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doi:10.2204/iodp.proc.339.102.2013

Lithostratigraphy

This section outlines the methods used to describe the sedimentary successions recovered during Expedition 339, including core description, core imaging (SHIL), color spectrophotometry and magnetic susceptibility (SHMSL), XRD analyses, smear slide description, and hand-drawn logs. Only general procedures are outlined, except where they depart significantly from IODP conventions.

Sediment classification

The sediment recovered during Expedition 339 are composed of biogenic and siliciclastic components. They were described using a classification scheme derived from those of Ocean Drilling Program (ODP) Leg 155 (Shipboard Scientific Party, 1995), IODP Expedition 303 (Expedition 303 Scientists, 2006), and Stow (2005). The biogenic component is composed of the skeletal debris of open-marine calcareous and siliceous microfauna (e.g., foraminifers and radiolarians), microflora (e.g., calcareous nannofossils and diatoms), and macrofossil shell fragments. The siliciclastic component is composed of mineral and rock fragments derived from igneous, sedimentary, and metamorphic rocks. The relative proportion of these two components is used to define the major classes of sediments in this scheme (Fig. F4).

Naming conventions for Expedition 339 follow the general guidelines of the ODP sediment classification scheme (Mazzullo et al., 1988), with the exception that a separate “mixed sediment” category was not distinguished during Expedition 339. As a result, biogenic sediments are those that contain >50% biogenic grains and <50% siliciclastic grains, whereas siliciclastic sediments are those that contain >50% siliciclastic grains and <50% biogenic grains. Sediments containing >50% silt- and sand-sized volcanic grains are classified as ash layers. During Expedition 339, no ash layers or neritic and chemical sediments were encountered except as accessory components; therefore, these categories are not addressed below. Sediment grain-size divisions for both biogenic and siliciclastic components are based on Wentworth (1922), with eight major textural categories defined on the basis of the relative proportions of sand-, silt-, and clay-sized particles (Fig. F5); however, distinguishing between some of these categories can be difficult (e.g., silty mud versus sandy mud) without accurate measurements of grain size abundances. The term “clay” is only used to describe particle size and is applied to both clay minerals and all other grains <4 µm in size. Size-textural qualifiers were not used for biogenic sediment names (e.g., nannofossil clay implies that the dominant component is detrital clay rather than clay-sized nannofossils).

The lithologic names assigned to these sediments consist of a principal name and modifiers based on composition and degree of lithification and/or texture as determined from visual description of the cores and from smear slide observations. The total calcium carbonate content of the sediments, determined on board (see “Sedimentary inorganic and organic carbon”), also aided in classification.

For a sediment that contains >90% of one component (either the siliciclastic or biogenic component), only the principal name is used. For sediments with >90% biogenic components, the name applied indicates the most limited group of grains that exceed the 90% threshold value. For example, a sediment composed of >90% calcareous nannofossils is called a nannofossil ooze, a sediment composed of 50% foraminifers and 45% calcareous nannofossils is called a calcareous ooze, and a sediment composed of 40% foraminifers, 40% calcareous nannofossils, and 15% diatoms is called a biosiliceous calcareous ooze. For sediment with >90% siliciclastic grains, the principal name is based on the textural characteristics of all sediment particles (both siliciclastic and biogenic) (Fig. F5).

For sediment that contains a significant mixture of siliciclastic and biogenic components (between 25% and 75% of both siliciclastic and biogenic components), the principal name is determined by the more abundant component. If the siliciclastic component is more abundant, the principal name is based on the textural characteristics of all sediment particles (both siliciclastic and biogenic) (Fig. F5). If the biogenic component is more abundant, the principal name is either (1) based on the predominant biogenic component if that component forms >75% of the biogenic particles or (2) the more encompassing term “biogenic ooze.”

If one component forms 75%–90% of the sediment, then the principal name is followed by a minor modifier (e.g., “with diatoms”), with the minor modifier based on the most abundant component that forms 10%–25% of the sediment. If the minor component is biogenic, then the modifier describes the most limited group of grains that exceeds the 10% abundance threshold. If the minor component is siliciclastic, the minor modifier is based on the texture of the siliciclastic fraction.

