Expedition 385 methods

A. Teske, D. Lizarralde, T.W. Höfig, I.W. Aiello, J.L. Ash, D.P. Bojanova, M.D. Buatier, V.P. Edgcomb, C.Y. Galerne, S. Gontharet, et al.

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To cite this version:

A. Teske, D. Lizarralde, T.W. Höfig, I.W. Aiello, J.L. Ash, et al. Expedition 385 methods. Guaymas Basin Tectonics and Biosphere, 385, International Ocean Discovery Program, 2021, Proceedings of the International Ocean Discovery Program, 10.14379/iodp.proc.385.102.2021. [https://hal.science/hal-04252267v1](https://hal.science/hal-04252267v1)

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# Expedition 385 methods<fnref n="1" />

## Contents

1 Introduction

7 Core handling and analysis

9 Lithostratigraphy

20 Igneous petrology and alteration

29 Structural geology

36 Biostratigraphy

42 Paleomagnetism

46 Inorganic geochemistry

52 Organic geochemistry

60 Microbiology

74 Petrophysics

100 References

## Keywords

International Ocean Discovery Program, IODP, *JOIDES Resolution*, Expedition 385, Guaymas Basin Tectonics and Biosphere, Gulf of California, Site U1545, Site U1546, Site U1547, Site U1548, Site U1549, Site U1550, Site U1551, Site U1552, Biosphere Frontiers, diatom ooze, sill, thermal alteration

## Core descriptions

## Supplementary material

## References (RIS)

MS 385-102

Published 27 September 2021

Funded by NSF OCE1326927

A. Teske, D. Lizarralde, T.W. Höfig, I.W. Aiello, J.L. Ash, D.P. Bojanova, M.D. Buatier, V.P. Edgcomb, C.Y. Galerne, S. Gontharet, V.B. Heuer, S. Jiang, M.A.C. Kars, S. Khogenkumar Singh, J.-H. Kim, L.M.T. Koornneef, K.M. Marsaglia, N.R. Meyer, Y. Morono, R. Negrete-Aranda, F. Neumann, L.C. Pastor, M.E. Peña-Salinas, L.L. Pérez Cruz, L. Ran, A. Riboulleau, J.A. Sarao, F. Schubert, J.M. Stock, L.M.A.A. Toffin, W. Xie, T. Yamanaka, and G. Zhuang<fnref n="2" />

# 1. Introduction

This chapter outlines the procedures and methods employed for coring and drilling operations as well as in the various shipboard laboratories of the research vessel (R/V) *JOIDES Resolution* during International Ocean Discovery Program (IODP) Expedition 385. The laboratory information applies only to shipboard work described in the Expedition Reports section of the *Expedition 385 Proceedings of the International Ocean Discovery Program* volume, using the shipboard sample registry, imaging and analytical instruments, core description tools, and the Laboratory Information Management System (LIMS) database. Methods used by investigators for shore-based analyses of Expedition 385 samples and data will be described in separate individual peer-reviewed scientific publications.

All shipboard scientists contributed in various ways to this volume with the following primary responsibilities (authors are listed in alphabetical order; see **Expedition 385 scientists** for contact information):

Summary chapter: *Expedition 385 Scientists*

## Methods and site chapters:

Background and objectives: D. Lizarralde, A.P. Teske

Operations: K. Grigar, T.W. Höfig

Lithostratigraphy: I.W. Aiello, M.D. Buatier, S. Gontharet, K.M. Marsaglia

Igneous petrology and alteration: S. Khogenkumar Singh, W. Xie

Structural geology: J.M. Stock

Biostratigraphy: S. Jiang, L.L. Pérez Cruz, L. Ran, J.A. Sarao

Paleomagnetism: M.A.C. Kars, L.M.T. Koornneef

Inorganic geochemistry: J.-H. Kim, L.C. Pastor, T. Yamanaka

Organic geochemistry: J.L. Ash, V.B. Heuer, A. Riboulleau, G. Zhuang

Microbiology: D.P. Bojanova, V.P. Edgcomb, N.R. Meyer, Y. Morono, F. Schubert

Petrophysics (physical properties and downhole measurements): C.Y. Galerne, R. Negrete-Aranda, F. Neumann, M.E. Peña-Salinas

The present introductory section provides an overview of drilling and coring operations, core handling, curatorial conventions, depth scale terminology, and the sequence of shipboard analyses. Subsequent sections of this chapter document specific laboratory instruments and methods in detail.

<footnote n="1">¹ Teske, A., Lizarralde, D., Höfig, T.W., Aiello, I.W., Ash, J.L., Bojanova, D.P., Buatier, M.D., Edgcomb, V.P., Galerne, C.Y., Gontharet, S., Heuer, V.B., Jiang, S., Kars, M.A.C., Khogenkumar Singh, S., Kim, J.-H., Koornneef, L.M.T., Marsaglia, K.M., Meyer, N.R., Morono, Y., Negrete-Aranda, R., Neumann, F., Pastor, L.C., Peña-Salinas, M.E., Pérez Cruz, L.L., Ran, L., Riboulleau, A., Sarao, J.A., Schubert, F., Stock, J.M., Toffin, L.M.A.A., Xie, W., Yamanaka, T., and Zhuang, G., 2021. Expedition 385 methods. In Teske, A., Lizarralde, D., Höfig, T.W., and the Expedition 385 Scientists, Guaymas Basin Tectonics and Biosphere. *Proceedings of the International Ocean Discovery Program*, 385: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.385.102.2021</footnote>

<footnote n="2">² *Expedition 385 Scientists' affiliations.*</footnote>
**1.1. Locations of sites and holes**

GPS coordinates (World Geodetic System 84 datum) obtained from preexpedition site surveys were used to position the vessel at the Expedition 385 sites. A SyQwest Bathy 2010 compressed high-intensity radar pulse (CHIRP) subbottom profiler was deployed to monitor the seafloor depth on the approach to the site to reconfirm the depth profiles from preexpedition surveys. Once positioned at a site, the thrusters were lowered, and the location of the ship was maintained over each hole of a site by means of the Neutronics 5002 dynamic positioning (DP) system on JOIDES Resolution. DP control of the vessel used navigational input from the GPS (Figure F1). The final hole position was the calculated mean position derived from the GPS data collected over a significant portion of the time the hole was occupied. In hydrothermally active areas, a deep-sea camera survey of the seafloor was implemented prior to drilling to ensure no proximal animal communities were present and to confirm suitable locations for spudding boreholes.

The drilling sites were numbered according to the series that began with the first site drilled by the Glomar Challenger in 1968. Starting with Integrated Ocean Drilling Program Expedition 301, the prefix “U” defines sites occupied by *JOIDES Resolution*. For all IODP drill sites, a letter suffix distinguishes each hole drilled at the same site. The first hole drilled is assigned the site number modified by the suffix “A,” the second hole takes the site number and the suffix “B,” and so forth. During Expedition 385, eight sites were drilled in Guaymas Basin in the central Gulf of California: Site U1545 (Holes U1545A–U1545C), Site U1546 (Holes U1546A–U1546D), Site U1547 (Holes U1547A–U1547E), Site U1548 (Holes U1548A–U1548E), Site U1549 (Holes U1549A and U1549B), Site U1550 (Holes U1550A and U1550B), Site U1551 (Holes U1551A and U1551B), and Site U1552 (Holes U1552A–U1552C).

**1.2. Drilling and logging operations**

To successfully drill both soft and indurated sediments as well as intruded sills, all four standard coring tools available on *JOIDES Resolution* were deployed during Expedition 385: the advanced piston corer (APC), half-length APC (HLAPC), extended core barrel (XCB), and rotary core barrel (RCB) systems. Operations took place in Mexican territorial waters in water depths of ~1600–2000 m.

The APC and HLAPC systems cut soft-sediment cores with negligible coring disturbance relative to other IODP coring tools. Upon lowering the APC/HLAPC core barrel through the drill pipe, it lands above the bit. Subsequently, the drill pipe is hydraulically pressured up until the two shear pins that hold the inner barrel and are attached to the outer barrel fail. The inner barrel then

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**Figure F1.** IODP conventions for naming sites, holes, cores, sections, and samples, Expedition 385. mbsl = meters below sea level. m DSF = meters drilling depth below seafloor.
advances into the formation and cuts the core (Figure F2A). The driller can identify a successful
cut, or full stroke, by observing the pressure gauge on the rig floor because the excess pressure
built up prior to the stroke drops promptly. Cores collected with the APC system are denoted by
the letter “H” (for hydraulic piston coring), and those collected with the HLAPC system are indi-
cated by the letter “F.”

APC refusal is conventionally defined in one of two ways: (1) the piston fails to accomplish a full stroke (as determined by the pump pressure and recovery reading) because the formation is too hard or (2) excessive force (>60,000 lbf or >266.9 kN) is required to pull the core barrel out of the formation. When a complete APC stroke could not be achieved, either the HLAPC system or the XCB system was deployed, depending on the severity of deterioration of the preceding APC coring progress and overall formation conditions. With each APC attempt, the bit was advanced by the length of the core barrel. Note that failed APC attempts resulted in a nominal recovery of ~100% based on the assumption that the barrel penetrated the formation by the length of the recovered core. If an APC core does not achieve a full stroke, the next core can be taken after advancing to a depth calculated from the recovery of the previous core (advance by recovery) or to a depth of a full APC core (typically 9.5–9.7 m). When a full or partial stroke was achieved but excessive force could not retrieve the barrel, the core barrel could be drilled over (i.e., after the inner core barrel was successfully shot into the formation, the drill bit was advanced to total depth to free the APC barrel).

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**Figure F2.** Coring systems used during Expedition 385. A. APC system. B. XCB system. C. RCB system. ID = inside diameter. OD = outside diameter. 1 inch = 2.54 cm. Note that the APC and XCB systems use the same bottom-hole assembly (see Figure F3 for schematic sketch). Modified from Graber et al. (2002). (Continued on next page.)
The standard APC system employs a 9.5 m long core barrel, whereas the HLAPC system uses a 4.7 m long core barrel. Both systems cut cores with a nominal diameter of 6.27 cm. The HLAPC system was deployed after the standard APC had <50% recovery or once the deployment of the XCB system emerged as a regular approach due to high abundance of infrequently occurring hard carbonate layers intercalated with soft clay- and ooze-rich sediments. While using the HLAPC system, the same criteria were applied in terms of refusal as for the APC system. Deployment of the HLAPC system allowed for considerably greater APC sampling depths to be attained than would have otherwise been possible.

The XCB system is typically used when the APC/HLAPC system has insufficient recovery. Cores collected with the XCB system are denoted by the letter “X” (for extended). The XCB system was utilized to advance the hole when APC or HLAPC refusal occurred before the target depth was reached or when drilling/formation conditions required it. The latter case applied once the APC/XCB drill bit encountered infrequently occurring hard carbonate layers or sediment/sill contact zones. The XCB system is equipped with a small coring shoe that extends below the large rotary APC/XCB drill bit (Figure F2B), cutting cores with a nominal diameter of 5.87 cm. The smaller XCB coring shoe is able to cut a semi-indurated core with less torque and fluid circulation than the main drill bit, possibly improving core recovery. The XCB cutting shoe typically 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 (Figure F2B). Shorter XCB cutting shoes can be used as well.

The joint bottom-hole assembly (BHA) used for APC and XCB coring is typically composed of an 11.4375 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 8.25 inch (20.96 cm) control-length drill collars, a tapered drill

<figure><img src="image_8.png" /><figcaption>**Figure F2 (continued).**</figcaption></figure>

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collar, two stands of 5.5 inch (13.97 cm) transition drill pipe, and a crossover sub to the drill pipe that extends to the surface (Figure F3).

The RCB system is a rotary system designed to recover sedimentary rocks and crystalline basement, such as igneous rocks. Its BHA, including the bit and outer core barrel, is rotated with the drill string while bearings allow the inner core barrel to remain stationary (Figure F2C).

A typical RCB BHA consists of, from bottom to top, a coring bit (typically 9.875 inch in diameter), a bit sub, an outer core barrel, a modified top sub, a modified head sub, a variable number of 8.25 inch control-length drill collars, one tapered drill collar, two stands of 5.5 inch drill pipe, and a crossover sub to the drill pipe that extends to the surface (Figure F3). Cores collected with the RCB system are denoted by the letter “R” (for rotary) and have a nominal diameter of 5.87 cm.

The recovery rate for each core was derived from the total length of a core recovered divided by the length of the cored interval (see **Curatorial core procedures and sampling depth calculations**). In soft sediments, recovery rates are typically ~100%, unless unconsolidated granular (e.g., loose sand) formation is cored (as happened at Site U1551). In firm sediments and igneous rocks, recovery rates are <100%, with the XCB system usually ranging from 50% to 90% and the RCB system generally ranging from 20% to 60% (rarely up to 80%).

