Expedition 352 methods1
M.K. Reagan, J.A. Pearce, K. Petronotis, R. Almeev, A.A. Avery, C. Carvallo, T. Chapman, G.L. Christeson, E.C. Ferré, M. Godard, D.E. Heaton, M. Kirchenbaur, W. Kurz, S. Kutterolf, H.Y. Li, Y. Li, K. Michibayashi, S. Morgan, W.R. Nelson, J. Prytulak, M. Python, A.H.F. Robertson, J.G. Ryan, W.W. Sager, T. Sakuyama, J.W. Shervais, K. Shimizu, and S.A. Whattam2
Keywords: International Ocean Discovery Program, IODP, JOIDES Resolution, Expedition 352, Izu-Bonin-Mariana fore arc, Site U1439, Site U1440, Site U1441, Site U1442, subduction initiation, magma genesis, ophiolites, basalt, boninite, high-magnesium andesite, volcanic rocks, dikes, drill core
This introduction provides an overview of operations, depth conventions, core handling, curatorial procedures, and analyses performed during International Ocean Discovery Program (IODP) Expedition 352. This information will help the reader understand the basis of our shipboard observations and preliminary interpretations. It will also enable interested investigators to identify data and select samples for further study.
GPS coordinates from precruise site surveys were used to position the vessel at Expedition 352 sites. A SyQwest Bathy 2010 CHIRP subbottom profiler was used to monitor seafloor depth on the approach to each site to confirm the depth profiles from precruise surveys. Once the vessel was positioned at a site, the thrusters were lowered and a positioning beacon was dropped to the seafloor at all sites except Hole U1439A. Dynamic positioning control of the vessel uses navigational input from the GPS system and triangulation to the seafloor beacon, weighted by the estimated positional accuracy. The final hole position was the mean position calculated from the GPS data collected over a significant portion of the time during which the hole was occupied.
The advanced piston corer (APC), extended core barrel (XCB), and rotary core barrel (RCB) systems were used during Expedition 352. The APC and XCB systems were used to recover the sedimentary sections at Sites U1439 and U1440, and the RCB system was used to recover the igneous basement sections at Sites U1439 and U1440 and the entire section at Sites U1441 and U1442.
The APC system cuts soft-sediment cores with minimal coring disturbance relative to other IODP coring systems. After the APC core barrel is lowered through the drill pipe and lands above the bit, the drill pipe is pressured up until the two shear pins that hold the inner barrel attached to the outer barrel fail. The inner barrel then advances into the formation and cuts the core. The driller can detect a successful cut, or “full stroke,” by observing the pressure gauge on the rig floor because the excess pressure accumulated prior to the stroke drops rapidly.
APC refusal is conventionally defined in one of two ways: (1) the piston fails to achieve a complete stroke (as determined from the pump pressure and recovery reading) because the formation is too hard, or (2) excessive force (>60,000 lb; ~267 kN) is required to pull the core barrel out of the formation. When a full or partial stroke can be achieved but excessive force cannot retrieve the barrel, the core barrel can be “drilled over” (i.e., after the inner core barrel is successfully shot into the formation, the drill bit is advanced to total depth to free the APC barrel).
The XCB system was used to advance the hole when APC refusal occurred before the target depth was reached or when drilling conditions required it. The XCB is a rotary system with a small cutting shoe that extends below the large rotary APC/XCB bit. The smaller bit can cut a semi-indurated core with less torque and fluid circulation than the main bit, potentially improving recovery. The XCB cutting shoe extends ~30.5 cm ahead of the main bit in soft sediments but is allowed to retract into the main bit when hard formations are encountered.
The bottom-hole assembly (BHA) used for APC and XCB coring was composed of an 11⁷⁄₁₆ inch (~29.05 cm) drill bit, a bit sub, a seal bore drill collar, a landing saver sub, a modified top sub, a modified head sub, five 8¼ inch control length drill collars, a tapered drill collar, two stands of 5½ inch transition drill pipe, and a crossover sub to the drill pipe that extended to the surface.
