An example of destructive diagenesis is the reductive dissolution of iron oxides within and below sapropels in the eastern Mediterranean (Passier et al., 1996 and 1998). Sapropels are recurrent organic-rich layers of centimetres to decimetres thickness in the Neogene sedimentary record of the eastern Mediterranean. These layers were deposited as a result of orbitally controlled climatic and oceanographic variations.

Within sapropels bacterial sulphate reduction occurs during and shortly after deposition of the layers. The predominant iron sulphide associated with the sapropels is pyrite. Pyrite formation was limited by iron availability within sapropels. This resulted in the downward diffusion of sulphide out of the organic-rich layers into the sediments directly below, causing reductive dissolution of iron oxides and pyrite formation there as well (Passier et al., 1998).

MAST 1994 Palaeoflux cruise with R/V Urania, Catania, Sicily

Whereas sulphate reduction and subsequent reductive dissolution of iron (hydr)oxides by sulphide stopped soon after burial of most sapropels, sulphate reduction presumably still occurs at very low rates in an extremely organic-rich Pliocene sapropel recovered during ODP Leg 160. In this sapropel other iron sulphide compounds than pyrite were found, which were magnetic (Roberts et al., 1998; Passier et al., 1998). 

Although pyrite is the predominant iron sulphide mineral in marine sediments, magnetic sulphides (greigite, pyrrhotite), which are intermediates in pyrite formation, have been reported to accumulate in marine sediments as well (e.g., Roberts and Turner, 1993). This is partly due to the recent development of rock-magnetic criteria for their detection (e.g., for pyrrhotite: Dekkers, 1988 and 1989; Menyeh and O’Reilly 1991; for greigite: Snowball and Thompson, 1990; Dekkers and Schoonen, 1996; Snowball, 1997).

It is not yet clear, however, what the exact contribution of magnetic iron sulphides to rock magnetic signals in sediments is. In addition, the exact influence of formation conditions and grain-size on mineral magnetic properties is not well known. Therefore, we further investigated the magnetic properties of natural and synthetic greigite and pyrrhotite.

• Garming, J.F.L, De Lange, G.J., Dekkers, M.J. and Passier, H.F. (2004). Changes in magnetic parameters after sequential iron phase extraction of Eastern Mediterranean sapropel S1, Stud. Geophys. Geod., 48, 345-362 

• Passier, H.F. and Dekkers, M.J. (2002). Iron oxide formation in the active oxidation front above sapropel S1 in the eastern Mediterranean Sea as derived from low-temperature magnetism, Geophys. J. Int., 150, 230-240.  
• Schenau S.J., H.F. Passier, G.J. Reichart and G.J. de Lange (2002). Sedimentary pyrite formation in the Arabian Sea. Marine Geology, 185, 393-402. 

 

• Passier, H.F., de Lange, G.J. and Dekkers, M.J. (2001). Rock-magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the Mediterranean, Geophys. J. Int., 145, 604-614. 
• Kruiver, P.P. and Passier, H.F. (2001). Coercivity analysis of magnetic phases in sapropel S1 related to variations in redox conditions, including an investigation of the S-ratio. Geochem. Geophys. Geosyst., 14 December 2001, Paper number 2001GC000181     [link to G-cubed]

• Dekkers, M.J., Passier, H.F. and Schoonen M.A.A. (2000). Magnetic properties of hydrothermally synthesized greigite (Fe₃S₄) II. High- and low-temperature characteristics, Geoph. J. Int., 141, 809-819. 

• Passier, H.F., Bosch, H.-J., Nijenhuis, I.A., Lourens, L.J., Böttcher, M.E., Leenders, A., Sinninghe Damsté, J.S., de Lange, G.J., and de Leeuw, J.W. (1999). Sulphidic Mediterranean surface waters during Pliocene sapropel formation. Nature,397, 146-149. 
• Passier, H.F., Middelburg, J.J., de Lange, G.J., and Böttcher, M.E. (1999). Modes of sapropel formation in the eastern Mediterranean: some constraints based on pyrite properties, Marine Geology, 153, 199-219. 
• Passier, H.F., Böttcher, M.E. and de Lange, G.J. (1999) Sulphur enrichments in organic matter of eastern Mediterranean sapropels: a study of sulphur isotope partitioning, Aquatic Geochemistry, 5(1), 99-118.

Passier, H.F (1998). Sulphur geochemistry and sapropel formation - Syngenetic and diagenetic signals in eastern Mediterranean sediments. (PhD thesis, Utrecht University) Geologica Ultraiectina, 158, 168 pp. [Thesis On Line]

• Passier, H.F., Dekkers, M.J. & de Lange, G.J. (1998). Sediment chemistry and magnetic properties in an anomalously reducing core from the eastern Mediterranean Sea. Chemical Geology, 152, 287-306. 
• Passier, H.F., and de Lange, G.J. (1998). Sedimentary sulfur and iron chemistry in relation to the formation of eastern Mediterranean sapropels, Proceedings ODP, Scientific Results, 160, 249-259. 
• Passier, H.F., Middelburg, J.J., de Lange, G.J., and Böttcher, M.E. (1998). Modes of sapropel formation in the eastern Mediterranean: some constraints based on pyrite properties, Marine Geology, 153, 199-219. 

• Passier, H.F., Middelburg, J.J., de Lange, G.J., and Böttcher, M.E., 1997. Pyrite contents, microtextures, and sulfur isotopes in relation to formation of the youngest eastern Mediterranean sapropel, Geology, 25, 519-522
• Passier, H.F., Luther III, G.W., and de Lange, G.J.,  1997. Early diagenesis and sulphur speciation in sediments of the Oman Margin, northwestern Arabian Sea, Deep-Sea Research II, 44, 1361-1380. 

• Passier, H.F., Middelburg, J.J., van Os, B.J.H., and de Lange, G.J., 1996. Diagenetic pyritisation under eastern Mediterranean sapropels caused by downward sulphide diffusion, Geochimica et Cosmochimica Acta, 60, 751-763. 
• Passier, H.F., de Lange, G.J., Middelburg, J.J., and van Os, B.J.H., 1996. Sulphur appearances in and around sapropels, eastern Mediterranean. In: S.H. Bottrell (ed.), Fourth International symposium on the Geochemistry of the Earth's Surface, 22-28 July 1996, Ilkley, Yorkshire, (England), University of Leeds, pp. 101-104.