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doi:10.2204/iodp.proc.340.102.2013

Physical properties

Physical properties measurements on sediment cores provide information that assists in the characterization of lithological units, stratigraphic correlation, heat flow, fluid flow, and consolidation history. They also help with the interpretation of seismic reflection profiles and downhole geophysical logging data. The primary objectives of the Expedition 340 physical properties program were to collect high-resolution data that (1) facilitate differentiation between mass transport events and background marine sedimentation; (2) constrain geothermal, geomechanical, and seismic properties; and (3) construct composite stratigraphic correlations.

We first measured physical properties on whole-round core sections using the Whole-Round Multisensor Logger (WRMSL), Natural Gamma Radiation Logger (NGRL), and thermal conductivity needle probe. Shear strength was measured on the core deck with a handheld penetrometer. We then split cores and measured shear strength, P-wave velocity, and moisture content and density on the working half of the cores. The archive half was subsequently imaged with the SHIL and then analyzed for color reflectance and point magnetic susceptibility using the SHMSL. A full discussion of all methodologies and calculations (except the NGRL) used in the JOIDES Resolution physical properties laboratory can be found in Blum (1997).

Whole-Round Multisensor Logger measurements

Compressional wave velocity (on the P-wave logger [PWL]), gamma ray attenuation (GRA), and magnetic susceptibility were measured with the WRMSL followed by natural gamma radiation with the NGRL. These measurements are all nonintrusive and nondestructive.

The sampling interval for all WRMSL measurements was 2.5 cm, with an integration time of ~8 s for each measurement. We assessed the reliability of WRMSL measurements with standards every 2–12 h.

The core liner was assumed to be completely full. The bulk density values obtained from the GRA, along with the magnetic susceptibility measurements, underestimate true values if the liner is not completely full. The liners were not completely full for most sections cored with the XCB. Partially filled core liners also sometimes occurred when the recovered material was sand rich. Anomalously low P-wave velocity and density values also occur where there are cracks and gaps in the core. To limit data manipulation, we left anomalous values in the raw data. When plotting data and using data for correlation, we removed data from within 5.1 cm of each end to avoid end effects.

Gamma ray attenuation bulk density

Bulk density is calculated by measuring the attenuation of gamma rays as they pass through the core. Attenuation of these rays is dominated by Compton scattering and depends on the density and thickness of the sample. Gamma rays with an energy of 0.662 MeV are generated by a ¹³⁷Cs source core (Evans, 1965; Harms and Choquette, 1965) and pass through the entire diameter of the core. The GRA detector records these gamma rays on a 75 mm × 75 mm sodium iodide detector. The spatial resolution of the GRA is <1 cm.

Bulk density (ρ) is proportional to the gamma ray count,

where

• µ = Compton attenuation coefficient,
• d = sample diameter,
• I₀ = gamma ray source intensity, and
• I = measured intensity of gamma rays passing through the sample.

µ and I₀ are treated as constants obtained by calibrating the gamma ray detector with a set of aligned aluminum cylinders of various diameters surrounded by distilled water in a sealed core liner that is the same as that used during coring operations. The relationship between I, µ, and d is

where A, B, and C are coefficients obtained from the calibration. Gamma ray counts through each cylinder were determined for a period of 60 s. The bulk density of each aluminum cylinder was 2.7 g/cm³, and d was 1, 2, 3, 4, 5, or 6 cm.

Drift was assessed by running water standards every few hours. Calibration was performed at least twice per day and was always performed if deviations from the standard exceeded 2%.

Magnetic susceptibility

Magnetic susceptibility measures the ability of a material to be magnetized by an external magnetic field. The dimensionless volume magnetic susceptibility (κ) is defined as

where M is the magnetization induced by a field of strength (H). Magnetic susceptibility is primarily sensitive to the concentration of ferrimagnetic minerals (e.g., magnetite and maghemite). It is also sensitive to magnetic mineralogy and can be related to the origin of the materials in the core and their subsequent diagenesis. Igneous materials typically have magnetic susceptibility a couple of orders of magnitude greater than their alteration products, such as clay.

The WRMSL includes a Bartington Instruments MS2 and MS2C sensor coil operating at a frequency of 565 Hz. Because the core has a smaller diameter (66 mm) than the instrument aperture (88 mm), a volume correction must be made offline. For a core diameter of 66 mm and coil aperture of 88 mm, instrument measurements must be multiplied by a factor of 0.68 (Blum, 1997).

