| IODP Proceedings Volume contents Search | |||
|
|||
| Expedition reports Research results Supplementary material Drilling maps Expedition bibliography | |||
|
doi:10.2204/iodp.proc.308.102.2006 Methods1Expedition 308 Scientists2Introduction to Expedition 308 shipboard methodsThe “Methods” chapter is designed to document the primary procedures and methods employed during Expedition 308 by the scientists in the various shipboard laboratories in order to understand the basis for our preliminary interpretations of the core and logging data. This information concerns only shipboard methods, the results of which are presented in the site reports in the “Expedition reports” section of the Expedition 308 Proceedings of the Integrated Ocean Drilling Program volume. Methods for shore-based analysis of Expedition 308 samples and data will be described in the individual scientific contributions to be published in scientific journals and the “Research results” section of the Expedition 308 Proceedings volume. OperationsTwo standard coring systems were used during Expedition 308: the advanced piston corer (APC) and the extended core barrel (XCB) systems. These standard coring systems and their characteristics are summarized in the “Explanatory Notes” chapters of previous Initial Reports volumes of the Ocean Drilling Program (ODP). The Leg 139 Initial Reports volume includes a particularly detailed description (Davis, Mottl, Fisher, et al., 1992), as does a variety of ODP Technical Notes (http://www-odp.tamu.edu/publications/pubs_tn.htm). Additional measurement-while-drilling (MWD) and logging-while-drilling (LWD) tools deployed during Expedition 308 are described in detail in “Downhole measurements.” Drilled intervals are measured from the Kelly bushing on the rig floor to the bottom of the drill pipe and referred to in meters below rig floor (mbrf). Meters below seafloor (mbsf) references for the core tops are calculated by subtracting the 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 partly filled core barrel. 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. Core handling and shipboard analysisAs soon as cores arrived on deck, gas void samples and headspace samples were taken by means of a syringe, if applicable, for immediate analysis as part of the shipboard safety and pollution prevention program. Core catcher samples were taken for biostratigraphic analysis. When the core was cut in sections, whole-round samples were taken for shipboard interstitial water examinations and microbiology analysis (both shipboard and shore based). Before splitting, whole-round core sections not dedicated to microbiology were run through the multisensor track (MST), and thermal conductivity measurements were taken. Whole-round samples dedicated to geotechnical analysis were then taken. Finally, the cores were split into working and archive halves, from bottom to top, so investigators should be aware that older material could have been transported upward on the split face of each section. The working half of each core was sampled for both shipboard analyses, such as physical properties, carbonate, and X-ray diffraction (XRD) mineralogy, and shore-based studies. The archive halves were photographed with both black-and-white and color film, scanned with the digital imaging system (DIS), described visually and by means of smear slides, measured for color reflectance on the archive-half multisensor track (AMST), and run through the cryogenic magnetometer. Close-up photographs were taken of particular features for illustrations in site summary reports, as requested by scientists. Both halves of the core were then put into labeled plastic tubes, sealed, and transferred to cold storage space aboard the ship. At the end of the expedition, the cores were transferred from the ship to cold storage at the Integrated Ocean Drilling Program (IODP) Gulf Coast Core Repository at Texas A&M University in College Station, Texas. Curatorial procedures and sample depth calculationsNumbering of sites, holes, cores, and samples follows the standard IODP procedure. A full curatorial identifier for a sample consists of the expedition, 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 308-U1319A-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 of Hole U1319A during Expedition 308 (H designates that this core was taken with the APC system [X = XCB]). 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 m), in which case its length will not match the drilled interval. In addition, a coring gap typically occurs between cores, as shown by composite depth construction (see the “Explanatory Notes” chapters for Legs 138, 177, and 184 [Shipboard Scientific Party, 1992, 1999, 2000]). Thus, a discrepancy may exist between the drilling mbsf and the curatorial mbsf. For instance, the curatorial depth (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. During Expedition 308, multiple APC/XCB holes were cored but continuous composite sections were not constructed. 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, resulting in an uncertainty, for instance, in age-depth analysis and correlation of core facies with downhole log signals. |
|||
