Core description forms provide a summary of data obtained during shipboard analysis of the sediments. Detailed observation of each core section of sediments was recorded initially by hand on standard ODP visual core description (VCD) forms. The sediment VCD was then transcribed using AppleCORE software. Separate VCDs were custom designed in Adobe Illustrator for the basalts (hard rock VCD [HR-VCD]). The basalt cores were described on hard copy HR-VCDs. These were then entered into the computer using Adobe Illustrator. The computerized versions of the VCDs are renamed electronic VCDs (eVCDs) or electronic HR-VCDs (eHR-VCDs).
The overall procedures used here are similar to those developed by the scientific parties during previous ODP legs. The emphasis of our onboard studies was to produce an integrated picture of the various units recorded from the hole. Note that depths recorded for recovered cores may differ from true depths owing to curation protocol, in which the top of a core is placed at the top of the cored interval. When recovery is <100%, the depths attached to the recovered cores will be shallower or equal to the true depths because all that is actually known is that the core came from within the cored interval.
Recovery of sediment during Leg 203 was modest, so our classification only considers pelagic sediment and limestone. Sedimentary terms and concepts in this chapter and in the site chapter are those in common usage (e.g., Boggs, 1995), except as otherwise referenced. Because Site 1243 is closely adjacent to Site 852, which was drilled during Leg 138, we have used the sediment classification scheme used by the Leg 138 Shipboard Scientific Party (Mayer, Pisias, Janecek, et al., 1992) that is in common use for biogenic pelagic sediments that fell into the borehole. Lithologic names of the ODP sediment classification scheme (Mazzullo et al., 1988) are more appropriate for detrital and hemipelagic sediments. For Legs 138 and 203, sediment names consist of a principal name selected from the appropriate corner of the foraminifer-nannofossil-diatom-radiolarian tetrahedron (e.g., foraminifer ooze) and a modifier that precedes the principal name of components >10%, given in order of increasing abundance (e.g., diatom nannofossil foraminifer ooze). None of the sediments from Site 1243 had nonbiogenic components >10%, which might have resulted in a modified name for the ooze. Composition was estimated from smear slides.
The recovered limestone was classified according to its composition and texture (Folk, 1962) and its texture when deposited (Dunham, 1962). Composition and texture were estimated from thin section. Specifically, with 10%-50% of the rock composed of allochemical grains (formed of calcite and moved, not formed in place), the adjective "sparse" is used. The name also includes any significant biogenic grains, which, in this case, are foraminifer microfossils. Abbreviations of the allochemical grains enter the rock name, in this case subequal amounts of peloidal and biogenic allochems. As more than two-thirds of the intergranular material is lime-mud matrix rather than sparry calcite cement, the rock name includes the term microcrystalline calcite (micrite). Thus, according to Folk (1962), the limestone is a sparse foraminiferal pelbiomicrite. At the time of deposition, its texture was that of grains of coarse silt and larger sizes (>0.03 mm), comprising >10% of the rock and supported by a muddy matrix. Thus, according to Dunham (1962), the limestone is a wackestone.
The electronic descriptions for sediments were created using AppleCORE (v. 8.1m) software, which generates a simplified annotated graphic for each core (Fig. F2). Columns on the AppleCORE sheets include depth, core section, graphic lithology, bioturbation, sedimentary structures and other lithologic and fossil features, core disturbance, sample type, and description of the core. Features related to the cores are either plotted on the graphic lithology near the interval where they are present or included in the "Description" column. The columns on the barrel sheets appropriate to Leg 203 include graphic lithology, where sediment lithologies are represented by patterns, core disturbance, shipboard samples, and description, as discussed below.
Deformation and disturbance of sediment that resulted from the coring process are illustrated in the "Disturbance" column. Intensity of disturbance is not denoted by a symbol but is described in the "Description" column. The pelagic oozes recovered at Site 1243 were highly disturbed from having sloughed into the borehole, followed by the coring and recovery process. Bedding cannot be seen, and original stratigraphic position cannot be determined.
Sample material taken for shipboard sedimentological and chemical analyses consists of smear slide, thin section, X-ray diffraction (XRD), carbon-carbonate, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) samples. The sample type and the location in the section are noted in the "Sample" column.
The written description for each core, located in the "Description" column on the AppleCORE sheets, contains a brief overview of both major and minor lithologies present, color gradation, grain-size gradation, location of samples in the section, and intensity of core disturbance.
