hrvatski

Podrijetlo, sastav i uvjeti nastanka terra rosse Istre

Terra rossa in Istria is situated on Jurassic-Cretaceous-Paleogene carbonate plain and represents a polygenetic reddish material which bears typical terra rossa Fe-oxide characteristics (e. g. preferential formation of hematite over goethite, Fed and Fe_d/Fe_t). Neutral to slightly alkaline pH conditions of formation are also supported with SLREE/SHREE and (La/Yb)_ ch ratios which are slightly higher than that of ES indicating slight LREE enrichment relative to HREE. The main mineral phases in the clay fraction of all terra rossa from Istria are kaolinites (Kl_D and Kl), illitic material, Fe-oxides and XRD amorphous inorganic compounds. Vermiculite, chlorite, mixed-layer clay minerals, quartz and boehmite are present in subordinate and scattered amounts. Kaolinites are scattered constituents in the clay fraction of insoluble residues of limestone and dolomite which is dominated with illitic material, and minor constituents of Upper Pleistocene loess which contains approximately similar amounts of illitic material, vermiculite, chlorite, and chlorite/vermiculite in the clay fraction. They were not detected in flysch whose main constituents in clay fraction are illitic material and smectite. Kaolinite which does not form intercalation compounds with DMSO (Kl) is more abundant in terra rossa than kaolinite which intercalates with DMSO (Kl_D). This may indicate that kaolinites are predominantly authigenic rather than inherited from parent materials. The differences in SREE (absolute REE abundances) observed among analysed terra rossa samples can primarily be attributed to the different REE content in parent rocks and less to fractionation during weathering processes. Mineralogical, chemical and granulometric composition of terra rossa indicate that additions of external materials have significantly diminished the influence of insoluble residue of limestone and dolomite as the primary parent material of terra rossa in Istria. Based on haevy mineral fraction, clay mineralogy and granulometric composition one can conclude that loess derived from the deflation of the Po plain sediments during the Middle and Late Pleistocene might have been the main external contributor to terra rossa. Due to processes of erosion and redeposition terra rossa may also contain fragments of reworked paleosols and bauxites of the Jurassic and Paleogene ages. In the north-western part of Istria, the Upper Pleistocene loess clearly covers terra rossa. When thinner, this loess may be mixed and digested by terra rossa, and is not easily recognisable. Due to these additions and recent pedogenesis the upper part of terra rossa profiles has more yellow hues.

Terra rossa; Kemijski sastav terra rosse; Mineraloški sastav terra rosse; Podrijetlo terra rossa; Geneza terra rossa; Istra

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