IODP Expedition 338 Scientific Prospectus

doi:10.2204/iodp.sp.338.2012

Sampling and sample coordination

Expedition 338 will sample cuttings and mud gas from riser drilling intervals that are not cored (860–2300 and 2400–3600 mbsf) as well as a limited number of sediment cores (2300–2400 mbsf). Sampling and sample coordination for cuttings and mud gas will involve a combination of shipboard analysis, sample collection, and sample archiving based on the approach that was first used at Site C0009 during Expedition 319. This approach built on experience transferred from the oil industry and from the International Continental Scientific Drilling Program SAFOD drilling program. The core and cuttings sampling strategy was developed by the PMT and Specialty Coordinators in consultation with the Sample Allocation Committee (SAC) (see “Sample requests and coordination” below) to best meet the drilling project’s objectives and the needs of the science party. Sampling of cores will include whole-round and discrete sampling following traditional IODP sample policies. Basic shipboard sampling, community samples, and individual sample requests will be coordinated by the SAC and exact numbers and location of samples will be based on core recovery. A short review of core sampling and archiving is provided below followed by a more detailed discussion of sampling and archiving of cuttings. Shipboard and shore-based researchers should also refer to the IODP Sample, Data, and Obligations Policy (www.iodp.org/program-policies/) for additional details about obtaining and using samples.

Sampling sediment cores

Prior to any whole-round or discrete sampling of cores, all cores will be imaged with X-ray computed tomography (CT). Time-sensitive sample (e.g., interstitial water, microbiology, and anelastic strain recovery) whole rounds will then be subsampled (Fig. F6). Whole-round core sections will then be nondestructively analyzed in the multisensor core logger. After nondestructive logging, nontime-sensitive whole-round samples (e.g., community whole rounds and science party research samples) will be taken as approved by the Co-Chief Scientists. Then cores will be split into a “working half” and “archive half” with the working half being available for sampling by shipboard and shore-based scientists. Although the archive half is also available for sampling in certain circumstances, it is primarily used for stratigraphic and structural characterization and archived to preserve retrieved material while providing flexibility and broader access to important material postexpedition.

The unique, multiexpedition nature of NanTroSEIZE has also required the modification of traditional IODP sampling policy and routines in sampling sediment cores. Specifically, these include: (1) community whole-round samples that are archived (at the Kochi Core Repository [KCC]) for postexpedition distribution as approved by the SAC and (2) cluster samples taken for a suite of basic scientific measurements collected onboard and shore-based from a much smaller (1–2 cm thick) whole-round core. These basic measurements consist of carbonate content, moisture and density (MAD), grain size, bulk X-ray fluorescence (XRF), bulk X-ray diffraction (XRD), and clay-size XRD. Community whole-round cores and sample clusters are typically adjacently located and collected approximately one or two per core. We note that, due to the highly lithified core expected at these depths, squeezing for pore water will be impossible, so fluid chemistry will have to follow the GRIND method (Expedition 315 Scientists, 2009a).

Community whole-round core samples

As usual, individual scientists will collect samples for shipboard analyses and their postexpedition research. In addition, we intend to collect “community” archive samples, especially whole-round samples. These community samples will augment and/or provide redundancy for whole-round core samples requested by shipboard and shore-based scientists. The goal is to preserve a wide range of sample material for geotechnical characterization to help achieve the overall science objectives after the expedition and over the duration of the NanTroSEIZE project. Community whole-round cores are typically collected from each core after X-ray CT imaging as determined by the Co-Chief Scientists.

Cluster samples

To ensure achievement of overall NanTroSEIZE scientific objectives and maximize the ability to correlate different shipboard and shore-based data sets, it will be essential to co-locate suites of essential data types (pore water, calcium carbonate content, MAD, bulk XRD, grain size, bulk chemistry, cation exchange capacity, and clay mineral XRD). This will be done with appropriate and consistent sample spacing throughout each site’s stratigraphic succession. Sample clusters are normally collected from each section. In addition, a cluster sample is taken adjacent to each whole-round sample.

Sampling and archiving drill cuttings

Unwashed drill cuttings are delivered continuously to the shale shaker, where they are sampled by the “Sample Catcher” at a frequency equivalent to every 5 m of drilling penetration (Fig. F7). The Sample Catcher then splits the cuttings into two splits: one for the Mud Logger and the second for IODP scientific analysis. The IODP cuttings sample has a volume of ~1.5 L, depending on the volume of total sample requests, and is transferred to the Laboratory Roof Deck (by a Mantle Quest Japan “Roustabout”), where it is again split into two portions: a 400 cm³ portion for archiving (the “archive portion”) and a 1000 cm³ portion for analysis and sampling (the “working portion”). The working portion is available for scientific sampling and analysis at any stage of the cleaning, sieving, and preliminary analysis shown in Figure F7 (potential sampling intervals are noted with diamonds). A portion of the archived cuttings (designated as a “temporary archive”) is also available for sampling and analysis after the moratorium and approval of the SAC. Shipboard analysis of the “working portion” normally includes gamma ray, MAD, lithologic and structural (microstructures) descriptions (through smear slides and thin sections, respectively), XRD and XRF analyses, magnetic susceptibility, total carbonate (using carbonate analyzer), and total carbon and nitrogen (using CHNS/O elemental analyzer). If possible, pore fluids will also be extracted from cuttings using the GRIND method (Expedition 315 Scientists, 2009a). The archive portion will be separated into an unwashed split and a washed split, both of which will be archived at KCC. Samples will be sorted, when possible, by lithology after sieving with magnets and seawater.

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