engleski

Geochemical conditions for the preservation of recent aragonite-rich sediments in Mediterranean karstic marine lakes (Mljet Island, Adriatic Sea, Croatia)

Conditions for the preservation of recent aragonite-rich sediments during early diagenesis in two semi-enclosed Mediterranean karstic marine (sea water) lakes on the island of Mljet (Adriatic Sea) were examined. The concentrations and stable isotope compositions of carbonate and sedimentary organic matter, as well as the geochemical parameters in pore water were measured. It was shown that the smaller lake (Malo Jezero) receives considerably more terrestrial detritus than the larger one (Veliko Jezero). The decrease in carbonate δ 13C values with depth indicated a rather intensive transfer of organically-derived C into the carbonate pool by diagenetic recrystallisation, masking the changes in carbonate δ 13C caused by the increasing amount of aragonite. Dissolution of calcite due to CO2 released from the decomposition of organic debris, and the upward diffusive flux of dissolved inorganic carbon (DIC) were together responsible for up to 24% of the DIC added to the pore water. This indicated locally occurring carbonate dissolution, irrespective of its saturation state in the bulk sediment. In spite of the larger input of terrigenous material into Malo Jezero, the carbonate content in the sediment was much higher than in Veliko Jezero, indicating a larger authigenic aragonite production. As magnesium calcite accounted for the major part of carbonate dissolution, aragonite preservation in the sediment is favoured.

aragonite ; Adriatic Sea ; carbon ; nitrogen ; sediments ; sedimentary organic matter ; stable isotopes.

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