If one component forms 50%–75% of the sediment, then the principal name is preceded by a major modifier that is based on the component that forms 25%–50% of the sediment. If the less abundant component is biogenic, then the major modifier describes the most limited group of grains that exceeds the 25% abundance threshold (e.g., nannofossil versus calcareous versus biogenic). If the less abundant component is siliciclastic, the major modifier is based on the texture of the siliciclastic fraction.

If the primary lithology for an interval of core has a major modifier, then that major modifier is indicated in the Graphic lithology column of the VCD sheets using a modified version of the lithologic pattern for the primary lithology (Fig. F6). The modified lithologic patterns are shown in Figure F7. The minor modifiers of sediment lithologies are not included in the Graphic lithology column.

The following terms describe lithification that varies depending on the dominant composition:

• Sediment composed predominantly of calcareous, pelagic organisms (e.g., calcareous nannofossils and foraminifers): the lithification terms “ooze” and “chalk” reflect whether the sediment can be deformed with a finger (ooze) or can be scratched easily by a fingernail (chalk).

• Sediments composed predominantly of siliceous microfossils (diatoms, radiolarians, and siliceous sponge spicules): the lithification terms “ooze” and “radiolarite/spiculite/diatomite” reflect whether the sediment can be deformed with a finger (ooze) or cannot be easily deformed manually (radiolarite/spiculite/diatomite).

• Sediments composed of a mixture of calcareous pelagic organisms and siliceous microfossils and sediments composed of a mixture of siliceous microfossils: the lithification terms “ooze” and “indurated sediment” reflect whether the sediment can be deformed with a finger (ooze) or cannot be easily deformed manually (indurated sediment).

• Sediments composed predominantly of siliciclastic material: if the sediment can be deformed easily with a finger, no lithification term is added and the sediment is named for the dominant grain size (i.e., sand, silt or clay). For more consolidated material, the lithification suffix “-stone” is appended to the dominant size classification (e.g., claystone).

• Sediments composed of sand-sized volcaniclastic grains: if the sediment can be deformed easily with a finger, the interval is described as “ash.” For more consolidated material, the rock is called “tuff.”

Visual core description

Preparation for core description

The standard method of splitting a core by pulling a wire lengthwise through its center tends to smear the cut surface and obscure fine details of lithology and sedimentary structure. When necessary during Expedition 339, the archive halves of cores were gently scraped across, rather than along, the core section using a stainless steel or glass scraper to prepare the surface for unobscured sedimentologic examination and digital imaging. Scraping parallel to bedding with a freshly cleaned tool prevented cross-stratigraphic contamination.

Sediment visual core description sheets

VCD sheets provide a summary of the data obtained during shipboard analysis of each sediment core. Detailed observations of each section were initially recorded by hand on paper, adjacent to the printed scanned image of that section. Copies of these original descriptions were scanned and converted to PDF files and are included in the DRAWVCD folder in “Supplementary material.” This information was subsequently entered into the DESClogik software, which provides data that can be used in Strater to generate a simplified, annotated graphical description (VCD) for each core (Fig. F6). Site, hole, and depth (in meters core depth below seafloor [CSF-A], also called mbsf or meters composite depth [mcd], if available) are given at the top of the VCD sheet, with the corresponding depths of core sections along the left margin. Columns on the VCD sheets include Lithologic unit, Core image, Graphic lithology, Coring disturbance (type and intensity), Average grain size, Sedimentary structures, Lithological accessories, Bioturbation intensity, Shipboard samples, Age, and Color. Profiles of magnetic susceptibility, natural gamma radiation (NGR), and reflectance (L*, a*, and b*) are also included. These columns are discussed in more detail below.