The calibration of the instrument is preset. Reliability of measurements was assessed prior to making any measurements by measuring κ on a 40 cm long piece of core liner filled with a mixture of magnetite and epoxy and ensuring that the accuracy is within 5%. Every 2–6 h, water standards were analyzed to ensure there was no drift in the measurements. Spatial resolution is 4 cm based on the response function of the instrument. If the core is not continuous over an interval >8 cm, κ will be underestimated; such data is evident at the ends of cores because of these volumetric edge effects. Anomalous measurements were not removed from the raw data.

Compressional wave velocity

The PWL measures the traveltime of 500 kHz ultrasonic waves horizontally across the core at 2.5 cm intervals while it remains in the core liner. Waves are transmitted to the core by plastic transducer contacts connected to linear actuators. Pressure is applied to the actuators to ensure coupling between the transducers and the core liner.

P-wave velocity (V) is calculated by

where d is the path length of the wave through the core and t is the traveltime. The total traveltime between the transducers includes the time delay related to transducer faces and electronic circuitry, the delay in the peak detection procedure, and the transit time through the core liner.

Traveltime is calculated by automated signal processing that detects the arrival of P-wave signals to a precision of 50 ns. The search method skips the first positive amplitude and finds the second positive amplitude using a detection threshold limit, typically set to 30% of the maximum amplitude of the signal. It then finds the preceding zero crossing and subtracts one wave period to determine the first arrival. To avoid extremely weak signals, minimum signal strength can be set (typically 0.02 V) and weaker signals are ignored. To avoid signal interference at the beginning of the record from the receiver, a delay (typically 0.01 ms) can be set to force the amplitude search to begin in the quiet interval preceding the first arrival. In addition, a trigger (typically 4 V) is selected to initiate the arrival search process, and the number of waveforms to be stacked (typically five) can also be set. A linear variable differential transformer (LVDT) measures the separation of the transducer to derive a signal path length (i.e., the core diameter). P-wave velocity is finally calculated after correction for system propagation delay, liner thickness, and liner material velocity.

The system is calibrated with a set of plastic cylinders with a range of diameters. Water standards were run every few hours to ensure measurements remained reliable. PWL velocities always remained within 2% of the room temperature value.

Natural gamma radiation logger measurements

Gamma rays are emitted from decay of 238-uranium (²³⁸U), 232-thorium (²³²Th), and 40-potassium (⁴⁰K). The NGRL measures this natural emission on whole-round cores using a system designed and built at IODP-USIO (Texas A&M University, USA) between 2006 and 2008 (Vasiliev et al., 2011). This system has been used on every IODP-USIO expedition starting with Expedition 320.

The NGRL contains eight NaI scintillator detectors, seven plastic scintillator detectors, and 22 photomultipliers. NaI detectors are covered by 8 cm of lead for passive shielding. Half of the lead shielding closest to the NaI detectors is composed of low-background lead, and the outer half is composed of regular (virgin) lead. NaI detectors are separated by 7 cm of low-background lead. The NGRL uses a plastic scintillator to suppress high-energy gamma and muon components of cosmic radiation by producing a canceling signal when these charged particles pass through the plastic scintillators. The NGRL was calibrated with ¹³⁷Cs and ⁶⁰Co sources and identifying peaks at 662 keV (¹³⁷Cs) and 1330 keV (⁶⁰Co) using the 1170 keV peak for verification. Calibration materials were provided by Eckert & Ziegler Isotope Products Inc. (Valencia, California, USA).

Gamma ray counts are summed over the range of 100–3000 keV and are thus comparable with data collected during previous cruises and can be directly compared with downhole logging data. Background measurements over a 36,000 s time span were made on an empty core liner upon arrival at the first site and two other times during the expedition.

Characterization of each section consisted of eight measurements at two positions for a total of 16 measurements at 10 cm intervals. Spatial resolution, defined by the full width at half-maximum, is 19 cm. An edge correction was applied to measurements within 20 cm of the ends of each section (Vasiliev et al., 2011). The quality of the energy spectrum depends on the concentration of radionuclides in the sample, but also on the counting time, with higher times yielding better spectra. A previous study on pelagic sediments (very little gamma radiation activity) with minor amounts of siliciclastic material used the same apparatus; with counting times of 5 min at each position, spatial variations in natural gamma radiation (NGR) were identified reliably and used for stratigraphic correlation (Vasiliev et al., 2011). We thus used counting times of 5 min at each position to ensure reliable counting statistics. Measurements made at the ends of each section appear to be systematically lower than adjacent measurements, even after end corrections are made.

