Sampling and sample coordination

Expedition 348 will sample cuttings and mud gas from all riser drilling intervals, including those that are not cored (860–2300 and 2400–3600 mbsf), as well as a limited number of sediment cores (2300–2400 mbsf). Previously (during Expedition 338), cuttings and mud gas were collected for analysis from the interval 860–2005 mbsf; because much of this interval will be redrilled, cuttings samples will be collected from this interval and stored for analysis (if desired) by the science party when they board the Chikyu. 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 in Hole C0009A (Expedition 319 Scientists, 2010) and refined for previous work in Hole C0002F (Expedition 338) (see the Cuttings Cookbook). This approach is built on experience transferred from the oil industry and from the 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 (see below), and individual sample requests will be coordinated by the SAC with exact numbers and location of samples 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 (​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 whole-round samples (e.g., interstitial water, microbiology, and anelastic strain recovery) will then be subsampled (Fig. F5). 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 the NanTroSEIZE project 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 Center [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 sample. 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 well-lithified core expected at these depths, high-pressure squeezing will probably not yield usable pore water samples, so fluid chemistry will have to follow the ground rock interstitial normative determination (GRIND) method (Expedition 315 Scientists, 2009a).

Community whole-round core samples

As is usual practice in IODP, individual scientists will be permitted to collect samples for shipboard analyses and their postexpedition research in accordance with approved sample requests. 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 is 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

During riser drilling, the unwashed drill cuttings are delivered continuously to the shale shaker, where samples are collected (by a Mantle Quest Japan [MQJ] roustabout) at a frequency equivalent to every 10 m of drilling penetration (Fig. F6). The roustabout then divides the cuttings into two splits: one for the Mud Logger (Geoservices) and the second for scientific analysis. The “science cuttings” sample (volume depends on volume of total sample requests) is transferred to the Core Cutting Area on the Laboratory Roof Deck (by a MQJ roustabout), where it is again split into two portions: a 400 cm3 portion for archiving (“archive portion”) and a 1000 cm3 portion for analysis and sampling (“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 F6 (diamonds indicate potential sampling intervals). 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 radiation, 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). When 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.