LITHOSTRATIGRAPHY

For each site chapter, lithostratigraphy and physical properties are presented within a single section titled "Lithostratigraphy." The purpose of integrating these results is twofold: sediment composition strongly affects physical properties, and physical properties commonly provide distinct step changes that are used to define lithostratigraphic unit boundaries. Thus, combining these results for each site chapter integrates complementary data and reduces descriptive redundancy. Within the "Explanatory Notes" chapter, however, we address lithostratigraphy and physical properties separately, given their different analytical techniques, methodologies, and classifications.

Sediment Classification

The lithologic classification scheme is based on three end-member grain components (i.e., siliceous biogenic, calcareous biogenic, and siliciclastic), the grain size of the siliciclastic component (i.e., clay, silt, or sand), and the degree of sediment induration (e.g., ooze vs. chalk, clay vs. claystone, etc.). Percentages of end-member grain components as well as siliciclastic textures were determined by smear slide examination and used to define lithologies reported on the visual core descriptions (VCDs) and barrel sheets. Area-based smear slide estimates of carbonate content often differed somewhat from mass-based coulometry determinations of carbonate content. Whereas these differences produced different sediment classifications, the smear slide–based classification was preferred. Each of the three end-member grain components is discussed below and is graphically related in Figure F1.

Calcareous Biogenic

Calcareous biogenic lithologies are composed of >50% biogenic grains, of which >50% are calcareous (Fig. F1A). Principal names indicate the degree of lithification and consist of ooze (i.e., readily deformed under the pressure of a finger or spatula blade), chalk (i.e., easily scratched by fingernail or edge of a spatula and cut by band or diamond saw), and limestone (i.e., not scratched by fingernail or edge of a spatula and cut by band or diamond saw). Major modifiers (>25% of total composition) describe the nature of the calcareous biogenic (e.g., foraminifer and nannofossil), siliceous biogenic (e.g., diatom and radiolarian), or siliciclastic (e.g., sand, silt, and clay) grains. Minor modifiers (10%–25% of total composition) are described in similar terms, followed by the suffix "-bearing." For example, a firm sediment composed of 5% foraminifers, 15% siliciclastic silt, 18% diatoms, and 60% nannofossils would be termed a silt- and diatom-bearing nannofossil chalk. Note that multiple modifiers are listed by increasing predominance and are followed by the principal name.

Siliceous Biogenic

Siliceous biogenic sediments are composed of >50% biogenic grains, of which >50% are siliceous (Fig. F1A). Principal names indicate the degree of lithification and consist of ooze (i.e., readily deformed under the pressure of a finger or spatula blade), porcellanite (i.e., easily scratched by fingernail or edge of a spatula and cut by band or diamond saw), and chert (i.e., not scratched by fingernail or edge of a spatula and cut by band or diamond saw). Major and minor modifiers are applied as above. For example, a soft sediment composed of 8% siliciclastic clay, 20% nannofossils, 35% radiolarians, and 37% diatoms would be termed a nannofossil-bearing radiolarian diatom ooze.

Siliciclastic

Siliciclastic sediments are composed of >50% siliciclastic grains and are classified according to the grain-size textures as clay (<3.9 Ám), silt (3.9–63 Ám), and sand (>63 Ám–2.0 mm). The percentages of these grain-size textures define the principal siliciclastic names as outlined in Figure F1B. If the sediment is indurated (i.e., not easily scratched by fingernail or spatula edge), the suffix "-stone" is added (e.g., claystone, siltstone, and sandstone). In addition, the terms "conglomerate" and "breccia" are principal names for gravels with well-rounded and angular clasts, respectively. Major and minor modifiers for siliciclastic (e.g., quartz, feldspar, glauconite, mica, and lithic) and biogenic components are applied as above. For example, a sediment composed of 15% foraminifers, 25% glauconite, and 60% sand would be termed a foraminifer-bearing glauconitic sand. A sediment composed of 65% gravel and 35% silt would be termed a silty gravel. A sediment composed of 20% volcanic ash, 30% silt, and 50% sand would be termed an ash-bearing silty sand.

