engleski

Mineralogy and geochemistry of soils/paleosols formed in contrasting pedoenvironments (oxidizing vs. reducing) on pure cretaceous limestones in Istria, Croatia

The main difference between terra rossa soils and GGP observed in the field is their color which indicates that, generally, terra rossa soils formed in oxidizing while GGP formed in reducing pedoenvironment. Our investigation showed that mineral data corresponds well with chemical data of those soils/paleosols. Higher SiO2 and Na2O in terra rossa soils compared to GGP is the result of quartz and plagioclase, mineral phases that were not detected in GGP. Higher Fe2O3 in terra rossa soils is the result of hematite and goethite formation, mineral phases that are specific for the oxidizing, well drained and slightly alkaline to neutral pH pedoenvironment in which terra rossa is formed. The values obtained for P2O5 and MnO in terra rossa match that finding well. Compared to GPP, terra rossa soils are slightly enriched in Co and Pb and significantly enriched in REE. The important difference in the total REE in analyzed terra rossa soils can be attributed to the REE content of both parent carbonate rocks (their insoluble residues) and different external materials which have contributed in the genesis of terra rossa (loess, flysch, bauxite), modified by weathering processes which characterize specific pedoenvironment in which terra rossa is formed and which favors LREE enrichment. Sequential extraction analysis showed that Mn, Co and Pb, mainly bound to reducible fraction (III), are the most mobile trace elements in terra rossa, while the most available are Cd, Ba, Sb and As, bound to adsorbed fraction (I). Mobility of Co, Pb and especially Mn, elements enriched in terra rossa soils is higher in terra rossa soils than in GGP showing that formation of Mn oxides might have played important role in their accumulation in terra rossa soils. Partitioning of REE in sequential fractions of terra rossa soils showed that authigenic Fe-oxides and/or Mn oxides are probably important sink for REE. K2O contents in GGP clearly indicate that illitic material is the dominant mineral phase in the GGP. Ottner et al. (1999) found that the smectites in illite/smectite mixed-layer minerals from clays in the Tri Jezerca quarry are aluminum rich montmorillonites without iron substitution in the octahedral position. The values obtained for MgO in GGP match that finding well. Higher SO3 in GGP is the result of pyrite and gypsum formation, mineral phases that were not detected in terra rossa soils. Pyrite indicates acidic and reductive pedogenic paleoenvironment of GGP formation. (Sub)recent pyrite oxidation at the surface results in the formation of the secondary mineral gypsum. The enrichment of GGP in Cd, Sb, Ni, V and especially in U and Mo is considered typical for reducing environments. Variation of the total REE content in GGP is much narrow compared to terra rossa soils. Total REE in GGP is dominated by residual fraction and probably also reflects parent materials (insoluble residue of limestone, aeolian and volcanic dust) modified in acidic and reductive marshy pedoenvironment which favors HREE enrichment. Enrichment of HREE in GGP is probably the result of higher mobility of LREE in this type of pedoenvironment. Cd, Ni and Co, mainly bound to adsorbed fraction (I) are most mobile and available trace elements in GGP. It is interesting to note that the mobility of Mo, Ni and Cd, trace elements enriched in GGP is higher in GGP than in terra rossa soils indicating that the adsorption processes might have played important role in their accumulation in GGP.

Mineralogy; geochemistry; soils/paleosols; pedoenvironment; Istria; Croatia

Projekt Hrvatske zaklade za znanost 2504