Diagenetic imprints on magnetic mineral assemblages in marine ...

Chapter 2
Synopsis of manuscripts and publications
12
During my PhD five manuscripts were produced, of which three already have been
published in international peer reviewed journals. The brief contents of these manuscripts
and publications are provided in the following section.
The results of sequential iron phase extraction from Sapropel S1 sediments from the
eastern Mediterranean and rock magnetic parameters measured prior and after are
discussed in the first manuscript. From the results it could be concluded that next to
silicates, iron is mainly incorporated into amorphous oxides in the oxidised part of the
sapropel, whereas pyrite is the main constituent in the still reduced part. Component
analysis of isothermal remanent magnetisation (IRM) identified three phases interpreted
as ‘detrital’ magnetite, hematite and biogenic magnetite.
In manuscript two, geochemical analysis of the pore waters recovered from cores from
the continental slope of the Argentine Basin identified strong reducing conditions, i.e.
sulphidic conditions, in a few meters depth. These are related to the anaerobic oxidation
of methane (AOM). A typical feature of these sediments is the formation of authigenic
sulphides accompanied by a nearly complete loss of magnetic susceptibility. Modelling of
the data revealed that a drastic change in sedimentation rate, which occurred during the
Pleistocene/Holocene transition, is needed to produce the features observed.
Detailed rock magnetic analysis, described in manuscript three, revealed that at the
iron redox boundary 40% of the fine grained magnetic fraction is already dissolved. Only
10% survives the strong reducing environment surrounding the sulphate methane
transition (SMT). Scanning electron microscope analysis in combination with X-ray
microanalysis showed that the magnetic particles survive either as inclusions in a
siliceous matrix or as intergrowths with titanohematite. Pyrite was the only secondary
sulphidic mineral found, unlike other studies investigating magnetic properties at around
the SMT.
Low-temperature properties of intergrown titanomagnetite and titanohematite are
discussed in the fourth manuscript. Warming a low-temperature saturation isothermal
remanent magnetisation (LT-SIRM) only shows a Verwey transition indicative for
magnetite, whereas cooling of a room temperature saturation isothermal remanent
magnetisation (RT-SIRM) shows a market drop in remanence at around 210 K,