engleski

Isotope analysis of Pleistocene tufa deposits at Roški Slap in Krka National Park, Croatia

Tufa barriers are dynamic systems responding to changes in environment. In the canyon walls of Krka River, at Roški slap location, remains of older destroyed tufa barriers can be found. Previous research suggested existence of two subsequent barrier-lake tufa systems formed during the Last Interglacial Period. Oxygen isotope analysis of these tufa sediments allowed improvement of chronology.
18O record of first barrier was wiggle-matched with more robust regional
18O record. Calculated growth rate indicates that in average first tufa barrier grew between 0.3 and 1.3 mm per year(mm/yr). Growth rate of 0.083 mm/yr of second tufa barrier was calculated based on lamina counting in available samples. Our results show that first tufa barrier started to grow around 140.8 ky BP during MIS-6 deglaciation period and existed until 96.4 ky BP. Less negative isotope values during MIS-5e indicate more optimum conditions and higher growth rate. Degradation of optimum interglacial conditions caused decrease of growth rate around onset of MIS-5d. During this period two cold events C24 and C23 are well recorded in tufa of Roški slap. By this time growth rate of first tufa barrier is very limited and the progressive deterioration of environmental conditions during MIS-5c caused erosion of this barrier. Second tufa barrier started forming upon destruction of first barrier and existed for limited period of time during MIS-5c. This research shows that erosion of these two barrier-lake systems was very fast in geological terms and further research is needed to reveal the causes of these tufa barriers destruction.

Krka, Oxygen isotope, tufa

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