Nonmagnetic core barrels were used for all APC, HLAPC, and RCB deployments during Expedition 385. APC cores were oriented with the Icefield MI-5 core orientation tool upon request when coring conditions allowed. Numerous in situ formation temperature measurements were taken with the advanced piston corer temperature (APCT-3) and sediment temperature (SET2) tools (see **Petrophysics**). Additionally, there was one single deployment of the Elevated Temperature

<figure><img src="image_10.png" /><figcaption>**Figure F3.** Schematic of the APC/XCB and RCB bottom-hole assemblies. ID = inside diameter. 1 inch = 2.54 cm. Modified from Graber et al. (2002).</figcaption></figure>
Borehole Sensor (ETBS) (upon completion of drilling in Hole U1547D). We deployed the two routine downhole logging tool strings, the triple combination (triple combo) and the Formation MicroScanner (FMS)-sonic tool suites, at two sites. Furthermore, we sampled borehole fluid by deploying the Kuster Flow Through Sampler (Kuster FTS) tool in several holes. Detailed information on recovered cores, drilled intervals, downhole tool deployments, and related information are provided in the Operations, Paleomagnetism, and Petrophysics sections of each site chapter.

**1.3. IODP depth conventions**

The primary depth scales used are defined by the length of the drill string deployed (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 core composite depth below seafloor [CCSF]), and the length of logging wireline deployed (e.g., wireline log depth below rig floor [WRF] and wireline log depth below seafloor [WSF]) (see IODP Depth Scales Terminology at http://www.iodp.org/policies-and-guidelines/142-iodp-depth-scales-terminology-april-2011/file). 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) scale. All units are always expressed in meters. The relationship between scales is defined either by protocol, such as the rules for computation of CSF depth from DSF depth, 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.

Depths of cored intervals are measured from the drill floor based on the length of drill pipe deployed beneath the rig floor (DRF scale). The depth of the cored interval is referenced to the seafloor (DSF scale; Figure F1) by subtracting the seafloor depth of the hole (i.e., water depth) from the DRF depth of the interval. Standard depths of cores in meters below seafloor (CSF-A scale) are determined based on the assumption that (1) the top depth of a recovered core corresponds to the top depth of its cored interval (on the DSF scale) and (2) the recovered material is a contiguous section even if core segments are separated by voids when recovered. Standard depths of samples and associated measurements (CSF-A scale) are calculated by adding the offset of the sample or measurement from the top of its section and the lengths of all higher sections in the core to the top depth of the core.

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. In addition, voids in the core are closed by pushing core segments together, if possible, during core handling. Therefore, the true depth interval within the cored interval is unknown. This result should be considered a sampling uncertainty in age-depth analysis or in correlation of core data with downhole logging data.

When core recovery is >100% (the length of the recovered core exceeds that of the cored interval), the CSF depth of a sample or measurement taken from the bottom of a core will be deeper than that of a sample or measurement taken from the top of the subsequent core (i.e., the data associated with the two core intervals overlap on the CSF-A scale). This overlap can happen when a soft to semi-soft sediment core recovered from a few hundred meters below the seafloor expands upon recovery (typically by a few percent to as much as 15%). Therefore, a stratigraphic interval may not have the same nominal depth on the DSF and CSF scales in the same hole.

During Expedition 385, all core depths below seafloor were initially calculated according to the CSF-A depth scale. Unless otherwise noted, all depths presented are calculated on the CSF-A scale and reported as meters below seafloor (mbsf).

**1.4. Curatorial core procedures and sampling depth calculations**

Numbering of sites, holes, cores, and samples follows standard IODP procedures. 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 (for cores/sections of igneous/metamorphic rocks only), and interval in centimeters measured from the top of the core section. For example, a sample identification of "385-U1545A-5H-2W, 23-25 cm" indicates a 2 cm long sample taken from the interval between 23 and 25 cm below the top of Section 2 (working half) of Core 5 ("H"
designates that this core was taken with the APC system) of Hole A at Site U1545 (Figure F1). The "U" preceding the hole number indicates the hole was drilled by a US platform (i.e., *JOIDES Resolution*). The coring system used to obtain a core is designated in the sample identifiers as follows: H = APC, F = HLAPC, R = RCB, and X = XCB. Integers are used to denote the "core" type of drilled intervals (e.g., a drilled interval before Core 2R would be denoted by Core 11 [i.e., "Core 1" and "Type 1"]).

**2. Core handling and analysis**

**2.1. Sediment**

When the core barrel reached the rig floor, the core catcher from the bottom of the core barrel was removed and a sample was extracted for paleontological (PAL) analysis. Next, the sediment core was extracted from the core barrel in its plastic liner. The liner was carried from the rig floor to the core processing area on the core receiving platform outside the core laboratory, where it was split into ~1.5 m sections. Blue (uphole direction) and clear (downhole direction) liner end caps were glued with acetone onto the cut liner sections. Prior to cutting the whole-round sections of sediment cores, the length of gas expansion-derived voids was measured when observed and void gas samples were taken (see **Organic geochemistry**).

Once the core was cut into sections, whole-round samples were taken for interstitial water (IW) chemical analyses. Additional whole-round samples were taken from cores recovered in holes dedicated to extensive personal sampling for microbiology and biogeochemistry studies based on a complex sampling protocol (see **Microbiology**). When a whole-round sample was removed, a yellow liner end cap was used to denote the missing interval. Syringe samples were taken for head-space gas analyses according to the IODP hydrocarbon safety monitoring protocol. Selected whole-round core sections were subjected to IW extraction using Rhizon samplers within minutes of recovery at three different sites (see **Inorganic geochemistry**).

Core sections were placed in a core rack in the core laboratory. When they reached equilibrium with laboratory temperature (typically after 3 h), they were run through the Whole-Round Multi-sensor Logger (WRMSL) for *P*-wave velocity on the *P*-wave logger (PWL), magnetic susceptibility (MS), and gamma ray attenuation (GRA) bulk density (see **Petrophysics**). The core sections were also run through the Natural Gamma Radiation Logger (NGRL) for natural gamma radiation (NGR), and thermal conductivity measurements were made once per core when the material was suitable.

The core sections 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 sediment core was described by the sedimentologists and structural geologists. Discrete samples were then taken for moisture and density (MAD) and paleomagnetic (PMAG) analyses and for remaining shipboard analyses such as X-ray diffraction (XRD), carbonate (CARB), and source rock analyzer (SRA) measurements. Samples were not collected or sampling was restricted when (1) the lithology was a high-priority interval for expedition or postexpedition research (e.g., ash layers, most of sediment/sill contact zone, etc.), (2) there was unsuitable core material, or (3) the core was severely deformed. During the expedition, samples were taken for personal expedition (e.g., in the radiation van) and postexpedition research when studies focused on examining ephemeral properties, such as microbiology and biogeochemistry research.

The archive half of each core was scanned on the Section Half Imaging Logger (SHIL). It was also measured for point magnetic susceptibility (MSP), as well as reflectance spectroscopy and colorimetry (RSC) on the Section Half Multisensor Logger (SHMSL). Occasionally, X-ray images of archive-half sections were taken as well. Labeled foam pieces were used to denote missing whole-round (WR) intervals in the SHIL images. The archive-half sections were then described visually and by means of smear slides for sedimentology. Finally, magnetization of archive-half sections
and working-half discrete pieces was measured with the cryogenic magnetometer and spinner magnetometer.

## 2.2. Igneous rock

Pieces were extracted from the core liner on the core receiving platform or directly from the core barrel on the rig floor and subsequently put into split plastic liners in consecutive order. The pieces were then pushed to the bottom of the 1.5 m liner sections, and the total rock length was measured. The length was entered into the database using the SampleMaster application as “recovered length.” This number was used to calculate recovery. The liner sections were then transferred to the core splitting room. If a core catcher sample was present, it was taken to the core splitting room separately and added to the bottom section of the recovered core.

In drilled depth intervals dedicated to microbiology sampling in sill intrusions, selected whole-round igneous rock pieces or sections were taken from certain cores for further microbiology sub-sampling according to an established sampling plan. Only the necessary five scientists (petrologist, structural geologist, and microbiologists on shift) and an assigned representative of the Sample Allocation Committee (SAC), wearing face masks and nitrile gloves, were present in the core splitting room for microbiology sampling to minimize contamination, and the samples/sections were immediately transferred to the microbiology laboratory for further processing (see Microbiology).

Oriented pieces of core were marked on the bottom with a blue- or red-colored wax pencil to preserve orientation. Adjacent but broken pieces that could be fit together along fractures were curated as single pieces. The petrologists and structural geologists confirmed piece matches and marked the split line on the pieces and denoted the working half with the letter “W,” 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 lithologic and mineralogic features in both archive and working halves. Any present dipping structures were then measured on the whole-round core pieces by the structural geologist on shift (see Structural geology). 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 core receiving platform. Ultimately, the eventual depth of each piece in the database was recalculated based on the curated length.

Core pieces were imaged around the full 360° circumference (at four different angles of 000°, 090°, 180°, and 270°) using the SHIL configured for whole-round sections and then placed in a core rack in the laboratory. When the core sections reached equilibrium with laboratory temperature (typically after 2 h), the whole-round core sections were run through the WRMSL (GRA and MS only) and NGRL (see Petrophysics).

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 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 oriented character of each piece was recorded in the database using the SampleMaster application.

The archive half of each core was scanned on the SHIL (with both a dry and wet surface) and measured for MSP and RSC on the SHMSL. Thermal conductivity measurements were made on selected archive-half pieces (see Petrophysics). After the archive-half sections of each core were fully described by the petrologist and structural geologist on shift, samples were taken from the working-half sections for shipboard analyses (billets for thin sections; chips for inductively coupled plasma-atomic emission spectroscopy [ICP-AES]; and cube samples (~8 cm³) for paleomagnetism analyses, MAD, and discrete P-wave velocity measurements; see Igneous petrology and alteration, Inorganic geochemistry, Paleomagnetism, Petrophysics). The magnetizations
of archive-half sections and pieces, as well as discrete cube samples taken from the working-half sections, were measured with the cryogenic magnetometer and spinner magnetometer, respectively (see **Paleomagnetism**).

When all laboratory processing 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 sent to the IODP Gulf Coast Repository (Texas A&M University, College Station, Texas [USA]), where personal nonephemeral samples for postexpedition research were taken and the cores are permanently stored.

**2.3. Handling drilling and core disturbance**

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” material. 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/HLAPC 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 by drilling holes into the plastic liner before the cores are cut into segments. These holes force some sediment as well as gas out of the liner. Such observed disturbances are described in each site chapter and graphically indicated on the visual core descriptions (VCDs).

**3. Lithostratigraphy**

Descriptions of sediment cores recovered during Expedition 385 are based on a combination of digital color imagery, visual core description (e.g., visual color determination of core disturbance, sediment structures, and color using a Munsell chart), microscopy, and various X-ray techniques. Lithologies were determined by (1) macroscopic description of the archive halves of split cores and/or (2) microscopic assessment of smear slides and thin sections using a petrographic microscope. All of these observations were saved to the LIMS database through data capture by the in-house core description software DESClogik. Additional X-ray techniques that were used to assist core material description and determination include X-ray imagery and XRD. A selection of data sets was combined to inform a VCD sheet for each core.

The methods employed are adapted from those used during Integrated Ocean Drilling Program Expedition 323 (Expedition 323 Scientists, 2011). The timescale used for Expedition 385 is that of Gradstein et al. (2012) and updated to the latest division of the formal series for the Pliocene and Pleistocene (version 2019/05 of the International Chronostratigraphic Chart available at http://www.stratigraphy.org). Note that because of both the drilling technique used to retrieve the cores (i.e., missing mudline) and/or possible hiatuses in the uppermost and most recent part of the sedimentary record (e.g., Barron et al., 2005), the first core collected in each hole at all sites could be missing the Holocene strata.

**3.1. Digital color image and core description sheets**

The SHIL captures an image of the flat face of the archive half of the split cores using a line-scan camera. Sediment cores are split, and the archive half is scraped with the edge of a glass slide or stainless steel rectangular plate to provide a “clean” surface for imaging. Note that this approach occasionally resulted in faint linear scratches on the flat surface of the archive half that made scrape markings appear on some core section images. The cleaned, flat face of the archive half was imaged as soon as possible after splitting and surface scraping to minimize color changes that may occur through oxidation and drying. Images were taken at an interval of 10 lines/mm. Camera height was adjusted so that image pixels are square. Light is provided by three pairs of Advanced Illumination high-current focused LED line lights with fully adjustable angles to the lens axis. We noted that compression of line-scanned images into compiled stacks (like the core image shown in
the VCDs) may result in visual artifacts (e.g., the false appearance of lamination). The stacked images were integrated into core description sheets that were printed before making observations to facilitate the implementation of core description through handwritten notes (Figure F4). These sheets contain field notes used to help organize whole-core observations prior to itemized entry into the DESClogik software, ensuring consistency between core describers and preserving information needed for later shore-based sampling in a format used in sedimentological studies.