When plotting data and using NGR data for correlation, we discarded data from within 10 cm of both ends of the each section to avoid end effects.

Thermal conductivity measurements

Thermal conductivity measures the ability of a material to transfer heat by conduction. It is used, in combination with measurements of temperature, to calculate heat flow. Its value also depends on composition, porosity, and structure and thus complements other physical property measurements.

Thermal conductivity was measured with a TeKa TK04. All measurements were made after the core had equilibrated with the ambient temperature in the laboratory (>2.5 h) and after WRMSL and NGR measurements. A 2 mm hole for insertion of the probe was drilled into the side of the sample liner, typically close to the midpoint of the section. The measurement is reported at the location in the core. Prior to each measurement, thermal drift within the sample was measured to ensure that it would not significantly affect measurements (<0.04°C/min). Measurements were made once the thermal drift was stable, typically after 5 min. A calibrated heat source was then turned on and the increase in temperature was recorded over 90 s. A heating power of 2 W/m was typically used; large values produce greater signals but also promote undesirable processes such as convection in the pore fluids. The solution to the heat conduction equation with a line source of heat was then fit to the temperature measurements to obtain the thermal conductivity. Very high water content, inhomogeneous samples, and highly disturbed samples may cause deviations from the solution to the conduction equation. In the case of a poor fit, we did not keep the data.

Prior to measurements, a test was performed on a standard of MACOR plastic standard with

Measured values were within 3%. This test was typically performed once per day.

Reported data are not corrected to in situ conditions. The effect of increasing pressure is to increase thermal conductivity (k). The pressure correction is +1% for each 1800 m depth assuming a hydrostatic pressure gradient (Ratcliff, 1960). The effect of temperature is more complicated. The thermal conductivity of the matrix solids is inversely proportional to temperature (Zoth and Haenel, 1988). In contrast, the thermal conductivity of water increases with temperature (Keenan et al., 1978). The temperature correction for each +20°C change in temperature can be as high as +5% for a high-porosity, water-saturated sediment (Ratcliff, 1960) and –3% for hard rocks (Clark, 1966). These corrections are similar to the TK04 measurement uncertainty, about 5% during routine evaluation.

Downhole temperature measurements

In Holes U1395–U1400, downhole temperature was measured using the APCT-3. This tool allows temperature to be measured while drilling. By shooting the tool forward ~9.5 m during coring, the thermal effects of drilling are minimized. The APCT-3 records temperature with a glass-encapsulated thermistor (Model YSI 55032) at the outside edge of the cutting shoe. Details of its calibration and testing are described by Heesemann et al. (2006). Temperature was recorded downhole for ~10 min (as short as 2 min and as long as 48 min) and sampled every 2 s. This is not long enough for the probe to thermally equilibrate with its surroundings. Consequently, the recorded evolution of temperature was fit to a theoretical solution to the temperature evolution using TP-Fit software (see APCT-3 user manual on the Cumulus/Techdoc database at iodp.tamu.edu/​tasapps/). This theoretical solution assumes all heat transfer occurs by conduction and that we can neglect fluid flow induced by the insertion of the tool and convection driven by the large temperature gradients produced by friction. The calculated temperature depends on thermal conductivity, density, and the specific heat capacity of the surroundings. Uncertainty in these thermal properties dominates the uncertainty in the recovered temperature. Typical uncertainties on the best-fit temperature determined by TP-Fit are <0.08°C, assuming a 10% uncertainty on these material properties.

Temperature at the seafloor was also estimated from the coldest stable temperatures recorded at the mudline before the probe enters the hole. The probe typically sat at the mudline for 5 min.

Moisture and density measurements

Several basic properties of interest (water content, bulk density, dry density, porosity, and void ratio) are measured more accurately through mass and volume determinations on discrete samples. MAD data were used for comparison with GRA bulk density data from the WRMSL. The shipboard MAD facility on the JOIDES Resolution includes a dual balance system and a hexapycnometer.

During Expedition 340, only soft to weakly lithified sediments were cored. In undisturbed core, 1–2 MAD samples were collected close to XRD/carbonate samples. From APC cores, cylindrical MAD samples were taken with a syringe. In XCB cores, fragmented domains, a result of the coring processes, were sampled with forceps in order to minimize further core damage.