Sediment and hard rock color was determined visually by comparison with standard Munsell color charts (Munsell Color Co., 1994; Rock-Color Chart Committee, 1991) and is reported in general terms in the "Description" column and in more detail on the original VCD sheets.
Grain size and composition of sediments were determined using smear slides. These were prepared according to the procedures described in the handbook for shipboard sedimentologists (Mazullo et al., 1988). Identification in terms of general components was undertaken in accordance with Rothwell (1989). For semiquantitative visual estimation of sediment textures and determination of major components, we used the Comparison Chart for Visual Percentage Estimation determined by Terry and Chilingar (1955), with the percentages corrected to compensate for the degree of dispersion of the grains in the smear slide. Quantitative estimates of grain size and of the main components are made to the nearest 5% on the smear slide worksheet and carried forward to the smear slide tables (see the "Core Descriptions" contents list). Care was taken to correct for the area taken on the smear slide by the mounting medium.
We examined thin sections from the cored intervals to complement and refine the hand specimen observations. Tables summarizing data from thin sections and smear slides are included this volume (see the "Core Descriptions" contents list). These tables include information about the locations of samples in the core and an estimate of the abundance, grain sizes, and other textural properties of the allochemical grains, micrite matrix, orthochemical crystals, and pores. No sedimentary structures were seen, except for some small burrows.
In order to describe important mineralogic and structural features in both the archive and working halves, we examined core sections containing igneous rocks prior to cutting with a diamond-impregnated saw.
After the core was split, lithologic descriptions were made of the archive half, and the working half was sampled for shipboard physical properties measurements (see "Physical Properties"), magnetic studies (see "Paleomagnetism"), thin sections, and ICP-AES analyses. The archive half was described on the eHR-VCD form and photographed.
We used eHR-VCD forms (Fig. F3) to document each section of the igneous rock cores. The eHR-VCD columns, from the left, are "Piece Number," "Graphic Representation," "Orientation," "Shipboard Studies," "Lithologic Unit," "Phenocrysts (%)," "Grain Size," "Vesicularity," and "Degree of Alteration and Veins." The Graphic Representation column on the form represents the archive half. A horizontal line across the entire width of the column denotes a plastic spacer. Oriented pieces are indicated on the form by an upward-pointing arrow to the right of the piece. The key to the symbols, colors, and other notations used on the eHR-VCDs are reported in Figure F4. As on the AppleCORE sediment descriptions, locations of samples selected for shipboard studies are indicated in the column headed Shipboard Studies with the following notation: XRD analysis, ICP-AES, petrographic thin section, physical properties measurements, and paleomagnetic measurements.
We subdivided the core into consecutively numbered lithologic units (denoted in the "Lithologic Unit" column on the eHR-VCD) on the basis of changes in color, structure, brecciation, grain size, vesicle abundance, mineral presence and abundance, and the presence of sedimentary interbeds.
The "Phenocryst" (in percent) column is used to represent a visual estimation of abundance and variation of phenocrysts throughout the core section using the following notations:
The "Grain Size" column shows, schematically, the nature of the groundmass and the presence of glass. The following notations were used:
The "Vesicularity" column describes the vesicle content and uses the following notations:
The "Degree of Alteration" and "Veins" column estimates the degree of alteration and denotes the presence of veins with the letter "V." The alteration was described using the following notations:
Written core descriptions accompany the schematic representation of the core sections. These include "Leg, Site, and Hole" and "Unit Number and Rock Name," in addition to the columns "Pieces," "Contacts," "Phenocrysts," "Groundmass," "Vesicles," "Color," "Structure," "Alteration," Veins/Fractures," and "Additional Comments."
The leg, site, hole, core type, and section number (e.g., 203-1243R-3R-2), as well as the top of the core section measured in mbsf, are located at the top.