**3.1.1. Visual color determination and spectrophotometry**

Descriptions of sediment color and the corresponding hue, value, and chroma data were determined qualitatively using Munsell soil color charts for each major and minor lithology (Munsell Color Company, 2000, 2009). Color reflectance spectrophotometry and MSP of the archive-half sections were measured on the SHMSL. Reflectance of visible light from the archive halves of sed-

<figure><img src="image_11.png" /><figcaption>**Figure F4.** Example of a manual, analog core description sheet, Expedition 385. The form was generated once the core section was scanned, and a core image was inserted into this template. Other columns include Drilling disturbance, Color, Sedimentary structures (and bedding features), Bioturbation, and Samples. Lithology is described in the comments section.</figcaption></figure>
iment cores was measured using an Ocean Optics USB4000 spectrophotometer mounted on the automated SHMSL. Additional detailed information about measurement and interpretation of spectral data and MSP can be found in **Petrophysics**, Balsam et al. (1997, 1998), and Balsam and Damuth (2000). The Munsell color data were added to the core description sheet and the VCDs (see **Visual core description summaries**).

### 3.1.2. Sedimentary structures

Sedimentary structures, bedding planes, and diagenetic features formed by natural processes (i.e., not as a result of drilling disturbance) were noted on the core description sheets (Figure F4) and are also represented on the VCDs with symbols in the Sedimentary structures column (Figure F5). Structures formed by both biogenic and physical processes are included.

<table><caption>**Figure F5.** Symbols used for sedimentary facies and structures, Expedition 385.</caption><thead><tr><th colspan="3">Main lithology</th><th colspan="5">Prefix lithology</th></tr></thead><tbody><tr><td>Diatom clay/clayey silt</td><td>Micrite</td><td>Clayey silt/Clay siltstone/ Silty clay</td><td>Micrite-rich</td><td>Clay</td><td>Chert</td><td></td><td></td></tr><tr><td>Diatom ooze</td><td></td><td></td><td></td><td>Sand/Sandstone</td><td>Ash(tuff)</td><td></td><td></td></tr><tr><td>Diatom micrite</td><td></td><td></td><td></td><td>Sandy clay</td><td>Gravel/conglomerate</td><td></td><td></td></tr><tr><td>Calcareous and biosiliceous ooze</td><td></td><td></td><td></td><td>Silty sand/Sandy silt</td><td>Breccia</td><td></td><td></td></tr><tr><td>Nannofossil clay</td><td></td><td></td><td></td><td>Silt</td><td>Igneous lithology</td><td></td><td></td></tr><tr><td>Dolomite</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Limestone</td><td></td><td></td><td></td><td>Siliceous claystone</td><td>WRND</td><td>Whole-round sample</td><td></td></tr><tr><th colspan="3">Drilling disturbance</th><th colspan="2">Sedimentary structures</th><th colspan="3">Boundary or contact</th></tr><tr><td>Biscuit</td><td>Punctured</td><td></td><td>Fining upward</td><td></td><td>Faulted contact</td><td></td><td></td></tr><tr><td>Cracked</td><td>Slurry</td><td></td><td>Lamination</td><td></td><td>Gradational boundary</td><td></td><td></td></tr><tr><td>Fall-in</td><td>Soupy</td><td></td><td>Mottling</td><td></td><td>Inclined boundary</td><td></td><td></td></tr><tr><td>Flow-in</td><td>Suck-in</td><td></td><td>Normal grading</td><td></td><td>Scoured contact</td><td></td><td></td></tr><tr><td>Fractured</td><td>Up-arching</td><td></td><td>Parallel lamination</td><td></td><td>Sharp boundary</td><td></td><td></td></tr><tr><td>Gas expansion</td><td>Void</td><td></td><td>Tilted bedding</td><td></td><td>Undulating or wavy boundary</td><td></td><td></td></tr><tr><td>Mousselike</td><td>Brecciated</td><td></td><td>Shell fragments</td><td></td><td></td><td></td><td></td></tr><tr><th colspan="3">Diagenetic</th><th colspan="2">Bioturbation</th><th colspan="3">Deformation structures</th></tr><tr><td>Carbonate concretion</td><td>Chondrites</td><td></td><td>Composite vein</td><td></td><td>Normal fault</td><td></td><td></td></tr><tr><td>Chert nodule</td><td>Open burrow</td><td></td><td>Uniform vein</td><td></td><td>Reverse fault</td><td></td><td></td></tr><tr><td>Concretion</td><td>Burrow</td><td></td><td>En echelon vein</td><td></td><td>Sharp bedding</td><td></td><td></td></tr><tr><td>Phosphatic nodule</td><td></td><td></td><td>Microfracture</td><td></td><td>Tilted bedding</td><td></td><td></td></tr><tr><td>Pyrite (disseminated)</td><td></td><td></td><td>Open fracture</td><td></td><td>Planar bedded</td><td></td><td></td></tr><tr><td></td><td></td><td></td><td>Joint fracture</td><td></td><td>Chevron fold</td><td></td><td></td></tr><tr><td></td><td></td><td></td><td>Sediment dike</td><td></td><td>Concentric fold</td><td></td><td></td></tr><tr><th colspan="9">Shipboard samples</th></tr><tr><td>CARB</td><td>Carbonate</td><td>ICP</td><td>Inductively coupled plasma</td><td>PAL</td><td>Micropaleontology</td><td>SED</td><td>Smear slide</td></tr><tr><td>DIAT</td><td>Diatom</td><td>IW</td><td>Interstitial water</td><td>PFT</td><td>Perfluorocarbon tracer</td><td>TS/TSB</td><td>Thin section</td></tr><tr><td>FORAM</td><td>Foraminifer</td><td>MAD</td><td>Moisture/Density</td><td>PMAG</td><td>Paleomagnetism</td><td>VAC</td><td>Vacutainer</td></tr><tr><td>HS</td><td>Headspace</td><td>MBIO/RMS</td><td>Microbiology</td><td>RADS</td><td>Radiolarians</td><td>XRD</td><td>X-ray diffraction</td></tr><tr><td>HYD</td><td>Gas hydrates</td><td>NANNO</td><td>Nannofossil</td><td>RHIZON</td><td>High resolution IW</td><td></td><td></td></tr></tbody></table>
Bed thickness in the core was defined according to McKee and Weir (1953):

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.

**3.1.3. Sediment diagenesis, hydrothermal alteration, and contact metamorphism**

The recovered sedimentary units have undergone various stages of postburial modification over a vast temperature range, spanning the realms of bottom seawater temperature at the seafloor (~4°C), burial diagenesis (<200°C), and hydrothermal alteration and thermal metamorphism resulting from heating and dewatering of sediments in contact with sill intrusions, which are abundant in the Expedition 385 study area. Temperatures of 200°–800°C can be expected in the contact aureoles of major sill intrusions in sedimentary basins (Aarnes et al., 2010, and references therein). Low-temperature alteration (diagenetic) features were documented through descriptions of degree of lithification, cementation, new mineral growth in pore spaces, and formation of concretions. Intervals of contact metamorphism or hydrothermal overprint were noted but not described in detail because of time and analytical constraints. The initial mineral identification and degree of alteration estimates were later refined by incorporating the results from thin section descriptions (using both transmitted and reflected light modes), scanning electron microscope (SEM) images, and XRD analyses.

**3.1.4. Drilling disturbance**

Sediment disturbance resulting from the coring process was recorded in the VCDs.

Types of drilling disturbances observed in soft and firm sediments include the following:

* Biscuits: sediment of intermediate stiffness that has vertical variations in the degree of disturbance. Softer intervals are washed and/or soupy, whereas firmer intervals are relatively undisturbed (this type of disturbance is considered moderate-high).

* Brecciated: sediment is broken up in a chaotic framework of pieces produced by the coring process.

* Cracked: firm sediments are broken during drilling but not displaced or rotated significantly.

* Fall-in: out-of-place material that has fallen downhole onto the cored surface after core barrel retrieval. This material is recovered in the top of the following core.

* Flow-in: out-of-place material is displaced along the sides of a core, often with a streaky appearance.

* Gas expansion: expansion of gas disrupts the stratigraphic sequence. It is described as slight if it does not disrupt the stratigraphic sequence or moderate-severe if the sequence is partially or completely disrupted, respectively.

* Punctured: sediment is displaced from puncturing the core liner.

* Soupy: water-rich sediments are liquefied to some degree.

* Suck-in: sediment is introduced (sucked in) at the bottom of the core barrel due to motion when drilling.

* Void: empty space occurs within the cored material. These may be products of gas expansion during core retrieval, partial strokes during the coring process, or partial recovery.

Additional types of drilling disturbance in more lithified sections include fracture and drilling breccia. Drilling disturbance is also displayed on the VCDs (e.g., fall-in, flow-in, void, and soupy).

**3.2. Sediment classification**

Sedimentary materials recovered during Expedition 385 are largely composed of biogenic sediments mixed with a minor siliciclastic component. Occasionally, pyroclastic deposits of ash to lapilli grain size occur.
Our approach for sediment classification consists of two parts: a principal name (e.g., silt or ooze) and a prefix (e.g., foraminifer-rich). The principal name applied to a sediment is determined by the component or group of components making up >60% of the sediment, and, in case of the main lithology being siliciclastic, the main particle size according to the Udden-Wentworth scale (Wentworth, 1922; Figure F6). For example, sediment composed of 70% silt-sized siliciclastic material and 30% foraminifers is classified as foraminifer-rich silt. When the biogenic components make up more than 60%, the principal name of the sediment contains the word ooze. For instance, a sediment composed of 20% clay, 40% foraminifers, and 40% diatoms is called clay-rich foraminifer and diatom ooze. Prefixes such as clay-rich or clay-bearing are used for components ranging from 5% to 40% of the sediment, as defined below. The naming scheme for sediments with subequal mixtures of biogenic and siliciclastic and/or volcanogenic material is described below (see *Mixed sediments*). Visual percentage estimates and textural attributes of biogenic and non-biogenic components are made from smear slides (see *Smear slide and thin section description*) (Figure F7) or macroscopic observation of the core with a hand lens.

### 3.2.1. Siliciclastic and volcaniclastic sediments

If total siliciclastic content is >60%, the principal name is determined by the texture of the siliciclastic grains (i.e., the relative proportions of sand-, silt-, and clay-grade components when plotted on a modified Shepard [1954] ternary classification diagram) (Figure F8A). The siliciclastic principal names are clay (<4 µm), silt (4–63 µm), sand (63–2000 µm), and combinations of the three end-members using a modifier (e.g., silty clay, sandy clay, clayey silt, sandy silt, clayey sand, and silty sand). Siliciclastic particles include terrigenous epiclasts produced by erosion of onshore volcanic units. If a sediment is entirely composed of pyroclastic particles (e.g., vitric/glass shards, pumice, or mineral fragments) and exhibits no evidence of reworking, then it is identified as unconsolidated tephra (e.g., ash or lapilli) or lithified/consolidated tephra (e.g., tuff or lapillistone) using the descriptive terminology of Fisher and Schmincke (1984).

### 3.2.2. Mixed sediments

Mixed sediments include sediment in which no single type of sedimentary component, either siliciclastic, biogenic, or pyroclastic, is dominant (i.e., >60%). If siliciclastic grains compose 40%–60% of the sediment, the principal name is determined by the texture/main particle size of the siliciclastic grains. For example, the principal name of a sample containing 10% ash, 40% diatoms, and 50% siliciclastic grains that are >75% silt sized is diatom silt. If the abundances of diatoms and siliciclastic grains are reversed (i.e., 50% diatoms and 40% siliciclastic grains), the principal name is still diatom silt, as neither composes >60% of the sediment.

<table><caption>**Figure F6.** Grain size of terrigenous and volcanic particles (Wentworth, 1922). We use the 4 µm cut-off for clay-sized material and define the term “mud” as a mixture of silt and clay.</caption><thead><tr><th></th><th>Millimeters (mm)</th><th>Micrometers (µm)</th><th>Phi (φ)</th><th>Wentworth size class</th></tr></thead><tbody><tr><td></td><td>4096</td><td></td><td>-12.0</td><td>Boulder</td></tr><tr><td></td><td>256</td><td>- - - - - -</td><td>-8.0</td><td>Cobble</td></tr><tr><td></td><td>64</td><td>- - - - - -</td><td>-6.0</td><td>Pebble</td></tr><tr><td></td><td>4</td><td>- - - - - -</td><td>-2.0</td><td>Granule</td></tr><tr><td></td><td>2.00</td><td></td><td>-1.0</td><td>Gravel</td></tr><tr><td></td><td>1.00</td><td>- - - - - -</td><td>0.0</td><td>Very coarse sand</td></tr><tr><td>1/2</td><td>0.50</td><td>- - - 500</td><td>1.0</td><td>Coarse sand</td></tr><tr><td>1/4</td><td>0.25</td><td>- - - 250</td><td>2.0</td><td>Medium sand</td></tr><tr><td>1/8</td><td>0.125</td><td>- - - 125</td><td>3.0</td><td>Fine sand</td></tr><tr><td>1/16</td><td>0.0625</td><td>63</td><td>4.0</td><td>Very fine sand</td></tr><tr><td>1/32</td><td>0.031</td><td>- - - 31</td><td>5.0</td><td>Coarse silt</td></tr><tr><td>1/64</td><td>0.0156</td><td>- - - 15.6</td><td>6.0</td><td>Medium silt</td></tr><tr><td>1/128</td><td>0.0078</td><td>- - - 7.8</td><td>7.0</td><td>Fine silt</td></tr><tr><td>1/256</td><td>0.0039</td><td>3.9</td><td>8.0</td><td>Very fine silt</td></tr><tr><td></td><td>0.00006</td><td>0.06</td><td>14.0</td><td>Clay</td></tr></tbody></table>
to classify the sediment during smear slide description (see **Smear slide and thin section description**), it was not used in the lithologic representation of the cores included in the VCDs.
This choice was made to reduce the number of lithologic patterns, thus making the VCDs more readable.

