Two cores recovered from different locations in the eastern Mediterranean contain intercalations of organic-rich sapropels in organic-poor hemipelagic sediments. In both cores enrichments of Mn and Fe were found in the oxidised section of the sediment, above the sapropel S1. The sediments followed a diagenetic cycle, which began after the sapropel formation finished (about 7000 years ago). First, during a non-steady-state diagenetic phase, metal-rich layers were formed at a downward moving oxidation front. The front decelerated at the top of the sapropel as a consequence of increasing amounts of Corg and sulphides that had to be oxidised. During the second part of this non-steady-state phase, the oxidation front starts moving upwards with respect to the sapropel. Manganese is remobilised in preference to iron due to thermodynamics, reinforced by kinetics. When the upward movement of the oxidation front becomes equal to the sedimentation rate, steady-state is established with respect to the new organic-poor sedimentary circumstances. At location 31G1, the system is at or close to steady-state. At location 9G1, however, this steady-state phase has never been reached. Between 1900 and 1350 years BP, the organic carbon accumulation rate probably increased suddenly, inducing a retreat of the oxidation front and the non-steady-state formation of double peaks.
Pruysers, P. A., De Lange, G. J., Middelburg, J. J., & Hydes, D. J. (1993). The diagenetic formation of metal-rich layers in sapropel-containing sediments in the eastern Mediterranean. Geochimica et Cosmochimica Acta, 57(3), 527-536. https://doi.org/10.1016/0016-7037(93)90365-4