Visual core description (VCD) forms (Fig. F2), or "barrel sheets," drafted in AppleCORE software (version 8.1m), summarize the data obtained during shipboard observation and analysis of each sediment core. Detailed observations of each section were recorded initially by hand on blank AppleCORE templates with two sections per page. This information was subsequently entered into the AppleCORE software, which generates a simplified, annotated graphical description (barrel sheet) for each core. These barrel sheets are linked to corresponding core photographs in the volume Core Descriptions (see the "Core Descriptions" contents list). The following text explains the ODP conventions used for compiling each part of the core description form and the exact protocols adopted by the Leg 206 shipboard scientific party.
Shipboard scientists, none of whom specialized in sedimentology, were responsible for visual core logging and smear slide analysis. Mineral abundance and identifications were augmented by X-ray diffraction (XRD) analysis. Data describing biostratigraphy (age), geochemistry (CaCO3, organic carbon [Corg], and major and trace element concentrations), paleomagnetics, and physical properties (wet bulk density and porosity) were integrated with the sedimentological information.
Cores are designated using leg, site, hole, core number, and core type as discussed previously (see "Numbering of Sites, Holes, Cores, and Samples" in "Introduction"). The cored interval is specified in terms of meters below seafloor. On the basis of drill pipe measurements, reported by the Transocean coring technician and the ODP operations manager, depths are corrected for the height of the rig floor dual elevator stool above sea level to give true water depth and correct meters below sea level.
Site, hole, and depth in meters below seafloor are given at the top of the barrel sheet, with depth positions of core sections indicated along the left margin. Columns on the barrel sheets include Graphic Lithology, Sedimentary Structures, Fossils (ichnofossils), Bioturbation, Color, Sediment Disturbance, Sample Types, and Remarks. These columns are discussed below, followed by an outline of the lithostratigraphic classification used during Leg 206.
Lithologies of the core intervals recovered are represented on barrel sheets by graphic patterns in the Graphic Lithology column (Figs. F2, F3). For intervals containing homogeneous mixtures of multiple lithologies, symbols are arranged within the column from left to right in order of their relative abundance. Graphic lithologies are used for components that compose 10% or more of the total sediment, with only the three most abundant components shown. The width of each pattern in the column approximates the relative abundance of that component. Relative abundances reported in this volume are useful for general characterization of the sediment, but they are not precise, quantitative data.
Sedimentary structures formed by natural processes and not as a result of drilling disturbance are represented on the barrel sheet in the Structure column (Fig. F4). Structures formed by both biogenic and physical processes are included. These include varying degrees of bioturbation, types of trace fossils, parallel laminations, and soft-sediment deformation structures.
Symbols are used to denote the location of clearly identifiable ichnofossils (Fig. F4).
The extent of general bioturbation is indicated in the Bioturbation column. Using a scheme similar to that proposed by Droser and Bottjer (1986), five levels of bioturbation were recognized. Bioturbation intensity is classified as abundant (>75%), common (50%-75%), moderate (10%-50%), rare (<10%), and barren (none); these levels are illustrated with graphic symbols in the Bioturbation column (Fig. F4).
Color is determined qualitatively using the Munsell rock color charts (Rock-Color Chart Committee, 1991) and is described immediately after the cores are split to avoid color changes associated with drying and oxidation. Color is generalized in the Color column with acronyms like "dk mo Br," which is dark mottled brown (Table T1).
Symbols are used to denote sediment disturbance induced by the coring process (Fig. F4). Symbols are positioned at the location in the section where that feature is observed. If the feature extends over an interval, the symbol appears centered on a vertical line to denote the stratigraphic extent of occurrence.
Sample material taken for shipboard sedimentologic and chemical analysis consisted of pore water from whole-round samples, "toothpick" samples (smear slides), and discrete samples for XRD, paleomagnetic, and physical property analyses. Typically, one to two smear slides (or thin sections) were made per core and one pore water and two physical property samples were taken per core. XRD samples were taken from the interstitial pore water squeeze cakes and from unique locations to better characterize the lithologic components. Data such as grain size and relative abundance of sedimentary components from smear slides are summarized in data tables that are independent of the AppleCORE sheets. An up-to-date list of samples that have been taken from the cores can be obtained from the ODP Janus database.
The written description for each core contains a brief overview of major and minor lithologies that are present, as well as notable features (e.g., sedimentary structures).
Lithologic names consist of a principal name based on composition, degree of lithification, and/or texture as determined from visual description and smear slide observations. 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% or more of the sediment. Minor components that represent between 10% and 25% of the sediment follow the principal name after a "with" in order of increasing abundance. Thus, an unconsolidated sediment containing 30% nannofossils, 25% clay minerals, 20% foraminifers, 15% quartz silt, and 10% manganese nodules would be described as a clayey nannofossil ooze with manganese nodules, quartz silt, and foraminifers. These naming conventions follow the ODP sediment classification scheme (Mazzullo et al., 1988), with the exception that during Leg 206 a separate "mixed sediment" category was not distinguished. During Leg 206, we did not encounter neritic sediments or chemical sediments and do not address these categories below.
Sediment was classified on the basis of composition estimated by visual examination of the core, smear slides, and thin sections and by shipboard measurements of carbonate content (see "Bulk Sediment Sampling and Chemical Analyses" in "Geochemistry") and shipboard XRD analyses (see "Sample Types" in "Visual Core Descriptions"). In volcaniclastic sediments, the term "ash" (or "tuff" if lithified) is used in place of "sand," whereas "lapilli" is used for granule and cobble size categories. Larger volcanic clasts (breccia) were not encountered, but discrete pumice lapilli are noted as "pumice clasts." Size divisions for grains are those of Wentworth (1922) (Fig. F5). Size-textural qualifiers were not used for pelagic sediment names (e.g., nannofossil clay implies that the dominant component is detrital clay rather than clay-sized nannofossils).
Terms that describe lithification vary depending upon the dominant composition: