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doi:10.2204/iodp.proc.336.102.2012

Physical properties

The material recovered during Expedition 336 was characterized by physical properties measurements. Most of the techniques used are noninvasive and allow correlation of the recovered material to the seismic and logging data. The two different types of material (hard rock and sediment) handled during this expedition were processed similarly, except where indicated in this report. A sketch of the core flow is provided for both: hard rock (Fig. F13) and sediment (Fig. F14). Please note that time estimates provided are for individual core sections.

Whole-round cores were placed in the core laboratory for 3 h (hard rock) or 4 h (sediment) to allow thermal equilibration at room temperature. Because oxygen measurements were done first for all sections of sediment recovered, the equilibration time for sediment was sometimes longer. Core sections longer than 8 cm were run through the Whole-Round Multisensor Logger (WRMSL) to measure gamma ray attenuation (GRA) density, magnetic susceptibility (MS), and P-wave velocity. During previous expeditions, the WRMSL also included a noncontact resistivity detector, but this piece of equipment was not on board the ship during Expedition 336. The P-wave logger (PWL) was turned off for hard rock cores because poor coupling between the liner and core material made meaningful measurements impossible. Whole-round images were taken of the entire surface of large rock pieces.

Sections longer than 50 cm were logged with the Natural Gamma Radiation Logger (NGRL), and total counts of NGR were obtained. Absolute concentrations of ⁴⁰K were obtained for both sediment and hard rock cores by calibrating the instrument using standards for this element.

Measurements of thermal conductivity were taken with the TK04 thermal conductivity meter on the archive halves of hard rock cores. This measurement was not performed on sediment cores because the high water content made it impossible to register values with the probe.

Sediment and hard rock cores were split into archive and working halves after measurements were taken on the WRMSL and NGRL. The archive halves of sediment cores were then scanned on the SHIL and run through the Section Half Multisensor Logger (SHMSL) to measure point magnetic susceptibility (MSP) and color reflectance. MSP was measured with a Bartington MS2E1 contact sensor probe. Color reflectance was also measured on this logger with an Ocean Optics photospectrometer. A laser on the SHMSL recorded piece heights and located gaps and cracks in the cores. Hard rock pieces were accommodated for this track with pieces of foam that helped the sensors land, avoiding piece tilting in most cases. The instrument software uses the laser estimations to avoid gaps between rocks. The data were also filtered for gaps not detected by the laser (see “Data processing and filtering”). Additionally, formation factor was calculated; however, this was only done on sediment working halves.

Discrete samples of both sediment and hard rock were processed for moisture and density (MAD). Hard rock samples were selected on the basis of lithology and degree of alteration to be representative of the lithologic units. Sediment samples were taken at a rate of one per section in representative areas. MAD measurements included bulk density, dry density, grain density, water content, void ratio, and porosity. Compressional P-wave measurements were taken for the three axes of the cube sample (hard rock) or the core half (sediment) on the Gantry system. Sediment working half samples were measured for P-wave velocity using the caliper and occasionally the bayonets (Hole U1383D). A more comprehensive description of the physical properties procedure can be found in Technical Note 26 (Blum, 1997).

All of the physical properties data recovered were uploaded to the LIMS database. The data were visually double-checked at the end of the process using LIMSpeak beta version.

Whole-Round Multisensor Logger measurements

MS, GRA density, and P-wave velocity (sediment only) were measured simultaneously with the three sensors at sampling intervals of 1 cm, with a time integration of 5 s for each measurement. A freshwater-filled section standard was run after each core for quality control to verify the calibration of the GRA densitometer and the PWL. Calibration for the GRA densitometer was performed with aluminum and water standards. GRA and MS measurements on hard rock underestimate the real value because the method assumes that cores fill the entire volume of the core liner, which never occurs in hard rock cores. However, this underestimation can be corrected if the diameter of the core is taken into account. Hard rock cores have in general a smaller diameter (~58 mm) than the internal diameter of the core liner (66 mm), which can be corrected by multiplying the system output by 66/58 = 1.138 (Jarrard and Kerneklian, 2007). MS and GRA data were filtered with a MATLAB code written during Expedition 336 to eliminate poor-quality data originating from cracks and gaps in recovery. A correction for the diameter of the samples was also included in the data process. The diameter of sediment cores was considered to be 66 mm, whereas the diameter of hard rock cores was considered to be 58 mm.