Sediment Description

Whole-core sections were analyzed by MST and measured for thermal conductivity (see "Physical Properties"). All APC and most XCB core sections were split from bottom to top by pulling a double-hook razor and wire assembly lengthwise through their center. This process frequently disrupted core surfaces into an irregular series of roughly parallel tears that obscured sedimentary features and core disturbance and also biased digital and photographic imaging toward darker coloration and overall lower sediment lightness (L*). Initially, tears in the archive half were not altered or were partially flattened perpendicular to the core axis with a clean stainless steel or glass-slide edge. Subsequent experimentation produced the more effective method of covering each core section with Glad Wrap clear plastic then annealing the tears with gentle stroking with a spatula toward the core bottom at a slight angle to the center axis of the core surface. This process revealed fine-scale (millimeter scale) features that were otherwise obscured (Fig. F2). More indurated XCB core sections were split from bottom to top by supersaw followed by rinsing the surface of both the archive and working halves with water. Thin intervals of limestone, siliceous limestone, and chert were split by diamond rocksaw.

Digital Imaging

All archive halves were scanned using the Geotek DIS. The DIS uses an interference filter and three line-scan charge-coupled device arrays (1024 pixels each) to continuously record the three red-green-blue (RGB) color channels at an 8-bit dynamic range. The standard DIS configuration produces 300 dpi on an 8-cm-wide core with a zoom capability of up to 1200 dpi on a 2-cm-wide core. Synchronization and track control is better than 0.02 mm, and a framestore card contains 48 MB of RAM for image acquisition. The camera aperture was set to maximize contrast within the lightest-colored sediment of each core. Each archive half, along with a neutral gray color chip and section identification bar code label, was DIS scanned to produce a TIFF (no compression) and a SID (compression) image. Using the Geotek Image Tools utilities, the SID files were resampled to produce a JPEG file with a resolution of ~300 dpi. The JPEG files are viewable using the Web browser as "photo table" composite images. Profiles for each RGB channel were produced by averaging pixels in 3 cm x 0.5 cm rectangles along the core's central axis. The DIS system was calibrated for black and white approximately every 12 hr, although no notable calibration drift occurred during Leg 208. During scanning of Site 1262 cores, we discovered that the software processing did not completely correct for images scanned at different aperture settings to a common brightness level. Therefore, subsequent Sites 1263 through 1267 were scanned at a fixed aperture setting of 11.

Diffuse Color Reflectance Spectrophotometry

Archive halves were measured at 2.5-cm intervals using a Minolta Spectrophotometer (model CM-2002) mounted on the AMST. For "critical intervals" such as the P/E and K/P boundaries, archive halves were scanned at 1-cm intervals. Prior to measurement, each core section's surface was covered with Glad Wrap clear plastic to maintain a clean spectrometer window. Spectrophotometric analysis produced three types of data: (1) intensity values for 31 contiguous 10-nm-wide bands across the 400- to 700-nm interval of the visible light spectrum; (2) L*, a*, and b* values, where L* (lightness) is a total reflectance index ranging from 0% to 100%, a* is the green (–) to red (+) chromaticity, and b* is the blue (–) to yellow (+) chromaticity; and (3) Munsell color values. Spectrophotometer calibration was performed every 24 hr with no notable change through time. Additional information about the measurement and interpretation of spectral data with the Minolta spectrophotometer is presented in Balsam et al. (1997, 1998, 1999).

We caution end users of these spectrophotometric data regarding three issues. First, data precision should not be confused with data accuracy; core disturbances, particularly biscuiting and flow-in, introduce spurious information. Furthermore, many cores from Site 1262 were not smoothed (Fig. F2), which slightly biases the digital and spectrophotometric data toward darker values. We recommend careful consideration of appropriate core photos and disturbance descriptions to cull data to workers' particular needs. Second, although AMST laser scanning identifies core gaps and elevations beyond measurement and subsequently skips these intervals during spectrophotometric scanning, uneven core surfaces that prevent complete contact between the integration window and sediment surface will bias L* toward lower values. Currently, the AMST reports only the core elevation for the integration interval and this relatively low resolution record precludes postanalysis culling of biased data. Third, surficial oxidation reactions may occur within seconds after splitting cores containing reduced sediment and these rapid reactions may be followed by additional reactions and core dessication. Therefore, documented surface colors are not necessarily identical to pristine unoxidized sediment colors or to sediment colors subsequently observed at core repositories.

Point Magnetic Susceptibility

Archive halves containing the P/E and K/P boundary intervals were measured at 1-cm resolution on the AMST with a Bartington MS2 magnetic susceptibility meter at a sensitivity setting of 0.1 instrument units.

