Brazilian shield

The Amazon basin comprises an area of about 6.4 millions km, extending between the Guyana Shield to the north and the Brazilian Shield to the south with the Andean and sub-Andean regions to the west. 

AssuMpgAo, M., James, D. E. Snoke, J. A. 2002. Crustal thickness in SE Brazilian shield by receiver function analysis Implications for isostatic compensation. Journal of Geophysical Research, 107(1). 

A survey of the streams and rivers crossing the highway between Cuiabi and Porto Velho revealed that the conductivity and caldum concentration of waters from the sandstones of the Pareds Formation between Diamentino and Pimenta Bueno are similarly low 6), This region of Mato Grosso is also located in the region of the Central Brazilian Shield. There are few water bodies in the world with such low mineral nutrient content, but values nearly as low have been recorded in New Guinea, where the conductivity of the rainwater was sometimes equivalent to that in the Rio das Mortes (7). 

In spite of the poverty in nutrients, the biotic communities of the headwater streams are moderately rich in species, some of which consume terrestrial organisms or detritus entering the water while others utilize nutrients that are introduced with rainfall or from decomposing animals that die near the streams. The activity of the biota serves to prevent or retard the further loss of nutrients from these ancient water courses. This explains why even temporary destruction of the biota in or bordering the streams on the Central Brazilian Shield can result in... 

Furch, K. Junk, W. J. Water Chemistry and Macrophytes of Creeks and Rivers of Southern Amazonia and the Central Brazilian Shield. In Tropical Ecology and Development, Furtado, J. I., Ed. Int. Soc. Trop. Ecol., Kuala Lumpur, 1980 pp 771-796. 

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