Dual balance system

The dual balance system was used to measure both wet and dry masses. The two coupled analytical balances (Mettler-Toledo XS204) were used to compensate for ship motion, one acting as a reference and the other used for measurement of the unknown. Before weighing sample-standard pairs, the balances were “tared” to zero across 300 measurements. Standard weights of similar value to the sample weight were placed upon the reference balance and the sample was placed on the unknown balance. We took 300 measurements (taking ~1.5 min).

Wet and dry mass

Immediately after sediment samples were collected, we measured wet sediment mass (M_wet). Dry sediment mass (M_dry) and volume (V_dry) were measured after drying the samples in a convection oven for >24 h at a temperature of 105° ± 5°C. Dried samples were then cooled in desiccator for >1 h before the dry mass was measured. Dry volume was measured using a helium-displacement pycnometer with a nominal precision of ±0.04 cm³. Each reported value consists of an average of three measurements. It is recommended that for future projects, weighing of samples in the dual balance should be done with a plastic lid on the glass container in order to avoid moisture loss/gain during measurement. This requires that tare of the glass containers should be measured with their lids at IODP-USIO, prior to the cruise.

Hexapycnometer system

The hexapycnometer system measures dry sample volume using pressurized, helium-filled chambers. At the start of the expedition, and whenever the helium gas tank was changed, a calibration was performed using stainless steel spheres of known volume. A batch of samples consisted of five cells with unknowns and one cell with two stainless steel spheres (3 and 7 cm³). The spheres were cycled through the cells to identify any systematic error and/or instrument drift. After conducting 12 calibrations (two on each of the six cells) using these spheres, we calculated a mean error of 0.126%. Samples should be close to 10 cm³; the larger the sample the higher the precision of the method. Individual volume measurements were preceded by three purges of the sample chambers with research grade (99.995% or better) helium heated to 28°C, followed by three data acquisition cycles.

Final calculation

For calculation of sediment bulk density, dry density, grain density, porosity, and void ratio, we used the traditional ODP method (“Method C”; Blum, 1997). Water content, porosity, and void ratio are defined by the mass or volume of extracted water before and after the removal of interstitial pore water through the drying process. Standard seawater density (1.024 g/cm³) is used for the density of pore water and a standard salinity of 0.035 (s = S/1000; Blum, 1997).

Water content

Water content was determined following the methods of the American Society for Testing and Materials (ASTM) designation D2216 (ASTM International, 1990). Corrections are required for salt when measuring the water content of marine samples. Pore water salinities of 0.035 were used for all Expedition 340 samples. In addition to the recommended water content calculation in ASTM D2216 (i.e., the ratio of pore fluid mass to dry sediment mass [percent dry weight]), we also calculated the ratio of pore fluid mass to total sample mass (percent wet weight). Moisture content is pore water mass expressed either as percentage of wet bulk mass or the mass of salt-corrected solids:

and

where

• M_t = total mass of the saturated sample,
• M_d = mass of the dried sample, and
• s = salinity.

Porosity, bulk density, and grain density

Porosity (φ) was calculated using

where

• ρ = measured bulk density,
• ρ_w = density of the pore fluid, and
• W_c = water content expressed as a decimal ratio of percent dry weight.

Bulk density is the density of the saturated samples, with ρ = M_t/V_t. Mass (M_t) was measured using the balance, and volume (V_t) was determined from pycnometer measurements of grain volume and the calculated volume of the pore fluid (V_t = V_pore + V_d). For lithified samples from Expedition 340, bulk density was determined directly from ρ = M_t/V_t.

Grain density (ρ_grain) of unconsolidated samples was determined from measurements of dry mass and dry volume made in the balance and the pycnometer, respectively. Mass and volume were corrected for salt using

and

where s is the salt content (in grams) and ρ_salt is the density of salt (2.257 g/cm³).

Compressional wave velocity measurements

The measurement of compressional wave velocity was carried out on wet sediment on the working half of the split cores. Measurements were made in two orientations with caliper-type contact probe and bayonet transducers. Measurements perpendicular to the core (x-axis) were made on every section unless core quality was compromised. X-axis measurements could be performed in most core sections. The initial plan was to make measurements parallel to the core (z-axis) once per core. Because z-axis measurements could only be carried out in loose, coarse sediments where the bayonets could enter the split core without damaging the sediment structure, almost no sections were ammenable to this measurement. This measure was abandoned after Hole U1394B.

