Naslov
Chemical weathering of Eocene flysch in two small catchments in the Dragonja watershed, Croatia.

Autori
Miko, Slobodan ; Peh, Zoran ; Hasan, Ozren ; Mesić, Saša, Bukovec, Dragan ; Petković, Saša

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
22nd IAS Meeting of Sedimentology - Opatija 2003: Abstracts Book / Igor Vlahović - Zagreb : Institute of Geology, Zagreb, 2003, 128-128

Skup
22nd IAS Meeting of Sedimentology - Opatija 2003

Mjesto i datum
Opatija, Hrvatska, 17.09.2003. - 19.09.2003

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
rare earth geochemistry; eocene flysch; weathering; Istria

Sažetak
Chemical weathering and physical erosion in the Dragonja watershed are related processes that control soil development, deliver sediments and solutes to the riparian zone and stream water and shape the landscape. Two neighboring catchments were studied, the river Argila which is a tributary of the river Dragonja and river Bazuja, which is an influent river with allogenic recharge and a wide floodplain in the swallow hole (ponor) zone. The catchments are a part of accumulation-denudation type of morphostructure characterized by rapid denudation processes developed on Eocene flysch deposits. The flysch bedrocks are turbidite deposits with alternating marls and arenites most individual layers are thinner than 30 cm. The calcarenites contain quartz, feldspar, mica grains and lithoclasts of both carbonate and silicate rocks (chert, quartzite and schists). Carbonate Nummulite breccia beds within the marls and sandstone are found. The arenite to marl thickness ratio (A/M) in the flysch deposits ranges from 1: 2 to 1: 50. Present-day chemical weathering was evaluated with the aid of bulk chemistry analysis focused on major elements, zirconium and rare earth elements (REE) at 32 sites and the mobility of elements was characterized with the mass transfer coefficient (eluvial-illuvial coefficient, EIC) assuming Zr as the conservative component and the saprolite-rock boundary samples as the least weathered. The advantage of the use of the individual c-horizon as a satisfactory parent composition source is that the variation of the marls and calcarenites is incorporated directly into the calculation, although a bias is also introduced if the c-horizons are weathered to varying degrees, which must not be neglected. Due to agricultural land-use practice in the Argila catchment the physical processes significantly contribute to amount fine carbonate rich rock debris within the soil profiles, which resulted in a mass transfer &#61627 ; 0 or slight accumulation for all major elements and REE in the 0-5 cm horizons and the 5-20 cm horizons. In the same horizons of the forest soils of the Bazuja catchment loses of over 30% of Mg and Ca were determined. Al and K, loss ranges from 23 to 28 %. Na is less mobilized and ranges from 13% in the deeper horizon to 15% in the surface horizons. Only 10% of Si is mobilized in the forest topsoils. The calculated mass loss of REE was 17.5 % in the topsoil horizons 14% in the deeper horizons. Also during weathering the a both in the soil horizons and weathering rinds and corresponding calcarenite rocks a fractionation of REE occurs indicating a higher mobility of light REE than of heavy REE. Changes in long-term weathering rates were evaluated through comparison of molar ratios of major elements in recent stream sediments, overbank sediment profiles in swallow hole zones and soil profiles. The elemental ratios and REE show that stream derived after storm events are mainly derived from less weathered material and plot close to calcarenite/marl composition. The REE geochemistry and molar ratios of the youngest and the oldest parts of a &#61627 ; 15m high overbank sediment profile in the swallow hole zone of the river Bazuja showed that the oldest sediments deposited are similar to present day Argila catchment soils. The younger overbank sediments geochemically correspond to soils of the eastern part of the Bazuja catchment. The effect that forestation and abandoning of arable lands has a critical effect on chemical weathering rates in these catchments causing a loss of base cations Ca and Mg from the top 50 cm of the soil profiles and increasing the overall acidification.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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