This section outlines the procedures followed to document the basic lithostratigraphy of the deposits recovered during Leg 201, including core description, XRD, color spectrophotometry, digital color imaging, and smear slide description. Only general procedures are outlined, except where they depart significantly from ODP conventions.
All seven sites drilled during Leg 201 were located very close to sites drilled during previous cruises. The biostratigraphic and magnetostratigraphic age framework presented in the site chapters follows those of the previous legs. The ages of biostratigraphic and magnetostratigraphic events are those of Berggren et al. (1995a, 1995b).
Information from macroscopic description of each core was recorded manually for each core section on visual core description (VCD) forms. A wide variety of features that characterize the sediment were recorded, including lithology, sedimentary structures, color, and sediment deformation. Compositional data were obtained from smear slides. The color (hue and chroma) of the sediments was determined by color spectrophotometry (see "Color Reflectance Spectrophotometry). This information was condensed and entered into AppleCORE (version 8.1b) software, which generates a simplified one-page graphical description of each core (barrel sheet) (Fig. F2). Barrel sheets are presented with split-core photographs (see the "Core Descriptions" contents list). The lithologies of the recovered sediments are represented on barrel sheets by symbols in the column titled "Graphic Lithology" (Fig. F3). Primary sedimentary structures, bioturbation parameters, soft-sediment deformation, structural features, and drilling disturbance are indicated in columns to the right of the graphic log. The symbols are schematic but are placed as close as possible to their proper stratigraphic position. For exact positions of sedimentary features, more detailed VCDs can be obtained from ODP. Deformation and disturbance of sediment resulting from the coring process are illustrated in the "Drilling Disturbance" column. Blank regions indicate the absence of coring disturbance. Locations of samples taken for shipboard analysis are indicated in the "Samples" column. A summary lithologic description with sedimentologic highlights is given in the "Description" column of the barrel sheet. This description provides information about the major sediment lithologies, important minor lithologies, and an extended summary description of the sediments, including color, composition, sedimentary structures, trace fossils identified and extent of bioturbation, and other notable characteristics. Descriptions and locations of thin, interbedded, or minor lithologies that could not be depicted in the "Graphic Lithology" column are also presented in "Description," where space permits.
The sediment classification scheme used during Leg 201 is descriptive and follows the ODP classification scheme (Mazullo et al., 1988), with some simplifying modifications for sediments that are mixtures of siliciclastic and biogenic components (Fig. F4). Classification is based primarily on macroscopic description of the cores and examination of smear slides. During Leg 201, the total calcium carbonate content of the sediments (see "Biogeochemistry") and XRD determined on board were also used to aid in classification.
Composition and texture are the criteria used to define lithology. Textural names for the siliciclastic sediment components are derived from the Udden-Wentworth (Wentworth, 1922) grain size scale (Fig. F5). The term clay is used only for particle size and is applied to both clay minerals and other siliciclastic material <4 µm in size. Genetic terms such as pelagic, neritic, hemipelagic, and debris flow do not appear in this classification.
The principal name applied to a sediment is determined by the component or group of components (e.g., total biogenic carbonate) that comprise(s) >60% of the sediment or rock, except for subequal mixtures of biogenic and siliciclastic material. The main principal names are as follows.
If the total siliciclastic content is >60%, the main name is determined by the relative proportions of sand, silt, and clay sizes when plotted on a modified Shepard (1954) classification diagram (Fig. F4A). Examples of siliciclastic principal names are clay, silt, sand, silty clay, sandy clay, clayey silt, sandy silt, clayey sand, and silty sand.
If the total biogenic content is >60% (i.e., siliciclastic material <40%), then the principal name applied is ooze (Fig. F4B). Biogenic components are not described in textural terms. Thus, a sediment with 65% sand-sized foraminifers and 35% siliciclastic clay is called clay-rich foraminifer ooze, not clay-rich foraminifer sand.
In mixtures of biogenic and nonbiogenic material where the biogenic content is 40%-60% (termed "mixed sediments" in the ODP classification), the name consists of two parts: (1) a major modifier(s) consisting of the name(s) of the major fossil group(s), with the least common fossil listed first, followed by (2) the principal name appropriate for the siliciclastic components (e.g., foraminifer clay) (Fig. F4B).
If any component (biogenic or siliciclastic) represents between 10% and 40% of a sediment, it qualifies for minor modifier status and is hyphenated with the suffix -rich (e.g., nannofossil-rich clay). When a component makes up only 5%-10% of the sediment, it can be indicated with a minor modifier that consists of the component name hyphenated with the word "bearing" (e.g. nannofossil-bearing clay). Where two minor components are present, the most abundant accessory component appears closest to the principal name. Major and minor modifiers are listed in order of increasing abundance before the principal name.
The following classes of induration or lithification were adopted and modified from ODP Leg 188 (Shipboard Scientific Party, 2001). They were separated into three classes for biogenic sediments and two classes for nonbiogenic sediments. For biogenic sediments and sedimentary rocks, the three classes of induration are
For nonbiogenic clastic sediments, the two classes of induration are
The definitions and nomenclatures of special rock types were adopted and modified from ODP Legs 112 and 138 (Shipboard Scientific Party, 1988, 1992) and adhere as closely as possible to conventional terminology. Three special rock types were especially important during Leg 201: authigenic carbonates, phosphates, and metalliferous sediments.