GRA bulk density

The bulk density of a material is defined as its mass divided by the volume it occupies. This measurement depends on the compaction of the material and therefore is susceptible to changes due to handling. GRA density is measured on the WRMSL with a beam of collimated gamma rays from a 10 mCi ¹³⁷Cs source with a gamma photopeak at 662 KeV. The gamma rays pass through the core sample and are detected on the opposite side of the liner. The Compton scattering experienced by the gamma rays attenuates their energy as they pass through the sample. The number of photons that travel through the sample without attenuation can be detected and used to calculate the bulk density of the sediment. The instrument has a 3 mm collimator that focuses the area of incidence of the gamma ray beam on the core. The detector of the system is a 3 inch diameter × 3 inch thick NaI(TI) crystal scintillator with an integrated PMT tube. During Expedition 336 this instrument was used to take measurements of the whole-round core at a rate of one per centimeter.

The bulk density of a sample was calculated as

ρ = (1/µd)ln(I₀/I),

where

• ρ = the bulk density of the sample,
• µ = the Compton attenuation coefficient,
• d = the sample diameter (assumed to be ~66 mm for sediment and ~58 mm for hard rock),
• I₀ = the gamma source intensity, and
• I = the measured intensity received by the detection system.

Bulk density was calculated on the basis of intensities measured through GRA calibration. Hard rock measurements were corrected afterward for the difference in sample diameter (e.g., Jarrard and Kerneklian, 2007).

A core liner filled with distilled water and an aluminum standard was used to calibrate this instrument before each hole and when needed (e.g., if the data obtained for the freshwater standard run after each core presented an error >1%–2%). Bulk density was registered in grams per cubic centimeter.

Magnetic susceptibility

Magnetic susceptibility indicates the response of a material to a known external magnetic field:

K = M/H,

where

• K = magnetic susceptibility,
• M = the magnetization induced in the material, and
• H = the magnetic field strength.

Based on its response to the magnetic field, a material can be paramagnetic, ferromagnetic, ferrimagnetic, antiferromagnetic, or diamagnetic. Magnetic susceptibility measurements are useful in identifying a material’s composition.

A Bartington loop sensor (MS2C) on the WRMSL track measured the magnetic susceptibility of both sediment and hard rock cores. In this system a low-intensity (~80 A/m root mean square [RMS]) magnetic field operating at 0.565 kHz is applied to the material in the core. The magnetic susceptibility of the sample is then calculated and corrected on the basis of an empirical relation for the difference in diameter of the core (66 mm) versus the loop sensor (88 mm) (see MS2 Magnetic Susceptibility System operation manual, www.bartington.com/​operation-manuals.html).

The magnetic susceptibility of core pieces shorter than 8 cm cannot be accurately determined because the resolution of this method is ±4 cm. Data from samples with gaps or fractures were filtered from the data set.

The MS2C coil is calibrated by the manufacturer; hence, no calibrations were done on this equipment offshore. The results are expressed in 10^–5 SI units. The MS2 recorder attached to the SHMSL has an output threshold of 9999 SI and truncates the most significant digit for higher measurements. Data were filtered for both sediment and hard rock cores (see “Data processing and filtering”).

P-wave logger

The PWL was used only for sediment cores and was deactivated during the processing of hard rock whole rounds because of the inaccuracy that the separation between the rock and liner creates. The system uses Olympus-NDT Microscan delay line transducers that transmit at 0.5 MHz. The system is automatized to take the value of the peak of first arrival of the P-wave. However, 10,000 measurements of amplitude versus time of the wave are taken and stored in case reanalysis is needed. The distance between transducers was measured with a built-in linear voltage displacement transformer (LDVT).

Calibration was done when necessary by using a standard acrylic cylinder with different diameters to take measurements. The values for the different diameters should present a known P-wave velocity of 2750 ± 20 m/s and a linear relation between measurements of the different diameters. After each core (or each section of hard rock core), a water-filled standard was used to push the last section and a measurement was taken on it to crosscheck the calibration. When the value for this water standard differed by >2% of 1500 m/s, recalibration was performed.

The time delay from calibration is subtracted from the measured arrival time to give a traveltime of the P-wave through the sample. The thickness of the sample is automatically divided by the traveltime to calculate P-wave velocity in meters per second.

