Shale Amazon River

Fig. 6-9 Ternary diagram showing proportions of dissolved Si(OH)4, carbonate alkalinity (HCOj + CO3"), and (Q + S04 ) in the Orinoco River and Amazon River basins. Charged species are in equivalents Si(OH)4 is in mole units. The curves in the larger figure are numbered in total cation concentration (mEq/L). Unlike previous figures, symbols represent the total cation concentration interval that includes the sample s concentration. The predominant symbol within each interval corresponds to samples whose concentrations plot within that interval. In the smaller figure, the patterned areas correspond to the predominant source of samples whose concentrations plot within the areas (A) streams that drain cratonic areas (B) streams that originate in mountain belts, but that drain large areas of cratons (C) streams that drain mountain belts with extensive black shales (D) streams that drain mountain belts with extensive carbonate rocks and evaporite deposits. Adapted from Stallard (1988) with the permission of Kluwer Academic Publishers.

The mineralogy of the suspended matter carried by rivers is not well documented. There are numerous analyses either of the clay fraction or of sands carried by rivers, but only a few total quantitative analyses are reported in the literature. As examples, the average mineralogical composition of two large river systems, the Amazon and the Mississippi, are presented in Table 9.9. This table also includes the mean mineralogical composition of shales for comparison with river suspended sediments. The overall average of 300 samples of shales analyzed by Shaw and Weaver (1965) is 30.8% quartz, 4.5% feldspar, 60.9% clay minerals, and... 

The behavior of uranium varies considerably across samples studied. Palmer and Edmond (1993) have reported increasing trends of uranium concentration with river alkahnity in the Orinoco, Amazon and Ganga river basins, showing the importance of limestone and black shale dissolution for the control of uranium concentrations in river waters. The association of uranium and major soluble elements is also reported by Elbaz-Poulichet et al. (1999) for the upper Amazonian basins of Bohvia. However, under the organic-rich conditions of Scandinavian rivers (Porcelli et al., 1997) or African rivers (Viers et al., 1997), uranium concentrations can be decoupled from those of major elements, due to the existence of a colloidal fraction of uranium. 

Fig. 8. Shale-normalized lanthanide compositions of 0.22 (tm filtrates of the Amazon, Fly (Papua New Guinea) and Mississippi River waters. Amazon and Mississippi data from Sholkovitz (1993, 1995) Fly River data from unpublished work of Sholkovitz. G/J Avg. refers to the averaged river water composition of Goldstein and Jacobsen (1988a).

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