Graphic lithology

Lithologies of the core intervals recovered are represented on the VCD sheets by graphic patterns in the Graphic lithology column, using the symbols illustrated in Figure F7A. A maximum of two different lithologies (for interbedded sediments) can be represented within the same core interval. The major modifier of a primary lithology is shown using a modified version of the primary lithology pattern. A secondary lithology present as interbeds within the primary lithology is shown by a pattern along the right side of the column, with a solid vertical line dividing the primary and secondary lithologies. Lithologic abundances are rounded to the nearest 10%; lithologies that constitute <10% of the core are generally not shown but are listed in the Description section. However, some distinctive secondary lithologies, such as ash layers, are included graphically in the Graphic lithology column as the primary lithology for a thin stratigraphic interval. Relative abundances of lithologies reported in this way are useful for general characterization of the sediment but do not constitute precise, quantitative observations.

Hand-drawn logs (draw logs)

The hand-drawn logs, which were drafted after the cruise, are a representation of the recovered sediment sequence made by Expedition 339 sedimentologist Emmanuelle Ducassou based on the visual descriptions of the core as recorded on the VCD sheets and in core photos. These graphic representations were drawn at the vertical scale of one square to 50 cm, with the core and section indicated on the left. Drafted (numerically drawn) hand-drawn logs are included in the DRAWLOG folder in “Supplementary material” for Sites U1386–U1388. An example log from Hole U1386A is shown in Figure F8, and the legend for the logs at Site U1386 is shown in Figure F9.

The average grain size is represented by a curve. The first line to the right represents a mud average grain size, the second line represents a silt average grain size, and the third line represents a sand average grain size. Clay or ooze is represented by half of the spacing corresponding to mud average grain size, and coarse sandy grains or pebbles are represented by a half spacing to the right of the sand average grain size. Other gradations for specific isolated or unique sedimentary characteristics have been included in the logs and legends for individual sites.

The lithologies are represented by patterns as follows:

• Mud and clay/ooze are represented by a gray color based on the Munsell color assigned (Munsell Color Company, Inc., 1994) (lighter gray = 6, medium gray = 4 and 5, darker gray = 3),

• Silty mud is represented by alternating dots and dashes,

• Sandy mud and sandy silt are represented by dots and few dashes,

• Silty sand is represented by dots, and

• Granules and pebbles are represented by large open dots.

Contacts are represented as follows:

• Gradational contact: no horizontal line is drawn and there is a gradational curve between the two lithologies.

• Bioturbated contact: no horizontal line is drawn. Occasionally, a burrow is drawn at the right of the average grain size curve to show if the contact is sharp and bioturbated.

• Irregular contact: an irregular horizontal line is drawn by hand between the two lithologies.

• Sharp contact: a ruled straight line is drawn between the two lithologies and a dash is shown to the right of the curve.

• Erosional/scoured contact: a wavy line is drawn between the two lithologies and a short wavy dash is shown to the right of the curve.

Debrites are represented by a drawing of the described clasts, and the matrix is represented with one of the patterns corresponding at the observed lithology. Identified slumps are represented by contorted strata, and presumed slumps are represented by “SS?” at the right of the intervals. Shelly sediments and shell hash are represented by small drawings to the right of the average grain size curve, woody fragments are represented by a leaf, parallel laminated sediments are represented by three small dashes arranged vertically, and cross laminations are represented by two small dashes forming a small angle.

The contact between cores is represented continuously if the previous core is full and the lithologies between the two cores are the same. If this is not the case, a small space is shown between the core catcher of the previous core and the first section of the following core.

Other specific annotations have been included at the right of the average grain size, such as a reddish or a greenish color, or “rock” in the case of fully indurated/lithified sediment.

Bioturbation

Six levels of bioturbation are recognized using the scheme similar to that of Droser and Bottjer (1986). Bioturbation intensity is classified as complete (100%), heavy (>60%), moderate (40%–60%), slight (10%–40%), sparse (<10%), and absent (none). These levels are illustrated with a numeric scale in the Bioturbation intensity column.

Stratification and sedimentary structures

The locations and types of stratification and sedimentary structures visible on the prepared surfaces of the split cores are shown in the Sedimentary structures column of the VCD sheet. Symbols in this column indicate the locations and scales of interstratification, as well as the locations of individual bedding features and any other sedimentary features, such as scours, ash layers, ripple laminations, and fining-upward, coarsening-upward, or bi-gradationally bedded intervals (Fig. F7B).

