Previous   |    Next

doi:10.2204/iodp.proc.313.202.2018

Methods and materials

Overlaps were identified from the curated expedition depths by rounding all depths to the nearest 1 cm and then identifying repeated depths and categorizing these into

• Overlap A, referring to overlap within the overlying core above and
• Overlap B, referring to overlap in the underlying core.

Material is collected at the very base of each run by metal blades referred to as “core catchers.” In general, this material is minor (in the region of centimeters), is not logged for core physical properties, and is often not competent material. However, because this core catcher material provides part of the recovered core, two versions of the overlaps should be considered, the first version including these core catcher pieces and the second version excluding them. Physical property measurements of the core provide an additional machine-precise core length measurement with occasional minor discrepancies between these measurements and the curated core measurements. Because core catcher material is seldom long enough for measurement of core physical property data or for digital linescan image acquisition, scaled depths excluding core catchers are used for the remainder of this report (Fig. F1, column 5b). This exclusion results in a continuous digital image and ensures correspondence to the overlying core physical property data.

Lithology, based on observations made of the split core surfaces, was recorded during the expedition and described in the Lithology sections of the “Site M0027,” “Site M0028,” and “Site M0029” chapters (Expedition 313 Scientists, 2010b, 2010c, 2010d) and graphically in the VCDs. These records are supported by systematic high-resolution digital linescan images of the split core face of the archive half (~62 mm diameter) of all core sections.

The Expedition 313 operational team and drillers recorded relevant observations during drilling, which is standard practice during expeditions. For example, the observation that the rate of penetration has changed may indicate a different lithology or the observation that a run recovered an empty core barrel potentially suggests the core has slipped and may be recovered by the subsequent run. For each interval of identified overlap, the notes taken during drilling operations were accessed for that core barrel to identify or rule out drilling-related disturbance causing the overlap. Consideration should also be given for excluding material that may be drilling in-fill or duplicated material. For this report, where intervals of overlap are found within clay lithologies, no recovered core is discounted for this reason. Elsewhere in the boreholes, visual evaluation of the degree of drilling disturbance (see the “Methods” chapter [Expedition 313 Scientists, 2010a]) is reinforced by the drilling notes, and the appropriateness of excluding material affected by drilling disturbance is most accurate by considering each individual core (Fig. F1).

Drilling parameter data were recorded in time and captured nearly continuously during drilling. The driller started and stopped the recording interval to coincide with drilling times. During Expedition 313 drilling parameter data were recorded in drilling data file format (DDF) in GMT – 8 (Pacific time) and converted by scientists (J. Inwood, G. Tulloch, and C. Delahunty) to expedition time (UTC – 5 h; Eastern standard time) for Hole M0027A. Files for Hole M0027A were renamed in YYMMDD format. Each DDF file represents ~2 h of operations, with the file size corresponding to seconds of recording time. Shorter files usually correspond to a pause in recording to enable file backup. Gaps exist where a driller accidentally turned the switch off (rare and typically short in duration); larger gaps in recording correspond to the switch being turned off while repairs or operational difficulties were resolved. The end time was recorded from file properties and metadata for all files imported into a single Microsoft Excel spreadsheet. The DDF files were input into the Racepak DataLink II program (https://store.racepak.com), which was designed for racing car systems and modified for drilling data by C. Delahunty. This program can output an ASCII file (WRI file extension) for a selected time interval (5 s was selected for Hole M0027A). A graph of selected properties (head rpm, torque force, and water flow) was produced (see M27DrillerInfoLog118to226.jpg in OVERLAP in “Supplementary material” for Runs 118–226). The drilling files were saved as individual files and combined into a single spreadsheet (see M27DrillFiles.xls in OVERLAP in “Supplementary material”), enabling careful correlation of the drilling time with the time that core was recovered on deck and sedimentological observations and the addition of each run number to the graph. Note that these correlations are estimates and may require minor adjustments in intervals for high-resolution studies.

Downhole logging data can be extremely useful as a tool for correlation between in situ data acquired in the borehole during logging and measurements and observations on core, especially where equivalent measurements (commonly NGR) are taken downhole and on the recovered core. During Expedition 313, spectral gamma ray logs were acquired for the complete formation and NGR measurements were taken every 9 cm on the recovered core (Fig. F1; also see the “Methods” chapter [Expedition 313 Scientists, 2010a]). Magnetic susceptibility measurements, where acquired during downhole logging operations, represent an effective method of correlating in situ measurements and core measurements taken every 1 cm (see the “Methods” chapter [Expedition 313 Scientists, 2010a]).

Coring and wireline logging depths are based on the length of the drill pipe and length of the wireline below the seafloor, respectively. Both are referred to as meters below seafloor (mbsf) in the remainder of this report, which is sufficient to point the reader to the appropriate point on the figures. However, depths on figures are specified precisely following IODP Depth Scales Terminology (http://www.iodp.org/top-resources/program-documents/policies-and-guidelines) to enable depths across measurements to be compared.

Top of page   |    Previous   |    Next