residual deposits of a megafan;
-The establishment of a megafan in this humid tropical region was
probably the due to the creation of new space for sediment
accommodation by tectonic reactivation added to a favorable,
monsoonal-like climate, with high summer temperatures and drought
contrasting with high water discharge during wet winters.
THANKS!
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