The RCB BHA included a 9⅞ inch drill bit, a bit sub, an outer core barrel, a modified top sub, a modified head sub, a variable number of 8¼ inch control length drill collars, a tapered drill collar, two stands of 5½ inch drill pipe, and a crossover sub to the drill pipe that extended to the surface.
Nonmagnetic core barrels were used in the APC and RCB sections. APC cores were oriented with the FlexIT tool when coring conditions allowed. Formation temperature measurements were taken with the advanced piston corer temperature tool (APCT-3) in APC sections (see Physical properties).
Most APC cored intervals were ~9.5 m long, and XCB cored intervals were ~9.7–9.8 m long, these distances being the length of a standard core barrel and the length of a joint of drill pipe, respectively. Depths of drilled intervals and recovered cores are provided in the Operations section of each site chapter.
In previous phases of ocean drilling, publications used three primary designations to reference depth: meters below rig floor (mbrf), meters below seafloor (mbsf), and meters composite depth (mcd). These designations evolved over many years to meet the needs of individual science parties but, over the course of time, issues with the existing depth scale designations and the lack of a consistent framework became apparent. A new classification and nomenclature for depth scale types was defined in 2006–2007 to ensure that data acquisition, scale mapping, and the construction of composite splices are unequivocal (see IODP Depth Scales Terminology at www.iodp.org/program-policies).
The primary depth scales are measured by the length of drill string (e.g., drilling depth below rig floor [DRF] and drilling depth below seafloor [DSF]), the length of core recovered (e.g., core depth below seafloor [CSF]), and the logging wireline (e.g., wireline log depth below rig floor [WRF] and wireline log depth below seafloor [WSF]). In cases where multiple logging passes are made, wireline log depths are mapped to one reference pass, creating the wireline log matched depth below seafloor (WMSF). All units are in meters. The relationship between scales is defined either by protocol, such as the rules for computation of CSF from DSF, or by user-defined correlations, such as core-to-log correlation. The distinction in nomenclature should keep the reader aware that a nominal depth value in different depth scales usually does not refer to the exact same stratigraphic interval.
During Expedition 352, unless otherwise noted, depths below rig floor were calculated as DRF and are reported as meters, core depths below seafloor were calculated as CSF-A and are reported as mbsf, and all downhole wireline depths were calculated as WMSF and are reported as mbsf.
Numbering of sites, holes, cores, and samples followed standard IODP procedure. A full curatorial identifier for a sample consists of the following information: expedition, site, hole, core number, core type, section number, section half, piece number (hard rocks only), and interval in centimeters measured from the top of the core section. For example, a sample identification of “352-U1440A-2H-5W, 80–85 cm” indicates a 5 cm sample removed from the interval between 80 and 85 cm below the top of Section 5 (working half) of Core 2 (“H” designates that this core was taken with the APC system) of Hole A at Site U1440 during Expedition 352 (Figure F1). The “U” preceding the hole number indicates the hole was drilled by the US platform, the R/V JOIDES Resolution. The drilling system used to obtain a core is designated in the sample identifiers as follows: H for APC, X for XCB, and R for RCB.
Cored intervals are defined by the length of drill string, the seafloor depth, and the amount the driller advanced the core barrel. The length of the core is defined by the sum of the lengths of the core sections. The CSF depth of a sample is calculated by adding the offset of the sample below the section top and the lengths of all higher sections in the core to the core-top depth measured with the drill string (DSF). A soft to semisoft sediment core from less than a few hundred meters below seafloor expands upon recovery (typically a few percent to as much as 15%), so the recovered interval does not necessarily match the cored interval. In addition, a coring gap can occur between cores. Thus, a discrepancy between DSF and CSF depths can exist with regard to a stratigraphic interval.
Furthermore, when core recovery is >100% of the cored interval, a sample taken from the bottom of a core may have a CSF depth that is deeper than that of a sample from the top of the subsequent core (i.e., the data associated with the two core intervals will overlap on the CSF-A scale).
