Information assembled in this chapter will help the reader understand the basis for our preliminary conclusions and will also enable the interested investigator to select samples for further analysis. This information concerns only shipboard operations and analyses described in the site reports in the Leg 201 Proceedings of the Ocean Drilling Program, Initial Reports volume. Methods used by various investigators for shore-based analyses of Leg 201 samples will be described in the individual contributions published in the Leg 201 Scientific Results volume and in publications in various professional journals.
The separate sections of the site chapters were written by the following shipboard scientists (authors are listed in alphabetical order, no seniority is implied):
Two standard coring systems were used during Leg 201, the advanced hydraulic piston corer (APC), and the extended core barrel (XCB). These standard coring systems and their characteristics are summarized in the "Explanatory Notes" chapters of various previous Initial Reports volumes as well a number of Technical Notes. Most cored intervals were ~9.5 m long, which is the length of a standard core barrel. In other cases the drill string was drilled, or "washed ahead," without recovering sediments to advance the drill bit to a target depth where core recovery needed to resume.
Drilled intervals are referred to in meters below rig floor (mbrf), which are measured from the kelly bushing on the rig floor to the bottom of the drill pipe, and meters below seafloor (mbsf), which are calculated from the length of pipe deployed less estimated seafloor depth. When sediments of substantial thickness cover the seafloor, the mbrf depth of the seafloor is determined with a mudline core, assuming 100% recovery for the cored interval in the first core. Water depth is calculated by subtracting the distance from the rig floor to sea level from the mudline measurement in mbrf. This water depth usually differs from precision depth recorder measurements by a few to several meters. The mbsf depths of core tops are determined by subtracting the seafloor depth (mbrf) from the core top depth (mbrf). The resulting core top datums in mbsf are the ultimate reference for any further depth calculation procedures.
When cores are split, many show signs of significant sediment disturbance, including the concave-downward appearance of originally horizontal bedding, haphazard mixing of lumps of different lithologies (mainly at the tops of cores), fluidization, and flow-in. Core deformation may also occur during retrieval because of changes in pressure and temperature as the core is raised and during cutting and core handling on deck.
Numbering of sites, holes, cores, and samples follows the standard Ocean Drilling Program (ODP) procedure (Fig. F1). A full curatorial identifier for a sample consists of the leg, site, hole, core number, core type, section number, and interval in centimeters measured from the top of the core section. For example, a sample identification of 201-1225A-1H-1, 10-12 cm, represents a sample removed from the interval between 10 and 12 cm below the top of Section 1, Core 1 (H designates that this core was taken with the APC system) of Hole 1225A during Leg 201. Cored intervals are also referred to in "curatorial" mbsf. The mbsf depth of a sample is calculated by adding the depth of the sample below the section top and the lengths of all higher sections in the core to the core top datum measured with the drill string.
A sediment core from less than a few hundred mbsf may, in some cases, expand upon recovery (typically 10% in the upper 300 mbsf), and its length may not necessarily match the drilled interval. In addition, a coring gap is typically present between cores. Thus, a discrepancy may exist between the drilling mbsf and the curatorial mbsf. For instance, the curatorial mbsf of a sample taken from the bottom of a core may be larger than that of a sample from the top of the subsequent core, where the latter corresponds to the drilled core-top datum.
If a core has incomplete recovery, all cored material is assumed to originate from the top of the drilled interval as a continuous section for curation purposes. The true depth interval within the cored interval is not known. This should be considered as a sampling uncertainty in age-depth analysis and correlation of core facies with downhole log signals.
To ensure as little damage as possible to the microbial communities present in cores, a unique core processing strategy was established for Leg 201. Since microorganisms existing at deepwater seafloor temperatures (2°-4°C) can be acutely sensitive to elevated temperature (>10°C) and oxygen, we recognized a critical need to prevent thermal equilibration and exposure of the cores to oxygen after recovery. To minimize equilibration of the cores, we modified the standard coring practice of shelving a recovered core barrel on the rig floor while a new core barrel is deployed and a joint of pipe is added. The core barrel was extracted from the drill string and immediately transferred to the catwalk and marked by the ODP curatorial staff into 1.5-m sections. Shipboard microbiologists identified one or more 1.5-m sections (hereafter referred to as the MBIO sections) for rapid microbiological processing. Once the MBIO sections were selected, they were labeled with a red permanent marker with orientation and section number and removed from the core. Ends of the removed sections were covered with plastic caps but not sealed, and the sections were carried into the hold refrigerator, which was set to ~4°C and served as a microbiology cold room. After some modifications to the cooling unit and installation of plastic sheets across the door to dampen air exchange, thermal loggers indicated an ambient temperature in the cold room of ~6°C. Multiple sections were moved to the cold room in order to ensure that sufficient undisturbed material was available for microbiology and coupled geochemistry sampling. Microbiology and geochemistry samples were rapidly extracted, as described in "Whole-Round Core Sampling in the Cold Room" in "Core Handling and Sampling" in "Introduction and Background" in "Microbiology." Unsampled microbiological subsections and the remainder of the core on the catwalk were processed according to the ODP standard core handling procedures as described in previous Initial Reports volumes and the Shipboard Scientist's Handbook (with minor modifications). In brief, prior to sectioning, an infrared (IR) camera was passed along the length of the core, capturing a thermally calibrated image (see "Infrared Thermal Imaging" in "Physical Properties"). Routine shipboard safety and pollution prevention samples were collected on the catwalk (see "Biogeochemistry"). The core was then cut into nominally 1.5-m sections. The remaining cut sections were transferred to the core laboratory for further processing.
Whole-round core sections not used for microbiological sampling were run through the multisensor track (MST), and thermal conductivity measurements were performed (see "Physical Properties"). The cores were then split into working and archive halves (from bottom to top); investigators should be aware that older material may have been transported upward on the split face of each section. When short pieces of sedimentary rock were recovered, the individual pieces were split with the rock saw and placed in split liner compartments created by sealing spacers into the liners with acetone.
Coherent and reasonably long archive-half sections were measured for color reflectance using the archive-half multisensor track (AMST) (see "Color Reflectance Spectrophotometry" in "Lithostratigraphy"). Visual descriptions were prepared of the archive halves, augmented by smear slides and thin sections (see "Lithostratigraphy"), and the archive halves were photographed with both black-and-white and color film. Close-up photographs were taken of particular features for illustrations in site chapters, as requested by individual scientists. All sections of core not removed for microbiological sampling were additionally imaged using a digital imaging track system equipped with a line-scan camera.
The working half of each core was sampled for shipboard analysis, such as physical properties, carbonate, and bulk X-ray diffraction (XRD) mineralogy, and for shore-based studies. Both halves of the core were then put into labeled plastic tubes, sealed, and placed in cold storage space on board the ship. At the end of the leg, the cores were transferred from the ship into refrigerated containers and shipped to the ODP Gulf Coast Core Repository in College Station, Texas.
1Examples of how to reference the whole or part of this volume can be found under "Citations" in the preliminary pages of the volume.
2Shipboard Scientific Party addresses can be found under "Shipboard Scientific Party" in the preliminary pages of the volume.
Ms 201IR-105