SAMPLING STRATEGYNew sampling guidelines specify that a formal, leg-specific sampling strategy be prepared by the Sample Allocation Committee (SAC = co-chiefs, staff scientist, and ODP curator on shore or Curatorial Representative on board ship) for each prospectus. Modifications to the strategy during the leg must be approved by the SAC. The sampling strategy is here keyed to the new guidelines and will be refined as the sample requests are evaluated and considered by the entire shipboard party before reaching site.
Based on the Scientific Prospectus, each Leg 193 scientist (shipboard or shore based) should prepare and submit to ODP/TAMU (Texas A&M University) a sampling request for his/her postcruise research. These should be submitted to ODP at least three months before sailing. One month before sailing, a complete sampling program should be completed, including resolution of possible conflicts.
Dynamic Sampling Strategy and Critical Interval Definition
At the beginning of the leg, a meeting of the full shipboard scientific party will review the sampling requests and define the procedures and a tentative schedule for sampling sessions. Given the characteristics of the drilling targets and scientific objectives of Leg 193, it is foreseeable that sampling may have to be carefully planned, with a permanent revision of the sampling strategy according to findings. This will be particularly true at "critical intervals," such as veins, massive sulfide intercalations, and other intervals of high scientific interest or low recovery. These may require special consideration and special sampling procedures, such as a higher (or lower) sampling density, reduced sample size, or sampling techniques not available on board ship. These will be identified during the core description process and in the sampling protocol established by the interested scientists and shipboard SAC. It will be the responsibility of SAC members to identify and label critical intervals. Progress of the leg may justify reclassification of a former critical interval into the unclassified status.
Minimum Permanent Archive
The minimum permanent archive will be the standard archive half of each core.
Shipboard scientists may nominally expect to obtain as many as 100 samples up to 15 cm3 in size. Additional samples may be obtained upon written request to ODP soon after the cores return to the ODP Gulf Coast Repository. This guideline will be adjusted upward or downward by the shipboard SAC, depending on penetration and recovery during Leg 193. All sample requests must be justified in writing on the standard sample request form and approved by the SAC. Larger samples can exceptionally be collected, subject to written justification and approval by the SAC. Larger samples will be considered the equivalent of multiple samples in complete or partial increments of 15 cm3.
Sampling for microbes and other living organisms and for biogenic molecules will take place immediately after retrieval of core barrels, except if and when critical intervals may be destroyed or rendered useless to other studies as a consequence of biological sampling. The overall number of 100 samples should be taken as a sampling rule. Exceptions (e.g., in the case of very small samples) must be cleared with the SAC.
Redundancy of Studies
Some redundancy of measurement is unavoidable, but minimizing this redundancy among the shipboard party and identified shore-based collaborators will be a factor in evaluating sample requests. Requests for independent shore-based studies that substantially replicate the intent and measurements of shipboard participants will require the approval of both those shipboard investigators and the SAC.
Shipboard Samples and Data
Following core labeling, measurement of nondestructive properties, and splitting, samples will be selected from core working halves by members of the shipboard party for routine measurement of physical and magnetic properties, bulk chemical analyses by inductively coupled plasma-atomic emission spectrophotometer (ICP-AES), carbon-hydrogen-nitrogen-sulphur (CHNS) analyzer, and X-ray diffraction as necessary. Polished thin sections will be prepared for identification of minerals, determination of mineral modes by point counting, and studies of texture and fabric.
We shall identify a suite of samples for full measurement characterization. At ~9.5-m intervals (once per full core), slabs measuring 10 cm x 6 cm x 1.5 cm, with a previously sampled central minicore, will be cut for all shipboard measurements then subdivided and split appropriately for further shore-based geochemical, mineralogical, and petrographic studies. Where necessary to avoid or include features like veins and alteration, full half-round slices or quarter slices may be taken instead of slabs.
Data from all shipboard studies, regardless of method or observer, including all core descriptions and measurements and the nondestructive measurements of physical and magnetic properties, are the property of the entire shipboard party and may be used exclusively by them in publication and preparation of manuscripts with proper citation to the Initial Reports volume until the publication of the Initial Reports volume or 12 months postcruise, whichever is later.
Shipboard Thin Sections
Shipboard thin sections will be selected from representative sections of the core and at some critical intervals. These sections will remain the property of ODP. The thin-section chips from which the sections are made will be retained by ODP and should normally be thick enough to allow for the production of additional sections unless the sampling plan for a critical interval precludes this. Members of the shipboard party can request the production of a thin section from these chips for their personal use as part of their nominal 100 sample limit, but must arrange for the prepaid manufacture of these thin sections with a third-party commercial service at their own expense unless otherwise approved by the ODP Curator. The thin-section chip will then be sent directly to the commercial service and returned directly to ODP by the service.
Sampling for Shore-Based Studies and Sampling Parties
To minimize the time and physical effort required for additional sampling for shore-based studies, we shall organize sampling consortia among the principal scientific teams (igneous, metamorphic, structural, physical, and magnetic properties) that will identify locations for similarly large (10 cm x 6 cm x 1.5 cma minicore) or even larger samples, averaging approximately once per 9.5 m of core. The actual size will depend on the number of investigators in the group, and it will be subdivided among them, to count against the nominal 100-sample limit of each consortium investigator. Follow-up sampling will be organized as short sample parties during reentries or logging runs, for individuals using the second-look lab, or at the ODP Gulf Coast Repository, as necessary.
Storage and Shipping Needs
The usual labeling, orientation, core placement, and storage procedures should be sufficient for safe transportation to the ODP Gulf Coast Repository. Core handlers should wear back supports while lifting and handling individual archive or working halves and especially when maneuvering core storage boxes. Additionally, sulfide-bearing cores may require storage in special sealed bags in an inert atmosphere.
Formation Water Sampling
Sampling and analysis of deep-seated hydrothermal fluids that enter the two outflow-zone boreholes (Sites PCM-2A and PCM-3A) at permeable aquifers will greatly enhance our ability to assess subsurface fluid-rock interactions and the chemical controls at the depth of sulfide mineral deposition. Such fluids will also provide key information for modeling hydrothermal processes deeper than the extent of coring, including additional pathways to assessing the sources of fluids and metals, as well as the first comparisons with vent fluids previously collected at active chimneys. Technologies used to collect high-temperature hydrothermal fluids from boreholes on previous cruises have not been particularly successful, and an effort will be made prior to Leg 193 to design new sampling instruments. Our intention is to deploy these into the open hole at staged intervals of drilling, or after completion of wireline logging, at depths where temperature anomalies have been detected. With simpler forms of instrumentation, we do not expect the samples to be pure end-member fluids from narrow formation intervals; rather, they will typically be variably mixed within the borehole from several aquifers and will have been diluted by seawater and drilling fluid. Procedures exist to resolve these effects of contamination. If suitable high temperature packers can be developed, sampling of more concentrated hydrothermal fluids with more specific sources will become an option. The exact strategies for collection of hydrothermal fluids will depend on the nature and time requirements of the instrumentation adopted. At a minimum, we will attempt one sample near the bottom of holes at Sites PCM-2A and PCM-3A, and one near the collar of these or the adjacent logging-while-drilling holes.
Logging Plan | Table of Contents