If a core has <100% recovery, for curation purposes all cored material is assumed to originate from the top of the drilled interval as a continuous section; the true depth interval within the cored interval is unknown. This should be considered a sampling uncertainty in age-depth analysis or in correlation of core data with downhole logging data.
Sediment cores were extracted from the core barrel in plastic liners. The liners were carried from the rig floor to the core processing area on the catwalk outside the core laboratory, where they were split into ~1.5 m sections. Blue (uphole direction) and clear (downhole direction) liner caps were glued with acetone onto the cut liner sections.
Once the cores were cut into sections, whole-round (WR) samples were taken for interstitial water analyses. When a WR sample was removed, a yellow cap was used to denote the missing interval. Syringe samples were taken for headspace gas analyses according to the IODP hydrocarbon safety monitoring protocol.
Core sections were placed in core racks in the laboratory. When the cores reached equilibrium with laboratory temperature (typically after 3 h), WR core sections were run through the Whole-Round Multisensor Logger (WRMSL) for P-wave velocity, magnetic susceptibility, and bulk density. The WR core sections were also run through the Natural Gamma Radiation Logger (NGRL), and thermal conductivity measurements were taken once per core (see Physical properties).
Sediment cores were then split lengthwise from bottom to top into working and archive halves. Investigators should note that older material can be transported upward on the split face of each section during splitting.
The working half of each core was described by the structural geologists. Samples were then taken, first for discrete physical properties and paleomagnetic analyses, followed by samples taken for shore-based studies based on the sampling plan agreed upon by the science party and shipboard curator. Finally samples were taken for remaining shipboard analyses such as bulk X-ray diffraction (XRD), carbonate, and inductively coupled plasma–atomic emission spectroscopy (ICP-AES) analyses.
The archive half of each core was scanned on the Section Half Imaging Logger (SHIL) and measured for color reflectance and point magnetic susceptibility on the Section Half Multisensor Logger (SHMSL). Labeled foam pieces were used in the place of missing WR intervals in the SHIL images. The archive halves were then described visually and by means of smear slides. Finally, the magnetization of archive halves and discrete pieces was measured with the cryogenic magnetometer and spinner magnetometer.
Pieces were extracted from the core liners on the catwalk or directly from the core barrel on the rig floor. The pieces were pushed to the bottom of 1.5 m liner sections, and the total rock length was measured. The length was entered into the database using the SampleMaster application as “created length.” This number was used to calculate recovery. The liner sections were then transferred to the core splitting room.
Oriented pieces of core were marked on the bottom with a wax pencil to preserve orientation. Adjacent but broken pieces that could be fit together along fractures were curated as single pieces. The structural geologist on shift confirmed piece matches and marked the split line on the pieces, which defined how the pieces were to be cut into two equal halves. The aim was to maximize the expression of dipping structures on the cut face of the core while maintaining representative features in both archive and working halves. A plastic spacer was secured with acetone to the split core liner between individual pieces or reconstructed contiguous groups of subpieces. These spacers can represent substantial intervals of no recovery. The length of each section of core, including spacers, was entered into the database as “curated length,” which commonly differs by several centimeters from the length measured on the catwalk. Finally, the depth of each piece in the database was recalculated based on the curated length.
Core sections were placed in core racks in the laboratory. When the cores reached equilibrium with laboratory temperature (typically after 1 h), the WR core sections were run through the WRMSL and the NGRL. Whole-round images of cylindrical oriented pieces were taken on the SHIL.
Each piece of core was split with a diamond-impregnated saw into an archive half and a working half, with the positions of plastic spacers between pieces maintained in both halves. Pieces were numbered sequentially from the top of each section, beginning with number 1. Separate subpieces within a single piece were assigned the same number but lettered consecutively (e.g., 1A, 1B, etc.). Pieces were labeled only on the outer cylindrical surfaces of the core. If it was evident that an individual piece had not rotated around a horizontal axis during drilling, an arrow pointing to the top of the section was added to the label. The piece’s oriented character was recorded in the database using the SampleMaster application.
The working half of each core was first described by the structural geologists. Samples were then taken for thin section preparation and shipboard geochemical, paleomagnetic, and physical properties analyses. The archive half of each core was scanned on the SHIL and measured for color reflectance and point magnetic susceptibility on the SHMSL. Thermal conductivity measurements were undertaken on selected archive-half samples (see Physical properties). The archive halves were then described visually, and selected pieces were analyzed by pXRF. Thin sections cut from the working half were also described. Finally, the magnetization of archive-half sections, archive-half pieces, and discrete samples taken from the working half was measured with the cryogenic magnetometer and spinner magnetometer.
Sampling for shore-based studies was delayed until the end of coring at each hole or at other appropriate times. Sampling was conducted based on the sampling plan agreed upon by the science party and shipboard curator.
When all steps were completed, cores were wrapped, sealed in plastic tubes, and transferred to cold storage space aboard the ship. At the end of the expedition the cores were kept on the ship and, following the transit to Subic Bay, Philippines, were sent to the IODP Kochi Core Center in Japan.
Cores may be significantly disturbed and contain extraneous material as a result of the coring and core handling process (Jutzeler et al., 2014). In formations with loose sand layers, sand from intervals higher in the hole may be washed down by drilling circulation, accumulate at the bottom of the hole, and be sampled with the next core. The uppermost 10–50 cm of each core must therefore be examined critically during description for potential “fall-in.” Common coring-induced deformation includes the concave-downward appearance of originally horizontal bedding. Piston action can result in fluidization (“flow-in”) at the bottom of APC cores. Retrieval from depth to the surface can result in elastic rebound. Gas that is in solution at depth may become free and drive apart core segments within the liner. When gas content is high, pressure must be relieved for safety reasons before the cores are cut into segments. This is accomplished by drilling holes into the liner, which forces some sediment as well as gas out of the liner. These disturbances are described in each site chapter and graphically indicated on the visual core descriptions.
The separate sections of the site chapters were written by the following scientists (authors are listed in alphabetical order; see Expedition 352 science party for contact information):
- Background and objectives: Pearce, Reagan, Petronotis
- Operations: Petronotis and Operations Superintendent Midgley
- Sedimentology: Kutterolf, Robertson
- Biostratigraphy: Avery
- Fluid geochemistry: Godard, Kirchenbaur, Y. Li, Ryan, Whattam
- Petrology: Chapman, Heaton, H.-Y. Li, Nelson, Prytulak, Shervais, Shimizu; Alteration: Python
- Sediment and rock geochemistry: Godard, Kirchenbaur, Y. Li, Ryan, Whattam
- Structural geology: Ferré, Kurz
- Physical properties: Almeev, Christeson, Michibayashi, Sakuyama
- Paleomagnetism: Carvallo, Sager
- Downhole logging: Morgan
In this section we outline the procedures used to document the composition, texture, structures, and the level of core disturbance of the sediment and sedimentary rock recovered during Expedition 352. The procedures included visual core description, smear slide and petrographic thin section analysis, digital color imaging, color spectrophotometry, XRD, carbonate analysis, and ICP-AES.
Core sections from the archive halves were available for sedimentary and petrographic observation. Sections dominated by soft sediment were split using a thin wire held in high tension. Recovered hard rock was split with a diamond-impregnated saw. The split surface of the archive half was then assessed for quality (e.g., smearing or surface unevenness) and, if necessary, gently scraped with a glass slide. After splitting, the archive half was imaged by the SHIL and then analyzed for color reflectance and magnetic susceptibility using the SHMSL (see Physical properties). The archive-half section was occasionally reimaged when visibility of sedimentary structures or fabrics improved following treatment of the split core surface.