For more efficient contact, deionized water was applied on the lower transducer in contact with the core liner for the measure of the x-axis.

The system uses Panametrics-NDT Microscan delay line transducers with a frequency of 500 kHz. The distance between the two transducers was measured with a built-in LVDT. The P-wave passing through the sample was recorded, and we picked first arrivals as the initial rise of the first peak using an automated procedure. The measure along the x-axis included the core liner of known thickness.

A series of calibrated acrylic cylinders of known P-wave velocities (2750 ± 20 m/s) and thicknesses were used at least once a day for calibration. This calibration compared the acrylic cylinder thickness multiplied by the time to cross the cylinder with the known P-wave velocity.

We speculate that this method may result in slightly different P-wave velocities than the WRMSL because transducers are in direct contact with the sediments and have better coupling.

Shear strength measurements

Shear strength is the resistance of a material to failure in shear. Shear stress in unconsolidated materials is resisted only by the skeleton of solid particles. Shear strength (τ_f) can be expressed as a function of the effective normal stress at failure (σ′), the effective cohesion (c′), and friction angle (ϕ′):

where c′ and ϕ′ are the shear strength parameters that define a linear relationship between τ_f and σ′, according to the Mohr-Coulomb failure criterion.

Shear strength parameters can be determined by means of multiple laboratory tests. c′ and ϕ′ are relevant in situations where field drainage conditions correspond to test conditions. The shear strength of a soil under undrained conditions (pore fluid drainage does not occur during failure) is different from that under drained conditions (pore fluid drainage occurs).

Undrained shear strength can be expressed in terms of total stress in the case of fully saturated materials of low permeability (e.g., clays), denoted by S_u. The most common strength tests in shipboard laboratories are the vane shear and penetrometer tests, which provide measurement of undrained shear strength (S_u) (Blum, 1997). The fall cone test also provides a good estimate of S_u (Hansbo, 1957; Wood, 1985).

During Expedition 340, S_u was measured in undisturbed fine-grained sediments using a handheld penetrometer at the base of each core section and the automated vane shear (AVS) system and the fall cone in working-half cores. Shear strength measurements with the AVS and the fall cone were performed in the y–z plane, whereas measurements with the handheld penetrometer were performed in the y–x plane. Measurements performed with these three methods were performed rapidly to avoid draining and evaporation, in order to provide measures of undrained shear strength.

Automated vane shear system

Using the AVS, undrained shear strength was determined by inserting a four-bladed vane into the split core and rotating it at a constant 90°/min to determine the torque required to cause a cylindrical surface to be sheared by the vane, which provides a measurement of the peak shear strength. The difference in rotational strain between the top and the bottom of a linear spring is measured using digital shaft encoders. Measurements were made with the vane rotation axis and penetrometer penetration direction perpendicular to the split surface. The residual shear strength was taken to be the constant and lowest measured shear strength after reaching the peak value during the test cycle. Sampling rates were one per core section unless the sediment was too firm for instrument penetration or was disturbed during coring.

Vane shear strength S_u(v) (kPa) is calculated as

where

• T = torque required to induce material failure (N·m),
• K_v = constant, depending on vane dimensions (m³),
• Δ = maximum torque angle (°) at failure, and
• B = spring constant that relates the deflection angle to the torque (°/N·m) (Blum, 1997).

All measurements used a vane with a height and diameter of 12.7 mm. Failure torque (T) was determined by measuring the degrees of rotation of one of four torsional springs. A linear calibration equation (specified by the manufacturer) relates the rotation angle to the torque for the particular spring being used. Selection of the appropriate spring was based on the anticipated shear strength of the material. Vane shear results were generally considered reliable for shear strength values less than ~150–200 kPa, above which excessive cracking and separation of the core material occurred.

Handheld penetrometer

A handheld penetrometer (Soiltest 29-3729) was used to obtain additional undrained shear strength measurements. A handheld penetrometer is a flat-footed, cylindrical probe that is pushed 6.3 mm into the base of sections on the catwalk that have not yet been split. The resulting resistance is the unconfined compressive strength (τ_f), which corresponds to twice the value of S_{u PP}, measured in kilograms per square centimeter. Therefore, undrained shear strength (in kPa) is obtained by

Measurements using the handheld penetrometer were attempted once per core section at the base of the section if undisturbed soft fine-grained sediment was present. The handheld penetrometer can measure a maximum value of 220 kPa, a value that characterizes firm sediment.

Fall cone

The fall cone test is a standardized test method for liquid and plastic limit determination that can also be used for undrained shear strength measurements. During Expedition 340 it was used only for undrained shear strength measurements. The apparatus consists of a penetrometer fitted with a 35 mm long and 30° angle stainless steel cone; the cone and the sliding shaft to which it is attached have a combined mass of 80 g, resulting in a 0.785 N cone, according to the British Standard (British Standards Institution, 1990).

Measurements were performed by placing working-half core sections below the cone. The cone was lowered so that it just touched the surface of the soil in the cup. The cone was locked in its support at this stage. The cone was then released, and its depth of penetration into the material was measured. One fall cone measurement was performed on each core section, except in heterogeneous material, where the number of measurements was dictated by material changes.

A number of studies have found that undrained shear strength at the liquid limit ranges from 1.7 to 2.3 kPa. Hansbo (1957) proposes

where

• S_{u FC} = undrained shear strength,
• k = cone factor,
• W = cone weight, and
• d = cone penetration in intact soils.

For the cone used (30°/0.785N), the depth of penetration corresponding to the liquid limit is 20 mm. The cone factor k is 0.85 for a 30° cone (Wood, 1985).

Stratigraphic correlation

Stratigraphic correlation consists of identifying common strata between holes at a site. This identification is important for clarifying the stratigraphic relationship between holes. Strata have distinct geophysical signatures identifiable in physical properties measurements. Although holes at a site may be offset by only tens of meters from each other along the seafloor, variations in stratigraphic depth between holes can sometimes be several meters. Differences in stratigraphic depth result from variations in seafloor depth, sedimentation rates, faulting or erosion histories at each hole. Small differences may arise from disruption of sediment during coring and recovery. Therefore, it is necessary to adjust the depth of core data between holes to ensure proper comparison of stratigraphic boundaries. It was sometimes difficult in this study to conduct stratigraphic correlations because of the complex nature of the sediment. The thickness and character of sediment in submarine slides and debris avalanches can have significant spatial variability over short distances, and it is possible that strata in one hole may not exist in another. We conducted only broad, first-order correlations during Expedition 340 that tie only clear and consistent changes in physical properties between holes.

Initial stratigraphic correlations between holes drilled at each site were generated using Analyseries software. Analyseries is freeware that runs on Macintosh computers, so adjustments and corrections to all stratigraphic correlations can be made by scientists postcruise as needed by downloading this software and the raw data files (www.ncdc.noaa.gov/​paleo/​softlib/​softlib.html). Analyseries provides linear depth adjustment between a reference hole and adjacent holes at the same site and calculates correlation coefficients for all depth adjustments. This is not the same procedure as that performed by the CoreWall correlator software commonly used during IODP expeditions to create meters composite depth (mcd) scales and calculate associated growth factors. As such, the correlated data cannot be considered composite depths, but they do allow for first order comparisons between holes. We typically used the hole with the most complete core recovery as the reference hole. Bulk density, magnetic susceptibility, and P-wave velocities measured with the multisensor loggers and NGR measured with the NGRL were all used to make stratigraphic correlations. Bulk density and magnetic susceptibility usually provided the most robust correlation tie points, although NGR was also a useful data set for checking correlations. Although only physical properties were used to generate the correlations, the final correlations were compared with the core descriptions. We conducted stratigraphic correlation only after core recovery was completed at a site. The analysis involved visually selecting signals that appeared consistently in both the reference and comparison holes. Tie points were first made using magnetic susceptibility, followed by bulk density, and if needed, NGR and P-wave data sets. To ensure consistency, tie points using one data set were compared to tie points picked with other data sets. After picking tie points, we generated correlation coefficients (R) between the two holes, and from this determined the quality of the fit. The correlation coefficient can range from –1 (exactly anticorrelated) to 1 (exactly correlated). The correlation coefficient calculation in Analyseries does not automatically remove data gaps. If large data gaps exist, correlations can therefore be anomalously low. During the picking process, we updated the correlation coefficient to ensure that R values improved for all of the data sets used in the correlation, regardless of which data set was used to make the tie point. It is important to note that only clearly defined correlation points associated with strong peaks and troughs are used for this initial run. Linear interpolations stretch and squeeze the stratigraphic record rather than hanging the data next to each other as in the CoreWall correlator software. More detailed correlations should be made postcruise, especially if sites require construction of a mcd scale.

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