### 3.2.4. Lithification

Sediments that range from unconsolidated to variably indurated have the suffix “-stone” added to the principal names sand, silt, and clay when a spatula and mallet, hammer and chisel, or saw was needed to take samples from the working half of the split core. For other biogenic-dominated lithologies, a different term was used (e.g., limestone) when they reached that level of induration.

Induration is separated into four classes:

* Soupy: water-saturated sediment with very little strength.

* Soft: sediment with little strength that is readily deformed under the pressure of a finger or broad-blade spatula.

* Stiff: partly lithified sediment that is readily scratched with a fingernail or edge of a spatula.

* Hard: well-lithified, compacted, and/or cemented sediment that is resistant or impossible to scratch with a fingernail or edge of a spatula or core that must be cut with a band saw or diamond saw.

## 3.3. Smear slide and thin section description

One or more smear slide samples of the main lithologies were collected from the archive half of most Hole A sediment cores to define the lithologies. These were used as guides for assigning

<figure><img src="image_12.png" /><figcaption>**Figure F8.** Lithologic classification, Expedition 385. A. Classification of siliciclastic sediments according to Shepard (1954). B. Modifiers used for secondary sedimentary components (the displayed example represents biogenic and siliciclastic components).</figcaption></figure>
lithologies in other nearby (in most cases ~20 m) holes at a given drill site owing to time con-
straints posed by high recovery rates. Additional samples were locally collected to characterize
small-scale lithologic variations across laminations and tephra layers. A small amount of sediment
was taken by toothpick from the cores and dispersed evenly in deionized water on a 2.5 cm × 7.5
cm glass slide to create a very thin (less than ~50 µm) uniform layer of sediment grains for quanti-
fication. The dispersed sample was then dried on a hot plate. A drop of mounting medium (Nor-
land optical adhesive Number 61) and a cover glass were added. The slide was then placed in an
ultraviolet light box for 10–15 min to cure.

Smear slides were examined through a Zeiss transmitted-light binocular petrographic microscope (AXIO10207) equipped with a standard eyepiece micrometer and photographed with an attached SPOT Insight camera built by Diagnostic Instruments, Inc. Visual percentage estimates of biogenic, nonbiogenic, and textural features were made from each slide using a 40× objective. Biogenic and mineral component percentage abundances were visually estimated following Rothwell (1989) (Figure F9). Clay-sized (3–4 µm) particles are visible at higher magnifications (40×), but clay minerals are often not visible as single particles using a petrographic microscope given their fine-grained nature (≤2 µm); the latter were identified based on the presence of cloudiness and slight pleochroism in plane-polarized light often accompanied by diffuse birefringence in cross-polarized light (Rothwell, 1989). Grain size distributions of the coarser silt (4–63 µm) and sand (63–2000 µm) siliciclastic fractions were estimated using an eyepiece micrometer calibrated by means of a stage micrometer (microscope slide with an inscribed micrometer scale). The texture/main particle size of siliciclastic grains (i.e., relative abundance of sand-, silt-, and clay-sized grains) and the proportions and presence of biogenic and mineral components were recorded on a smear slide sample sheet (Figure F7), and data were entered into DESClogik. It should be noted that because sand-sized and larger grains are difficult to incorporate into a smear slide, such

<figure><img src="image_13.png" /><figcaption>**Figure F9.** Standard visual composition chart for estimating relative percentages of sedimentary components (Rothwell, 1989).</figcaption></figure>
petrographic analyses may underestimate their abundance and estimates are best made macroscopically using a hand lens.

Thin sections of lithified core material were made to enable a more accurate definition of lithologies. These were ground to a thickness of 30 µm and polished for examination using the petrographic microscope described above. Observations include the nature of components and their relative proportions, including grain types, porosity, and cementation. They were tallied on a thin section description sheet similar to that used for smear slides and data were entered into DESClogik.

**3.4. Visual core description summaries**

Core description was initially carried out visually, and observations were logged on paper forms (Figure F4) based on figure 7 in Mazzullo et al. (1988). Reporting included notes and observations, drawings of sedimentary structures, Munsell colors, and the location of samples collected for smear slides, thin sections, and XRD. The handwritten notes were then transferred into DESClogik, from which VCDs were created.

VCDs of the archive half of the split cores provide a summary of the lithologic composition, age (based on biostratigraphy and magnetostratigraphy), and physical properties data obtained from shipboard analyses (Figure F10). IODP VCDs are equivalent to the barrel sheets used during the Deep Sea Drilling Project (DSDP), Ocean Drilling Program (ODP), and, partially, the Integrated Ocean Drilling Program. Lithologic data for VCDs were digitally recorded shipboard using the customized core description software DESClogik (version 16.1.0.22), which generates a spreadsheet for data entry, providing extensive data validation support. Prior to drilling operations, a

<figure><img src="image_14.png" /><figcaption>**Figure F10.** Example visual core description (VCD) form, Expedition 385. This VCD sheet was used to summarize data from core imaging, macroscopic description (including lithology, sedimentary structures, major disturbances), and physical properties measurements.</figcaption></figure>
spreadsheet template with specific tabs was constructed in Tabular Data Capture mode and cus-
tomized for Expedition 385. Spreadsheet tabs were used to record the following information:

* Drilling disturbance,

* General (lithologic core description and sedimentary structures),

* Core summary (written description of major lithologic findings by core, sedimentary struc-
tures, lithostratigraphic unit, and age), and

* Hole summary (lithostratigraphic unit and age).

To aid core description, core data are displayed graphically in LIMS Information Viewer (LIVE,
version 4.0), a separate browser-based application that displays core images alongside physical
properties and geochemical data. The commercial plotting software Strater was deployed by JRSO
personnel to compile the digital VCDs for each core using the data retrieved from the LIMS data-
base or DESClogik. Site, hole, core number, and depth intervals in core depth below seafloor,
Method A (CSF-A), are given at the top of the VCD together with a summary core description.
The written description for each core contains a succinct overview of major lithologies, their
Munsell colors, and notable features such as sedimentary structures, boundary contacts, dia-
genetic features (e.g., authigenic precipitates), extent of lithification, and major disturbances re-
sulting from the coring process (Figure F10). Core depth below seafloor (recorded on the CSF-A
scale in meters; represented in text, tables, and figures on the equivalent mbsf scale), core length
(in centimeters), section breaks, lithostratigraphic unit, and age are indicated along the left side of
the digital color image of the core. The two columns between the color image and the graphic
lithology columns show the locations of shipboard samples. Columns to the right of the graphic
lithology column show drilling disturbance, extent of bioturbation, lithologic accessories, sedi-
mentary structures, and physical properties data collected using the WRMSL and SHMSL (see
Petrophysics). Data collected include NGR, GRA bulk density, MS, lightness (L*), and color re-
flectance (a* and b*). Symbols used in the VCDs are given in Figure F5.

**3.5. Lithostratigraphic units**

Lithostratigraphic units are stratigraphic intervals (between tens and hundreds of meters thick) containing similar sediment or rock types. They are numbered sequentially (Unit I, Unit II, etc.) from top to bottom of the cored interval. Lithostratigraphic units are clearly distinguishable from each other by several characteristics such as composition, bed thickness, grain size class, sedimentary structures, and internal homogeneity. Lithostratigraphic units are informal “formations” that are not defined by age, geochemistry, or paleontology, although changes in these parameters may coincide with boundaries between lithostratigraphic units. When downhole changes in the lithologic characteristics of sediments are distinctive but not significant enough to require a unit division, more informal subunit designators (Subunit IA, Subunit IB, etc.) are used. This occurred at several Expedition 385 sites where only one unit but several subunits were designated when using diagenetic boundaries.

**3.6. X-ray imaging**

X-radiograph images were produced at all sites to evaluate bioturbation intensity, drilling distur-
bance, sedimentary structures, and clast abundance. Images were obtained from archive-half sec-
tions after splitting. The onboard X-Ray Imager (XRI) is composed of a Teledyne ICM CP120B
portable X-ray generator and a detector unit. The generator works with a maximum voltage of 120
kV and a tube current of 1 A and has a 0.8 mm x 0.5 mm focal spot. The generator produces a
directional cone at a beam angle of 50° x 50°. The detector unit is located 65 cm from the source
and consists of a Go-Scan 1510 H system composed of an array of CMOS sensors arranged to offer
an active area of 102 mm x 153 mm and a resolution of 99 µm. Core sections were run through the
imaging area at 12 cm intervals, providing 15 cm images onto the detector and allowing overlap of
3 cm. The X-ray source and detector are housed in the source shield constructed with 6 mm of
lead with an internal baffle on the unload side. The exterior corners are covered with 6 mm lead
strips and lead vinyl (0.5 mm) overspreading the sides. The GRA-MS shield section is constructed
with 2 mm of lead with an internal baffle on the load side, and both the load and unload ends of the
track are shielded by lead vinyl (0.5 mm).
During Expedition 385, tests were conducted on archive halves to obtain the best image resolution for determining the internal structure of cores. The XRI settings were then tailored to the varying lithologies of the cores. The number of images stacked was 20, taken at exposure times of 300–400 ms. The voltage ranged between 60 and 70 kV, and the current varied between 0.7 and 1.0 A.

The raw images were collected as 16 bit images and processed with the IODP in-house processing utility in the Integrated Measurement System (IMS) software (version 1.2). The software applies gain and offset corrections for the detector, compensates for core shape and thickness, and adjusts the image contrast. The Savitzky-Golay finite impulse response (FIR) filter was chosen to smooth images. The resulting processed images include a masked background, the depth scale within the section, and the acquisition parameters. X-ray images taken during Expedition 385 can be retrieved from the Zenodo database (https://zenodo.org; search the International Ocean Discovery Program community for Expedition 385 data).

**3.7. Scanning electron microscopy and X-ray diffraction analysis**

SEM imaging of the bulk sediment and lithologic accessories (i.e., concretions) was performed to confirm smear slide identification of major, minor, and trace lithologic components using a Hitachi TM3000 tabletop SEM. The sample was mounted on a stub and secured on an exchange rod inside a vacuum chamber. If image quality was low, the sample was sputter coated with an ultra-thin coating of gold-palladium. Sputter coating reduces sample charging and improves emission of secondary electrons, which enhances the signal-to-noise ratio.

Bulk sample XRD analyses were performed to assess lithologic components using two instruments: a Bruker D4 Endeavor X-ray diffractometer with a Vantec detector and an AERIS Malvern PANalytical with a PIXcel1D-Medipix3 detector, both using Ni-filtered CuKα radiation. The number of XRD analyses depended on the degree of lithologic complexity in various parts of the core. Generally, we analyzed approximately 5–10 samples per site to assess the mineralogy of the bulk sediment and lithologic accessories. Samples were freeze-dried, ground in a metal ball mill, and top-mounted onto a sample holder prior to analysis. The instrument settings used were

* Voltage = 40 kV.

* Current = 40 mA.

* Goniometer scan = 2°–70°2θ (freeze-dried bulk samples).

* Step size = 0.01°2θ.

* Scan speed = 1.2°2θ/min.

* Count time = 0.5 s.

The samples analyzed for clay minerals were prepared as follows:

1. ~2 g of the sample was placed in a 50 mL centrifuge tube with 10% acetic acid, sonicated for 15 min, and allowed to stand overnight to remove organic carbon and carbonates.

2. After centrifuging for 15 min at 1500 rpm, the acetic acid was decanted, 25 mL of distilled water was added, the sample was centrifuged again, and the water was decanted.

3. The washing procedure in Step 2 was repeated two more times to remove both the acid and salts from the sample.

4. After decanting the final wash, 25 mL of borate solution was added to the sample in a 50 mL beaker.

5. The sample was placed in an ultrasonic bath for 5 min to suspend the clays by ultrasonic disaggregation and then centrifuged for 5 min at 1000 rpm to settle the >2 µm particles.

6. The clays that remained in suspension were removed from the top ~1 cm of the centrifuge tube and pipetted onto three amorphous quartz sample discs.

7. The sample discs were then left to air dry in a desiccator.

8. After drying, the first disc was analyzed, the second disc was solvated with ethylene glycol for ~8 h at 65°C and reanalyzed to determine the presence of expandable clays, and the third disc was baked in the oven at 400°C and 550°C for at least 30 min.
Diffractograms were interpreted using the EVA (Bruker) software package, which enabled mineral identification, basic peak characterization, and the estimation of the relative abundance of each mineral (e.g., baseline removal and maximum peak intensity).

**3.8. Shipboard sampling**

VCDs (Figure F10) display the interval where sample material was taken for shipboard analysis (whole-round and discrete samples taken to aid core description). Whole-round samples consist of material taken for IW and paleontological analyses (see **Inorganic geochemistry**, **Organic geochemistry**, **Biostratigraphy**, and **Microbiology**). Samples taken to aid core description include toothpick samples for microscopic analyses using both transmitted light and SEM, as well as 5–10 cm² samples for mineralogic XRD analysis, MAD, inorganic and organic carbon, total nitrogen content, and paleomagnetic properties. Typically, one smear slide was prepared and examined per core for Hole A at each site; however, the number of smear slides analyzed was adjusted to the degree of lithologic variability in various parts of the core.

# 4. Igneous petrology and alteration

**4.1. Lithology**

Description procedures used for unaltered and altered igneous rocks of Expedition 385 were adapted from IODP Expeditions 367/368 and 376 (Sun et al., 2018; de Ronde et al., 2019). Data for the macroscopic and microscopic descriptions of recovered cores were entered into the LIMS database by means of the customized DESClogik core description software application. Our shipboard studies sought to systematically describe the physical appearance, petrology, mineralogy, and alteration of the recovered igneous rock material. Phenocryst abundance and appearance, vesicularity, alteration, characteristic igneous textures, and presence/absence of veins were described at a macroscopic level and investigated in more detail through the study of thin sections.

**4.2. Core description work flow**

The procedures applied to description and documentation of the igneous rocks recovered included visual core description, thin section assessment under a petrographic microscope, digital color imagery, color reflectance spectrophotometry, XRD analysis, and ICP-AES (see **Inorganic geochemistry**). Prior to splitting the cores into working- and archive-half sections, each whole-round section was subjected to nondestructive physical properties measurements (see **Petrophys-ics**) and imaged using the SHIL (see **Lithostratigraphy**) on a wet surface at four different angles (0°, 90°, 180°, and 270°). These images were then combined to create a 360° whole-round image for each core section. All cores were processed following the established shipboard procedure for igneous rocks. Accordingly, fragmented pieces of igneous rock were oriented prior to splitting. From those igneous rock sections that were considered for microbiology screening and partial sampling, a photograph of each selected core section and corresponding interval was taken using a high-resolution digital single-lens reflex (DSLR) camera. This step was necessary because the microbiology laboratory group removed some of the whole-round sections before the cores were split (see **Microbiology** for sampling procedure). Also, the image was used to reconstruct the sampled section interval for the leftover material that was returned from subsampling of the microbiology whole-round core pieces. These were generally a few centimeters to ~30 cm in length, depending on the presence and abundance of veins and amygdules. After the microbiology sampling, structural geology measurements were made on the remaining igneous rock sections and/or pieces (see **Structural geology**) and splitting lines were drawn by a petrologist and/or a structural geologist to preserve significant compositional and structural features in both the archive- and working-half sections. The cores were then split using a diamond-impregnated saw along the splitting lines. Afterward, fragmented pieces of igneous rock that fit together were assigned a joint number and labeled with a letter in consecutive order downsection (e.g., 1A, 1B, and 1C). Plastic spacers were mounted to separate pieces with different numbers. An arrow added to the labels of single pieces that showed no evidence of rotation indicates the orientation by pointing to the top of the section. Upon splitting and labeling, the archive-half section was used for macroscopic
investigation and the working-half section was subjected to shipboard sampling as needed. Scanning the cut dry and wet archive-half surfaces using the SHIL produced high-resolution color images. Then, color reflectance and MSP were measured at a step size of 1–2.5 cm on the archive-half section surfaces using the SHMSL (see Lithostratigraphy and Petrophysics). The working halves were sampled for destructive shipboard analyses such as physical properties measurements, paleomagnetic measurements, thin section preparation, XRD analysis, and geochemical analysis by ICP-AES. Most of the samples chosen for XRD and ICP-AES analyses were also from the same piece taken for thin section petrography. The presence of precious metals that could be utilized for postexpedition geochemical analysis was expected in samples recovered during this expedition, so no jewelry was allowed near the core and gloves were used for handling the samples at all times.

All archive-half sections of each core were first macroscopically examined and described for primary (igneous) and secondary (alteration) petrologic characteristics (aided by a 10× magnification field hand lens and a binocular microscope). Lithologic descriptions and most structural observations (see Structural geology) were made on the archive halves. For both macroscopic and microscopic observations, DESClogik was used to record igneous characteristics (e.g., groundmass and phenocryst mineralogy as well as vesicle shape and abundance) and alteration features (e.g., color, vesicle filling, secondary minerals, and vein/fracture fillings).

**4.3. Macroscopic visual core description**

Macroscopic features observed in the cores are summarized and displayed in the VCDs. They illustrate the following entries in terms of igneous, vesicularity, alteration, structural, and physical properties features for each core section (Figure F11):

* Curated CSF-A depth scale (equivalent to mbsf);

* Core section length scale (0–150 cm);

* Number and orientation of hard rock pieces;

* Interval and type of shipboard samples;

* Scanned digital image of the archive half;

* Graphic representation of lithology;

* Symbol “G” (for igneous rocks, next to the graphic lithology), which indicates the presence of volcanic glass either in the glassy rind of chilled margins or in hyaloclastite, if encountered);

* Igneous lithologic unit number;

* Structure;

* Vein type, texture, and connectivity represented by different symbols/patterns;

* Vein dip angle (°);

* Symbol “S” if sediment intermingled with igneous rock is present;

* Column displaying variable patterns of vesicularity (in vol%);

* Stacked line chart displaying phenocryst abundance (in vol%) for plagioclase (PLAG; red line), olivine (OL; green line), and clinopyroxene (CPX; blue line) if present;

* Stacked line chart showing grain size distribution (i.e., variations in crystal size that define different types of texture);

* Stacked line chart depicting present alteration intensity;

* Diagram showing whole-round (WRMSL) and point (SHMSL) MS measurements;

* Plot displaying color reflectance, including total reflectance (L*), red (a*), and blue (b*); and

* Outline of the description of each igneous lithologic (sub)unit and possible lithologic variation within that (sub)unit identified in the corresponding section (see below for details).

The section unit summary (presented on the right side of the VCD) for each igneous lithologic unit contains the following details:

* Expedition, site, hole, core, core type (XCB or RCB), number of archive-half section, and interval (in cm);

* Igneous lithologic unit/subunit number(s);

* Lithology;

* Description of magmatic emplacement type (e.g., sill);
<table><caption>Hole 385-U1547E-21R Section 1, Top of Section: 177.3 m (CSF-A)</caption><thead><tr><th>Depth CSF-A (m)</th><th>Core length (cm)</th><th>Piece number</th><th>Orientation</th><th>Shipboard samples</th><th>Scanned image</th><th>Lithology</th><th>Glass</th><th>Lith. unit</th><th>Structure</th><th>Vein type</th><th>Vein texture</th><th>Vein connectivity</th><th>Dip angle (°)</th><th>Sediment intermingled</th><th>Vesicularity</th><th>Phenocrysts distribution</th><th>Grain size distribution</th><th>Magnetic susceptibility (10<sup>5</sup> Si)</th><th>Reflectance L* (%)</th><th>Description</th></tr></thead><tbody><tr><td>177.3</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>177.4</td><td>10</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>177.5</td><td>20</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

<table><thead><tr><th>Lithology</th><th>Grain size distribution</th><th>Vesicularity</th><th>Vein texture</th></tr></thead><tbody><tr><td>Basaltic rock</td><td>Bimodal</td><td>Highly vesicular</td><td>Polycrystalline</td></tr><tr><td>Brecciated basaltic rock</td><td>Rank 1<br>Inequigranular</td><td>Moderately vesicular</td><td>Slip fiber</td></tr><tr><td>Chert</td><td>Rank 2<br>Equigranular</td><td>Sparsely vesicular</td><td>Massive</td></tr><tr><td>Doleritic rock</td><td>Rank 3<br>Equigranular</td><td>Nonvesicular</td><td>Cross fiber</td></tr><tr><td>Gabbroic rock</td><td></td><td></td><td>Vuggy</td></tr><tr><td>Peperite</td><td></td><td></td><td></td></tr></tbody></table>

<table><thead><tr><th>Vein type</th><th>Vein connectivity</th><th>Structure</th><th>Contact type</th><th></th></tr></thead><tbody><tr><td>Composite vein</td><td>Branched</td><td>/fr Open fracture</td><td>Chilled margin</td><td>S Sediment intermingled</td></tr><tr><td>En echelon vein</td><td>Network</td><td>† Microfracture</td><td>Sharp contact</td><td>G Glass</td></tr><tr><td>Uniform vein</td><td>Single</td><td>⁄ Joint fracture</td><td>Gradational boundary</td><td></td></tr><tr><td>Haloed vein</td><td>Isolated</td><td>⁄ Normal fault</td><td>Glassy margin</td><td></td></tr><tr><td>Banded vein</td><td></td><td></td><td>Stylolitic fracture</td><td></td></tr><tr><td>Intravenous vein</td><td></td><td></td><td></td><td></td></tr><tr><td>Dendritic vein</td><td></td><td></td><td></td><td></td></tr></tbody></table>

Shipboard samples

<table><tr><td>CARB</td><td>Carbonate</td><td>MAD</td><td>Moisture/Density</td><td>PFT</td><td>Perfluorocarbon tracer</td><td>TS/TSB</td><td>Thin section</td></tr><tr><td>DIAT</td><td>Diatom</td><td>MBIO</td><td>Microbiology</td><td>PMAG</td><td>Paleomagnetism</td><td>VAC</td><td>Vacutainer</td></tr><tr><td>HS</td><td>Headspace</td><td>NANNO</td><td>Nannofossil</td><td>SED</td><td>Smear slide</td><td>XRD</td><td>X-ray diffraction</td></tr><tr><td>ICP</td><td>Inductively coupled plasma</td><td></td><td></td><td></td><td></td><td></td><td></td></tr></table>

**Figure F11.** Example of visual core description (VCD) form for igneous rocks, displaying patterns and symbols used, Expedition 385 (modified from Expedition 367/368). This form was applied to summarize data obtained from core imaging, macroscopic description, and physical properties measurements. Note that the three different ranks of grain size distribution (bimodal, inequigranular, equigranular) are depicted as patterns in the legend of the plot for illustration purposes only, whereas the VCD form itself shows these ranks as vertical black lines in the grain size distribution column.
* Color of the bulk rock determined on dry rock surfaces using standard Munsell soil color charts (Munsell Color Company, Inc., 2000, 2009);

* Texture (microstructure) based on total percentage of (micro)phenocrysts and their textural relation;

* Phenocryst abundance (in vol%) and type based on minerals identifiable by the unaided eye, hand lens, or binocular microscope;

* Groundmass texture and/or mineralogy;

* Abundance and general shape of vesicles;

* Upper and lower unit contact relations and boundaries based on physical changes observed in retrieved core material (e.g., presence of chilled margins, sediment/igneous contact, or baked layer), including information regarding their position within the section (information provided if contact present);

* Alteration intensity and vein presence; and

* Comment (if applicable).

**4.4. Identification of igneous lithologic units**

The division of igneous lithologic units and subunits was guided by groundmass texture and primary modal composition. The combined color and texture of the groundmass and the major phenocryst(s) found in hand specimen were used to assign principal lithology names to igneous lithologic units. Based on the intersection of what was always interpreted as a single cooling unit in each hole where igneous rocks were recovered, we defined a single Igneous Lithologic Unit 1 with no subunits. Because all igneous rock cores recovered represent hypabyssal intrusion bodies and do not mark the top of the continuous oceanic crust, we assigned each igneous unit to the lithostratigraphic unit and subunit that hosted the intrusion (see Lithostratigraphy).

**4.4.1. Magmatic rock classification**

The International Union of Geological Sciences (IUGS) system (Le Maitre et al., 2005) was used to classify igneous rocks according to abundance, grain size, and texture of primary minerals.

**4.4.2. Grain size classification**

The categorization of Neuendorf et al. (2005) was used for grain size:

* Coarse grained (crystal diameter = 5 to ≤30 mm),

* Medium grained (crystal diameter = 1 to <5 mm), and

* Fine grained (crystal diameter = 0.2 to <1 mm).

**4.4.3. Grain size distribution**

Distribution of grain (crystal) sizes are described as bimodal (two dominant mineral grain sizes), inequigranular (principal minerals have different grain sizes), or equigranular (principal minerals are in the same size range).

**4.4.4. Texture**

Textures (microstructures) were characterized macroscopically for all igneous rock core sections and assessed microscopically for a subset of intervals sampled for thin sections. Based on Sun et al. (2018), the following textural descriptors were applied:

* Aphyric,

* Ophitic (pyroxene encloses plagioclase laths),

* Subophitic (pyroxene partially encloses plagioclase laths),

* Holocrystalline,

* Hypocrystalline (comprising both crystals [major component] and glass),

* Hypohyaline (comprising both crystals [minor component] and glass),

* Holohyaline (vitric; only glass),

* Poikilitic (larger crystals enclose smaller grains),

* Porphyritic,

* Phaneritic,

* Aphanitic,
* Trachytic,

* Flow banding,

* Perlite (rounded hydration fractures in glass),

* Glomeroporphyritic (clusters of phenocrysts),

* Chilled margin (a glassy or micro- to cryptocrystalline contact margin), and

* Layered.

**4.5. Primary lithology names (hypabyssal/intrusive rocks)**

Four rock categories were defined for igneous rock description based on primary matrix texture/color as well as nature of major phenocrysts and/or groundmass minerals:

* Basaltic rock: gray to dark gray, potentiallyphyric rock with a microcrystalline to cryptocrystalline matrix (groundmass) that contains plagioclase and pyroxene and/or olivine. Groundmass size is <0.5 mm.

* Doleritic rock: dark gray to greenish gray rock with a microcrystalline matrix that contains pyroxenes and/or feldspar and/or amphibole. Groundmass size is >0.5 mm but <2 mm.

* Gabbroic rock: dark gray to greenish gray rock with porphyritic texture that contains pyroxenes and/or feldspar and/or olivine and/or amphibole. Groundmass size is ≥2 mm.

* Peperite: genetic term attributed to a rock that contains sediment mingled with or intruded by magma that was disintegrated by the contact with the sediment; the latter is usually wet and unconsolidated or poorly consolidated (after White et al., 2000).

**4.5.1. Prefixes**

Prefixes were chosen to provide additional classification information where possible, such as an estimated modal composition, further specification of grain sizes, or textural information. Where appropriate, combinations of prefixes were adopted. Prefixes are as follows:

* Aphyric (<1 vol% phenocrysts),

* Phyric (1%–5 vol% phenocrysts or more),

* Plagioclase phyric (if phenocryst is plagioclase), and

* Pyroxene phyric (if phenocryst is pyroxene).

**4.5.2. Suffixes**

The suffix of the principal lithology name points to the nature of the hypabyssal or intrusive body. We used the following classification scheme:

* Sill intrusion: sills are defined as tabular intrusions that run parallel to horizontal or gently dipping sedimentary layers. They are generally concordant between beds of layered sediment or rock. Their thickness may vary from a few centimeters to hundreds of meters.

* Dike intrusion: unlike sills, dikes cut across horizontal or gently dipping planar structures or rock strata. They are discordant with country rock strata. They usually range from centimeters to meters or even hundreds of meters in thickness.

**4.5.3. Matrix (groundmass)**

The following nomenclature was applied to describe the groundmass for both macro- and microscopic characterization (MacKenzie et al., 1982; Neuendorf et al., 2005):

* Aphanitic: crystalline, but individual grains are not distinguishable with a magnifying lens.

* Phaneritic: minerals are coarse enough to be seen with the naked eye.

* Equigranular: similar crystal sizes.

* Glomeroporphyritic: containing clusters of phenocrysts.

* Felty: tightly, irregularly interwoven feldspar microlites.

* Inequigranular: different crystal sizes.

* Intergranular: plagioclase crystals surrounded by interstitial granular pyroxene, olivine, and/or oxide minerals.

* Porphyritic: significant presence of (micro)phenocrysts.

* Ophitic: large pyroxene grain encloses small random plagioclase laths.
* Subophitic: plagioclase laths are larger and only partially enclosed by the pyroxene.

* Interstitial: glassy, crypto-, or microcrystalline material between coarser grained crystals.

#### 4.5.4. Sediment mingling

Sediment mingling was included in the igneous rock description upon encountering magma/sediment contacts or mixing demonstrated by fragmentation of igneous material or injection of sediment as veins in igneous rock. We included a yes/no column in DESClogik and used “yes” to indicate intervals where we found any igneous/sedimentary contact. Also, additional description of the nature of contact was entered in DESClogik as needed.

#### 4.5.5. Contact types

The description of margins and contacts of hypabyssal or intrusive rocks was based on the observed features of the chilled sections that indicate a possible hiatus between two igneous rocks. A chilled contact, with or without glass, was identified by observing the terminal end of the margin for sediment that was not entrenched within the rock but rather baked or cooked onto the rock, designating a baked or chilled contact with the latter. A chilled margin was identified through a sudden change in matrix over a very short interval. In contrast to a chilled contact, establishing the nomenclature of an igneous body did not require the presence of sediment at its terminal end. Several sections were characterized as having a chilled contact (typically with glass) in direct contact with sediments with an adjoining (or grading into a) chilled margin where the matrix was described to be cryptocrystalline and graded into a microcrystalline texture further up- or downhole. Glassy margins, chilled margins, and contact boundaries were inserted individually for the top and bottom of each section where they could be determined.

The following contact types were defined:

* Baked contact: boundary to sediments overprinted (baked) by proximity of magma.

* Bottom (or top) chilled contact: chilled contact with sediments, with or without glass adjacent to sediments.

* Bottom (or top) chilled margin: chilled contact without sediments, without glass, defined by cryptocrystalline groundmass, and typically found quenched next to the chilled contact.

* Chilled contact: boundary cannot be determined to be top or bottom of a pulse that has sediment attached, such as a magma/sediment mingling or peperite.

* Chilled margin: chilled contact without sediment or obvious glass that cannot be determined to be the top or bottom of a magma pulse, or nearby obvious sediment contact is not preserved.

* Glassy margin: demarcation between two hypabyssal/intrusive pulses or presumably between magma and country sediment without displaying the latter. Potentially, igneous bodies have fused together, showing no clear indication of the boundary between the pulses as originally deposited.

## 4.6. Alteration

### 4.6.1. Alteration minerals

Procedures developed specifically to investigate hydrothermal alteration encountered during Expedition 385 are detailed in the following sections. Significant detail was incorporated into DESClogik, which enabled a comprehensive report of the predominant style of hydrothermal alteration of specific intervals of the recovered igneous rocks. Identified alteration minerals or mineral mixtures include carbonate (calcite, dolomite, or siderite), chlorite, copper sulfate, clay minerals, zeolites (e.g., natrolite), epidote, iron hydroxides, iron oxide, mica (sericite), spinel (magnetite), and sulfides (chalcopyrite or pyrite); “unknown” was used when the mineral could not be identified.

### 4.6.2. Alteration intensity

Low- to high-temperature and low-pressure (i.e., seafloor) mineralization, veins, and background alteration were defined as alteration. Alteration description includes secondary mineralogy, groundmass texture/color, phenocryst alteration, and infilling of vesicles and halos. Textures used to define groundmass alteration are patchy, corona, pseudomorphic, and recrystallized. Detailed
description of the alteration ranks, texture of alteration, and grain size distribution are given in Tables T1, T2, and T3, respectively. Alteration rank for igneous rock is equivalent to what has been applied by the lithostratigraphy classification. Levels of background alteration were recorded as follows:

* Unaltered = <2 vol%.

* Slight = 2–10 vol%.

* Moderate = >10–50 vol%.

* High = >50–75 vol%.

* Intense = >75–95 vol%.

* Complete = >95 vol%.

## 4.7. Vesicularity

Vesicularity is defined by vesicle abundance:

* Nonvesicular = <1 vol% vesicles.

* Sparsely vesicular = 1–5 vol% vesicles.

* Moderately vesicular = >5–20 vol% vesicles.

* Highly vesicular = >20 vol% vesicles.

Size, shape, and roundness of vesicles were described in line with the classification charts from Integrated Ocean Drilling Program Expedition 330 and IODP Expedition 349 (Expedition 330 Scientists, 2012; Li et al., 2015), modified from Wentworth (1922) (Figure F12). An estimate of the abundance of vesicles (in vol%) is included in the VCDs.

<table><caption>**Table T1. Alteration rank of igneous rocks. Download table in CSV format.**</caption><thead><tr><td>Rank</td><td>Intensity</td><td>Description</td></tr></thead><tbody><tr><td>0</td><td>Unaltered</td><td>The sediment or the rock does not display any trace of alteration.</td></tr><tr><td>1</td><td>Slightly altered</td><td>The sediment or the rock displays alteration halos, veins, secondary minerals, patches of alteration.</td></tr><tr><td>2</td><td>Moderately altered</td><td>The sedimentary/igneous textures are preserved but color changes, partial replacement by secondary minerals occur.</td></tr><tr><td>3</td><td>Highly altered</td><td>Color changes, partial replacement by secondary minerals affect more than 20% of the sediments/igneous rock.</td></tr><tr><td>4</td><td>Intensely altered</td><td>More than 75% of the sediment/igneous rock is replaced by secondary minerals, but the primary texture is preserved.</td></tr><tr><td>5</td><td>Completely altered</td><td>The sedimentary/igneous texture is lost. The sediment/igneous rock is completely replaced by secondary minerals.</td></tr></tbody></table>

<table><caption>**Table T2. Texture of alteration of igneous rocks. Download table in CSV format.**</caption><thead><tr><td>Texture</td><td>Description</td><td>References</td></tr></thead><tbody><tr><td>Coating</td><td>Externally derived alteration phase; occurs as a film on primary phases</td><td>Salvatore et al., 2013</td></tr><tr><td>Infilling</td><td>Hydrothermal minerals partly or completely fill vugs (including vesicles, interstitial voids, etc.)</td><td>Gifkins et al., 2005</td></tr><tr><td>Patchy</td><td>Heterogeneous alteration of the host rock showing patchy distribution of hydrothermal minerals</td><td>Gifkins and Allen, 2001</td></tr><tr><td>Pseudomorphic</td><td>Alteration occurs as replacement of former mineral phase with the shape of parent crystal preserved</td><td>Putnis, 2002</td></tr><tr><td>Recrystallized</td><td>Transformed from a mineral or a glass to a new grain size or new mineral phase</td><td>Folk, 1965</td></tr><tr><td>Brecciated</td><td>Introduced into the host rock alongside a distinct brecciation event</td><td>Jébrak, 1997</td></tr><tr><td>Fracture controlled</td><td>Alteration along veins and fractures as selvages and alteration halos</td><td>Shipboard Scientific Party, 2002</td></tr></tbody></table>

<table><caption>**Table T3. Grain size distribution of igneous rocks. Download table in CSV format.**</caption><thead><tr><td>Rank</td><td>Label</td><td>Description</td></tr></thead><tbody><tr><td>1</td><td>Bimodal</td><td>Two dominant mineral sizes.</td></tr><tr><td>2</td><td>Inequigranular</td><td>Principal minerals have different grain sizes.</td></tr><tr><td>3</td><td>Equigranular</td><td>Principal minerals are in the same size range.</td></tr></tbody></table>
**4.7.1. Veins and halos**

While we reserved the term “dike” to describe any later crosscutting feature that formed by intro-
duction of magma, the term “vein” was deployed to refer to any later crosscutting feature formed
by sediment injection or precipitation from hydrothermal fluids. The term “halo” refers to alter-
ation zones around veins or secondary minerals identified by discoloration through change of the
primary mineral assemblage. The density (i.e., the visually estimated percentage of veins within a
piece or interval 10 cm in length), mineralogy, width, color, vein type (banded, composite, non-
uniform, or uniform), connectivity (isolated, single, branched, or network), texture (cross-fiber,
slip-fiber, massive, polycrystalline, or vuggy) (Figure F13), and contacts with host rocks (diffuse,
irregular, or sharp) were described using criteria modified from ODP Leg 209 (Shipboard Scien-
tific Party, 2004). The length, width, and orientation of representative veins in a section were mea-
sured.

**4.8. Microscopic (thin section) description**

Thin section investigation was used to complement and refine macroscopic core observations for igneous rocks (Figure F14). All thin section observations were entered into the LIMS database through a special DESClogik thin section template (see DESC\_WKB in **Supplementary material**). Thin section descriptions include both primary (igneous) rock-forming minerals (including phenocrysts, groundmass, etc.) and secondary (alteration) mineral phases (in veins, vesicles, groundmass, etc.). Their mineralogy, abundance (modal volume percentages), sizes, shapes, habits, textural relationships, inclusions, alteration color, intensity and style, veins (type and number), and vesicles (type and fillings) were determined, enabling verification of macroscopic observations. The volume percentages of the original primary mineral phases, groundmass, and vesicles are also included when entering mineral abundances in DESClogik.

<figure><img src="image_15.png" /><figcaption>**Figure F12.** Comparison chart for describing vesicle sphericity and roundness in (sub)volcanic rocks, Expeditions 385 (modified from Wentworth, 1922; Li et al., 2015; Sun et al., 2018).</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>**Figure F13.** Descriptors used to characterize the texture of veins, Expedition 385 (modified from Li et al., 2015; Sun et al., 2018).</figcaption></figure>
Thin section descriptions include the following terms:

* Sample domain: if there is more than one domain on the slide, each domain is described separately. For example, a slide that shows a large sedimentary vein (25% of the slide) in a basaltic matrix (75% of the slide) is described as two slides (samples): the first sample domain as “vein” and the second one as “host rock.” Other possible domains include clast, glass, halo, lithology, and xenolith.

* Lithology prefix: lithology prefix for the described sample domain.

* Principal lithology: refers only to the lithology of the described sample domain, which includes basalt, brecciated basalt, breccia, and hyaloclastite.

* Average groundmass grain size modal name: grain sizes follow Neuendorf et al. (2005) using the division of glass, cryptocrystalline (<0.1 mm), microcrystalline (0.1–0.2 mm), and fine, medium, and coarse grained (see **Primary lithology names (hypabyssal/intrusive rocks)**).

* Maximum grain size modal name: analogous to “average groundmass grain size modal name.”

* Grain size distribution: bimodal, equigranular, granular, inequigranular, poikilitic, and seriate (see **Texture**).

* Texture: aphanitic, aphyric, granular, glomeroporphyritic, holocrystalline, holohyaline, hypocrystalline, hypohyaline, intergranular, intersertal, interstitial, ophitic, porphyritic, seriate, spherulitic, subophitic, trachytic, and vitrophyric (see **Texture**).

<figure><img src="image_17.png" /><figcaption>**Figure F14.** Example of thin section report for igneous rocks, Expedition 385.</figcaption></figure>
* Mineral phenocryst shape: the dominant (>50% of crystals) shape of the olivine, plagioclase, clinopyroxene, orthopyroxene, and spinel crystals in euhedral, subhedral, and anhedral.

* Mineral phenocryst habit: the dominant (>50% of crystals) habit of olivine, plagioclase, clino-pyroxene, orthopyroxene, and spinel crystals divided into elongate, equant, subequant, and tabular habits (see definitions below).

* Plagioclase phenocryst zoning type: continuous, discontinuous, oscillatory, and patchy.

* Plagioclase phenocryst zoning extent: none, scarce, abundant, and very abundant.

* Clinopyroxene and orthopyroxene phenocryst exsolution: blebs and lamellae.

* Vesicle shape.

* Mineral groundmass shape: for olivine, plagioclase, clinopyroxene, orthopyroxene, spinel, and Fe-Ti oxides and sulfides, mineral groundmass shapes are euhedral, subhedral, and anhedral.

* Mineral groundmass habit: for olivine, plagioclase, clinopyroxene, orthopyroxene, spinel, and Fe-Ti oxides and sulfides, mineral groundmass habits are elongate, equant, subequant, and tabular.

* Additional features such as dissolution/resorption textures, sieve textures, and inclusions are noted in the comments section.

# 5. Structural geology

This section outlines methods for documenting structural features observed in Expedition 385 cores, such as faults, fractures, folds, bedding, laminations, paleosurface features, and veins. Structures were measured before and after the cores were split. For solid cores, we measured structures that could be seen externally on the surface of the whole-round core prior to splitting. We used the resulting measurements to split the core most evenly into archive and working halves. After a core was split and described by the sedimentologists or petrologists on shift, we documented structural features observed on the archive half using the following process:

1. Identifying structural features and classifying their structural types;

2. Determining the top and bottom locations of structural features in the core;

3. Measuring the orientation of a structural feature where applicable;

4. Determining the sense of displacement on a structural feature where applicable;

5. Determining the temporal relation between structures, especially for crosscutting structures such as shear zones; and

6. Assessing the role of fluids in deformation processes.

Our methods largely follow those used by structural geologists from Integrated Ocean Drilling Program Expedition 344 and IODP Expeditions 349 and 367/368 (Harris et al., 2013; Li et al., 2015; Sun et al., 2018). The types of structural measurements and key parameters (either observed or calculated) were recorded on spreadsheets. We made different spreadsheets for sedimentary rock observations and for igneous rock observations because the type of information needed in each case was different (Tables T4, T5, T6). These data were then entered in the LIMS database using the DESClogik software application. We were not able to correct any of the orientation measurements for rotation related to drilling using paleomagnetic declination and inclination information (see Paleomagnetism) or by comparison to observed features in the FMS log (see Azimuth correction based on Formation MicroScanner log).

## 5.1. Graphic symbols and terminology

A predefined set of commonly observed structural features was used in the structural description of cores. The terminology and graphic symbols used are presented in Figures F5, F11, and F15. Note that there are more graphic symbols for structures in sedimentary cores than in igneous cores. The major structural features identified include the following:

* Fractures: brittle failure with unknown displacement and no secondary infill minerals; these were further classified as microfractures, open fractures, and joint fractures. However, breaks
clearly resulting from drilling were logged separately as drilling-induced fractures in the Drilling disturbance spreadsheet of DESClogik.

* Faults: brittle failure with measurable offset or juxtaposition of different lithologies.

* Veins: fractures filled with secondary minerals.

* Shear zones: strongly deformed zones surrounded by less deformed rocks.

* Sedimentary bedding: layering of sediments or lamina and sedimentary rocks.

* Folds: folded sedimentary or rock layers.

* Igneous contacts: material contacts of hypabyssal igneous rocks, including glassy margins.

* Magmatic fabrics: magmatic foliations defined by the preferred orientations of primary minerals with no evidence of crystal-plastic deformation.

## 5.2. Structural observation and description

Structural features were described from top to bottom of each section of the core. For fractures and faults, we examined and measured the following parameters:

* Location: where a fracture occurs in a core, measured in centimeters from the top of the section.

<table><caption>**Table T4.** Examples of the structural geology observation sheets used during Expedition 385. Download table in CSV format.</caption><thead><tr><th>Site</th><th>Hole</th><th>Core</th><th>Section</th><th>Structure ID</th><th>Top depth (m)</th><th>Bottom depth (m)</th><th>Average depth (m)</th><th>Top of structure (m)</th><th>Bottom of structure (m)</th><th>Average depth (m)</th><th>Thickness (cm)</th><th>Core face app. dip (°)</th><th>2nd app. dip (°)</th><th>Striation on surface</th></tr></thead><tbody><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table><table><thead><tr><th rowspan="2">Site</th><th rowspan="2">Hole</th><th rowspan="2">Core</th><th rowspan="2">Section</th><th colspan="4">Plane-normal orientation</th><th colspan="3">Plane orientation (RHR)</th><th colspan="7">Striation</th></tr><tr><th>L</th><th>M</th><th>N</th><th>A<sub>z</sub></th><th>Dip</th><th>Dip dir</th><th>Strike</th><th>Dip</th><th>CSF rake</th><th>Str rake</th><th>L</th><th>M</th><th>N</th><th>Trend</th><th>Plunge</th><th>Slip sense</th></tr></thead><tbody><tr><td></td><td></td><td></td><td></td><td>0.00</td><td>0.00</td><td>0.00</td><td>90</td><td>270</td><td>180</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>0.00</td><td>0.00</td><td>0.00</td><td>90</td><td>270</td><td>180</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>0.00</td><td>0.00</td><td>0.00</td><td>90</td><td>270</td><td>180</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

<table><caption>**Table T5.** Example of an observation sheet for sedimentary rock structures. Download table in CSV format.</caption><thead><tr><th rowspan="2">Site</th><th rowspan="2">Hole</th><th rowspan="2">Core</th><th rowspan="2">Section</th><th colspan="2">Coherent interval (for P-mag)</th><th colspan="2">P-mag pole</th><th colspan="3">Corrected orientation (RHR)</th><th colspan="4">Striation</th><th rowspan="2">Remarks</th></tr><tr><th>Top</th><th>Bottom</th><th>Dec.</th><th>Inc.</th><th>Dip dir</th><th>Strike</th><th>Dip</th><th>Rake</th><th>Trend</th><th>Plunge</th><th>Slip sense</th></tr></thead><tbody><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>270</td><td>180</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>270</td><td>180</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>270</td><td>180</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

<table><caption>**Table T6.** Example of an observation sheet for igneous rock structures. Download table in CSV format.</caption><thead><tr><th>Site</th><th>Hole</th><th>Core</th><th>Section</th><th>Normal</th><th>Massive</th><th>Tilted</th><th>Contorted</th><th>Drilling deformation</th><th>Measured on photo</th><th>Measured on spreadsheet</th><th>Ash/black layer</th><th>Notes</th></tr></thead><tbody><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>U1548</td><td>E</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>U1548</td><td>E</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>U1548</td><td>E</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

<table><thead><tr><th>Site</th><th>Hole</th><th>Core</th><th>Section</th><th>Bin</th><th>Distance (cm)</th><th>Fault (cm)</th><th>Vein (cm)</th><th>Other feature</th><th>Dip from whole round</th><th>Filling material?</th><th>Drilling deformation</th><th>Notes</th></tr></thead><tbody><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>U1548</td><td>C</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>U1548</td><td>C</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>U1548</td><td>C</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>
* Morphology: morphological shape of a fracture (e.g., straight, curved, banded, irregular, composite, isolated, single, or branched).

* Displacement: lateral offset and/or opening of a fault measured in centimeters. A closed fracture with no lateral offset is recorded as 0 cm of displacement.

* Orientation: dip angle and dipping orientation of a fracture or fault measured in degrees if seen on the archive-half core face or X-ray image or true dip angle if measured on the outside of the whole-round core.

* Frequency: occurrence frequency of fractures per section.

* Type: type of deformation of a fracture or fault (e.g., normal, reverse, dextral, sinistral displacement, or a combination of the above).

For veins, we examined and measured several parameters:

* Location: where a vein occurs in a core, measured in centimeters from the top of the section.

* Vein type: see list of deformation structures in **Lithostratigraphy** and overview of vein types in **Igneous petrology and alteration**.

* Orientation: dip angle and dipping direction of a vein if seen on the core face or X-ray image of the archive half or true dip angle if measured on the outside of the whole-round core.

* Frequency: occurrence frequency of veins per section.

* Mineral infill and alteration: these features are recorded as described by petrologists.

<figure><img src="image_18.png" /><figcaption>**Figure F15.** Vein description scheme, Expedition 385 (from figure F17 of Sun et al., 2018).</figcaption></figure>
For shear zones, we examined and measured the following parameters (although very few were
seen):

* Location: interval where a shear zone occurs in a core, measured in centimeters from the top of the section.

* Nature (or type) of shear zone: cataclasite, gouge, or fault breccia.

* Morphology: morphological shape of the deformed zone and the clasts.

* Orientation: dip angle and dipping direction of the preferred orientation of the clasts, where applicable.

* Frequency: occurrence frequency of shear zones per section.

* Mineral and alteration: matrix and clasts are recorded as described by petrologists.

For sedimentary bedding, we described the following parameters:

* Location: where a nonsubhorizontal bedding occurs in a core (>5°), measured in centimeters from the top of the section.

* Orientation: dip angle and dipping direction of sedimentary bedding as seen on the core face or X-ray image.

For folds, we described the following parameters:

* Location: where a fold contact occurs in a core, measured in centimeters from the top of the section.

* Type: type of fold (e.g., chevron or concentric; see definitions in Fossen [2016]).

* Frequency: occurrence frequency of fold axis per section.

For igneous contacts, we described the following parameters:

* Location: where an igneous contact occurs in a core, measured in centimeters from the top of the core (usually a binned specimen).

* Type of contacts: type of igneous contact boundary.

* Orientation: dip angle and dipping direction of an igneous contact.

* Frequency: occurrence frequency of igneous contacts per section.

* Mineral assemblage and alteration: these features are recorded as described by petrologists.

For sediments and sedimentary rocks, if XRI scans were available, we further examined the X-ray images to detect and measure additional faults if they were made visible by X-ray imaging but were not seen on the split core face. Note that the location measurement of a feature in the X-ray scans could differ by 1 cm compared to the location of the same feature in the archive half of the split core (e.g., see Figure F9 in the Site U1552 chapter (Teske et al., 2021a)).

Finally, we processed the SHIL color composite photos of the core to produce false-color images that more clearly highlighted the compositional difference in the sediments. This was another way to check for faults. Processing was performed in Adobe Photoshop CS6 version 13.0 × 64 on a Windows PC by choosing File > Scripts > Image Processor and then running it in batch mode on a set of files within a specified directory. A “run action” was first specified to include three processing steps:

1. Image > Adjustment > Levels,

2. Image > Adjustment > Brightness/Contrast, and

3. Layer > Flatten Image.

**5.3. Orientation measurements and correction**

**5.3.1. Orientation measurements**

We used a plastic goniometer for orientation measurements. For sealed structures in igneous rocks, we wrapped a transparent plastic protractor template around the whole-round core to determine the true dip prior to splitting the core (Figure F16). For split cores (igneous or sedimentary) the orientations of planar and linear features in the archive half were determined relative to the core reference frame (Figure F17). The vertical axis of the core reference frame is
aligned with the upcore direction of the core section, whereas the double line marked on the archive half of the core liner is defined as 180° in the cross-sectional plane perpendicular to the core vertical axis.

