2
Physical Properties of Marine Sediments
32
Fig. 2.3 Gamma counts for a 1 m long core section of gravity core PS2557-1 used to illustrate the influence of various
integration times and measuring increments. Curve A is recorded with an increment of 1 cm and an integration time of
10 s, curve B with an increment of 1 cm and an integration time of 20 s, curve C with an increment of 0.5 cm and an
integration time of 60 s and curve D with an increment of 0.2 cm and an integration time of 120 s. To facilitate the
comparison each curve is set off by 800 counts. Modified after Weber et al. (1997).
for the gamma ray attenuation gamma counts must
be integrated over a sufficiently long time interval.
How different integration times and measuring
increments influence the quality, resolution and
reproducibility of gamma ray logs illustrates
Figure 2.3. A 1 m long section of gravity core
PS2557-1 from the South African continental
margin was repeatedly measured with increments
from 1 to 0.2 cm and integration times from 10 to
120 s. Generally, the dominant features, which can
be related to changes in the lithology, are
reproduced in all core logs. The prominent peaks
are more pronounced and have higher amplitudes
if the integration time increases (from A to D).
Additionally, longer integration times reduce the
scatter (from A to B). Fine-scale lithological
variations are best resolved by the shortest
measuring increment (D).
A comparison of wet bulk densities derived
from gamma ray attenuation with those measured
on discrete samples is shown in Figure 2.4a for
two gravity cores from the Arctic (PS1725-2) and
Antarctic Ocean (PS1821-6). Wet bulk densities,
porosities and grain densities of the discrete
samples were analyzed by their weight and volume.
These grain densities and a constant ‘processing
porosity’ of 50% were used to evaluate the gamma
counts. Displayed versus each other both data sets
essentially differ by less than ±5% (dashed lines).
The lower density range (1.20 - 1.65 g cm
-3
) is
mainly covered by the data of the diatomaceous
and terrigenous sediments of core PS1821-6 while
the higher densities (1.65 - 2.10 g cm
-3
) are
characteristic for the terrigenous core PS1725-2.
According to Gerland and Villinger (1995) the
scatter in the correlation of both data sets probably results from (1) a slight shift in the depth
scales, (2) the fact that both measurements do not
consider identical samples volumes, and (3)
artefacts like drainage of sandy layers due to core
handling, transportation and storage.
A detailed comparison of both data sets is
shown in Figure 2.4b for two segments of core
PS1725-2. Wet bulk densities measured on discrete
samples agree very well with the density log
derived from gamma ray attenuation. Additionally,
Physical Properties of Marine Sediments
32
Fig. 2.3 Gamma counts for a 1 m long core section of gravity core PS2557-1 used to illustrate the influence of various
integration times and measuring increments. Curve A is recorded with an increment of 1 cm and an integration time of
10 s, curve B with an increment of 1 cm and an integration time of 20 s, curve C with an increment of 0.5 cm and an
integration time of 60 s and curve D with an increment of 0.2 cm and an integration time of 120 s. To facilitate the
comparison each curve is set off by 800 counts. Modified after Weber et al. (1997).
for the gamma ray attenuation gamma counts must
be integrated over a sufficiently long time interval.
How different integration times and measuring
increments influence the quality, resolution and
reproducibility of gamma ray logs illustrates
Figure 2.3. A 1 m long section of gravity core
PS2557-1 from the South African continental
margin was repeatedly measured with increments
from 1 to 0.2 cm and integration times from 10 to
120 s. Generally, the dominant features, which can
be related to changes in the lithology, are
reproduced in all core logs. The prominent peaks
are more pronounced and have higher amplitudes
if the integration time increases (from A to D).
Additionally, longer integration times reduce the
scatter (from A to B). Fine-scale lithological
variations are best resolved by the shortest
measuring increment (D).
A comparison of wet bulk densities derived
from gamma ray attenuation with those measured
on discrete samples is shown in Figure 2.4a for
two gravity cores from the Arctic (PS1725-2) and
Antarctic Ocean (PS1821-6). Wet bulk densities,
porosities and grain densities of the discrete
samples were analyzed by their weight and volume.
These grain densities and a constant ‘processing
porosity’ of 50% were used to evaluate the gamma
counts. Displayed versus each other both data sets
essentially differ by less than ±5% (dashed lines).
The lower density range (1.20 - 1.65 g cm
-3
) is
mainly covered by the data of the diatomaceous
and terrigenous sediments of core PS1821-6 while
the higher densities (1.65 - 2.10 g cm
-3
) are
characteristic for the terrigenous core PS1725-2.
According to Gerland and Villinger (1995) the
scatter in the correlation of both data sets probably results from (1) a slight shift in the depth
scales, (2) the fact that both measurements do not
consider identical samples volumes, and (3)
artefacts like drainage of sandy layers due to core
handling, transportation and storage.
A detailed comparison of both data sets is
shown in Figure 2.4b for two segments of core
PS1725-2. Wet bulk densities measured on discrete
samples agree very well with the density log
derived from gamma ray attenuation. Additionally,