Geochemical results from river-bottom sediments taken from the lowermost Am
azon River are presented. Bedload sediments were analyzed for 10 major and
38 minor elements. Mud bulk sediments exhibit a tendency to a slight enrich
ment in Cr, Mn, Rb, Sr, Zr, Cs, Ba and Hf, pointing to the importance of th
ese elements in the silt fraction. Generally, Cu, Zn, Rb, Cs, Ba and Sn are
clearly associated with clay minerals, while Y, Zr, Hf, Th and U are assoc
iated with heavy minerals. The location of this area in an intensive chemic
al weathering environment results in the strong modification of sediment co
mposition. Chemical weathering processes strongly modify original sediment
composition and can be recognized apart from provenance processes on the ba
sis of their geochemical signature. Discriminant analysis makes the detecti
on of less marked differences in sediment characteristics possible, thus, i
mproving the accuracy of distinctions between groups. The Amazon Mouth and
Xingu Mouth (XM) are discriminated principally by the textural maturity of
their sediments. The Jari Mouth (JM) shows highest Co and Fe2O3 contents. D
espite similarities between the Amazon North Branch (ANB) and Amazon South
Branch (ASB), the ANB can be differentiated on the basis of its higher Sr,
P2O5, and Na2O contents, the ASB on the basis of its higher Zn, MnO, and Ca
O contents, and the Estreitos de Breves (EST) based on its higher abundance
of Ni and Cu. Higher contents in P2O5, Fe, and Mn are related to laterite
covers. (C) 2000 Elsevier Science B.V. All rights reserved.