29
2.2
Porositiy and Wet Bulk Density
indirectly by determining one or several related
parameters and computing the desired property by
empirical or model-based equations. For consolidated sedimentary, igneous and metamorphic
rocks Schön (1996) described a large variety of
such methods for all common physical properties.
Some of these methods can also be applied to
unconsolidated, water-saturated sediments, others
have to be modified or are completely inappropriate. Principally, if empirical relations or sediment
models are used, the implicit assumptions have to
be checked carefully. An example is Archie’s law
(Archie 1942) which combines the electrical resistivities of the pore fluid and saturated sediment
and with its porosity. An exponent and multiplier
in this equation depend on the sediment type and
composition and change from fine- to coarsegrained and from terrigenous to biogenic sediments. Another example is Wood’s equation
(Wood 1946) which relates P-wave velocities to
porosities. This model approximates the sediment
by a dilute suspension and neglects the sediment
frame, any interactions between particles or
particles and pore fluid and assumes a ‘zero’
frequency for acoustic measurements. Such
assumptions are only valid for a very limited set of
high porosity sediments so that for any comparisons these limitations should be kept in mind.
Traditional measuring techniques use small
chunk samples taken from the split core. These
techniques are rather time-consuming and could
only be applied at coarse sampling intervals. The
necessity to measure high-resolution physical
property logs rapidly on a milli- to centimeter
scale for a core-to-core or core-to-seismic data
correlation, and the opportunity to use highresolution physical property logs for stratigraphic
purposes (e.g. orbital tuning) forced the development of non-destructive, automated logging
systems. They record one or several physical
properties almost continuously at arbitrary small
increments under laboratory conditions. The most
common tools are the multi sensor track (MST)
system for P-wave velocity, wet bulk density and
magnetic susceptibility core logging onboard of
the Ocean Drilling Program research vessel
JOIDES Resolution (e.g. Shipboard Scientific
Party 1995), and the commercially available multi
sensor core logger (MSCL) of GEOTEK™
(Schultheiss and McPhail 1989; Weaver and
Schultheiss 1990; Gunn and Best 1998).
Additionally, other core logging tools have simultaneously been developed for special research
interests which for instance record electrical resistivities (Bergmann 1996) or full waveform transmission seismograms on sediment cores (Breitzke
and Spieß 1993). They are particularly discussed
in this paper.
While studies on sediment cores only provide
information on the local core position, lateral
variations in physical properties can be imaged by
remote sensing methods like high-resolution seismic or sediment echosounder profiling. They
facilitate core-to-core correlations over large distances and allow to evaluate physical property
logs within the local sedimentation environment.
In what follows the theoretical background of
the most common physical properties and their
measuring tools are described. Examples for the
wet bulk density and porosity can be found in
Section 2.2. For the acoustic and elastic parameters first the main aspects of Biot-Stoll’s
viscoelastic model which computes P- and S-wave
velocities and attenuations for given sediment
parameters (Biot 1956a, b, Stoll 1974, 1977, 1989)
are summarized. Subsequently, analysis methods
are described to derive these parameters from
transmission seismograms recorded on sediment
cores, to compute additional properties like elastic
moduli and to derive the permeability as a related
parameter by an inversion scheme (Sect. 2.4).
Examples from terrigenous and biogenic
sedimentation provinces are presented (1) to
illustrate the large variability of physical
properties in different sediment types and (2) to
establish a sediment classification which is only
based on physical properties, in contrast to
geological sediment classifications which mainly
uses parameters like grain size distribution or
mineralogical composition (Sect. 2.5).
Finally, some examples from high-resolution
narrow-beam echosounder recordings present
remote sensing images of terrigenous and biogenic sedimentation environments (Sect. 2.6).
2.2
Porosity and Wet Bulk Density
Porosity and wet bulk density are typical bulk
parameters which are directly associated with the
relative amount of solid and fluid components in
marine sediments. After definition of both parameters this section first describes their traditional
analysis method and then focuses on recently
developed techniques which determine porosities
2.2
Porositiy and Wet Bulk Density
indirectly by determining one or several related
parameters and computing the desired property by
empirical or model-based equations. For consolidated sedimentary, igneous and metamorphic
rocks Schön (1996) described a large variety of
such methods for all common physical properties.
