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The techniques and procedures used to describe, analyze, and name the lithologies recovered during Expedition 308 are detailed below and follow ODP Technical Note 8 (Mazzullo and Graham, 1988). These include visual core descriptions (VCDs), smear slide and thin section descriptions, XRD analyses, color spectrophotometry, and high-resolution digital color imaging. Any significant deviations from the procedures outlined in this section are discussed in the individual site chapters.

Sediment classification

Principal names were assigned to sediments based on composition, texture, and degree of lithification as determined primarily from visual description and smear slide analyses. Modifiers to the principal name were determined based on both the abundance and type of the nonprincipal component or components (e.g., siliciclastic or biogenic). Total inorganic carbon content, including calcium carbonate, of the sediments (see “Solid-phase chemistry” in “Geochemistry and microbiology” in the “Site U1319,” “Site U1320,” “Site U1322,” and “Site U1324” chapters) was also used to aid in classifying sediments. Major modifiers, those components that form >25% of the sediment, precede the principal name and are listed in order of increasing abundance. Genetic terms, such as “pelagic,” “neritic,” “turbidite,” and “debris flow,” were not used in classifying the sediments and are used only in geologic interpretations of the sedimentary unit. The conventions used here were applied only to granular sediments. Chemical sediments were only encountered as accessory minerals and nodules.

Siliciclastic sediments

For sediments and rocks composed of >60% siliciclastic components, the principal name was determined by the size of the grains, derived from the Udden-Wentworth grain-size scale (Wentworth, 1922) (Fig. F1). In this classification scheme, the term “clay” is independent of mineralogy and refers to all siliciclastic grains <3.9 µm in size. The relative proportion of different grain sizes was determined by visual percentage estimation using a standard comparison chart with half-ϕ unit intervals (e.g., Terry and Chilingar, 1955). Where possible in sand beds, the modifiers “upper” and “lower” are used to describe whether the sediment is predominantly in the upper half or lower half of an individual ϕ-size class (e.g., medium upper sand for grains with a typical size between 1.5ϕ and 1ϕ). For silt and clays, the grain size was estimated using smear slides. Once the relative proportion of the various grain sizes was estimated, a modified Shepard (1954) classification scheme was used to modify, if necessary, the principal name using the ternary diagram in Figure F2. Clay, silt, and sand are the principal names in the diagram. If either the silt or sand component exceeds 25% of the total siliciclastic grains, it becomes a modifier to the principal name. For example, sediment composed of 10% clay and 90% silt is simply silt, whereas sediment composed of 30% silt and 70% sand is silty sand. Where the proportions of silt and clay were difficult to quantify, the term “mud” was used for sediment containing mixtures of clay and silt.

Where diagnostic minerals (e.g., glauconite), biogenic sediments (e.g., foraminifers), or unusual components (e.g., volcanic glass) compose ≥5% of the sediment, the naming conventions of biogenic and mixed sediments were adopted. Thus, if the mineral component represents between 5% and 10% of the sediment, it is hyphenated with the suffix “-bearing” and precedes the major siliciclastic component name. If the component is 10%–40% of the sediment, it is hyphenated with the suffix “-rich” instead. For example, sediment composed of 15% sand-sized foraminifer tests, 30% silt, and 55% clay is called a foraminifer-rich silty clay. Where volcanic glass composed >40% of the sedimentary components, the name volcanic ash was used.

Biogenic sediments

Unlike siliciclastic sediments, biogenic sediments, defined as containing >60% biogenic components, are not described based on grain size. Rather, the principal name for all biogenic sediments is ooze. If the siliciclastic component represents 5%–40% of a sediment, the naming conventions using “-rich” and “-bearing” as described for mixed sediments below are used. Thus, a sediment composed of 30% siliciclastic clay and 70% sand-sized foraminifers is called a clay-rich foraminifer ooze, not a clay-rich foraminifer sand.

