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Clay Minerals; June 2007; v. 42; no. 2; p. 161-179; DOI: 10.1180/claymin.2007.042.2.03
© 2007 Mineralogical Society of Great Britain and Ireland
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Land erosion and associated evolution of clay minerals assemblages from soils to artificial lakes in two distinct climate regimes in Portugal and Brazil

R. FONSECA1,*, F. J. A. S. BARRIGA2 and K. TAZAKI3

1 Department of Geosciences, University of Évora, 7002-554 Évora, Creminer LA/ISR, Faculty of Sciences, University of Lisbon, Campo Grande, 1794-016 Lisbon, Portugal, 2 Department of Geology and Creminer LA/ISR, Faculty of Sciences, University of Lisbon, Campo Grande, 1794-016 Lisboa, Portugal, and 3 Department of Earth Sciences, Faculty of Science, Kanazawa University, Kakuma, Kanazawa, Ishikawa, 920-1192, Japan

* E-mail: rfonseca{at}uevora.pt

(Received 1 June 2006; revised 12 January 2007)

Given that reservoirs contain most of the leached materials from soils, we have studied the sediments accumulated in the bottom of two groups of reservoirs developed under different climatic conditions and thus with contrasting rates of weathering/erosion regimes. Through detailed comparative study of clay minerals of the parent rocks and soils with the clay fractions of the dam sediments, we have concluded that, during cycles of erosion-transport-deposition, the leached materials have complex transformation mechanisms, making them much more active in the environment. All clay-mineral groups are well represented in the reservoir sediments, including abundant mixed-layer and partly disordered minerals. Moreover, the sediments are nutrient-rich and potentially useful as agricultural fertilizers and hence in reversing the declining soil productivity in some regions.

KEYWORDS: soil erosion, dam reservoirs, clay minerals of sediments, mineralogical transformations, Brazil, Portugal






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