The unit number (consecutive downhole) and the rock name are located next to the unit. We assigned provisional rock names on the basis of hand specimen observation (hand lens and binocular microscope) and later checked these assignments by examining thin section and ICP-AES analyses. Porphyritic rocks were named by phenocryst type; the term "phenocryst" was used for a crystal that was significantly, typically five times, larger than the average size of the groundmass crystals and generally euhedral to subhedral in shape. This nomenclature is sensitive to changes in the groundmass grain size; for example, a single cooling unit could have a moderately phyric aphanitic margin and an aphyric fine-grained interior without any change in the distribution or size of the early formed crystals. In order to avoid the problem of describing pillow margins as phyric and cogenetic pillow interiors as aphyric, we based our terminology on the aphanitic margins of cooling units. Thus, if aphanitic pillow margins were sparsely olivine phyric basalt, we described the fine-grained interiors using the same name, even though the euhedral olivine phenocrysts in the pillow interiors were similar in size to groundmass plagioclase laths. Phenocryst phases, in order of decreasing abundance, were included in the rock name. Thus, a "highly olivine plagioclase phyric basalt" contains >10% (by volume) phenocrysts, the dominant phenocryst being olivine, with lesser amounts of plagioclase. As long as the total content >1%, the minerals named include all of the phenocryst phases that are present in the rock.
The "Contacts" column includes contact relations and unit boundaries. After we made lithologic descriptions, we attempted to integrate the observations in order to define unit boundaries. The boundaries commonly reflect physical changes in the core (e.g., pillowed vs. massive) that were also observed in the physical properties and downhole measurements. Intervals of sediment and/or breccia, changes in vesicularity, glass, chilled margins, alteration, volume fraction, and type of matrix also define lithologic contacts. Where possible, whole-rock chemical analyses by ICP-AES were used to investigate chemical differences between units.
The "Phenocryst" column describes the types of minerals visible with a hand lens or a binocular microscope and their distribution within the unit and for each phase its abundance (in volume percent), size range (in millimeters), shape, and degree of alteration, with further comments if appropriate.
The "Groundmass" column includes texture and grain size: glassy, aphanitic (<1 mm), fine grained (1-2 mm), medium grained (>2-5 mm), or coarse grained (>5 mm). Changes in grain size and proportions of crystals and glass within units were also noted.
The "Vesicles" column records vesicle abundance (visual estimates of the volume fraction of vesicles were supplemented by observations using a binocular microscope), size, shape (sphericity and angularity), whether the vesicles are empty or filled, and the nature of the filling.
The "Color" column includes a color name and code (for the dry rock surface) according to the standard rock color charts (Munsell Color Co., 1994).
The "Structure" column describes fractures that are lined with various alteration minerals, which may have adjacent zones of altered rock or alteration halos. In addition, this entry refers to whether the unit is massive, pillowed, or brecciated. Pillowed sequences were inferred using the presence of glassy margins, groundmass grain-size variations, and vesicle-rich bands. A section was described as massive if there was no evidence for pillows, even though it may be part of a pillowed sequence.
The "Alteration" column describes the degree of alteration as unaltered (<2% by volume of alteration products), slight (2%-10%), moderate (>10%-40%), high (>40%-80%), very high (>80%-95%), or complete (>95%-100%). Changes in alteration through a section or a unit were noted, in addition to the type of alteration material.
The "Veins/Fractures" column describes the abundance, width, and mineral linings and fillings of the veins and fractures.
The "Additional Comments" column describes any general descriptions of the unit that were not included under another column.
We examined thin sections in order to confirm the VCDs and to define the textures and relationships among the various constituents of the units. Thin section descriptions also helped to define the secondary alteration mineralogy. In general, the same terminology was used for thin section descriptions, as for the VCDs. The percentages of individual phenocryst, groundmass, and alteration phases were estimated visually, and textural descriptions are reported in "Site 1243 Thin Sections." Mineral identifications were made using standard optical mineralogical techniques. The textural terms used are defined by MacKenzie et al. (1982). Thin section descriptions also include thumbnail copies of photomicrographs.
Alteration and vein core description logs were tabulated to provide a consistent characterization of the rocks and to quantify the different alteration types. Descriptions are based mostly on hand specimen observations of wet cut surfaces; specific clay, zeolite, and carbonate minerals are not generally distinguished except where crystal morphology allows unequivocal identification. We recorded the following information in the alteration and vein logs:
We performed chemical analyses of basalt during Leg 203 using ICP-AES. Selected representative samples of each unit were first cut with a diamond-impregnated saw blade and ground on a diamond wheel to remove surface contamination. Samples were washed in an ultrasonic bath containing methanol for ~10 min, followed by three consecutive ~10-min washes in an ultrasonic bath containing nanopure deionized water, and then dried for ~12 hr in an oven at 110°C. The cleaned whole-rock samples (~20 cm3) were reduced to fragments <1 cm in diameter by crushing them between two disks of Delrin plastic in a hydraulic press followed by grinding them for ~5 min in a Spex 8510 shatterbox with a tungsten carbide barrel. The sample powders were weighed on a Scientech balance and ignited to determine weight loss on ignition.
