Modes of sapropel formation in the eastern Mediterranean: some constraints based on pyrite properties |
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| Institution: | 1. Paleomagnetic Laboratory ‘Fort Hoofddijk’, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands;2. Geological Institute, Russian Academy of Sciences, Pyzhevskiy per. 7, Moscow 119017, Russia;3. Institute of Geological Sciences, National Academy of Sciences of Ukraine, O. Honchar str., 55_b, Kyiv 01601, Ukraine;4. Borissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow 117997, Russia;1. Institute of Earth Sciences, Hebrew University of Jerusalem, Edmond Y. Safra Givat Ram Campus, 9190401 Jerusalem, Israel;2. Geological Survey of Israel, 30 Malkhei Israel Street, Jerusalem 9550161, Israel;3. Institute for Geochemistry and Petrology, Department of Earth Sciences, ETH Zurich, NW D81.4, Clausiusstrasse 25, 8092 Zurich, Switzerland;4. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom |
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| Abstract: | Pyrite formation within and directly below sapropels in the eastern Mediterranean was governed by the relative rates of sulphide production and Fe liberation and supply to the organic-rich layers. At times of relatively high SO2?4 reduction, sulphide could diffuse downward from the sapropel and formed pyrite in underlying sediments. The sources of Fe for pyrite formation comprised detrital Fe and diagenetically liberated Fe(II) from sapropel-underlying sediments. In organic-rich sapropels, input of Fe from the water column via Fe sulphide formation in the water may have been important as well. Rapid pyrite formation at high saturation levels resulted in the formation of framboidal pyrite within the sapropels, whereas below the sapropels slow euhedral pyrite formation at low saturation levels occurred. δ34S values of pyrite are ?33‰ to ?50‰. Below the sapropels δ34S is lower than within the sapropels, as a result of increased sulphide re-oxidation at times of relatively high sulphide production and concentration when sulphide could escape from the sediment. The percentage of initially formed sulphide that was re-oxidized was estimated from organic carbon fluxes and burial efficiencies in the sediment. It ranges from 34% to 80%, varying significantly between sapropels. Increased palaeoproductivity as well as enhanced preservation contributed to magnified accumulation of organic matter in sapropels. |
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