Development of the Amazon Valley During the Middle to Late Quaternary: Sedimentological and Climatological Observations

Irion, Georg; Mello, José Alberto Sampaio Nunes de; Morais, Jáder Onofre de; Piedade, Maria Teresa Fernandez; Junk, Wolfgang J.; Garming, Linda

doi:10.1007/978-90-481-8725-6_2

Cited by 57 publications

(52 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Nevertheless, in the region of ARIX2 and JABU1, generalized incision might have coincided with important low sea level stages (down to circa 100 m) that occurred after 5 Ma (Haq et al, 1987), a dynamics that was also described for the Quaternary of the Amazon valley (Irion, 2011).…”

Section: Geological Meaning Of Agesmentioning

confidence: 83%

Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

et al. 2018

View full text Add to dashboard Cite

This study focuses on the dating of millimetric pisoliths from ferruginous duricrusts located in central Amazonia (Brazil), by coupling detailed mineralogy and two relevant dating methods: (i) (U-Th)/He analysis of goethites by mass spectrometry; (ii) analysis of radiation-induced defects of kaolinites embedded in duricrusts by electron paramagnetic resonance spectroscopy (EPR). Three samples collected at different elevations in the landscape were selected. The goethite corrected ages range from 1.1-15.2 Ma and consistently increase with elevation. EPR was performed on kaolinites after several cycles of a deferration procedure. Considering extreme geochemical scenarii, the ages of kaolinites are 1.7-7.1 Ma for a closed system and 4.0-16.7 Ma for an open system with 100% Rn loss. Ages of goethites and kaolinites are close, in the limit of the uncertainty of the methods. They show important periods of duricrust formation at Middle Miocene and at Late Miocene/Pliocene. Data allow the estimation of lowering rates between 3 and 8 m/Ma, in agreement with independent data available in the literature for the central Amazonia region or even for erosion of other cratons in the world. The two dating methods can be compared on common duricrust samples. By revealing single or multi-step weathering/erosion episodes related to relictual paleosurfaces, they also bring promising contributions to an advanced knowledge of ancient and complex lateritic geosystems.

show abstract

Section: Geological Meaning Of Agesmentioning

confidence: 83%

Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

et al. 2018

View full text Add to dashboard Cite

show abstract

“…To date, studies addressing Amazonian fluvial rias focus mainly on climatic and sediment deposition changes, without consensus about their genesis (Sioli, 1984;Keim et al, 1999;Vital and Stattegger, 2000;Bertani et al, 2014). The extant Amazon rias appear to have been formed after the Last Glacial Maximum (LGM, (Archer, 2005;Irion et al, 2011). The prevailing hypothesis suggests that the incised valleys formed during the low sea level phase of the LGM were flooded and accumulated sediments during the Holocene transgression (Archer, 2005;Irion et al, 2006Irion et al, , 2011.…”

mentioning

confidence: 99%

“…The extant Amazon rias appear to have been formed after the Last Glacial Maximum (LGM, (Archer, 2005;Irion et al, 2011). The prevailing hypothesis suggests that the incised valleys formed during the low sea level phase of the LGM were flooded and accumulated sediments during the Holocene transgression (Archer, 2005;Irion et al, 2006Irion et al, , 2011. Sediment cores retrieved from the Tapajós Ria contain fine-grained sediments with 2.2-3.5% of total organic carbon and sedimentation rates reaching up to 6.5 mm yr −1 (Irion et al, 2006).…”

mentioning

confidence: 99%

“…Despite the widespread distribution in the Amazon and dominance of organic-rich sediments (Irion et al, 2011), rias are poorly studied with respect to their role as sink or source of carbon in the Amazon basin. According to Sawakuchi et al (2014), methane fluxes in Amazon rivers account for 22-28% of the global river emissions of methane and the Amazon rias are hotspots of methane production.…”

mentioning

confidence: 99%

See 1 more Smart Citation

The Fate of Carbon in Sediments of the Xingu and Tapajós Clearwater Rivers, Eastern Amazon

Bertassoli

Sawakuchi

et al. 2017

Front. Mar. Sci.