Smear Slide Analyses

For each smear slide, a small amount of archive-half sediment was removed with a wooden toothpick, dispersed evenly in deionized water on a 2.5 cm x 7.5 cm glass slide, and dried on a hot plate at a low setting. A drop of Norland optical adhesive was then applied, overlain by a 2.2 cm x 4.0 cm cover glass, and dried in an ultraviolet light box. Smear slides were examined with a transmitted-light petrographic microscope equipped with a standard eyepiece micrometer to assess siliclastic grain-size distribution among the clay (<3.9 Ám), silt (3.9–63 Ám), and sand (>63 Ám) fractions. Standard petrographic techniques were employed to identify microfossil and mineral components. An area-percent technique was employed to estimate relative proportions of each grain size and type. We note two biases in smear slide analyses. First, sand-sized and larger grains (e.g., foraminifers, radiolarians, and siliciclastic sand) are difficult to incorporate and often heterogeneously distributed in smear slides. Second, clay-sized sediments (e.g., clay minerals, micrite, coccoliths, and biosilica) may be difficult to distinguish and quantify and are often underestimated because of multiple layers. Smear slide data tables are included in this volume and contain sample location; whether the sample represents a dominant (D), minor (M), or accessory (A) lithology; percentages of identifiable components; and siliclastic percentages of sand, silt, and clay.

Visual Core Description and Barrel Sheets

Information from macroscopic and microscopic examination of each core section was recorded by hand on a VCD form. This information was then condensed and entered into the AppleCORE (version 8.1m) program to generate simplified core "barrel sheets." Site, hole, and depth interval (in mbsf) are given at the top of the barrel sheet, with depth and core section intervals along the left margin. Copies of the original VCD sheets, which may contain additional and more detailed core descriptions, are available from ODP by request. Barrel sheet columns are discussed below.

Text Description

The lithologic description on each barrel sheet consists of (1) a heading listing the major sediment lithologies and (2) a detailed text description containing the descriptions and location of thin interbedded or minor lithologies, color, samples, coring conditions, and so on. Average and end-member Munsell color variations through each core, where given, represent qualitative summaries of high-resolution Minolta spectrophotometer data that are available through the Janus database.

Graphic Columns

The key for lithologic and contact symbols and bioturbation is presented in Figure F3. Lithologic symbols are arranged in the lithologic column in order of their relative abundance from left to right. Minor lithologic modifiers (10%–25% in smear slide) are represented by 20%, major lithologic modifiers (>25%–50% in smear slide) by 30%, and the primary lithology by the remaining 50%–100%. If two minor modifiers are present, each is represented by 10% within the lithologic column, and if two major modifiers are present, each is represented by 15%. Lithologic contacts ranged from gradational (hatched thick line) to sharp (solid thin line). Bioturbation is noted in a graphic column, with shading from white to black, reflecting a range from barren to abundant.

Drilling Disturbance

Different types of drilling disturbance were recorded graphically and textually in each barrel sheet; symbols for the type and degree of disturbance are shown in Figure F3. Drilling disturbance of relatively soft sediments (i.e., where intergrain motion was possible) was classified into four categories:

Slightly disturbed: Bedding contacts are slightly bent.
Moderately disturbed: Bedding contacts are extremely bowed.
Extremely disturbed: Bedding is completely deformed and may show diapiric or minor flow structures.
Soupy: Sediments are water saturated and show no traces of original bedding or structure.

Drilling disturbance of lithified sediments (i.e., wherein intergrain motion was not likely because of compaction, cementation, etc.) was classified into three categories:

Fractured: Core pieces are in situ or partly displaced, but the original orientation is preserved or recognizable; pieces may be supported by drill slurry or breccia.
Biscuited: Core pieces are from the cored interval and are probably in correct stratigraphic sequence (although they may not represent the entire section), but the original orientation is lost. Pieces are supported in drill mud.
Breccia: Core pieces have completely lost their original orientation and stratigraphic position.
Samples

The positions of various core samples are indicated in the sample column as SS (smear slide), IW (interstitial water), PAL (micropaleontology), XRD (X-ray diffraction analysis), and TS (thin section). The number and location of smear slides were identified by variations and changes in macroscopic lithology; where macroscopic lithology appeared uniform, generally at least two smear slides per core were analyzed.

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