Abstract

The amount and type of organic matter (OM), chemical and mineralogical compositions, and the amount and isotopic ratio of sulphur were measured and benthic foraminiferal assemblages were analysed in a 70 m thick core section comprising marine marls from the Eocene of Hungary. On the basis of Benthic Foraminiferal Oxygen Index (BFOI), the studied sediments were deposited under a range of anoxic to oxic bottom water conditions. The amount of C org mineralised during early burial was calculated in two steps. First, carbon mineralised by sulphate reduction was calculated from the amount of sedimentary sulphur, corrected for escaped/oxidised H 2S by taking into account the isotopic composition of sulphur. Then, on analogy of recent sediments which are deposited with a similar rate of sedimentation and beneath bottom waters of similar O 2 content, carbon loss by aerobic respiration was estimated. A good stratigraphic control and knowledge of variation of mineralogical composition along the section permitted to estimate past variation of local organic carbon flux (C flux) from calculated original C org contents. During deposition of the studied strata, C flux first decreased from 1.16 to 0.41 g C org/m 2/y, then it progressively increased to 1.81 g C org/m 2/y. Changes in local C flux are explained by changes in water depth, flux of terrestrial organic components and availability of nutrients liberated by alteration of products of the coeval pyroclastic activity.

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