engleski

The origin and composition of Eocene flysch deposits as an attribute to the excessive erosion of the Slani Potok valley ("Salty creek"), Croatia

Flysch deposits that crop out in the elongated coastal area of Vinodol Valley (External Dinarides) and particularly in the Slani Potok (‘Salty creek’) catchment area have particular composition. Sandstones and biocalcrudites from the flysch in Slani Potok contain appreciable amount of siliciclastic material opposite to the other Eocene flysch domains in the External Dinarides where carbonate detritic material prevails. Siliciclastic component of sandstones and biocalcrudites contains ca 50% quartz, 30% lithic and 20% feldspar grains. Lithic fragments are represented by volcanic rocks revealing porphyric structures (possibly andesite) or altered volcanic glass fragments. The differences in flysch composition, also documented by high amount of sodium and barium measuring 0.93-1.09 % and 267- 276 mg/kg, respectively, is essentially ascribed to the different rocks in the provenance area of the Gorski Kotar region located in the hinterland of the Vinodol Valley. Occurrence of andesite near Fužinski Benkovac and Palaeozoic complex with barite mineralization in the Gorski Kotar, are considered as source. Proximity of the source area and its position straight north of Slani Potok imply that the direction of turbidity currents that deposited the flysch sediments in Slani Potok were transverse to the main axis of the Eocene foreland basin striking NW-SE. A particular composition of sandstones and biocalcrudites in the Slani Potok area attributed the formation of thenardite mineral. Source of sodium and sulphur for formation of thenardit is volcanic particles found in the flysch. Unusually intense erosion, having a varied character to the landscape, is caused by dispersive effect of sodium in solutions to clay particles derived from pelitic flysch rocks, as well as by expanding of thenardite while transforming into a deckahydrate (enlarging its volume at least 4 times).

composition of flysch deposits ; origin of flysch deposits ; excessive erosion ; Slani Potok ; External Dinarides ; Croatia

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