engleski

Rare - Earth Elemental Analysis as a Tool for Assessment of Chemical Weathering Rates of Eocene Flysch Deposits in Two Catchments in Istria, Croatia

Geochemical research determined relative intensities of chemical weathering in neighbouring catchments of rivers Argilla, a tributary of the river Dragonja, and river Bazuja, river with a floodplain in the swallow hole (ponor) zone. Catchments differ by intensity of agricultural activity - Argilla catchment with high activity, while Bazuja catchment is mostly abandoned. Catchments are characterized with rapid denudation processes of flysch bedrock composed of turbidite deposits. Recent weathering was evaluated using bulk chemistry analysis focused on rare earth elements (REE), major elements and zirconium at 32 sites. Land-use in Argilla catchment significantly contributes to amount of fine carbonate rich rock debris within the soil profiles. Result is a mass transfer 0 or slight accumulation of all major elements and REE in the surface horizons and the deeper 5-20 cm horizons. In the same horizons of the forest soils of Bazuja catchment mass loss of REE was 17.5% in the topsoil horizons, and 14% in the deeper horizons. During the weathering both in soil horizons and weathering rinds in corresponding calcarenite rocks the fractionation of REE occurs indicating a higher mobility of light REE than of heavy REE. Changes in long-term weathering were evaluated through comparison of REE geochemistry and molar ratios of major elements in recent stream sediments, overbank sediment profiles in ponor zone and soil profiles. The REE geochemistry and molar ratios in the overbank profile of the ponor zone showed that the oldest sediments deposited are similar to present day Argilla catchment. The younger overbank sediments geochemically correspond to the eastern part of the Bazuja catchment. The mass balance calculations show that flysch rocks and overlying soils are more intensively chemically weathered with significant base cation loses and enrichment of conservative elements (REE, Zr, Ti) in the soil profiles in areas covered by forest (the r. Bazuja catchment).

REE; weathering; flysch

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