Following imaging, the archive-half sections of the sediment cores were macroscopically described for lithologic and sedimentary features (aided by use of a 20× wide-field hand lens and binocular microscope). Lithostratigraphic units were defined following visual inspection and smear slide analysis. Visual inspection yielded information particularly concerning lithologic variation, color, sedimentary structures, and drilling disturbance, whereas smear slide analysis was used to identify sedimentary constituents, including microfossils. All of the descriptive data were entered into DESClogik (see IODP use of DESClogik for details). Based on preliminary visual descriptions and physical property data, samples were taken from the working-half sections to make thin sections and to provide samples for XRD and ICP-AES. All descriptions and sample locations were recorded using curated depths (CSF-A) and documented on visual core description (VCD) graphic reports (Figure F2).
Color was determined qualitatively for core intervals using Munsell Color Charts (Munsell Color Company, Inc., 2000). Visual inspections of the archive-half sections were used to identify compositional and textural elements of the sediment, including rock fragments, sedimentary structures, and diagenetic features such as color mottling and the results of element mobility (e.g., manganese oxide segregation).
Pelagic/hemipelagic and volcaniclastic sediment and sedimentary rock were the principal sedimentary materials recovered during Expedition 352. The sedimentary classification scheme that was employed emphasizes important descriptors for sediment and rock that could be quantified and recorded in the DESClogik database in the same time frame as shipboard core description.
Sediment and sedimentary rock were classified using an approach that integrates the nature of volcanic particles into the sedimentary descriptive scheme typically used by IODP. In the scheme used here, sediment and sedimentary rock were divided into four lithologic classes based on composition (types of particles) (Figure F3):
- Volcaniclastic sediment and rock of pyroclastic origin with >75% volcaniclastic or pyroclastic particles,
- Tuffaceous/volcaniclastic sediment and rock of sedimentary origin (25%–75% volcaniclastic or pyroclastic particles),
- Siliciclastic sediment and sedimentary rock with <25% volcaniclastic and tuffaceous particles and <5% biogenic particles, and
- Pelagic to hemipelagic sediment (rock) with <25% volcaniclastic and tuffaceous particles and >5% biogenic particles.
Examples of each of the four lithologic classes were encountered during this expedition. Within each class, the principal lithology name is based on particle size. In addition, appropriate prefixes and suffixes were applied. For example, the prefix “tuffaceous” was used for the tuffaceous lithologic classes, and prefixes that indicate the dominant biogenic component as determined by microscopic examination were used for pelagic/hemipelagic sediments and sedimentary rocks. Suffixes were also used to indicate minor components within each principal lithologic type.
To emphasize the differences in the composition of the volcaniclastic sandstones recovered, the rocks were further classified using the scheme of Fisher and Schmincke (1984), which is well established and used worldwide. In general, coarser grained sedimentary rocks (63 µm to 2 mm average grain size) are designated as “sand(stone)” where the volcaniclastic components are <25% of the total clasts. Volcaniclastic rocks can be (1) reworked and commonly altered heterogeneous assemblages of volcanic material, including lava, tuff fragments, and compositionally different ash lenses/particles, or (2) fresh, or relatively unaltered, compositionally homogeneous, unconsolidated pyroclastic material directly resulting from explosive eruptions on land or effusive/explosive vents on the seafloor. Pyroclasts are composed of volcanogenic material (“pyro,” meaning fire; magma) that is fragmented (“clast,” meaning fragmented) during explosive eruption.
Where there are ≥25% volcaniclasts but <25% pyroclasts the sediment or sedimentary rock is designated as a “volcaniclastic sand(stone).” Where the clast composition is 25%–75% pyroclasts, the sediment/sedimentary rock is classified as “tuffaceous sand(stone).” However, if the clast composition is ≥75% pyroclasts, it is classified using the volcanological terms ash/tuff (<2 mm), lapilli/lapillistone (2–64 mm), and bombs, blocks/pyroclastic breccia/agglomerate (modified after Fischer and Schmincke, 1984).
A breccia-conglomerate is composed of predominantly rounded and/or subrounded clasts (>50 vol%) and subordinate angular/subangular clasts. A breccia is predominantly composed of angular and subangular clasts (>50 vol%). The description was refined by indicating whether the fabric is either clast supported or matrix supported (see below). For the equivalent pyroclastic lithologic class the term “agglomerate” or “pyroclastic breccia” is used in the place of conglomerate and breccia (Fisher and Schmincke, 1984) (Table T1; Figure F4). Depending on grain size, degree of compaction, and lithification, the nomenclature was adjusted accordingly.
Table T1. Particle size nomenclature and classifications. Download table in .csv format.
For relatively coarse grained material (coarse sand and above), sediment grain size, particle shape, and sorting were determined using the Wentworth scale (Wentworth, 1922). However, for finer grained sediments the textural analysis required inspection at high magnification, which was performed on smear slides and thin sections (see below). The classification of sorting and rounding that was used is shown in Figure F5.
Sedimentary structures observed in the recovered cores included bedding, grading (normal and reverse), soft-sediment deformation, bioturbation, and diagenetic effects. Bed thickness (see Ingram, 1954) was defined as the following units:
- Very thick bedded = >100 cm.
- Thick bedded = 30–100 cm.
- Medium bedded = 10–30 cm.
- Thin bedded = 3–10 cm.
- Very thin bedded = 1–3 cm.
- Laminae = <1 cm.
- R = rare (<1 vol%).
- C = common (1–10 vol%).
- A = abundant (10–50 vol%).
- D = dominant (50–80 vol%).
- M = major (>80 vol%).
The abundance of bioturbation was estimated using the semiquantitative ichnofabric index, as described by Droser and Bottjer (1986, 1991), aided by visual comparative charts (Heard and Pickering, 2008). These charts exhibit the degree of biogenic disruption of primary fabric, such as lamination, ranging from nonbioturbated sediment to total homogenization:
- Nonbioturbated = no bioturbation recorded; all original sedimentary structures preserved.
- Slight bioturbation = discrete, isolated trace fossils; up to 10% of original bedding disturbed.
- Moderate bioturbation = approximately 10%–60% of original bedding disturbed; burrows largely overlap and are commonly poorly defined.
- Strong bioturbation = bedding is completely disturbed, but burrows can still be discerned in places; the fabric is not mixed although the bedding may be nearly or totally homogenized.
Smear slides and thin sections were used to identify basic textural and compositional features. The textures of the sediment were estimated with the help of a visual comparison chart (Rothwell, 1989). Smear slides were used to help identify lithology, texture, diagenesis, and composition and were also used to help define the boundaries of units and subunits. Particular attention was paid to the recognition of ash layers and mineral-rich sands, and these were sampled extensively. The results are summarized in the smear slide tables (see Core descriptions).
The qualitative abundance of major components was confirmed by XRD for selected samples (see X-ray diffraction). Also, the absolute weight percent of carbonate was determined by chemical analysis (see Sediment and rock geochemistry). Samples for whole-rock chemical and carbonate analysis were generally taken close together, in most cases from relatively fine-grained background sediment, typically nannofossil ooze or clay-rich sediment.
Data for the macroscopic and microscopic descriptions of recovered cores were entered into the IODP Laboratory Information Management System (LIMS) database using the IODP data-entry software, DESClogik. Data were entered in the Sediment tab of the Macroscopic template. DESClogik is core description software used to store macroscopic and/or microscopic descriptions of cores. Core description data are available through the Descriptive Information LIMS Report (web.iodp.tamu.edu/DESCReport). A single row in DESClogik defines one descriptive interval, which is commonly one bed but may also be used, for example, to designate marked color variation that may be of diagenetic origin. In addition, the position of each smear slide or petrographic thin section is shown in the VCDs with a sample code of “SED” or “TS,” respectively. The VCDs were generated using the plotting software Strater.
Routine XRD analysis was carried out on bulk powders using a Bruker D-4 Endeavor diffractometer mounted with a Vantec-1 detector using nickel-filtered Cu-Kα radiation. Our principal goal was to identify the different minerals that are present in the sediments of the different units, notably total phyllosilicate minerals, quartz, plagioclase, and calcite. Clay minerals either were not identified or only broadly categorized because advanced analytical techniques (e.g., differential thermal analysis and glycolation) were not available at sea.