We have adopted the classification procedures suggested by Mazzullo et al. (1988) as modified by Leg 113 shipboard sedimentologists (Shipboard Scientific Party, 1988). According to Mazzullo's classification scheme, sediments encountered at the Leg 177 sites are granular sediments consisting of pelagic, siliciclastic, and volcaniclastic particles. Pelagic particles are defined as bioclastic grains composed of the skeletal remains of open-marine calcareous and siliceous microfauna and microflora derived from foraminifers, nannofossils, diatoms, and radiolarians as well as subordinate sponge spicules and silicoflagellates. The siliciclastic component consists of mineral and rock fragments that originated from igneous, sedimentary, and metamorphic rocks. In some recovered sediment cores, greenish brown glass shards were identified as volcaniclastic components that may occur as dispersed sand-sized particles in the host sediment or may form individual tephra beds.
We used the relative proportions of
biogenic and siliciclastic components to define the major lithologic classes. Biogenic
("pelagic") sediment is composed of 
50% biogenic grains, and
siliciclastic deposits are composed of >50% siliciclastic grains. We modified the
Mazzullo et al. (1988) terminology to avoid the designation of "mixed sediments"
that includes biogenic and siliciclastic components in the range between 40% and 60%. We
also define "mud" as the sum of silt and clay.
The principal name of biogenic sediments and sedimentary rocks relates to the chemical composition of the major component and the degree of compaction. The following names are used:
For siliciclastic sediments, the principal name describes the texture and is assigned according to the following guidelines:
Lithologies consisting of >50% volcaniclastic components are referred to as "tephra."
The principal name of biogenic and siliciclastic sediments is preceded by major modifiers and followed by minor modifiers that may refer to mixed biogenic, siliciclastic, and volcaniclastic components:
For a better understanding of the applied lithologic terminology, we give three examples:
Visually distinctive glaciogenic sediment components are present in Leg 177 sediments, particularly ice-rafted debris (IRD). These sediments are described using the classification for siliciclastic sediments. They are often identified by the presence of isolated angular to subangular dropstones of varying composition and origin in the midst of fine-grained sediments as dropstone clusters, or as dropstones with other sand-sized IRD. Dropstones are defined as grains >1 cm in diameter. Characteristics of these sediments are detailed on core description forms within the general description portion of the lithologic description text.
In some core intervals, sediment composition and grain-size characteristics together with structural features (e.g., graded or contorted bedding) document sediment redeposition. In the barrel sheets, such lithologies are indicated by their descriptive terms with additional remarks concerning their mode of transportation (e.g., "graded volcanic vitric ash layer that may represent a turbidite" or "contorted beds that probably originate from sediment slumping processes").
The core description forms, or "barrel sheets" (Figs. F3, F4; see the "Core Descriptions" contents list), summarize the data obtained during a visual inspection of the core. The following text explains the ODP conventions used for compiling each part of the core description form and modifications to these procedures adopted by the Leg 177 scientific party.
Shipboard scientists were responsible for visual core inspection, smear-slide analyses, thin-section descriptions, and color analysis. Biostratigraphic (age), geochemical (calcium carbonate), and XRD (opal) data were integrated with other sedimentological information to augment core descriptions.
Cores are designated using leg, site, hole, core number, and core type information (see "Introduction"). The cored interval is specified in terms of mbsf and mcd (see "Composite Depths").
The lithology of the material recovered is represented on the core description form by up to three patterns in the column titled "Graphic Lithology" (Fig. F3). Constituents accounting for <10% of the sediment in a given lithology are not shown in the "Graphic Lithology" column and are not included in the lithologic name. The "Graphic Lithology" column shows only the composition of layers or intervals exceeding 20 cm in thickness.
In sediment cores, natural structures and structures created by the coring process can be difficult to distinguish. Natural structures observed are indicated in the "Structure" column of the core description form (Fig. F3). The symbols on the "Structure" column indicate the location of sediment features such as primary sedimentary structures, discrete trace fossils, soft-sediment deformation features, structural features, and diagenetic features. The apparent intensity of bioturbation is shown in the "Bioturbation" column of the barrel sheet in the conventional manner (none, rare, moderate, common, or abundant). Leg 177 sedimentologists recognize that sediment may be the product of deposition of material of homogeneous color and grain size resulting in sediment with no observable lamination or color change, or may be the product of total mixing by the action of bioturbating organisms. The symbols used to describe each of these biogenic and physical sedimentary structures are shown in Figure F4.
Deformation and disturbances of sediment that clearly resulted from the coring process are illustrated in the "Disturbance" column (Fig. F4). Blank regions indicate the absence of drilling disturbance. The degree of drilling disturbance is described for soft and firm sediments using the following categories:
The degree of fracturing in indurated sediments was described using the following categories:
The positions of smear-slide samples taken from each core for shipboard analysis are indicated by "SS" in the "Sample" column on the core description form.