For Expedition 339, the following terminology (based on Stow, 2005) was used to describe the scale of stratification:

• Thin lamination = <3 mm thick.

• Medium lamination = 0.3–0.6 cm thick.

• Thick lamination = 0.6–1 cm thick.

• Very thin bed = 1–3 cm thick.

• Thin bed = 3–10 cm thick.

• Medium bed = 10–30 cm thick.

• Thick bed = 30–100 cm thick.

• Very thick bed = >100 cm thick.

Lithologic accessories

Lithologic, diagenetic, and paleontologic accessories, such as nodules, sulfides, and shells, are indicated on the VCD sheets. The symbols used to designate these features are shown in Figure F7B. The following terminology was used to describe the abundance of lithologic accessories observed during visual core description:

• Barren = none observed per section of core.

• Present = 1 observed per section of core.

• Rare = 2–10 observed per section of core.

• Few = 10–20 observed per section of core.

• Common = 20–50 observed per section of core.

• Abundant = >50 observed per section of core.

Sediment disturbance

Drilling-related sediment disturbance is recorded in the Disturbance column using the symbols shown in Figure F7B. The style of drilling disturbance is described for soft and firm sediments using the following terms:

• Fall-in: out-of-place material at the top of a core has fallen downhole onto the cored surface.

• Bowed: bedding contacts are slightly to moderately deformed but still subhorizontal and continuous.

• Flow-in, coring/drilling slurry, along-core gravel/sand contamination: soft-sediment stretching and/or compressional shearing structures are severe and are attributed to coring/drilling. The particular type of deformation may also be noted (e.g., flow-in, gas expansion, etc.).

• Soupy or mousselike: intervals are water saturated and have lost all aspects of original bedding.

• Biscuit: sediments of intermediate stiffness show vertical variations in the degree of disturbance. Softer intervals are washed and/or soupy, whereas firmer intervals are relatively undisturbed.

• Cracked or fractured: firm sediments are broken but not displaced or rotated significantly.

• Fragmented or brecciated: firm sediments are pervasively broken and may be displaced or rotated.

Shipboard samples

Sample material taken for shipboard sedimentologic and chemical analyses consisted of interstitial water whole rounds, micropaleontology samples, smear slides, and discrete samples for XRD and carbonate analysis. Typically, 1–5 smear slides were made per core. One interstitial water sample and one microbiology sample were taken at designated intervals (so that core is missing from those intervals), and a micropaleontology sample was obtained from the core catcher of most cores. XRD samples were taken from core catchers at some sites and from a split of the carbonate sample at other sites. Additional samples were selected to better characterize lithologic variability within a given interval. Tables summarizing relative abundance of sedimentary components from the smear slides were also generated.

Color

Color is determined qualitatively using Munsell Soil Color Charts (Munsell Color Company, Inc., 1994) and described immediately after cores are split to minimize color changes associated with drying and redox reactions. When portions of the split core surface required cleaning with a stainless steel or glass scraper, this was done prior to determining the color. Munsell color names and the corresponding hue and chroma value are provided in the Color column on the VCD sheets.

Remarks

The written description at the top of the VCD sheets for each core contains a brief overview of primary and secondary lithologies present, as well as notable features such as sedimentary structures, grading, and disturbances resulting from the coring process. Note that the fossil identified as scaphopod during the onboard visual description of the lithostratigraphy has subsequently been identified as Arenaria. This has been changed for the reports; however, “scaphopod” will still appear in the VCD sheets and DESClogik output.