Natural Gamma Radiation Logger

NGR from sediment and hard rock cores is the result of the decay of ²³⁸U, ²³²Th, and ⁴⁰K isotopes. The NGR detector used during Expedition 336 was designed by Texas A&M (Vasiliev et al., 2011) and installed on board the JOIDES Resolution in 2009. Eight 4 inch NaI (TI) custom-shaped detectors simultaneously measure adjacent sections of the recovered material. Each detector center is separated by 20 cm from the next. Each detector PMT is attached to an ORTEC ScintiPack-296, which maximizes counting times and minimizes error in the limited time available during core flow for this instrument (~10 min per core section). Two types of shielding are used in this instrument to reduce background noise. Low-activity passive lead spacers act as shields in between detectors. Lead plugs are also placed between each PMT and the Scintipack to reduce the ⁴⁰K gamma background from the internal parts of the Scintipack. The passive shielding above and around the detectors also reduces the electromagnetic showers generated by cosmic rays and environmental gamma rays. Active shielding can reduce the background created by the high-energy part of comic rays and cosmic muons. Because of the implemented energy threshold, the NaI scintillators do not detect gamma rays with energy below 100 keV and thus are not affected by X-rays created by the cosmic rays in the passive lead shielding. The data acquisition and readout systems were assembled from commercial modules produced by ORTEC, Phillips Scientific, and CAEN. The data acquisition logic was adapted for low counting rates on the basis of empirical data (Vasiliev et al., 2011).

The interface allows users to set experimental parameters. The data collected are comparable with previous data from IODP and logging data. The detector counts were summed for the range (100–3000 keV). Background counts were done on an empty core liner for 5 h after our arrival at each site. NGR measurements were taken every 20 cm on the recovered material for both sediment and hard rock cores. The system averages the NGR over 46 cm (23 cm on each side of the detector), making more intense coverage too time-intensive and not extremely scientifically beneficial. Longer detection periods give more accurate values than shorter measurements at higher spatial resolution. The counting time was set to 2 h per section for hard rock cores and 30 min per section for sediment. These detection periods were chosen to balance good counting statistics with optimal core flow.

Sample location accuracy, as with other physical properties systems, is determined within millimeters and averaged over 46 cm surrounding the detector. The detector has enough resolution to identify the energy contributions of ²³⁸U, ²³²Th, and ⁴⁰K in marine sediments and rocks, even with low count records. NGR measurements can be related to geological strata and the geochemistry of the recovered material. NGR measurements can also help to correlate the core material recovered with the downhole logs and adjacent boreholes (Michibayashi et al., 2008).

The NGR detector unit was energy-calibrated using ¹³⁷Cs and ⁶⁰Co sources and identifying the peaks at 662 and 1330 keV, respectively (calibration materials are from Eckert and Ziegler Isotope Products, USA). Calibration standards of ⁴⁰K and ²³²Th were run for each detector so that quantitative spectral analysis could be performed. Obtaining quantitative values for ⁴⁰K, ²³²Th, and ²³⁸U can help with future quantification of the radionuclide daughters (International Atomic Energy Agency, 2003).

Edge effects due to the geometry of the core and the geometry of the system are unavoidable. Corrections were applied when the core edge was between 0 and 18 cm away from the center of the detector. Initial data reduction is automatically performed by the system’s software. A density function based on NGR detection for the instrument’s geometry was used to calculate the potassium values. The GRA density data were used as an indicator of the distribution of the core pieces. This is particularly useful in hard rock cores.

Thermal conductivity

Thermal conductivity is the rate at which heat flows through a material and depends on the material temperature, pressure, composition, porosity, structure, and type of saturating fluid. Thermal conductivity is calculated on the basis of a heating curve, which is temperature versus time of the probe. The thermal conductivity calculation for steady state is

ka(t) = (q/4π) {[ln(t₂) – ln(t₁)]/[T(t₂) – T(t₁)]},

where

• k_a(t) = apparent thermal conductivity for long time intervals,
• q = heat flux downgradient,
• t = time, and
• T = temperature corresponding to time intervals.

Because the correct time intervals are difficult to choose, the system analyzes the heating curve data by using the “special approximation method (SAM) algorithm” (see TK04 Thermal Conductivity Meter User’s Manual, www.te-ka.de/​de/​pdf/​TK04-Manual.pdf). This algorithm divides the heating curve into several thousand time intervals and determines the thermal conductivity for each one. Finally, the software automatically chooses the least disturbed of the solutions.

