from boreal region - an indication of weathering
Stanislav Franciskovic-Bilinski1, Halka Bilinski1, Darko Tibljas2,
Darko Hanzel3, and Alenka Mertelj3
Physical Chemistry, Rudjer Boskovic Institute, POB 180, HR-10002
Mineralogy and Petrology, Department of Geology, Faculty of Sciences,
University of Zagreb, Horvatovac bb, 10000 Zagreb, Croatia
3Jozef Stefan Institute, Jamova 39, SI-1001
Sediments from Öre estuary (North Sweden) were
studied in details to characterize weathering products of silicate rocks.
This estuary was chosen as a model for other anropogenically unpolluted
estuaries in boreal region, in which both physical and chemical weathering
products could be observed. The primary rocks are composed mostly of granite
and granodiorite. Chemical analysis was performed by XRF method. Organic
matter was characterized as total carbon, hydrogen and nitrogen. IR spectra
were not particularly useful, due to the presence of different minerals, but
have confirmed the presence of organic matter. Thermal behavior was studied
using TG and DTA techniques. Mineralogical composition was studied by XRD
method. The minerals found were quartz, alkaline feldspars, plagioclases,
biotite, chlorite and hornblenda. In silt and clay fraction < 32 μm
some weathering products were detected such as montmorillonite-15A, hematite
and Al(OH)3 in trace quantities.
Since iron is substantially present in sediments
and most of trace elements are in very good correlation with iron, additional
characterization of iron compounds was performed by 57Fe Mössbauer
spectroscopy. Measured at room temperature, Mössbauer spectra do not display
magnetic ordering. In only one sample, closest to the river mouth, better fit
was obtained adding one sextet pattern, but it was of minor significance.
Spectra were fitted with three to four doublets,
showing different isomer shifts (δ) and quadrupole parameters (Δ).
Relative amounts of Fe(II) and of Fe(III) was determined in each sample.
However, it was not possible to distinguish Fe(II) from biotite and chlorite,
as they have similar parameters. Fe(II) was not observed in M1 site.
It was observed that the amount of Fe(III)
increases with the distance from the river mouth. It can be retained in the
silicate sites or precipitated as amorphous iron oxide, what could not be
Mössbauer spectroscopy indicates that studied sediments are mostly formed
from metamorphic rocks on the basis of the presence of altered biotite and
The results of this work prove that weathering can
be studied in sediments and that some of the reactions are connected with
consumption of CO2 from atmosphere.
part of this work is from M.Sc. Thesis of S. Franciskovic-Bilinski,
University of Zagreb (2001).