DISCUSSION OF SAMPLING STRATEGY

Communal and Composite Geochemical Samples
Too often ODP cores are sampled by individual investigators who perform a unique set of analyses. This process produces a dispersed data set, and it is often difficult to relate the different studies. Our overall objective is to have the investigators work on a common set of samples. This is a novel approach and requires good organization, communication, and cooperation at all stages. The benefits, however, are substantial, and the geochemical database archived for Leg 185 will be a unique contribution to the GERM initiative.
In addition to personal samples taken for specific studies in the cores, such as vein-rock interaction, microbiology, in situ laser, and ion probe analyses, a representative suite of rocks was sampled for use by the scientific party for geochemical analysis. These samples were taken to represent the major lithologies in the cores: massive flows, pillowed or sheet flows, interflow material, breccia, and also the different alteration types: veins, halos, and pervasively altered basalt. A representative group of samples were taken for each of the different lithologic divisions. In all, the sample set comprises 118 samples.
Each sample was described, crushed, and powdered. Each sample was subdivided for a thin section, a slab for crushing and powdering, and an archive piece. For most samples an aliquot of clean chips was also archived. A summary description of each sample, the sampling interval, and the weight of powder and rock chips were recorded. The communal samples will serve as the base sample set for all geochemical work. The geochemical results, in combination with the geophysical logs, core descriptions, and physical properties data, will be used to construct a numerical average for all elements for the composition of Hole 801C basement. A subset of these samples will be used to construct a physical mixture of different lithologies, "a composite" sample, which will be prepared following standard procedures. The composite samples will also be analyzed by various geochemical procedures to determine the bulk geochemistry of Hole 801C basalts. The composite samples will also be large enough in volume to accommodate future analytical efforts, and therefore, represent the legacy of the site.
Initial shore-based analyses of the communal samples will focus on inductively coupled plasma-mass spectrometry analysis for major elements and selected trace elements (Sr, Ba, and some trace metals), and CO2 and H2O determinations. In addition, a selection of 20 samples will be taken for representative key lithologies and will be distributed for general analysis. Using the geochemical data, additional subsets will be selected for more detailed geochemical and isotopic analysis. Although subject to interpretation of the shore-based geochemical data and detailed analysis of logs, a composite sample will be prepared that is representative of each of the major divisions. The analyses proposed for the communal samples and the composites are given in Table 3. The data will be updated on a regular basis on the Leg 185 World Wide Web site and distribution and curation of the samples will be controlled by the Leg 185 co-chief scientists.

Glass Samples
Fresh glass is important for determining the chemical composition of magmas because it is unaffected by mineral accumulation and posteruption alteration. Glass is also usually chemically homogenous so that chemical analyses made with microbeam techniques are applicable to the bulk sample. Fresh glass from flow and pillow margins and from hyaloclastites were identified under the binocular microscope during the routine description of the cores. The locations of most of the pieces that contain glass are given in Table 4. A subset of ~50 glasses was sampled on board ship for a coordinated effort to obtain a wide variety of analyses on the same samples (Table 4). Glass chips and thin sections will be analyzed first by electron microprobe for 10 major elements (Si, Al, Fe, Mg, Ca, Na, K, P, Ti, and Mn). This will determine how many different compositions are present in the cores. Based on the major element analyses, selected thin sections and chips will be distributed among the other investigators who wish to conduct laser and ion beam microanalyses and water measurements by Fourier transform infrared spectroscopy. Also, based on the major elements, samples will be distributed for mass spectroscopy for heavy isotopes, halogens, Li, and B. Some samples were distributed on board the ship for magnetic intensity measurements, and additional samples will be distributed after thin-section billets are cut from the samples. Thin sections examined for evidence of microbial activity (Fisk) will also be measured for the relative chemical and microbial alteration (Staudigel).

Analysis of Logs
An important aspect of the construction of a reference site involves integrating the geophysical and chemical logs with the core information to create a complete crustal section. In the case of the basement logging at Site 801, of particular interest is determining the relative proportions of interflow material, thick flows, and thin sheet flows or pillows. The strategy involves an integration of the FMS logs, geochemical data, and core lithology data for the Hole 801C basement. The porosity-sensitive logs (resistivity, velocity, density, and neutron porosity) will be studied for Hole 801C to characterize very old oceanic crust formed at a very fast spreading rate. In addition, a modeling study of the temperature log in Hole 801C will be undertaken to further constrain the porosity/permeability of basement.
Given the interest in the magnetic reversal history of Jurassic ocean crust, the magnetic logs will be used to establish the magnetic polarity stratigraphy of Hole 801C basement from the log data and to construct a model of the surface magnetic field using the various polarity intervals as input.

Paleomagnetic and Paleointensity Analysis
A number of the fresh glass samples from flow and pillow margins and from hyaloclastites were distributed on board the ship for magnetic intensity measurements.

Microbiology
The majority of the microbiology data will be generated in shore-based studies. The major efforts will be to determine community composition by DNA extraction, in situ hybridization, characterization of microbes isolated from enrichment cultures, and culturing of microbes from samples maintained at in situ pressure. Culturing at high pressure and at 1 atm will be done at different shore-based laboratories. These studies will be coordinated with additional study of igneous rocks, veins, and sediment from which biological samples were collected. Rock samples will be examined by scanning electron microscope for microbes and microbial alteration textures. The amount of microbial vs. chemical alteration will be measured in thin sections, and the types and compositions of secondary minerals will be determined by electron microprobe. The lithology of sediments used for cultures and ATP measurements will be determined from smear slides.

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