La. Martinelli et al., CHEMICAL AND MINERALOGICAL COMPOSITION OF AMAZON RIVER FLOODPLAIN SEDIMENTS, BRAZIL, Applied geochemistry, 8(4), 1993, pp. 391-402
The total and exchangeable concentration of major elements and the min
eralogical composition of sediments collected along the Amazon River f
loodplain (varzea) were determined. Average elemental composition (wt%
) decreased in the order: Si > Al > Fe > Na > Ca > K > Mg > Ti. There
was some spatial variability: the concentration of Al, Na and Mg decre
ased downstream; the concentration of Fe, K and Ti remained constant;
the Si concentration increased toward the Amazon River mouth. Mineralo
gically, there was a downriver increase in the concentration of quartz
and kaolinite, and a concurrent decrease in the concentration of Na-
and Ca-plagioclases. On the other hand smectite-vermiculite clay miner
als increased and the mica (illite) concentration remained constant. A
mass balance indicated that, except for illite, downriver changes in
the other minerals were not caused solely by mixing of Amazon River wa
ter with water from the major tributaries, which have a distinctly dif
ferent composition. Therefore, the mass balance indicated that plagioc
lases and smectite-vermiculite had been lost in the varzea, while kaol
inite was formed there.