Preferential settling of smectite on the Amazon continental shelf |
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Authors: | S M Patchineelam A G de Figueiredo |
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Institution: | (1) Universidade Santa úrsula, Instituto de Ciências Biológicas e Ambientais, Rua Jornalista Orlando Dantas 59, 22231-010 Botafogo, Rio de Janeiro, Brazil e-mail: sorayap@usu.br, BR;(2) Universidade Federal Fluminense, Departamento de Geologia – LAGEMAR, Av. Litoranea, s/n 24210-340 Niterói, Rio de Janeiro, Brazil, BR |
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Abstract: | Seventy-five surface and subsurface sediment samples collected on the Amazon continental shelf were analyzed by X-ray diffraction
(XRD) in the grain-size fractions smaller than 2 μm. The groups of clay minerals thus identified were smectite, kaolinite,
illite, and mixed-layer illite/smectite. Calculation of relative abundance shows a predominance of smectite (37%) in the whole
area, followed by kaolinite (27%), illite (23%), and a small percentage of mixed-layer illite/smectite (12%). The distal,
northwest region of the continental shelf is characterized by a high abundance of smectite (41%), high salinity values, and
high sediment accumulation rates (10 cm year−1), whereas the proximal region is characterized by a comparatively low abundance of smectite (30%), low salinity values, and
low sediment accumulation rates (<1 cm year−1). This trend of increasing abundance northwestwards documents a preferential settling of smectite in the distal and more
saline regions of this estuarine system.
Received: 17 September 1999 / Revision accepted: 17 January 2000 |
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