From source to sink: Preserving the cosmogenic 10Be-derived denudation rate signal of the Bolivian Andes in sediment of the Beni and Mamoré foreland basins

Abstract

The denudation rate signal of the Bolivian Andes as measured by cosmogenic 10 Be in sediment is preserved in the floodplain of adjacent foreland basins even though these basins store the sediment for thousands of years. This conclusion is drawn from comparing published Andean source area denudation rates with new cosmogenic 10 Be data as measured in the floodplains of the large Beni and Mamoré basins. For the entire Beni basin including the sediment producing Andes and the vast flooded plains of the foreland, the cosmogenic nuclide-derived denudation rate is 0.45 ± 0.06 mm/yr, while that of the Mamoré basin is 0.55 ± 0.19 mm/yr. By comparison, the respective Andean source areas erode at averaged rates of 0.37 ± 0.06 mm/yr (upper Beni), and at 0.56 ± 0.09 mm/yr (upper Mamoré). We notice a decrease in variability of denudation rate with increasing spatial scale as small-scale processes are averaged out. Sediment mixing within the floodplain damps scatter of nuclide-derived denudation rates picked up in the source area. On the temporal scale, a remarkable agreement between cosmogenic nuclide-derived rates averaging over a few kiloyears with those from fission track dating averaging over millions of years seems to suggest that cosmogenic nuclide-derived denudation rates capture the long-term erosional characteristics of the mountain belt. The sum of these observations suggests that any sample collected along a river traversing a floodplain will yield the denudation rate of the source area. This finding opens the unique possibility of constraining cosmogenic nuclide-derived paleo-sediment budgets for these large basins as the long-term, spatially-averaged denudation rate signal of the sediment-producing area is preserved in sedimentary archives.

The dependence of meteoric 10Be concentrations on particle size in Amazon River bed sediment and the extraction of reactive 10Be/9Be ratios

“…Five bedload samples, sampled from the active river bed, were chosen as representative of the three main tectonic units present in the Amazon basin, which are the Andes, the Shields, and the lowlands (see Figure 1 and Tables 1 and 2 for sample localities). The chemical composition of river sediment in the Amazon basin and their rates of production in the Andes and in the cratonic shields have recently been reported by Bouchez et al 2011 andWittmann et al 2011 (for details on samples and sampling procedures see Wittmann et al, 2009 andWittmann et al, 2011).…”

“…Sample "Gr 19" from the Grande River represents the dry Bolivian Andes to the south of the Beni basin. For details on sampling procedures and locations for these samples, we refer to Wittmann et al (2009), who have used the sandy fractions of these samples for in-situ 10 Be analysis, to derive basin-wide denudation rates of 1340 t/km 2 /yr for samples Be 1 and Be 2, and 1690 t/km 2 /yr for Gr 19, respectively.…”

OCTOPUS: An Open Cosmogenic Isotope and Luminescence Database

“…These two collections are not officially supported by the OCTOPUS project, and are included here only for completeness. The first collection consists of five studies with samples 25 from the Yangtse (Chappell et al, 2006), Amazon (Wittmann et al, 2009(Wittmann et al, , 2011, Ganga (Lupker et al, 2012), and Brahmaputra basins (Lupker et al, 2017). These studies focused on very large basins that could only be handled by CAIRN when ran using a 500 m resolution DEM that, however, produced drainage basins that were substantially different to what was published, especially in the case of rivers in the Amazon basin.…”

“…These studies focused on very large basins that could only be handled by CAIRN when ran using a 500 m resolution DEM that, however, produced drainage basins that were substantially different to what was published, especially in the case of rivers in the Amazon basin. Further, Chappell et al (2006) do not report denudation rates -suggesting that calculating these might have little meaning for their samples -, and both Wittmann et al (2009;Lupker et al 30 (2012;2017) perform corrections to the data, some of which (e.g., removing floodplain areas from production rate calculations)…”

Alluvial plain dynamics in the southern Amazonian foreland basin

“…In the last few decades, an increasing number of studies in the Andean-Amazonian foreland basin have furthered our knowledge of river dynamics and floodplain erosion/sedimentation processes and forest disturbance (do Nascimento Jr. et al, 2015;Dunne et al, 1998;Salo et al, 1986;Peixoto et al, 2009;Constantine et al, 2014;Aalto et al, 2003;Latrubesse et al, 2009a;Wittmann et al, 2009). In the southern Amazonian foreland basin (SAFB) (Espurt et al, 2007) it has been shown that large river floodplain sediment accumulation observed in ∼ 100 dated floodplain cores is primarily controlled by the El Niño/Southern Oscillation (ENSO) cycle (Aalto et al, 2003), with warm (El Niño) phases causing smaller shorter floods and low sedimentation rates and cold (La Niña) phases causing larger longer floods and high sedimentation rates (Aalto et al, 2003;Schöngart and Junk, 2007).…”