Diagenetic imprints on magnetic mineral assemblages in marine ...

Chapter 2.1
extracted in the reduced part of the sapropel. The residual minerals (step 9) were mainly
composed of aluminium, iron, and titanium.
22
Depth (cm)
26
28
30
32
34
36
(a) Mn (g/kg)
0 4 8 12
Markerbed
Oxidised Sapropel
Active oxidation zone
Reduced Sapropel,
S1
Coatings and carbonates
Amorphous oxides
Crystalline oxides
Amorphous silicon
Silicates
(b) Fe (g/kg)
0 10 20 30 40
Pyrite and organically bound minerals
Residual minerals
Fig. 3. (a) The amount of manganese (g/kg), and (b) the amount of iron (g/kg) extracted in the
different steps of the sequential extraction. The vertical hatched lines represent the amount
removed during the removal of the coatings and carbonates (step 1 – 3, Table 2). Horizontal
hatched lines indicate the removal of the ‘amorphous’ oxides (step 4). The dashed line represents
the amount of silicon also extracted in step 4. The diagonally hatched lines indicate the removal of
the crystalline oxides and the silicates. The tiles refer to the removed pyrite and organically bound
minerals. No filling was applied for the amount removed from the remaining fraction. Dashed
horizontal lines indicate the approximate boundaries of different geochemical zones in the core.
3.3 Magnetic parameters
The IRMcfb (calculated on a carbonate free basis, suffix cfb) acquired by the sediments
after the different extraction steps is given in Fig. 4a, the remanent coercivity (Hcr) is
presented in Fig. 4b. The IRMcfb is calculated with the assumption that the calcium
extracted in the different steps of the sequential extraction is solely related to carbonates.
The IRMcfb acquired by the untreated samples displays values ranging from
6.8*10 -3 Am 2 /kg in the markerbed, via ~4.5*10 -3 Am 2 /kg in the oxidised part of the