Geoscience Reference
In-Depth Information
close-by cores shows that these greigite spots are situated in specific layers and
depth ranges and may also, with some caution, be used for zonation and correla-
tion. p-Wave velocity
V
p
depends on the strength
K
(compression modulus) and the
density (dwb) of the sediments (
V
p
=
dwb).
In soft homogeneous mud deposits, the sound velocity will drop below the sound
velocity of water because the compression modulus remains about the same, but the
density increases. In case of the deposition of laminated sediments, the thin layers
have a higher strength but about the same density as the homogeneous mud result-
ing in a higher sound velocity in comparison to the homogeneous mud. Harff et al.
geneous sediments using an acoustic index, which is the detrended and normalized
p-wave velocity.
K
/
5.4.4 Geochemical Data
X-ray fluorescence (XRF) logging has been deployed to describe the down-
core changes in chemical composition of the sediments of core 303610-12. For
measurements an Avaatech XRF Core Scanner of the Royal Netherlands Institute for
Sea Research (NIOZ) has been used. XRF analyses were carried out on the surface
of split sediment cores. The surface of the split cores has been carefully flattened
and covered finally with a thin (4
m) Ultralene film, further diminishing surface
roughness and preventing contamination of the measurement unit during core log-
ging. While measuring the scanning system is flushed with helium to prevent partial
or complete absorption of emitted radiation by air. The X-ray fluorescence signal
which arrives at the detector originates from a sediment depth from about 50
μ
m
for light elements up to 1 mm for heavy elements. The following components have
been measured in a 0.5 cm step size: Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Co. The
raw data were processed with WinAxil PC XRF analysis software. Data acquired are
qualitative, given in numbers of counts per 30 s of measurement time. For method
μ
5.4.5 Diatomological Data
Diatom analysis covered the sediment interval between 20 and 520 cm of the core
303610-12. Subsamples for the diatom analysis were taken at a sample space of
1-10 cm, depending on the lithology. In general the first 100 samples were col-
lected in core interval of 20-330 cm at every 3 cm. The total number of samples
analysed amounted to 132. Approximately 300 valves were counted in each sample.
Based on the diatom counting results auto-ecological properties of particular taxa
were determined and the grouping of diatoms in terms of habitat, salinity, and tro-
phy was performed. The percentages of particular ecological groups were computed
by means of the OMNIDIA ver. 3 software, which has a database (Omnis7) with
information on more than 11,000 species. Diagrams showing the percentages of