119
cially in the case of barium at a depth of
somewhat more than 1 m below the sediment
surface, a much steeper rise of the measured
values is recognizable than is characteristic
of the other elements also controlled by
terrestric processes. A similar steep rise at
this depth is otherwise only encountered by
strontium which is predominately controlled
by marine processes. Various authors conceive barium as a proxy parameter of paleoproductivity in the surface water of oceans
(e.g. Kasten et al. 2001). Also the elements
copper, nickel and zinc which produced
curves similar to barium reach the sediment
when they are bound to organic matter, and
thus create similar imprints in the sediment.
•
The earth alkali metals calcium and strontium
are almost exclusively determined by marine
routes of entry. They predominately reach the
sediment in the shape of calcareous shells
originating from perished marine organisms. In
this case, various organisms contain slightly
different amounts of strontium, while others
incorporate strontium to a variable degree, a
process which depends on the surrounding
temperature. For this core, and other sediment
cores obtained from the Cape Basin, it could be
demonstrated that a profile of the Sr/Ca ratio
matched perfectly with the corresponding δ
18
Ocurve (SPECMAP curve, Imbrie et al. 1984),
permitting an immediate deduction of an age
model (cf. Wien et al. 2005b).
•
The two elements in this core, calcium and
strontium, were not even essentially
influenced by diagenesis. Wherever the
sediment’s pCO 2 and concentration of dissolved carbonate changes in course of the
degradation of organic matter, the respective
dissolution/precipitation
reactions
of
carbonate minerals can also be concomitantly
determined (Pfeifer et al. 2002, Wenzhöfer et
al. 2001).
• Large parts of the silicon curves show a
resemblance to the elements which are
introduced from land. This element obviously
also reaches the marine sediment on similar
routes of entry. However, individual peaks
display a similarity to the elements which are
controlled by marine conditions and thus
provide evidence in favor of biogenic opal as
the route of entry, which is also quantitatively relevant.
• Sulfur reaches the sediment essentially only by
means of diagenetic processes. Here, the
fixation of sulfate-bound sulfur in the form of
barite in the sulfate-methane transition (SMT)
zone produces an interesting signal, but is
quantitatively irrelevant on account of the low
barium concentrations in the pore water. Sulfur
precipitates in much greater amounts in shape
of sulfide (Mackinawite FeS, pyrite FeS 2 )
wherever sulfide resulting from the reduction
of sulfate comes into contact with divalent
iron by means of diffusion. In the core shown
in Figure 3.29 this obviously proceeded at a
depth of about 7 m below the sediment surface
over a relatively long period of time.
•
The two halogens Cl and Br also provide
some interesting pieces of information. Since
a high concentration of chlorine prevails in
ocean water, but is practically not involved in
any diagenetic processes, chlorine can make
its way into the XRF sample only by means
of pore water extraction. The curve of chlorine shown in Figure 3.29 represents the
porosity of the sediment material so precisely
that its concentration could be reconstructed.
This influence can also be seen in the case of
bromine which is, however, overlain by a
similar signal of nearly the same intensity as
those of the elements Ba, Cu, Ni, Zn which
are controlled by organic matter.
3.7.3
Correlation of Sediment Cores
by the Contents of Elements
A stratigraphic correlation of different sediment
cores only makes sense if the element applied in a
correlation of a given core is practically not
influenced by any diagenetic process at all, and
when its curve is practically only influenced by
its input into the sediment.
Diagenetic influences would not be coupled to
the stratigraphy, but would reach various depths
at various locations instead, totally independent
of the diagenetic processes. Especially suited for
correlations are elements that do not display too
low concentrations and whose input into the
sediment is essentially determined by one single
route of entry. This can be, for example, either
one of elements aluminum or iron for the terrestrial input, or calcium or strontium for the marine
3.7
Signals in the Sediment Solid Phase
cially in the case of barium at a depth of
somewhat more than 1 m below the sediment
surface, a much steeper rise of the measured
values is recognizable than is characteristic
of the other elements also controlled by
terrestric processes. A similar steep rise at
this depth is otherwise only encountered by
strontium which is predominately controlled
by marine processes. Various authors conceive barium as a proxy parameter of paleoproductivity in the surface water of oceans
(e.g. Kasten et al. 2001). Also the elements
copper, nickel and zinc which produced
curves similar to barium reach the sediment
when they are bound to organic matter, and
thus create similar imprints in the sediment.
•
The earth alkali metals calcium and strontium
are almost exclusively determined by marine
routes of entry. They predominately reach the
sediment in the shape of calcareous shells
originating from perished marine organisms. In
this case, various organisms contain slightly
different amounts of strontium, while others
incorporate strontium to a variable degree, a
process which depends on the surrounding
temperature. For this core, and other sediment
cores obtained from the Cape Basin, it could be
demonstrated that a profile of the Sr/Ca ratio
matched perfectly with the corresponding δ
18
Ocurve (SPECMAP curve, Imbrie et al. 1984),
permitting an immediate deduction of an age
model (cf. Wien et al. 2005b).
•
The two elements in this core, calcium and
strontium, were not even essentially
influenced by diagenesis. Wherever the
sediment’s pCO 2 and concentration of dissolved carbonate changes in course of the
degradation of organic matter, the respective
dissolution/precipitation
reactions
of
carbonate minerals can also be concomitantly
determined (Pfeifer et al. 2002, Wenzhöfer et
al. 2001).
• Large parts of the silicon curves show a
resemblance to the elements which are
introduced from land. This element obviously
also reaches the marine sediment on similar
routes of entry. However, individual peaks
display a similarity to the elements which are
controlled by marine conditions and thus
provide evidence in favor of biogenic opal as
the route of entry, which is also quantitatively relevant.
• Sulfur reaches the sediment essentially only by
means of diagenetic processes. Here, the
fixation of sulfate-bound sulfur in the form of
barite in the sulfate-methane transition (SMT)
zone produces an interesting signal, but is
quantitatively irrelevant on account of the low
barium concentrations in the pore water. Sulfur
precipitates in much greater amounts in shape
of sulfide (Mackinawite FeS, pyrite FeS 2 )
wherever sulfide resulting from the reduction
of sulfate comes into contact with divalent
iron by means of diffusion. In the core shown
in Figure 3.29 this obviously proceeded at a
depth of about 7 m below the sediment surface
over a relatively long period of time.
•
The two halogens Cl and Br also provide
some interesting pieces of information. Since
a high concentration of chlorine prevails in
ocean water, but is practically not involved in
any diagenetic processes, chlorine can make
its way into the XRF sample only by means
of pore water extraction. The curve of chlorine shown in Figure 3.29 represents the
porosity of the sediment material so precisely
that its concentration could be reconstructed.
This influence can also be seen in the case of
bromine which is, however, overlain by a
similar signal of nearly the same intensity as
those of the elements Ba, Cu, Ni, Zn which
are controlled by organic matter.
3.7.3
Correlation of Sediment Cores
by the Contents of Elements
A stratigraphic correlation of different sediment
cores only makes sense if the element applied in a
correlation of a given core is practically not
influenced by any diagenetic process at all, and
when its curve is practically only influenced by
its input into the sediment.
Diagenetic influences would not be coupled to
the stratigraphy, but would reach various depths
at various locations instead, totally independent
of the diagenetic processes. Especially suited for
correlations are elements that do not display too
low concentrations and whose input into the
sediment is essentially determined by one single
route of entry. This can be, for example, either
one of elements aluminum or iron for the terrestrial input, or calcium or strontium for the marine
3.7
Signals in the Sediment Solid Phase