Smear slides

Smear slide samples were taken from the archive halves during core description. For each sample, a small amount of sediment was removed with a wooden toothpick, dispersed evenly in deionized water on a 25 mm × 75 mm glass slide, and dried on a hot plate at a low setting. A drop of mounting medium and a 22 mm × 30 mm cover glass were added, and the slide was placed in an ultraviolet light box for ~15 min. Once fixed, each slide was scanned at 100×–200× with a transmitted light petrographic microscope using an eyepiece micrometer to assess grain-size distributions in clay (<4 µm), silt (4–63 µm), and sand (>63 µm) fractions. The eyepiece micrometer was calibrated once for each magnification and combination of ocular and objective, using an inscribed stage micrometer.

Relative proportions of each grain size and type were estimated by microscopic examination. Note that smear slide analyses tend to underestimate the abundance of sand-sized and larger grains (e.g., foraminifers, radiolarians, and siliciclastic sand) because these are difficult to incorporate into the smear. Clay-sized biosilica, which is transparent and isotropic, is also very difficult to quantify. Clay minerals, micrite, and nannofossils can also be difficult to distinguish at the very finest (<4 µm) size range. After scanning for grain-size distribution, several fields were examined at 200×–500× for mineralogic and microfossil identification. Standard petrographic techniques were employed to identify the commonly occurring minerals and biogenic groups, as well as important accessory minerals and microfossils.

Smear slide analysis data tables are included in “Core descriptions.” These tables include information about the sample location, description of where the smear slide was taken, the estimated percentages of texture (i.e., sand, silt, and clay), and the estimated percentages of composition (i.e., ash, siliciclastics, detrital carbonate, biogenic carbonate, and biogenic silica). Relative abundances of identified components such as mineral grains, microfossils, and biogenic fragments were assigned on a semi-quantitative basis using the following abbreviations:

• A = abundant (>20% of field of view).

• C = common (>5%–20% of field of view).

• F = few (1%–5% of field of view).

• R = rare (<1% field of view).

• P = present (1 per 1–10 fields of view).

• B = barren (none in field of view).

For smear slide data from Site U1385 only, note that subsequent comparison to carbonate contents determined geochemically indicated that smear slide estimates were too high by a factor of ~2. The smear slide data and individual VCD sheets have not been corrected for this overestimation, but the lithologic names used in “Lithostratigraphy” in the “Site U1385” chapter [Expedition 339 Scientists, 2013] were adjusted to indicate the lower carbonate content. The adjusted lithologies also are used in the summary lithologic columns shown for Site U1385.

Section Half Multisensor Logger

Spectrophotometry and magnetic susceptibility of the archive-section halves were measured with the SHMSL. The SHMSL takes measurements in empty intervals and intervals where the core surface is well below the level of the core liner but cannot recognize relatively small cracks, disturbed areas of core, or plastic section dividers. Thus, SHMSL data may contain spurious measurements, which should be edited out of the data set by the user. Additional detailed information about measurement and interpretation of spectral data can be found in Balsam et al. (1997, 1998) and Balsam and Damuth (2000).

Spectrophotometry

Reflectance of visible light from the archive halves of sediment cores was measured using an Ocean Optics USB4000 spectrophotometer mounted on the automated SHMSL. Freshly split soft cores were covered with clear plastic wrap and placed on the SHMSL. Measurements were taken at 2.0 cm spacing at Site U1385 and at 5.0 cm spacing at all other sites to provide a high-resolution stratigraphic record of color variations for visible wavelengths. Each measurement was recorded in 2 nm wide spectral bands from 400 to 900 nm.

Magnetic susceptibility

Magnetic susceptibility was measured with a Bartington Instruments MS2E point sensor (high-resolution surface-scanning sensor) on the SHMSL. Because the SHMSL demands flush contact between the magnetic susceptibility point sensor and the split core, measurements were made on the archive halves of split cores that were covered with clear plastic wrap. Measurements were taken at 2.0 cm spacing at Site U1385 and at 5.0 cm spacing at all other sites. Measurement resolution was 1.0 SI, and each measurement integrated a volume of 10.5 mm × 3.8 mm × 4 mm, where 10.5 mm is the length perpendicular to the core axis, 3.8 mm is the width along the core axis, and 4 mm is the depth into the core. Only one measurement was taken at each measurement position.

