engleski

Heavy and light mineral fractions indicate polygenesis of extensive terra rossa soils in Istria, Croatia

Terra rossa is the most widespread soil type in Istria, Croatia, a region that has been affected by karst processes, (neo)tectonic activity and sediment supply since the Late Tertiary. Analysis of the heavy and light mineral fractions of the terra rossa in Istria reveals a polygenetic origin. For comparative purposes, the heavy and light mineral composition in the insoluble residue of underlying limestones and dolomites, and that in the insoluble residue of other potential source formations such as fl ysch and loess, have been analysed. The extent of pyroclastic infl uence on these terra rossa soils was also evaluated. Amphiboles, zircon, tourmaline, garnet, kyanite, clinopyroxene and orthopyroxene, present in both loess deposits in Istria and in the terra rossa, prove that detritus mineralogically similar to that found in Late Pleistocene loess has been incorporated into the terra rossa. Heavy mineral data indicate that material was also derived from Istrian fl ysch during terra rossa formation. Air-fall of particles from the Roman- Campanian Volcanic Province may also have contributed, and hypidiomorphic Kfeldspars accompanying clinopyroxene and orthopyroxene in some loess and terra rossa samples might be of this volcanic origin. It is diffi cult to estimate to what extent materials other than the insoluble residue of limestones and dolomites have contributed to terra rossa in Istria, though analytical data available to date suggest that this might have reached 50%. We conclude that the main external contributor is Middle Pleistocene loess, followed by fl ysch and tephra. Late Pleistocene loess may have become incorporated in the upper parts of already formed terra rossa. In the terra rossa on the island of Korcˇ ula, devitrifi ed pumice clasts, sanidine, hyalophane, Ti-andradite, potassic hastingsite, along with orthopyroxene and black mica, clearly represent volcanic input.

terra rossa, parent materials, heavy and light mineral fraction, polygenetic nature, Istria, Croatia

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