Chemical and physical denudation in the
Amazon River Basin
Chemical Geology, Volume 142, Issues 3-4,
Jérôme Gaillardet, Bernard Dupré, Claude J. Allègre and
Philippe Négrel
Summary of
Points:
·
The
study presents major and trace element data on the suspended and dissolved
phases of the
·
Special
attention is paid to the abundances of REE and to their fractionation between
the dissolved and suspended phase. The rivers of the
·
However
a greater range of fractionation between LREE and HREE is reported here. At a
global scale the rivers have intermediate patterns between those of the
·
The
study proposes a model based on mass budget equations, that allow the
proportions derived from the different sources to be calculated. As a
consequence silicate, carbonate and evaporite
weathering rates can be estimated as well as the consumption of CO2
by weathering of each of these lithologies.
·
Physical
weathering rates can be estimated by two complementary approaches. On the one
hand, the multi-year average of suspended sediments yields can be used to
estimate physical denudation. On the other hand, a steady-state model of
erosion has been developed that allows calculation of physical erosion rates on
the basis of the dissolved load of rivers.
·
Comparison
of the rates predicted by the model to the observed rates shows good agreement
for the lowland rivers, but a strong discrepancy for the rivers derived from
the
·
Two
interpretations can account for this inconsistency. The first is that these
rivers are not in steady state and hence that the soils are being destroyed.
The second requires that the local continental crust is different from the
average continental crust of Taylor and McLennan, and contains a large
proportion of sedimentary rocks.
·
Using
the measured sediment yields, and assuming a steady state, we can estimate the
amount of sediment recycling for each drainage basin. For the Amazon at
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