X-ray diffraction analysis

Samples for XRD analyses were selected from the working half of sections the first time a particular depth interval was cored. In general, one 5 cm³ sample was taken per core, with the sample mostly taken in Section 5 or 6. Whatever lithology was present at that depth interval was sampled. Additional samples were occasionally taken and analyzed based on visual core observations (e.g., color variability and visual changes in lithology and texture) and smear slides. Except for Site U1385, samples taken once per core for X-ray analysis were generally also analyzed for sedimentary inorganic (i.e., carbonate analysis) and organic (i.e., CHNS analysis) carbon in the Geochemistry Laboratory (see “Geochemistry”). Samples analyzed for bulk mineralogy were freeze-dried in the case of unlithified samples and ground by hand or in an agate ball mill, as necessary. Prepared samples were top-mounted onto a sample holder and analyzed using a Bruker D-4 Endeavor diffractometer mounted with a Vantec-1 detector using nickel-filtered CuKα radiation. The standard locked coupled scan was as follows:

• Voltage = 37 kV.

• Current = 40 mA.

• Goniometer scan = 4°–70°2θ.

• Step size = 0.0174°2θ.

• Scan speed = 1 s/step.

• Divergence slit = 0.3 mm.

Shipboard results yielded only qualitative results on the presence and relative abundances of the most common mineralogical components.

Diffractograms of bulk samples were evaluated with the aid of the EVA software package, which allowed for mineral identification and basic peak characterization (e.g., base line removal and maximum peak intensity). Files were created that contained d values, diffraction angles, and peak intensities without and with background removed. These files were scanned by a computer program to find d spacing values characteristic of a limited range of minerals, using quartz or calcite as an internal standard, that we anticipated would be present in the sediments and that had peaks with little interference from other minerals present in the sample (Table T1) (Cook et al., 1975; Flood, 1978; Shipboard Scientific Party, 1995). Peak intensities were reported for each mineral identified in an effort to provide a semiquantitative measure about how each mineral identified varied downhole and between sites. Although some of the secondary peaks were checked to confirm the mineral identifications for some samples, not all sample identifications were checked to be sure that there were no false identifications. Thus, if the peak of a rare mineral fell within the detection window of a mineral to be identified, then the identification of the mineral will be wrong. Also, on occasion there were peaks on the XRD patterns that did not match the minerals being searched, and the materials responsible for those peaks have not yet been identified. Digital files with the diffraction patterns are available from the IODP Laboratory Information Management System (LIMS) database (iodp.tamu.edu/tasapps/).

Glauconite is one mineral that was often identified in smear slides but not identified in the XRD data. A diffraction pattern was run on a sample of glauconitic sand recovered from a core catcher and on a standard in the shipboard XRD. The resulting pattern showed a broad peak from ~7° to 9°2θ, suggesting an amorphous structure, and then numerous peaks at angles higher than 19°2θ. However, no single peak was identified that would allow us to quantify glauconite in these samples.

One way to evaluate the potential usefulness of the bulk X-ray intensities is to compare the peak intensities to an independent measurement of the same material. As noted previously, XRD studies and CaCO₃ determinations (sample code COUL) were generally made on the same samples starting with Site U1386, and thus we can compare percent CaCO₃ with peak intensity of the carbonate minerals, calcite, and dolomite (aragonite was only rarely observed in these samples; Fig. F10). For the purposes of this analysis, we have added together the values of the calcite (CaCO₃) and dolomite (CaMg[CO₃]₂) XRD peaks to compare with percent CaCO₃ from the COUL analysis. The resulting plot shows a fairly good relationship between CaCO₃ percentage and peak height with some noticeable exceptions. In particular, the sample with the highest peak intensity has an intermediate CaCO₃ percentage. This sample (339-U1387C-45R-1W, 76–77 cm) is from a sandstone rock which has a calcite cement. The recrystallized calcite apparently creates a much stronger reflection than the biogenic carbonate, detrital calcium carbonate, authigenic dolomite, or detrital dolomite that make up the rest of the samples analyzed. Except for this sample, these data suggest that there is a good correlation between the intensity of a particular X-ray peak and the amount of that material in a sediment sample.

Clay minerals were also of interest to this study, and clay mineral analyses were used in two ways during Expedition 339. First, the clay minerals chlorite, illite, and kaolinite make identifiable peaks. We confirmed the presence of kaolinite by heating a sample to 550°C and noting that the kaolinite peak disappeared. We could not identify any particular peak for smectite, but we did observe that there was a region of raised baseline between peaks identified for illite and chlorite. At Site U1385, the bulk samples were glycolated to expand the smectite minerals, and this treatment depressed the baseline between illite and chlorite to more normal levels and created a broad peak near 4.96°2θ, d spacing 17.8 Å, as expected for smectite. It was not possible to treat all bulk samples with glycolation, so, based on the analysis of glycolated and untreated bulk mineralogy samples from Site U1385, we estimate the smectite peak intensity using the following method. A baseline is drawn from 5.8° to 9.5°2θ on the diffraction plot, and the number of counts between that baseline and the diffraction trace at 7.85°2θ was measured. Multiplying this value by 1.27 and adding 242 resulted in a number that closely matched the glycolated smectite peak at 4.96°2θ. This value was used to characterize smectite on bulk XRD samples during Expedition 339.

For selected samples, clay materials were separated from the coarser sediments and scanned separately as oriented samples. The separated clay material was scanned before treatment, subjected to ethylene glycol treatment, and then scanned again to allow additional analysis of the clay mineral fraction. At Site U1385, clays were separated from a few of the samples, treated with ethylene glycol, and rescanned. No treatment was done at Site U1386, but the clay fraction was separated by centrifuge on a portion of the sample from every fourth core from Sites U1387–U1391. We did not interpret these later analyses in terms of clay mineral percentages, but instead the X-ray diffractograms for both the untreated and treated samples are shown to allow a qualitative evaluation of the nature of the clay mineral assemblage. The digital diffraction patterns are available from the IODP LIMS database (iodp.tamu.edu/tasapps/).

The clay separation method is described in the X-Ray Diffractometer User Guide onboard the JOIDES Resolution as follows:

1. Bulk sample (1 cm³; fresh, not freeze-dried) sediment was mixed with 1% borax solution (total of 30 mL of solution). The sample/borax solution was placed in a dismembrator for 2 min.

2. The sample/borax solution was centrifuged at 1500 rpm for 5 min to remove the particle size fraction >2 µm.

3. The sample/borax solution was decanted into a new centrifuge tube and spun at 1500 rpm for 15 min to remove the remaining ~2 µm particle size fraction.

4. The sample/borax solution was decanted, and the remaining clay residue was washed with distilled water.

5. The distilled water and clay residue was centrifuged at 1500 rpm for 15 min to help remove any borax from the clay residue. These last two steps were repeated.

6. An oriented clay mount was made on a zero-background single-crystal quartz disk by placing several drops of solution onto the quartz disk and allowing it to dry in the desiccator.

7. The quartz disk with the clay material was placed in a sample holder and was scanned using the same settings as for the bulk samples, except that the scanning range was 4°–35°2θ.

Digital color imaging

The archive half of each core was placed in the SHIL. The high-resolution digital core images were used to generate digital images that aided in core description. The SHIL collects digital images with three line-scan charge-coupled device arrays (2048 pixels each) behind an interference filter to create three channels (red, green, and blue). The image resolution is fixed at 20 lines at 500 dpi, and image acquisition was controlled by a 2 nm encoder. A constant aperture setting of f/22 was used. The SHIL system was calibrated with a white, mid-gray, and dark gray color chip (QPCard 101) placed at the top of each section that was checked frequently. A microscanner was used to identify samples, and the software-generated digital label was appended to the image.

For each section, scanned output from the SHIL included an ROI file of the original data with links to the TIFF file and an enhanced, uncropped JPEG file. A manually cropped JPEG image was generated to assist in visual core description. Postprocessing of data included color balance (performed by the Imaging Specialist) and the construction of a composite JPEG image of each core.

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