per 2 s.The composition and texture of recovered sediments and sedimentary rocks were determined aboard ship by visual observation of the core and visual estimates of composition of particles in smear slides. X-ray diffraction (XRD) analyses were also used for identification of mineral assemblages. Color and digital images of sediments and sedimentary rocks were recorded by the spectrophotometer and digital camera to identify lithologic structure and quantitative color variation.
For each core we created an electronic core description sheet, which is a one-page graphic representation of the core lithology and other visual features, along with a text description (see the "Core Descriptions" contents list). The core description sheets were produced using the software package AppleCore (version 0.7.5g). Historically these have been referred as "barrel sheets," but here we use the term core description sheet. The information within these sheets is derived from smear-slide descriptions, handwritten descriptions, and hand-drawn graphics of each section, which were placed on "visual core description (VCD) sheets." These handwritten notes are archived by ODP and are available upon request.
Each core description sheet includes a core identification label, which gives the site, hole, core number, and core type information following standard ODP nomenclature (see "Introduction"). In addition, the cored interval is given in terms of the depth in mbsf. The body of the sheet includes a text description along with a graphic representation of lithology, drilling disturbance, bioturbation, structures, lithologic accessories, ichnofossils and fossils, samples, and fractures, along with a text description. The details of these are described below.
The lithology of the material recovered is represented on the core description sheet in the column titled "Graphic Lithology." Sediment type is represented graphically using the patterns illustrated in Figure F2A. The major lithologies are divided into three main components: biogenic, siliciclastic, and volcaniclastic. The relative proportions of these shown in the Graphic Lithology column are based on smear-slide observations.
As many as three patterns, representing the three major components, may be used in the graphic lithology column. Constituents accounting for <10% of the sediment in a given lithology are not shown and are generally not included in the lithologic name. The graphic lithology column shows only the composition of layers or intervals exceeding 20 cm in thickness. Interbedded lithologies are represented as discrete layers divided by contacts as shown in Figure F2B.
Observations of drilling-related disturbance are recorded in the "Disturbance" column using the symbols shown in Figure F2B. The degree of drilling disturbance in soft and firm sediments is as follows:
In addition to the degree of disturbance, the character of the disturbance is also described as follows:
The apparent intensity of bioturbation is shown in the "Bioturbation" column of the barrel sheet in the conventional manner. The intensity of bioturbation is recognized on the basis of the following criteria (Fig. F2B):
Natural structures and induced structures from the coring process can be difficult to distinguish in sediment cores. Natural structures observed are indicated in the "Structure" column of the core description form.
Sedimentary structures related to deposition and erosion, such as graded bedding, discrete trace fossils, soft-sediment deformation features, and diagenetic features, are illustrated in the structure column using the symbols shown in Figure F2B. Contacts (sharp, scoured, undulating, etc.) between lithologic beds, however, are illustrated in the graphic lithology column. Detailed features of these boundaries can be observed in the color image or photograph taken of each core. When scattered particles are sufficiently dense to form a discrete region but the boundaries are diffuse or unclear, the term "accumulation" is used. "Patch" means a circular or discrete region that has a different color or composition from the major lithology. Patches are commonly composed of clay, silt, or ash, and usually result from bioturbation.
The observed deformational structures interpreted to be of primary origin are graphically and descriptively represented on the VCD and core description sheets, using the symbols shown in Figure F2B. We describe the following visible characteristics: (1) the shape of the fracture (sharpness, straightness, and anastomosing or branching pattern); (2) apparent dip angle (measured with a conventional contact goniometer on the split surface of the archive-half core); (3) fracture infill thickness; (4) slickenside orientation; and (5) crosscutting relationships. The sense of relative displacement and amount of offset is noted where determinable.
A clear distinction was made between healed and open fractures because the moderate- to steep-dipping open fractures are interpreted to be drilling-induced ruptures of pre-existing healed fracture planes. These fractures are represented by the symbol for artificial fractures (this does not include the usual drilling fractures). The healed fractures are further divided into joints (without relative displacement of hanging to footwall blocks) and faults (with a finite value of displacement between hanging and footwall blocks). If the relative sense of movement could be determined, the symbols for normal and reverse faults are used. Evidence of displacement without apparent sense is termed a fault. Conjugate faults are also noted.
The occurrence of ichnofossil genera and major groups of macro- and microfossils are assigned to the "Ichnofossils and Fossils" column. Symbols shown in this column are described in Figure F2C.
The positions of a variety of features are shown in the "Accessories" column. Symbols shown in this column are described in Figure F2D.
The positions of samples taken from each core for analysis are indicated by letters in the "Sample" column of the core description form as follows: SS (smear slide), WHC (whole-round core sample), PAL (micropaleontology), and IW (interstitial water). Other samples collected for analysis during and after the cruise are listed in the Janus database.
The text describing the lithology, found in the "Description" column of the core description sheet, 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 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.
Tables summarizing data from smear-slide analyses are provided (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 in the core, and the estimates of sand, silt, and clay proportions, together with all identified components.
