Description of sedimentary deposits recovered during Leg 197 generally followed standard ODP methodology. The visual description of sedimentary units encountered during Leg 197 was made on split cores and includes documentation of (1) sediment composition based on visual inspection, smear slides, thin sections, and carbonate content and (2) degree of consolidation and presence of sedimentary and deformational structures (i.e., drilling-induced disturbance and bioturbation).
Barrel sheets (Fig. F2) provide a summary of the most relevant information on the entire core and are presented with core photographs in the "Core Descriptions" for each site chapter (see the "Core Descriptions" contents list). Observations are first recorded on visual core description (VCD) forms and then summarized for entry into AppleCORE (version 8.1m) software, which generates a one-page graphical log of each core ("barrel sheet"). More specifically, the barrel sheets contain a wide variety of information such as graphic representation of lithology (Fig. F3), evidence of drilling disturbance and sedimentary structures, sample type (i.e., smear slide, thin section, whole-core sample, and X-ray diffraction), and lithologic description including texture and structure of sediment and sedimentary rocks and their color. In the graphic log, the symbols for sedimentary structures (e.g., bed thickness, bioturbation intensity, soft-sediment deformation) and structural and diagenetic features (Fig. F4) of soft and consolidated sediment are indicated either by patterns and symbols or by arrows placed as close as possible to their proper stratigraphic position. Copies of the detailed section-by-section VCD forms for each site can be accessed from the "Core Descriptions" contents list. Barrel sheets include the following information.
Sediment lithology is represented by patterns in the "Graphic Lithology" column. This column may consist of one or as many as three vertical strips, depending on the number of the major end-member constituents (see "Classification of Sediment and Sedimentary Rocks") for mixed sediment. However, for Leg 197, only the pattern for the dominant lithologic component was entered. Because of the limitations of the AppleCORE software, thin intervals of interbedded lithologies cannot be adequately displayed at the scale used for the barrel sheets, but they are described in the "Description" column on the barrel sheet, where appropriate.
Natural structures (physical or biological) can be difficult to distinguish from disturbances created by the coring process. Deformation and disturbance of sediment that resulted from the coring process are illustrated in the "Drilling Disturbance" column (Fig. F2), using symbols shown in Figure F4. Blank regions indicate the absence of drilling disturbance. The degree of drilling disturbance for soft sediment was described using the following categories:
Standard ODP categories exist for describing fragmentation in indurated sediment and rocks, but the only one appropriate to Leg 197 hard rock material is "highly fragmented," which means pieces from the cored interval are probably in correct stratigraphic sequence (although they may not represent the entire section), but are not in their original position or coring orientation.
The "Bioturbation" column of the barrel sheet shows four levels of intensity:
Stratification thickness was characterized as follows (McKee and Weir, 1953; Ingram, 1954):
The stratigraphic position of samples taken for shipboard analysis is indicated in the "Samples" column of the barrel sheet according to the following codes:
Owing to instrumental problems, the XRD data were not used except for general identification of dolomite. The XRD data provided should be used with caution. The low-angle data are not reliable.
A summary of the lithologic observations is given in the "Description" column of the barrel sheets. It consists of three parts: (1) a denomination in capital letters listing only the dominant sediment lithologies (major and minor lithology) observed in the core (e.g., CLAY and CALCAREOUS CLAY with FORAMINIFERAL OOZE and VOLCANIC ASH layers); (2) a general description of the core, including composition, color, sedimentary structures, bed thickness, and drilling disturbance, as well as any other general features in the core; and (3) descriptions and locations of thin, interbedded, or minor lithologies (e.g., normally graded FORAMINIFERAL OOZE, at Section 2, 45-80 cm).
Sediment color was determined visually by comparison with standard color charts (Munsell Color Company, Inc., 1975; Rock Color Chart Committee, 1991) and is reported in the VCD "Color" column and the "Description" column of the barrel sheet. In addition to determining color visually, select cores were scanned at 2- to 5-cm intervals using a Minolta CM-2002 spectrophotometer mounted on the archive multisensor track (AMST). The spectrophotometer measures reflectance in thirty-one 10-nm-wide bands of the visible spectrum (400-700 nm) on the archive half of each core section. Spectrophotometer readings were taken after cleaning the surface of each core section and covering it with clear plastic film. Calibration of the color scanner did not include a correction for the plastic film because it only had minor effects even with very bright-colored lithologies. The measurements were taken automatically and recorded by the AMST at evenly spaced intervals along each section. The area measured is a 8-mm-diameter circle, and the spectrophotometer integrates the sensed color over this area. It was not possible to program the AMST software to avoid measurements in intervals with a depressed core surface or in disturbed areas of core containing drilling slurry or biscuits. The color data are recorded in the Janus database and can be obtained from ODP. Additional detailed information about measurement and interpretation of spectral data with the Minolta spectrophotometer can be found in Balsam et al. (1997, 1998; Balsam and Damuth, 2000).
Primary and secondary sedimentary structures were described from observations of the archive cores. For granular sediment classification, we used the lithologic names according to the ODP sediment classification scheme (Mazzullo et al., 1988), which is shown in Figure F5. These naming conventions consist of a principal name based on depositional depth or environment (i.e., pelagic or neritic), degree of lithification (i.e, ooze, chalk, or chert), and texture (silt, sand, or clay). Sediment names for Leg 197 sites consist of a principal name identifying the dominant composition of the sediment (e.g., clay, diatom ooze, or radiolarian ooze [where any one of these three is >50%], or siliceous ooze [if neither diatoms nor radiolarians is >50%, but together they are]), and a modifier that precedes the principal name. A component with 10%-25% abundance is termed component-bearing, and one with 25%-50% abundance is termed component-rich (e.g., ash-rich clay- or radiolarian-rich diatom ooze). For a mixture of components, the principal name is preceded by major modifiers (in order of increasing abundance) that refer to components making up >25% of the sediment. Minor components that represent between 10% and 25% of the sediment follow the principal name in order of increasing abundance. As an example, an unconsolidated sediment that contains 30% nannofossils, 25% clay minerals, 20% foraminifers, 15% feldspar silt, and 10% manganese nodules would be described as a clayey nannofossil ooze with manganese nodules, feldspar silt, and foraminifers. Granular sediment is subdivided on the basis of composition and abundance of different grain types estimated from visual examination of the core, smear slides, thin sections, and by shipboard measurements of carbonate content. For naming the siliciclastic sediment we used the Udden-Wentworth grain-size classification scheme (Wentworth, 1922) (Fig. F6) and the ternary diagram (silt-sand-clay) (Fig. F7).
We used "volcaniclastic" as a nongenetic term, as described in "Volcaniclastic Deposits" in "Physical Volcanology." In volcaniclastic sediment, the term ash (or tuff, if lithified) is used for sand-sized fractions, whereas lapilli is used for granule and cobble size categories. Terms that describe lithification vary depending on the dominant composition (i.e., calcareous pelagic organisms, siliceous microfossils, and siliciclastic/volcaniclastic material). In particular, we have the following:
Grain shapes of coarse-grained components such as lithics in the gravel/pebble fraction are described using the major modifiers "rounded," "subrounded," "subangular," and "angular" (Fig. F8).
We determined grain size and composition of sediment using smear slides and thin sections. Smear slide samples were prepared according to the procedures described in the handbook for shipboard sedimentologists (Mazzullo et al., 1988). Identification of mineral and biogenic components was carried out in accordance with Rothwell (1989). Sediment texture and mineral/biogenic components were estimated visually using the comparison chart shown in Figure F9. Tables summarizing data from thin sections and smear slides are included in the "Core Descriptions" for each site (see the "Core Descriptions" contents list). These tables include information about the sample location, whether the sample represents a dominant (D) or a minor (M) lithology, and the estimated abundance of different grain sizes and different grain types (percentages of sand, silt, and clay size fractions), together with all of the identified components.
We must emphasize that smear slide analysis provides only rough estimates of the relative abundances of detrital constituents. This circumstance reflects the fact that (1) mineral identification of fine silt to clay particles is difficult using only a petrographic microscope and (2) sand-sized grains tend to be underestimated because they cannot be incorporated into the smear. Accuracy of the carbonate content, estimated from smear slides and thin sections, was confirmed by chemical carbonate analyses performed according to standard shipboard procedures by the coulometer method (see Rea, Basov, Janecek, Palmer-Julson, et al., 1993).
Thin section analysis of microfacies followed the textural classification scheme of Dunham (1962). Matrix-supported rocks are classified as mudstone if they contain <10% and wackestone if they contain >10% grains.
For some samples, sieving for foraminifers was performed to improve smear slide estimation of this component.