Original scientific paper

Estuarine Sediments from the Boreal Region – an Indication of Weathering

Stanislav Frančišković-Bilinski ; Department of Physical Chemistry, Ruđer Bošković Institute, P. O. Box 180, HR-10002 Zagreb, Croatia
Halka Bilinski ; Department of Physical Chemistry, Ruđer Bošković Institute, P. O. Box 180, HR-10002 Zagreb, Croatia
Darko Tibljaš ; Division of Mineralogy and Petrology, Department of Geology, Faculty of Science, University of Zagreb, Horvatovac bb, HR-10000 Zagreb, Croatia
Darko Hanžel ; Jožef Stefan Institute, Jamova 39, SI-1001 Ljubljana, Slovenia

Abstract

Öre estuary (Northern Sweden) was chosen as a model for other anthropogenically unpolluted estuaries in the boreal region. Sediments were studied in detail in order to characterize the weathering products of silicate rocks. Primary rocks are mostly composed of granite and gneiss. Chemical analysis of total sediments was performed by the XRF method. SiO₂ predominated (71.1–59.2 %) in all samples, decreasing seaward. Al₂O₃ (11.58–12.89 %) and Fe₂O₃ (3.71–6.92 %) were the other main chemical components and they increased seaward. Fourteen elements within the fine silt and clay fraction (f < 32 µm) were analyzed by the ICP-AES method. The most abundant microelement was Ti, followed by Mn, Zn, Ba, Cr, Sr, V, while Cu, Co and Ni were the least abundant. Organic matter was characterized as total carbon, hydrogen and nitrogen. Mineralogical composition was studied by the XRD method. The minerals found were quartz, different minerals from the feldspar group (albite, microcline, plagioclase, sanidine), biotite, chlorite and hornblende. Some weathering products, such as montmorillonite-15Å and Al(OH)₃, were detected in the fine silt and clay fraction (f < 32 µm). Amorphous iron hydroxide could not be detected by the XRD method. Most of the trace elements determined by ICP-AES (Co, Mg, Cr, Ni, Cu, Mn, Zn) were in very good correlation with iron. 57Fe Mössbauer spectroscopy was used for further characterization. Measured at room temperature, Mössbauer spectra did not display magnetic ordering. In only one sample, closest to the river mouth, a better fit was obtained by adding one sextet pattern, but it was of minor significance. Relative amounts of Fe(II) and of Fe(III) were determined in each sample and the Fe(III)/Fe(II) ratio was calculated. It was observed that the amount of Fe(III) increased with the distance from the river mouth and it was either retained at the silicate sites or precipitated as amorphous iron oxide. Mössbauer spectroscopy indicates that the sediments sampled are mostly formed from metamorphic rocks due to the presence of altered biotite and chlorite. The results of this work demonstrate that sediments can be used to study weathering. Some of the reactions, according to the literature, are connected with the consumption of CO₂. Examples of such reactions include the weathering of K-feldspar, albite and hornblende.

Keywords

silicate weathering; estuarine sediments; boreal region; X-ray diffraction; X-ray fluorescence; Mössbauer spectroscopy

Hrčak ID:

103093

URI

https://hrcak.srce.hr/103093

Publication date:

30.6.2003.

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