Tables summarizing data from smear-slide analyses appear in the "Core Descriptions" contents list. These tables include information on the sample location and core depth interval, whether the sample represents a primary or a minor lithology in the core, and the estimated percent-ages of identified components. The visual estimates are based on area percentage and are qualitative in nature.
The text describing the lithology, found in the "Description" column of the core description form, consists of two parts: (1) a heading that lists all the major sediment lithologies observed in the core, and (2) a general description of major and minor lithologies, including location of significant features in the core. Descriptions and locations of dropstones; concretions; thin, interbedded lithologies; and other minor lithologies are included in the text as is any clarifying information regarding sediment disturbance produced by drilling/coring or natural processes.
Qualitative visual impressions of sediment color were noted by sedimentologists as part of the core description process. In addition, quantitative estimates of sediment reflectance were collected using the Oregon State University Split Core Analysis Track (OSU-SCAT), an automated spectrophotometer, and the handheld Minolta CM-2002 spectrophotometer (see "Physical Properties"). As an aid to defining lithostratigraphic units, we employed the red band that is near the instrument's maximum response. For shipboard analysis, the raw OSU-SCAT data were converted to percent reflectance and averaged into four 100-nm-wide bands defined as: (1) ultraviolet (UV; 250-350 nm), (2) blue (450-550 nm), (3) red (650-750 nm), and (4) near infrared (nIr; 850-950 nm). These bands are 50 nm wider than those used during previous ODP legs to allow integration of a greater fraction of the spectral signal. These bands were also used as an aid in constructing composite sections (see "Composite Depths"). The blue band is used for comparison to shipboard measurements of the calcium carbonate content of sediments because calcite has a somewhat higher reflectance at this wavelength than at longer wavelengths (see Mix et al., 1992).
Selected core samples were analyzed
with an X-ray diffractometer (Philips PW 1729) to estimate opal contents and the
composition of the terrigenous sedimentary fraction. Before XRD measurements,
bulk-sediment samples were treated with 10% hydrochloric acid to remove the carbonate
fraction, were washed for salt removal, oven dried at 105ºC, and ground. This procedure
may alter some clay mineral species but permits a quick shipboard XRD analysis within 1.5
days. Step scan measurements were run on random powder mounts with Cu
radiation (40 kV and 35 mA) from 3º to 50º2
at steps of 0.02º2 per 2 s.
Graphic evaluation of the diffractograms was facilitated with the interactive MacDiff software (R. Petschick, public domain). It was used for mineral identification, on the basis of peak positions and relative intensities, as well as semiquantitative estimation of mineral abundances according to both peak intensities and integrated peak areas.
Opal contents were estimated from
the maximum peak height of the broad opal hump at 24.5º2 extending between 15º and 35º2 in the X-ray
diffractograms (Eisma and Van der Gaast, 1971; Hempel and Bohrmann, 1990). Eight external
standard samples containing opal amounts between 5 and 70 wt% were run for calibration
(Fig. F5). Opal standards consist of mixtures of
pure diatom ooze, taken from a surface sample of the Conrad Rise in the western Indian
Ocean sector of the Southern Ocean, and pure terrigenous sediment from the <63-µm
fraction of a Quaternary till from the Baltic Sea, which shows a similar composition to
terrigenous matter found in the Southern Ocean. Generally, a linear correlation exists
between absolute intensities of the XRD opal hump of the standard samples and weight
percentages of opal in the standard samples. Values of the regression equation depend on
the XRD device, type of radiation, and the scan modes applied. For samples containing
>10% opal, accuracy and precision of determined opal values are within ±3% of measured
opal concentrations. Errors are higher for samples containing <10% opal.
Relative abundances of the minerals in the lithogenic fraction are presented only as relative changes in the peak areas or peak-area ratios of minerals. Diagnostic peaks of minerals found in the recovered sediments are (1) quartz (4.26 Å, multiplied by a factor of five for quantification), (2) feldspar (3.18-3.24 Å), (3) pyrite (2.71 Å), (4) clinoptilolite (8.9 and 7.9 Å), (5) hornblende (8.6 Å), and (6) clinopyroxene (3.0 Å). Clay mineral proportions were estimated collectively and are not clearly distinguished as individual clay mineral species. In X-ray diffractograms of random powder mounts, most clay minerals yield a broad diffraction peak at ~4.5 Å. The integral peak area can be used for the determination of clay mineral proportions. In some samples, a distinction between relative abundances of the 10-Å clay minerals (illite and sericite) and 7-Å clay minerals (kaolinite and chlorite) can be made using the 10-Å/7-Å peak intensity ratio. Smectite and mixed-layer clay minerals produce a very broad peak between 10 and 15 Å that is difficult to match precisely in the X-ray diffractograms.
XRD data are compiled in a separate table in the "Lithostratigraphy" section of each site chapter. We use the abbreviations Qz for quartz, Fsp for feldspar, and CM for clay minerals.