Quantitative expression of sediment color was collected using the Minolta CM-2002 spectrophotometer on the archive multisensor track (AMST) for Site 1150 and using the scanner in handheld mode for Site 1151. The Minolta CM-2002 measures diffuse reflected visible light intensity in 31 bands ranging from 400 to 700 nm, with 10-nm resolution, and calculates and outputs data sets of L*a*b* value with XYZ and reflected intensity from 400 to 700 nm. Routine measurements were made every 2 cm for Site 1150 cores and every 5 cm for Site 1151. These measurements were determined on the archive split-core surface by covering each section with plastic wrap. The spectrophotometer was calibrated for white color reflectance and "zero calibrated" once or twice a day, typically at the beginning of each work shift.
The data collected for Site 1150 using the AMST has enhanced reflectance values, which result from an erroneous correction made by the AMST software. The software attempts to correct for the loss of reflectance that can happen when the scanner is not in direct contact with the core surface. In most cases, the true height offset is zero or very near zero; therefore, no correction should occur. The software, however, incorrectly estimates the height offset. It appears that a constant height-offset value has been hardwired into the software. The data appear to be useful, however, for determining where subtle color changes occur downcore, but some caution is warranted. The data for Site 1151 are unaffected by the height-offset correction because all values were collected using the scanner in handheld mode with the scanner in contact with the core.
Digital color images of recovered core were taken for most cores from Site 1150 using a Kodak DSC460 digital camera with xenon flash lightings attached to the AMST. Each image covers a 10-cm interval. All images from a section are automatically combined into a single image and saved as a TIF image. Each image has a spacial resolution of 127 pixels/cm. Unfortunately, the two power supplies available for this unit failed and no digital images were taken of Site 1151 cores.
Selected core samples were
analyzed with an X-ray diffractometer (Philips PW 1729) to identify mineral
assemblages and to estimate opal content and the composition of the terrigenous
sedimentary fraction, semiquantitatively. Before analysis, bulk-sediment samples
were freeze-dried and then ground. Step-scan measurements were run on random
powder mounts with Cu radiation (40 kV and 35 mA) from 2° to 70° at steps of
0.02°
per 2 s.
Graphic evaluation of the diffractograms was facilitated with the interactive MacDiff software (R. Petschick, public domain). Data were used for mineral identification on the basis of peak positions and relative intensities, as well as semiquantitative estimation of mineral abundances on the basis of both peak intensities and integrated peak areas.
Relative abundances of the minerals in the lithogenic fraction are presented only as relative changes in the peak height or peak areas of minerals. Diagnostic peaks of minerals found in the recovered sediments are listed in Table T1. Opal-A contents were estimated from the maximum peak height at 21.78° after subtracting the average height of background intensities extending between 16° and 39° in the X-ray diffractograms. In X-ray diffractograms of random powder mounts, most clay minerals yield a broad diffraction peak at ~4.5 Å. 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. The integral peak areas centered at 14, 10, and 7 Å are only used for the estimation of relative clay mineral variations with depth. XRD data are compiled in a separate table in each site chapter. The halite peak at 2.82 Å results from crystallization of halite from interstitial water during drying of samples, and it is compiled for comparison with the salinity of interstitial water.
The major lithology of Leg 186 was predominantly mixed sediments, consisting of various admixtures of pelagic siliceous tests (mainly diatoms), silty clay and clay-sized siliciclastic grains, and volcaniclastic glass (ash). Pelagic calcareous grains were very rare. To increase clarification of the dominant component in the sediment, we modified Mazzullo et al. (1988) terminology (the standard ODP sediment classification scheme) to expand the designation of mixed sediments that includes biogenic and siliciclastic components in the range between 40% and 60%.
We used the relative proportions of biogenic, siliciclastic, and volcaniclastic components to define the three major sediment classes (Fig. F3). Biogenic (pelagic) sediment is composed of >50% biogenic grains, siliciclastic sediments are composed of >50% siliciclastic grains, and volcaniclastic sediments are composed of >50% volcaniclastic grains. The definitions of biogenic, siliciclastic, and volcaniclastic particles are as follows:
Sediments and rocks were named on the basis of composition and texture using a principal name together with major and minor modifiers. Principal names define the degree of consolidation (induration) and granular sediment class as described above (Fig. F3).
Induration of recovered sediments was defined using the modified terminology for calcareous sediments of Gealy et al. (1971). Three classes of induration were used to describe siliceous sediments and rocks during Leg 186. These classes are used as prefixes to sediment names.
The principal name refers to the component that comprises more than 50% of the lithology (Table T2). If no single component comprises more than 50%, the dominant component is given as the principal name. The principal name of biogenic, siliciclastic, or volcaniclastic sediments is preceded by major modifiers and by minor modifiers, which have the suffix "-bearing." Both major and minor modifiers refer to mixed biogenic, siliciclastic, or volcaniclastic components. The principal name (a) and modifiers (b and c) are used as follows, where the name of the sediment is given by c-bearing + b + a:
For siliciclastic sediments, the principal name describes the texture and is assigned according to the following guidelines:
The texture column in the smear-slide data tables (see the "Core Descriptions" contents list) shows the composition of texture, including all biogenic, siliciclastic, and volcaniclastic grains. The texture of siliciclastic sediment is given by relative proportion of texture only in siliciclastic grains.
For a better understanding of the lithologic terminology, we give the following examples:
