Mineralogical and geochemical influences on sediment color of Amazon wetlands analyzed by visible spectrophotometry

Acta Amazonica

José Tasso Felix Guimarães²  Marcelo Cancela Lisboa Cohen¹  Marlon Carlos França¹  Any Kelly Terra Da Silva¹  Suyanne Flavia Santos Rodrigues¹ 

[1] ,Instituto Tecnológico ValeBelém PA ,Brasil

关键词: Sedimentology;    Amazon region;    Munsell color systems;    Mineralogy;    chemical composition;    Sedimentologia;    Região Amazônica;    Sistema de cor Munsell;    Mineralogia;    Composição química;   

DOI  :  10.1590/S0044-59672013000300009

来源: SciELO

【 摘 要 】

Based on sedimentological and geochemical data, this work relates spectrophotometric measurements with sediment composition and its application in palaeoecological studies of Amazon wetlands. The CIELAB values are directly related to mineralogical and chemical composition, mostly involving quartz, iron oxyhydroxides and sulfides (e.g. pyrite), and total organic carbon. Total organic carbon contents between 0.4-1%, 1-2%, 3-5% and 15-40% were related to L* (lightness) data of 27, 26-15, 7-10 and 7 or less, respectively. The CIELAB values of a deposit in Marabá, Pará, were proportional to variations in quartz and total organic carbon contents, but changes in zones of similar color, mainly in the +a* (red) and +b* (yellow) values of deposits in Calçoene, Amapá and Soure, Pará, indicate a close relationship between total organic carbon content and iron oxyhydroxides and sulfides. Furthermore, the Q7/4 diagram (ratio between the % re?ectance value at 700 nm to that at 400 nm, coupled with L*) indicated iron-rich sediments in the bioturbated mud facies of the Amapá deposit, bioturbated mud and bioturbated sand facies of Soure deposit, and cross-laminated sand and massive sand facies of the Marabá core. Also, organic-rich sediments were found in the bioturbated mud facies of the Amapá deposit, lenticular heterolithic and bioturbated mud facies of the Soure deposit, and laminated mud and peat facies of the Marabá deposit. At the Marabá site, the data suggest an autochthonous influence with peat formation. The coastal wetland sites at Marajó and Amapá represent the development of a typical tidal flat setting with sulfide and iron oxyhydroxides formation during alternated flooding and drying.

【 授权许可】

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