We weighed 100 and mixed them with 400 2) flux that had been preweighed on shore. Standard rock powders and full procedural blanks were included with the unknowns for each sample run. All samples and standards were weighed on the Cahn Electrobalance. Weighing errors are conservatively estimated to be
Mixtures of flux and rock powders were fused in Pt-Au crucibles at 1050°C for 10-12 min in a Bead Sampler NT-2100. Ten microliters of 0.172-mM aqueous lithium bromide (LiBr) solution was added to the mixture before fusion as an antiwetting agent to prevent the cooled bead from sticking to the crucible. Cooled beads were transferred to 125-mL polypropylene bottles and dissolved in 50 mL of 2.3-M HNO3 by shaking with a Burrell Wrist Action bottle shaker for 1 hr. After digestion of the glass bead, all of the solution was filtered to 0.45 clean 60-mL widemouthed polypropylene bottle. Next, 2.5 mL of this solution was transferred to a plastic vial and diluted with 17.5-mL of 2.3 M of nitric acid (HNO3) to bring the total volume to 20 mL. The solution-to-sample dilution factor for this procedure is ~4000. Dilutions were conducted using a Brinkman Dispensette (0.25 mL).
Major (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P) and trace (Zr, Y, Sr, Ba, Ni, Cr, Sc, V, Nb, Co, Cu, and Zn) element concentrations of powder samples were determined with the JY2000 Ultrace ICP-AES. The JY2000 sequentially measures characteristic emission intensities (with wavelengths between ~100 and 800 nm). Murray et al. (2000) developed protocols for dissolution and ICP-AES analysis of rock powders. The hard rock analytical procedure was refined during Leg 197 (Shipboard Scientific Party, 2002). The elements analyzed, emission lines used, and the specific analytical conditions for each sample run during Leg 203 are provided in Table T1.
The JY2000 plasma was ignited 30 min before each run to allow the instrument to warm up and stabilize. After the warm-up period, a zero-order search was performed to check the mechanical zero of the diffraction grating. After the zero-order search, the mechanical step positions of emission lines were tuned by automatically searching with a 0.002-nm window across each emission peak using BCR-2 standard prepared in 2.3-M HNO3. The only exception is P, which was automatically searched by using a single-element standard. During the initial setup, an emission profile was collected for each peak, using BCR-2, to determine peak-to-background intensities and to set the locations of background points for each element. The JY2000 software uses these background locations to calculate the net intensity for each emission line. The photomultiplier voltage was optimized by automatically adjusting the gain for each element using the U.S. Geological Survey standard, BHVO-2 or BIR-1, with the highest concentration for that element. Before each run, a profile of BCR-2 was collected to assess the performance of the machine from day to day.
All ICP-AES data presented in the site chapter report were acquired using the Gaussian analytical mode of the Windows 5 JY2000 software. This mode fits a Gaussian curve to a variable number of points across a peak and then integrates to determine the area under the curve. Each unknown sample was run at least twice, nonsequentially, in all sample runs.
A typical ICP-AES run included the following:
Following each sample run, the raw intensities were transferred to a data file and data reduction was completed using a spreadsheet to ensure proper control over standardization and drift correction. Once transferred, intensities for all samples were corrected for the full procedural blank. A drift correction was then applied to each element by linear interpolation between drift-monitoring solutions run before and after a particular batch of samples. The interpolation was calculated using the lever rule. Following blank subtraction and drift correction, concentrations for each sample were calculated from the average intensity per unit concentration for the standards BHVO-2, BIR-1, and JB-1, which were analyzed twice during the run.
Estimates of accuracy and precision for major and trace element analyses were based on replicate analyses of BHVO-2, BIR-1, and JB-1, the results of which are presented in Table T2. In general, run-to-run relative precision by ICP-AES was better than 2% for the major elements. Run-to-run relative precision for trace elements was within 5%. Exceptions typically occurred when the element in question was near the detection limit of the instrument (see Table T1 for instrument detection limits).