Thermal conductivity measurements were performed on split samples of hard rock cores with a TK04 system. No measurements were taken for sediment cores because they contained excessive fluid and this measurement can be strongly affected by convection in sediment cores. Measurement attempts in nearly all sections of the first sediment core were unsuccessful.

The archive halves of hard rock cores were used for thermal conductivity measurements. The probe was used in half-space mode, where a needle probe is embedded in the surface of an acrylic glass block with low thermal conductivity (0.184 W/[m·K]). Samples were polished before use. After the samples were saturated in seawater under vacuum at room temperature over 24 h, both the sample and probe were isolated in an extruded polystyrene foam–covered seawater bath for at least 15 min prior to measurement in order to eliminate the effect of drafts in the laboratory. Before each measurement, the temperature of the core was monitored to ensure that the drift was <0.04°C/min. The different probes have specific configurations and calibrations that are integrated into the software. Heating power and time were input by the user so that the heating power was approximately twice the value of the expected thermal conductivity. Measuring time was set to 80 s. The manufacturer suggests smoothing the split surface with 120–320 gauge silicon carbide powder to improve the contact of the probe. For preservation reasons, no silicon gel can be used to improve contact when this measurement is taken in archive samples.

Thermal conductivity was measured at least once per core section when the pieces recovered had sufficient length (>6 cm) to avoid edge effects. When time and sample constraints allowed, several measurements per section were taken. Three repeated measurements were done per sample and the mean and standard deviation was calculated. The measurements were not mathematically corrected for subseafloor conditions.

Section Half Multisensor Logger measurements

The SHMSL is the next step in the core flow after splitting the core. In this part of the process the archive halves are scanned on the SHIL to produce a high-resolution image. Color reflectance spectra and MSP are measured on the SHMSL every centimeter. A laser sensor detects the height of the sample and locates the end of the section.

Color reflectance spectrometry

An Ocean Optics, Inc., system was used to measure UV to near-infrared light using a halogen light source. Measurements were taken every centimeter, and each measurement took ~5 s. Resolution was one measurement per 1 cm on hard rock cores and at least one measurement per 2 cm on sediment cores.

In general, the results from this instrument are given as luminescence (L*) and color indexes a* (green to red; green being negative and red being positive) and b* (blue to yellow; blue being negative and yellow being positive). The ratio a*/b* was also calculated for all boreholes because it can be used as a better proxy to identify changes in sediment characteristics than the independent a* and b* values. Although this is the most general output of results, the system also records spectral data at a 2 nm resolution in the range of 380–900 nm wavelengths and tristimulus values for x-, y-, and z-axes. All of the raw data were uploaded to the database.

Calibration was performed with two main sources, black and white, every ~12 h. When sediment cores were processed, the material was covered with plastic film to avoid fouling the sensor with sediment. Hard rock cores were not covered.

Point magnetic susceptibility

A Bartington MS2E contact probe was used to take MSP measurements. The probe has a flat 15 mm diameter sensor operating at a frequency of 0.580 kHz. Measurements were taken every centimeter at a rate of one per second. Three measurements were taken and averaged to obtain a final value with an accuracy of 5%. Point measurements are more accurate than those obtained from whole-round cores. The area of response of the MS2E sensor is 3.8 mm × 10.5 mm, with a depth response of 50% at 1 mm and 10% at 3.5 mm (see MS2 Magnetic Susceptibility System operation manual, www.bartington.com/​operation-manuals.html). This response makes the system capable of measuring core fragments smaller than 8 cm, which cannot be done with the whole-round system.

The probe takes a measurement in air before each actual measurement, and from this the software performs an automatic correction.

The instrument is calibrated so that the value output is measured assuming the probe is buried in the sample; however, because the probe is only in contact with the upper, flat surface, a correction factor of 2 is automatically applied by the software. No other corrections are needed for this system.

SI dimensionless units are used for the results, making them comparable to the ones obtained in the first part of the core flow. The system was calibrated every ~12 h for MSP. No calibration was done for the loop in the WRMSL because this sensor is master calibrated by the manufacturer.

The MS2 recorder attached to the SHMSL has an output threshold of 9999 SI and truncates the most significant digit for higher measurements. Data for this system were filtered on the basis of the color reflectance spectra calculated on the same track.