Authigenic minerals are indicated in the "Diagenesis" column of the core description forms (barrel sheets). Carbonates (calcite and dolomite) are present as beds and nodules. In cases where it was possible to clearly identify the carbonate mineralogy, symbols for the respective carbonate minerals were used. The degree of lithification is noted in the core description as friable where the rock showed only partly lithification or lithified where fully cemented. Phosphate-rich sediments were also present, designated by a "Ph" in the "Lithologic Accessories" column (distinct from "P," which is commonly used during ODP legs to designate pyrite). In accordance with the terminology used during Leg 112, two different types of phosphatic materials are distinguished. F-phosphate is the designation given to friable, generally light-colored lenses and layers of fine-grained carbonate fluorapatite (francolite). The term D-phosphate is used for those phosphatic peloids, nodules, gravels, and phosphatic hardgrounds composed mainly of dense, hard, dark-colored francolite. The term "phosphorite" is restricted to layers composed mainly of phosphatic grains.
Metalliferous sediments are composed of fine-grained granular sulfides, oxides, and hydroxy oxides rich in iron and other transition elements. They may be present near or within basement rocks in the sedimentary section or as dispersed grains as a minor component of other sediments. In the former instance, the metal-rich sediments may include both primary precipitates and altered crystalline phases. They may also include X-ray amorphous semiopaque oxides. Metalliferous sediments are generally distinguished from other fine-grained nonbiogenic sediments on the basis of their chemistry (e.g., Fe [10 wt% on a carbonate-free basis]; [(Fe + Mn)/Ti] [25]). In the absence of such information at the time the cores were described, we distinguished this sediment lithology on the basis of color, opaque mineral content of smear slides, and/or presence at the base of the sediment column.
Other metal-rich oxides, such as dispersed or nodular manganese oxides, are also present in equatorial Pacific sediments. They may be present near the sediment surface or may lie buried within the sediment. They are distinguished by color, mineralogy, and, in the case of nodules, by their physical appearance.
Petrographic analysis of the sand- and silt-sized components of the sediment was primarily conducted by smear slide description. The slides were fixed by ultraviolet (UV) curing using Norland optical adhesive immersion medium. Alternatively, some of the slides were prepared with heat cure medium. Tables summarizing data from smear slides are available (see "Smear Slides" for each site in 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 estimated percentage ranges of sand, silt, and clay, together with all identified components. We emphasize here that smear slide analysis provides only crude estimates of the relative abundances of detrital constituents. The mineral identification of finer-grained particles can be difficult using only a petrographic microscope, and sand-sized grains tend to be underestimated because they cannot be evenly incorporated into the smear. The presence of authigenic minerals such as manganese oxides, pyrite, or carbonates was especially noted. The mineralogy of smear slide components was validated by XRD. The relative proportions of carbonate and noncarbonate materials estimated from smear slides were validated by chemical analysis of the sediments (see "Biogeochemistry").
XRD was used to support and verify the observations of the smear slide analysis to identify small-scale compositional changes, potential authigenic minerals, and to detect main silica phases. Each sample was freeze-dried, ground, and mounted with a random orientation into an aluminum sample holder. For the measurements, a Philips PW-1729 X-ray diffractometer with a CuK
source (40 kV and 35 mA) and Ni filter was used. Peak intensities were converted to values appropriate for a fixed slit width. The goniometer scan was performed from 2° to 40°2
at a scan rate of 1.2°/min (step = 0.01° and count time = 0.5 s). Diffractograms were peak-corrected to match the (100) quartz peak at 4.26 Å. Common minerals were identified based on their peak position and relative intensities in the diffractogram using an interactive software package (MacDiff version 4.1.1).
In addition to visual estimates of the color, reflectance of visible light from soft sediment cores was routinely measured using a Minolta spectrophotometer (model CM-2002) mounted on the AMST. The AMST measures the archive half of each core section and provides a high-resolution stratigraphic record of color variations for visible wavelengths (400-700 nm). Freshly split cores were covered with clear plastic wrap and placed on the AMST. Measurements were taken at 2.0-cm spacing. The AMST skips empty intervals and intervals where the core surface is well below the level of the core liner but does not recognize relatively small cracks or disturbed areas of core. Thus, AMST data may contain spurious measurements that should, to the extent possible, be edited out of the data set before use. Each measurement recorded consists of 31 separate determinations of reflectance in 10-nm-wide spectral bands from 400 to 700 nm. Additional detailed information about measurement and interpretation of spectral data with the Minolta spectrophotometer can be found in Balsam et al. (1997, 1998) and Balsam and Damuth (2000).
Systematic high-resolution line-scan digital images of the archive-half core were obtained using the GEOTEK X-Y digital imaging system (DIS). The DIS system was calibrated for black-and-white imaging approximately every 12 hr.
After cores were visually described, they were placed in the DIS and scanned. A spacer holding a neutral gray color chip and a label identifying the section was placed at the base of each section and scanned along with each core. Output from the DIS includes a Windows bitmap (.bmp) file and a Mr.Sid (.sid) file for each section scanned. The bitmap file contains the original data with no compressional algorithms applied, whereas the Mr.Sid files apply extensive compressional algorithms.
Additional postprocessing of data was done to achieve a medium-resolution JPEG image of each section and a composite JPEG image (stored as a Microsoft PowerPoint slide) of each core, which is comparable to the traditional photographic image of each core. The JPEG image of each section was produced by an Adobe Photoshop batch job that opened the bitmap file, resampled to a width of 0.6 in at a resolution of 300 pixels/in, and saved the result as a maximum-resolution JPEG.