Mixed sediments

Mixtures of biogenic and nonbiogenic material, where the biogenic content is 40%–60%, are termed “mixed sediments” (Mazzullo and Graham, 1988). The name of a mixed sediment consists of a major modifier(s) consisting of the name(s) of the major fossil group(s), with the least common fossil listed first, followed by the principal name appropriate for the siliciclastic components (e.g., foraminifer clay). The same naming conventions for using “-bearing” and “-rich” apply to mixed sediments as described above. Sediment containing 5% foraminifers, 40% nannofossils, and 55% silt is, thus, called foraminifer-bearing nannofossil silt. Sediment containing 5% diatoms, 40% clay, and 55% nannofossils is called diatom-bearing nannofossil clay.

Visual core descriptions

Detailed sedimentologic observations and descriptions were recorded manually for each core section on paper (barrel sheets). A variety of features that characterize the sediments were recorded, including lithology, sedimentary structures, color, diagenetic precipitates, and core disturbance. Compositional data were obtained from smear slides. The color of the sediments was determined first by visual observation at the description table and then quantitatively by color spectrophotometry using the AMST. This information was then transcribed into VCD forms using AppleCORE software (version 9.4a), which generated a one-page graphical description of each core. An example of such a VCD from Expedition 308 is shown in Figure F3. The legend for the symbols used for lithology, sedimentary structures, and other features seen in Expedition 308 cores are explained in Figure F4. The VCD forms are available digitally in the core descriptions, and the scanned barrel sheets are available upon request.

Lithology and grain size

Lithology and grain size of the described sediments are represented graphically in a column on the VCD using the symbols illustrated in Figure F4. A maximum of three different lithologies (for interbedded sediments) or three different components (for mixed sediments) can be represented within the same core interval using AppleCORE software. Intervals that are a few centimeters thick or thicker can be portrayed accurately in the Lithology column. Percentages are rounded to the nearest 10%, and lithologies that constitute <10% of the core are generally not shown but are listed in the Description column.

Sedimentary structures

Each type of sedimentary structure and its exact location are displayed in the Structure column of the VCD (Fig. F3). Symbols used for sedimentary structures encountered throughout Expedition 308 are listed in Figure F4. Some of the more common structures and accessories observed were parallel laminations, climbing ripples, graded bedding, mud clasts, contorted beds, wood fragments, plant debris, and mottling.


The presence of macroscopic fossils such as shell fragments and preserved whole shells were identified whenever possible and displayed in a separate column on the barrel sheet.

Sediment disturbance

Drilling-related sediment disturbance is recorded in the Disturbance column on the VCD (Fig. F3). Separate terms are used to describe the degree of drilling disturbance:

  • Slightly disturbed = bedding contacts are slightly deformed.
  • Moderately disturbed = bedding contacts have undergone extreme bowing.
  • Highly disturbed = bedding is completely deformed as flow-in, coring/drilling slough, and other soft-sediment stretching and/or compressional shearing structures attributed to coring/drilling (e.g., gas expansion).
  • Soupy = intervals are water saturated and have lost all primary sedimentary structures.
  • Drilling biscuits = drilling slurry surrounding an intact or slightly fractured drilling biscuit, usually associated with XCB coring.

Cores recovered from gas-bearing sediments are often disturbed by gas expansion and fracturing as they are brought to surface conditions. In cases where it is possible to distinguish between disturbance of the core resulting from drilling and disturbance resulting from gas expansion, notes were made in the Comments section of the barrel sheet listing the depths at which gas fracturing was observed.


The locations of samples are indicated in the Sample column on the VCD. The abbreviations used are as follows:

  • SmS = smear slide.
  • IW = interstitial water.
  • MBI/BIO = microbiology.
  • PAL = micropaleontology.
  • WHC = whole-round core.

Smear slide analyses

Smear slides were prepared from the archive halves of the cores. With a toothpick, a small amount of sediment was taken and put on a 2.5 cm × 7.5 cm glass slide, homogenized, and dispersed over the slide with a drop of deionized water. The sample was then dried on a hot plate at a low temperature. A drop of Norland optical adhesive and a 2.5 cm × cm cover glass were added. The smear slide was fixed in an ultraviolet light box. With a transmitted-light petrographic microscope, both the grain size and abundance of dominant components in a sample were determined. Abundance was estimated with the help of a comparison chart for visual percentage estimation (after Terry and Chilingar, 1955). Note that smear slide analyses tend to underestimate the amount of sand-sized and larger grains because these grains are difficult to incorporate into the slide. The smear slide results are available from the IODP database, and the tables include information about the location of samples, their grain-size distribution, and whether the sample represents the dominant or the minor lithology in the core. Additionally, it provides estimates of the major mineralogical and biological components from the examination of each smear slide. The presence of authigenic minerals, such as manganese oxides, iron sulfides, or carbonates, as well as the presence of rare trace minerals, was noted in the Comments column. The mineralogy of the major smear slide components was also validated by XRD analysis, and the relative proportion of carbonate and noncarbonate material was validated by chemical analysis of the sediments (see “Solid-phase chemistry” in “Geochemistry and microbiology” in the “Site U1319,” “Site U1320,” “Site U1322,” and “Site U1324” chapters).

X-ray diffraction analyses

XRD analyses were used to support and verify smear slide descriptions. Each sample was freeze-dried, ground, and mounted with a random orientation into an aluminum sample holder. For these measurements, a Philips PW-1729 X-ray diffractometer with a CuKα source (40 kV and 35 mA) and a Ni filter was used. Peak intensities were converted to values appropriate for a fixed slit width. The goniometer scan was performed from 2°2θ to 70°2θ at a scan rate of 1.2°/min (step = 0.01° and count time = 0.5 s). Diffractograms were peak-corrected to match the (100) quartz peak at 4.26 Å. Common minerals were identified based on their peak position and relative intensities in the diffractogram using the software package MacDiff (version 4.2.5;​Software).

Color reflectance spectrophotometry

In addition to visual estimates of color, reflectance of visible light from soft sediment was measured using a Minolta spectrophotometer (model CM-2002) mounted on the AMST. The AMST measures the archive half of each core section and provides point measurements of downcore color variations for the visible wavelengths (400–700 nm). Freshly split cores were covered with clear plastic wrap and placed on the AMST. The AMST skips empty intervals and intervals where the core surface is well below the level of the core liner but does not recognize relatively small cracks or disturbed areas of core. Thus, AMST data may contain spurious measurements that should be edited out of the data set before use. Each measurement consists of 31 separate determinations of reflectance in 10 nm wide spectral bands from 400 to 700 nm. Additional detailed information about the measurement and interpretation of spectral data with the Minolta spectrophotometer can be found in Balsam et al. (1997, 1998) and Balsam and Damuth (2000). The AMST was also used to acquire point magnetic susceptibility measurements (see “Paleomagnetism”). Color reflectance and magnetic susceptibility measurements were useful to distinguish turbidites and hemipelagic sediments.

Digital color imaging

All core sections were imaged using the Geotek X-Y DIS soon after being split and scraped. Scraping the cores immediately prior to imaging helped capture ephemeral sedimentary features, particularly faint color banding and laminations, which often become oxidized within minutes of core splitting. Core sections were routinely loaded into each imaging tray of the DIS as soon as the previous sections were imaged so that the imaging system ran continuously during section loading and unloading. Digital images were displayed after scanning to ensure they were stored.

All images were acquired at a crosscore and downcore resolution of 100 pixels/cm. At the beginning of Expedition 308, the acquisition aperture was varied in an attempt to maximize the dynamic range captured. The barcode label and the polystyrene inserts (e.g., for voids and whole-round samples) were placed at the end of each section. Output from the DIS includes an uncompressed TIFF file (available upon request) and a compressed Mr.Sid (.sid) file (available in the Janus database) for each scanned section. Red-green-blue (RGB) profiles for all images were also automatically saved (available upon request) but were generally not used on board. Additional postprocessing of the color imagery was done to achieve a “medium”-resolution JPEG (.jpg) image of each section and a composite PDF (.pdf) image of each core.

In addition to the DIS scanning of the core sections, whole-core photographs were acquired with a large-format color camera. The photographs took place between 30 and 60 min after the core was scraped. Consequently, some of the sedimentary details may be lost using the more conventional archive-core table photographs. For this reason, cores were scraped before close-up digital photographs were taken.