Formation factor measurements

Measurements of electrical conductivity were taken approximately every 10 cm on sediment cores from Sites U1382B, U1383D, and U1384A. The formation factor of the sediment was calculated based on electrical resistivity measurements. Two platinum electrodes ~1 cm long in a nonconductive Teflon piece connected to a Metrohm 712 system were used for this measurement. This system was successfully used for the same type of measurements during Expedition 329 (Expedition 329 Scientists, 2011a). Temperature was also measured at each location. A standard of IAPSO seawater was used before and after measurements had been taken on each section to detrend the wasting of the electrodes. Temperature was also measured on the IAPSO standard. Areas of the core with disturbed sediment, gravel, or sandy textures were avoided because the electrodes could be damaged and the measurements would not give reliable values.

All the electrical conductivity values (inverse of electrical resistivity) were adjusted to a standard temperature of 20°C by a fifth-order polynomial (Janz and Singer, 1975),

χ = a + bT + cT ² + dT ³ + dT ⁴ + eT ⁵,

where

• a = 29.05128,
• b = 0.88082,
• c = –0.000198312,
• d = 0.00033363,
• e = –0.000010776, and
• f = 0.000000112518.

Both seawater and sediment measurements were corrected for the effect of temperature. The formation factor was calculated as

F = χ_IAPSO/χ_sed.

This method is useful as a proxy for tortuosity in high-porosity sediments where surface conductivity effects are not a major component.

Discrete sample measurements

Cubic samples (~7 cm³) were cut from the working halves of hard rock cores at an approximate frequency of one per lithologic unit. Alteration of the sample was taken into account when selecting samples. The different lithologies were sampled in order to obtain a good representation of the entire borehole. Hard rock samples were selected on the basis of the amount of material recovered and the prioritization of other sample types. Samples taken for physical properties were used for both P-wave discrete measurements on the three axes of the sample and for MAD measurements. No paleomagnetism measurements were conducted during Expedition 336, so the discrete samples taken were used solely for physical properties data acquisition.

MAD sediment samples were taken with a syringe at a rate of one per core section. The samples were carefully chosen to be representative of the stratigraphy of the core.

Compressional P-wave velocity discrete measurements

Sediment samples can be measured with three sensors, one in each of the three-dimensional axes; however, because of time constraints, only the caliper was used for the recovered cores.

P-wave velocity measurements of hard rock were performed during the MAD process, which saved time during the physical properties processing. Seawater-saturated samples were used for wet mass determinations immediately before P-wave measurements. The rest of the MAD process took place after P-wave measurement. P-wave velocities for the three axes were measured by changing the orientation of the samples in the x-axis caliper contact transducers on the P-wave velocity gantry.

The transducers used by this system are the same as those used for the whole rounds; however, the software and optimizations used to calculate the P-wave are different. The discrete measuring system has an amplifier that provides an improved signal-to-noise ratio compared to that provided by the whole-round system. The discrete measurements register the wave preinverted (and therefore are more accurate). To maximize contact with the transducers, deionized water was applied to the sample surfaces and water-saturated hard rock samples were used.

Velocity measurements on calibration standard cylinders were taken as often as necessary. The calibration was made with acrylic cylinders of differing thicknesses and a known P-wave velocity of 2750 ± 20 m/s. The distance between transducers was measured with a built-in LDVT. The wave was automatically processed to find the first arrival value, but all of the wave amplitude measurements over time were recorded in case reprocessing was needed.

As in the whole-round system, the P-wave velocity is directly output by the system in meters per second. Each measurement was repeated three times for data consistency on hard rock samples and only once for sediment samples to avoid disturbance effects.

Moisture and density measurements

Intergranular water content, bulk density, dry density, porosity, and void ratio were determined on discrete samples. A vacuum water saturator, a dual balance system, and a hexapycnometer were used for these measurements.

The vacuum pump system was used to keep the hard rock samples completely saturated. The samples were kept in a vacuum bath of seawater for at least 24 h. During this time the system was checked every 4 h to make sure the vacuum was maintained. After this, the samples were kept in sample containers with water to avoid desiccation. Immediately before the measurement was taken, the samples were carefully patted with a paper towel to remove excess water. They were then weighed on the dual balance system to obtain their wet mass.

The dual balance system is composed of two analytical balances (Mettler-Toledo XS204) that compensate for ship motion. One balance acts as a reference, in which a known weight close to the weight of the sample is placed. The sample is placed in the other balance. The balance takes 300 measurements of the sample over a period of 1.5 min (default).

After wet weight was measured on the dual balance system, the sample was placed in a convection oven at 105° ± 5°C for >24 h. Once the sample was dried, it was cooled in a desiccator for 30–60 min before dry mass was measured. The sample was placed in the hexapycnometer system to measure dry volume. For sediment samples, premeasured vials were used during the process; the weight of the vial was subtracted from the wet and dry mass of the sample.

The hexapycnometer measures dry sample volume with a nominal precision of ±0.04 cm³. The pycnometer increases the amount of helium gas required to maintain a target pressure in the sample chamber. The calculation of dry volume is made by comparing the pressure in the chamber with a known volume reference.

Calibrations of this instrument were done in an adjacent chamber with two stainless steel spheres every time a measurement was taken. Four measurements and a standard were measured simultaneously when possible. A fifth measurement was not performed simultaneously because one of the chambers was defective. The chamber used for the measurement of the standard was different each time in order to test each chamber.

MAD calculations are directly implemented by the software and described in detail in Blum (1997). However, the basic equations are presented here.

Salt correction for mass is defined as

M_s = s[(M_w – M_d)/(1 – s)],

where

• M_s = mass corrected for salinity,
• s = salinity,
• M_w = wet mass, and
• M_d = dry mass.

Grain density is defined as

ρ_g = (M_d – M_s)/[V_d – (M_s – ρ_s)],

where

• ρ_g = grain density,
• V_d = dry volume, and
• ρ_s = density of salt (2.257 g/cm³).

The salt-corrected mass of pore water (M_pw) is defined as

M_pw = (1/s)M_s.

Pore water volume (V_pw) is defined as

V_pw = M_pw/ρ_pw,

where the density of pore water (ρ_pw) is assumed to be 1.024 g/cm³.

Bulk density (ρ_b) is defined as

ρ_b = M_w/(V_d + V_pw),

and porosity (ϕ) is defined as

ϕ = V_pw/(V_d + V_pw).

Data processing and filtering

The physical properties measurements are mainly automatized, making it necessary to filter and discard (“clean”) poor measurements. In order to perform all of the necessary filtering for this expedition, MATLAB codes were written to handle each step of the physical properties process.

Gamma ray attenuation, magnetic susceptibility, and P-wave filters

The GRA data, particularly for hard rock cores, contain a high number of measurements that are not representative of the real bulk density of the material because of underfilled liners and unsaturated samples. As mentioned previously, a correction was done for the diameter of the core. This correction assumed a ~58 mm diameter for hard rock cores and a ~66 mm diameter for sediment cores. Hard rock cores contain multiple pieces, with gaps in between them. In order to exclude the data from these gaps and cracks, a filter was designed using MATLAB to compare each point with three adjacent points and check if the value obtained for them differs by a small amount (0.15 for hard rock cores and 0.05 for sediment cores). This value was determined by comparing the values obtained from MAD samples. When the points present a higher difference than the aforementioned values, they are filtered out of the data. The filter does this in three steps, initially checking the points farthest away and ending with the adjacent ones. Different intensities of gray shading have been used in the graphs presented in this volume to indicate these three steps of filtering. Measurements less than the density of water (1 g/cm³) were not included in this report because they relate to empty core liners.

MS and P-wave velocity data were filtered using the same procedure. Because MS and P-wave velocity are measured on the same logger as GRA density, the depths at which data points eliminated (as bad data) by filtering the GRA are likely unreliable in both the MS and P-wave velocity data sets. All three sensors measure at the same resolution and location, making it easy to filter all of the data on the basis of GRA values.

The P-wave sensor on the WRMSL can have poor contact when measuring sediment cores that will not equate to the site of a poor GRA measurement. Therefore, an extra filtering step was implemented for P-wave velocity to eliminate all values less than the velocity of water (1500 m/s).

Color reflectance and point magnetic susceptibility filters

A MATLAB filter was implemented for the SHMSL on the basis of color reflectance measurements. The color reflectance sensor registers the normalized spectrum of the material. These data are not included in the primary database.

Two different filters were used for hard rock and sediment. When the sensor lands incorrectly on a piece of hard rock, it can tilt the rock, causing light from the surrounding environment to be detected in the spectrum. A filter was implemented that detects peaks at the wavelength of the light in the laboratory where the system is installed. This signal is easily differentiated in hard rock cores but is not as obvious in sediment cores. In sediment cores, therefore, this filter was complemented with an additional filter that checks for unsmooth distributions that indicate poor sensor contact.

MSP was filtered on the basis of the points that were eliminated for color reflectance values, following a similar procedure as that explained for the GRA filters.

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