View full text Add to dashboard Cite

The Xingu and Tapajós rivers in the eastern Amazon are the largest clearwater systems of the Amazon basin. Both rivers have "fluvial rias" (i.e., lake-like channels) in their downstream reaches as they are naturally impounded by the Amazon mainstem. Fluvial rias are widespread in the Amazon landscape and most of the sedimentary load from the major clearwater and blackwater rivers is deposited in these channels. So far, little is known about the role of Amazon rias as a trap and reactor for organic sediments. In this study, we used organic and inorganic geochemistry, magnetic susceptibility, diatom, and pollen analyses in sediments (suspended, riverbed, and downcore) of the Xingu and Tapajós rias to investigate the effects of hydrologic variations on the carbon budget in these clearwater rivers over the Holocene. Ages of sediment deposition (∼100 to 5,500 years) were constrained by optically stimulated luminescence and radiocarbon. Major elements geochemistry and concentration of total organic carbon (TOC) indicate that seasonal hydrologic variations exert a strong influence on riverine productivity and on the input and preservation of organic matter in sediments. Stable carbon isotope data (δ 13 C from −31.04 to −27.49‰) and pollen analysis indicate that most of the carbon buried in rias is derived from forests. In the Xingu River, diatom analysis in bottom sediments revealed 65 infrageneric taxa that are mostly well-adapted to slack oligotrophic and acidic waters. TOC values in sediment cores are similar to values measured in riverbed sediments and indicate suitable conditions for organic matter preservation in sediments of the Xingu and Tapajós rias at least since the mid-Holocene, with carbon burial rates varying from about 84 g m −2 yr −1 to 169 g m −2 yr −1 . However, redox-sensitive elements in sediment core indicate alternation between anoxic/dysoxic and oxic conditions in the water-sediment interface that may be linked to abrupt changes in precipitation. The variation between anoxic/dysoxic and oxic conditions in the water-sediment interface controls organic matter mineralization and methanogenesis. Thus, such changes promoted by hydrological variations significantly affect the capacity of Amazon rias to act either as sources or sinks of carbon.

show abstract

“…These rivers (e.g. Rio Negro, Tapajós, Tocantins and Araguaia) originate in Precambrian formations, notably the Guiana Shield and Central Brazilian Shield, with deeply weathered soils and thus carry black water and clear water, respectively (Irion et al 2010), with a reduced load of suspended inorganic compounds compared to white-water rivers. The fertility of igapó floodplains is therefore much lower than that of floodplains which are inundated by sediment-rich white water rivers (várzea floodplains).…”

Section: Introductionmentioning

confidence: 99%

Stand dynamics of the drought-affected floodplain forests of Araguaia River, Brazilian Amazon

2017

View full text Add to dashboard Cite

Background: The floodplain forests of Araguaia River, a clear-water river in the southeastern Amazon (Tocantins State, Brazil), are characterized by seasonal flooding up to 3.5 m height, low nutrient levels in the water, and seasonal drought periods of 4-5 months. Methods: We studied the forest dynamics (tree diameter growth, tree mortality and recruitment) of this unique forest ecosystem over a 5-year period by repeated censuses in 12 permanent plots established along a flooding gradient. Results: The cumulative basal area in the plots increased by 0.84 (±0.45) m

show abstract

Development of the Amazon Valley During the Middle to Late Quaternary: Sedimentological and Climatological Observations

Cited by 57 publications

References 18 publications

Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

The Fate of Carbon in Sediments of the Xingu and Tapajós Clearwater Rivers, Eastern Amazon

Stand dynamics of the drought-affected floodplain forests of Araguaia River, Brazilian Amazon

Contact Info

Product

Resources

About