Some of these methods can also be applied to
unconsolidated, water-saturated sediments, others
have to be modified or are completely inappropriate. Principally, if empirical relations or sediment
models are used, the implicit assumptions have to
be checked carefully. An example is Archie’s law
(Archie 1942) which combines the electrical resistivities of the pore fluid and saturated sediment
and with its porosity. An exponent and multiplier
in this equation depend on the sediment type and
composition and change from fine- to coarsegrained and from terrigenous to biogenic sediments. Another example is Wood’s equation
(Wood 1946) which relates P-wave velocities to
porosities. This model approximates the sediment
by a dilute suspension and neglects the sediment
frame, any interactions between particles or
particles and pore fluid and assumes a ‘zero’
frequency for acoustic measurements. Such
assumptions are only valid for a very limited set of
high porosity sediments so that for any comparisons these limitations should be kept in mind.
Traditional measuring techniques use small
chunk samples taken from the split core. These
techniques are rather time-consuming and could
only be applied at coarse sampling intervals. The
necessity to measure high-resolution physical
property logs rapidly on a milli- to centimeter
scale for a core-to-core or core-to-seismic data
correlation, and the opportunity to use highresolution physical property logs for stratigraphic
purposes (e.g. orbital tuning) forced the development of non-destructive, automated logging
systems. They record one or several physical
properties almost continuously at arbitrary small
increments under laboratory conditions. The most
common tools are the multi sensor track (MST)
system for P-wave velocity, wet bulk density and
magnetic susceptibility core logging onboard of
the Ocean Drilling Program research vessel
JOIDES Resolution (e.g. Shipboard Scientific
Party 1995), and the commercially available multi
sensor core logger (MSCL) of GEOTEK™
(Schultheiss and McPhail 1989; Weaver and
Schultheiss 1990; Gunn and Best 1998).
Additionally, other core logging tools have simultaneously been developed for special research
interests which for instance record electrical resistivities (Bergmann 1996) or full waveform transmission seismograms on sediment cores (Breitzke
and Spieß 1993). They are particularly discussed
in this paper.
While studies on sediment cores only provide
information on the local core position, lateral
variations in physical properties can be imaged by
remote sensing methods like high-resolution seismic or sediment echosounder profiling. They
facilitate core-to-core correlations over large distances and allow to evaluate physical property
logs within the local sedimentation environment.
In what follows the theoretical background of
the most common physical properties and their
measuring tools are described. Examples for the
wet bulk density and porosity can be found in
Section 2.2. For the acoustic and elastic parameters first the main aspects of Biot-Stoll’s
viscoelastic model which computes P- and S-wave
velocities and attenuations for given sediment
parameters (Biot 1956a, b, Stoll 1974, 1977, 1989)
are summarized. Subsequently, analysis methods
are described to derive these parameters from
transmission seismograms recorded on sediment
cores, to compute additional properties like elastic
moduli and to derive the permeability as a related
parameter by an inversion scheme (Sect. 2.4).
Examples from terrigenous and biogenic
sedimentation provinces are presented (1) to
illustrate the large variability of physical
properties in different sediment types and (2) to
establish a sediment classification which is only
based on physical properties, in contrast to
geological sediment classifications which mainly
uses parameters like grain size distribution or
mineralogical composition (Sect. 2.5).
Finally, some examples from high-resolution
narrow-beam echosounder recordings present
remote sensing images of terrigenous and biogenic sedimentation environments (Sect. 2.6).
2.2
Porosity and Wet Bulk Density
Porosity and wet bulk density are typical bulk
parameters which are directly associated with the
relative amount of solid and fluid components in
marine sediments. After definition of both parameters this section first describes their traditional
analysis method and then focuses on recently
developed techniques which determine porosities