To determine the orientation of a planar structural element (shaded plane in Figure F17), two apparent dips of the element were measured in the core reference frame. The first apparent dip measures the intersection angle between the planar structural element and the split face of the core ($β_1$ in Figure F17); it is determined by measuring the dip direction and angle of the planar structural element in the core reference frame. A planar structural element could have a trend of 90° or 270°, with a plunge angle ranging from 0° to 90°. The second apparent dip measures the intersection angle between the central line of the planar structural element and the split face of the core ($β_2$ in Figure F17). In most cases, this is a plane either parallel or perpendicular to the core

<figure><img src="image_19.png" /><figcaption>**Figure F16.** Goniometer and plastic protractor template used during Expedition 385 to measure dip and dip direction of structures.</figcaption></figure>

<figure><img src="image_20.png" /><figcaption>**Figure F17.** Diagram of core reference frame and coordinates used in orientation data calculation, Expedition 385.</figcaption></figure>
axis. In the former case, the apparent dip trends 0° or 180° with plunge angle ranging from 0° to 90°; in the latter case, the trend ranges from 0° to 360° with a plunge angle of 0°.

A linear feature observed on the surface of a split core is often associated with a planar structural element (e.g., a fault plane) in the core; the orientations of the planar structural element are determined by measuring either the rake (or pitch) of the associated plane or the trend and plunge of the planar element in the core reference frame. All measured data were manually written into the log sheet together with the measured depths in the core section and descriptive information (Table T4).

### 5.3.2. Plane orientation calculation

For a planar structural element (e.g., a bedding or fault plane), two apparent dips on two different surfaces (one being the split core surface, which is east-west vertical, and the other being the horizontal surface, or north-south vertical) were measured in the core reference frame. The two apparent dips are the azimuth (measured clockwise from north, looking down) and plunge. An x, y, z coordinate system was defined so that the positive x-, y-, and z-directions coincide with north, east, and vertical downward, respectively. If the azimuths and plunges of the two apparent dips are given as (α₁, β₁) and (α₂, β₂), respectively (as in Figure F17), the unit vectors representing these two lines, v₁ and v₂, are given by the following expressions:

$$v_1 = \begin{pmatrix} l_1 \\ m_1 \\ n_1 \end{pmatrix} = \begin{pmatrix} \cos \alpha_1 \cos \beta_1 \\ \sin \alpha_1 \cos \beta_1 \\ \sin \beta_1 \end{pmatrix}; \quad v_2 = \begin{pmatrix} l_2 \\ m_2 \\ n_2 \end{pmatrix} = \begin{pmatrix} \cos \alpha_2 \cos \beta_2 \\ \sin \alpha_2 \cos \beta_2 \\ \sin \beta_2 \end{pmatrix}. \quad (1)$$

For any plane, the direction of the normal to the plane can be found by taking the cross product of two (nonparallel) vectors that lie within the plane. Using the above equations for v₁ and v₂, therefore, the unit vector normal to plane vₙ (Figure F18) is defined as follows:

$$v_n = \begin{pmatrix} l_n \\ m_n \\ n_n \end{pmatrix} = \frac{v_1 \times v_2}{|v_1 \times v_2|}, \quad (2)$$

where

$$v_1 \times v_2 = \begin{vmatrix} m_1 & m_2 \\ n_1 & n_2 \\ n_1 & n_2 \\ l_1 & l_2 \\ l_1 & l_2 \\ m_1 & m_2 \end{vmatrix} = \begin{pmatrix} m_1 n_2 - m_2 n_1 \\ n_1 l_2 - n_2 l_1 \\ l_1 m_2 - l_2 m_1 \end{pmatrix}. \quad (3)$$

The azimuth αₙ and plunge βₙ of vₙ are given by

$$\alpha_n = \tan^{-1}(m_n/l_n) \text{ and} \quad (4)$$

$$\beta_n = \sin^{-1}n_n. \quad (5)$$

The dip direction αₘ and dip angle β of this plane are calculated as follows:
$$ \alpha_d = \alpha_n \text{ and } \beta = 90^\circ + \beta_n \text{ when } \beta_n < 0^\circ, \text{ and} \qquad (6) $$

$$ \alpha_d = \alpha_n \pm 180^\circ \text{ and } \beta = 90^\circ - \beta_n \text{ when } \beta_n \ge 0^\circ. \qquad (7) $$

The strike of this plane $\alpha_s$ according to the right-hand rule is then given by $\alpha_s = \alpha_d - 90^\circ$ (Figure F18).

### 5.3.3. Azimuth correction based on paleomagnetic data

Provided that a core is vertical, its magnetization is primary, the core was magnetized in the Northern Hemisphere, and its bedding is horizontal, its paleomagnetic declination $\alpha_p$ indicates the magnetic north direction when its inclination is $\beta_p \ge 0^\circ$ (Figure F19); in contrast, the angle $\alpha_p$ indicates the magnetic south direction when $\beta_p < 0^\circ$. The dip direction ($\alpha_d^*$) and strike ($\alpha_s^*$) of a planar structural element in the geographic reference frame are therefore

$$ \alpha_d^* = \alpha_p - \alpha_d \text{ and } \alpha_s^* = \alpha_p - \alpha_s \text{ when } \beta_p \ge 0^\circ, \text{ or} \qquad (8) $$

$$ \alpha_d^* = 180^\circ + \alpha_p - \alpha_d \text{ and } \alpha_s^* = 180^\circ + \alpha_p - \alpha_s \text{ when } \beta_p < 0^\circ. \qquad (9) $$

If a core section was complete and continuous, one paleomagnetism sample per section (1.5 m in length) was deemed sufficient to determine the paleomagnetic orientation of the core section. If the core was discontinuous, one paleomagnetism sample was required for each continuous sub-section of the core that was deemed structurally important. Paleomagnetism samples were taken as cubic or cylindrical samples close to a planar structural element of interest (usually within 5 cm) and from a coherent core interval that included that structural element of interest. In general, we avoided core fragments that were so small that potential spinning during drilling might cause significant deviation from the core axis (e.g., fragments of brecciated segments).

### 5.3.4. Azimuth correction based on Formation MicroScanner log

If an FMS log is available for the section of the drill hole that contains the core, there may be distinctive features that can be correlated between the FMS log and the core, such as bedding, frac-

<figure><img src="image_21.png" /><figcaption>**Figure F18.** Diagram of dip direction ($\alpha_d$), right-hand rule strike ($\alpha_s$), and dip ($\beta$) of a plane deduced from its normal azimuth ($\alpha_n$) and dip ($\beta_n$). $V_n$ denotes the unit vector normal to plane. A. $\beta_n < 0^\circ$. B. $\beta_n > 0^\circ$.</figcaption></figure>
<figure><img src="image_22.png" /></figure>

<figure><img src="image_23.png" /><figcaption>**Figure F19.** Diagrams of azimuth correction based on paleomagnetic data. αp = paleomagnetic declination, αd and αs = dip direction and right-hand rule strike of a plane. A. βp > 0°. B. βp < 0°.</figcaption></figure>

tures, folds, veins, stratification, and bioturbation. In this case, the core can be oriented with
respect to geographic north. However, this orientation has to be done after the FMS log is
obtained and all the cores in the hole have been collected. See the discussion of the details of ori-
enting the cores in **Petrophysics**.

**6. Biostratigraphy**

Preliminary shipboard biostratigraphy for Expedition 385 was provided by fossil marine diatoms and calcareous nannofossils. Biostratigraphic age assignments were based on analysis of core catcher samples from selected holes at all drill sites, provided that the core catcher sample was sedimentary in origin. As time permitted, additional toothpick samples were taken from core section halves (typically the archive half) as needed to refine biostratigraphic horizons (biohorizons) or where changes in lithology suggested changes in sediment deposition. Biostratigraphy focused mainly on the identification of biohorizons in the cores, generally the top (T) or base (B) of the stratigraphic range of the age-diagnostic species, including the top common (Tc) and base common (Bc) occurrences and the top acmes (Ta) and base acmes (Ba). The top and base of a species correspond to its last appearance datum (LAD) and first appearance datum (FAD), respectively. Each biohorizon was assigned an absolute age based on the geological timescale of Gradstein et al. (2012) (Figure F20).

**6.1. Slide preparation and microscopic examination**

All micropaleontological data gathered during shipboard investigations were entered using DESC-
logik data entry software and are available from the LIMS database in accordance with IODP pol-
icy. Species distribution and abundance are included for every sample of each hole and each
taxonomic group (calcareous nannofossils and marine diatoms) studied. These data are provi-
sional because of time constraints for cross-checking and searching for rare species. Generally,
this study focused on biostratigraphic marker species. The provisional, incomplete, and systemat-
ically biased nature of the data makes them unsuitable for further meta-analytical studies.
## 6.2. Calcareous nannofossils

### 6.2.1. Zonal scheme and taxonomy

Calcareous nannofossil zonation was based on the schemes of Okada and Bukry (1980) and Martini (1971) supplemented with Backman et al. (2012). Calibrated ages for bioevents are from Gradstein et al. (2012) (Table T7). The geological timescale of Gradstein et al. (2012) assigns the Pleistocene/Pliocene boundary an age between the Gelasian and Piacenzian stages (2.59 Ma), the

<figure><img src="image_24.png" /><figcaption>**Figure F20.** Calcareous nannofossil and marine diatom events and scaled ages, Expedition 385 (based on Gradstein et al., 2012). B = base, Ba = base acme, Bc = base common, T = top, Ta = top acme, Tc = top common, X = abundance crossover.</figcaption></figure>
<table><caption>**Table T7.** Calcareous nannofossil events and scaled ages (GTS2012; Gradstein et al., 2012), Expedition 385. T = top/last appearance datum, B = base/first appearance datum. Bold text indicates age-diagnostic datum. (Continued on next page.) **Download table in CSV format.**</caption><thead><tr><th rowspan="2">GTS2012<br>Chronostratigraphy</th><th colspan="2">Standard tropical-subtropical biozone (biochron)</th><th rowspan="2">Biohorizon (datum)</th><th rowspan="2">GTS2012 age<br>(Ma)</th></tr><tr><th>CN Zones<br>(Okada & Bukry, 1980)</th><th>NN Zones<br>(Martini, 1971)</th></tr></thead><tbody><tr><td>0.126<br>Ionian (Middle Pleistocene)</td><td>CN15/CN14b<br>CN14b/CN14a</td><td>NN21/NN20<br>NN20/NN19</td><td>B Emiliania huxleyi<br>T Pseudoemiliania lacunosa</td><td><strong>0.29</strong><br><strong>0.44</strong></td></tr><tr><td>0.781<br>Calabrian</td><td>CN14a/CN13b<br>CN13b</td><td></td><td>T Reticulofenestra asanoi (common)<br>T small (&lt;4 µm) Gephyrocapsa spp. dominance<br>B medium (&gt;4 µm) Gephyrocapsa spp. reentrance (reemG event)<br>B Reticulofenestra asanoi (common)<br>T large (&gt;5.5 µm) Gephyrocapsa spp.<br>B small (&lt;4 µm) Gephyrocapsa spp. dominance<br>T Helicosphaera sellii<br>T Calcidiscus macintyrei<br>B large (&gt;5.5 µm) Gephyrocapsa spp.<br>B medium (&gt;4 µm) Gephyrocapsa spp. (= bmG event)</td><td>0.91<br>1.02<br>1.04<br>1.14<br>1.24<br>1.24<br>1.26<br>1.60<br>1.62<br>1.73</td></tr><tr><td>1.806<br>Gelasian</td><td>CN13a<br>CN13a/CN12d<br>CN12d</td><td>NN19/NN18<br>NN18</td><td>T Discoaster brouweri<br>T Discoaster triradiatus<br>B acme Discoaster triradiatus<br>T Discoaster pentaradiatus<br>T Discoaster surculus</td><td><strong>1.93</strong><br>1.95<br>2.22<br><strong>2.39</strong><br><strong>2.49</strong></td></tr><tr><td>2.588<br>Piacenzian</td><td>CN12b<br>CN12b/CN12a</td><td></td><td>T Discoaster tamalis (subtop)<br>T Sphenolithus spp. (subtop)</td><td>2.80<br>3.54</td></tr><tr><td>3.600<br>Zanclean</td><td>CN12a<br>CN12a/CN11b<br>CN11b<br>CN11b/CN11a<br>CN11a/CN10c<br>CN10c</td><td>NN16<br>NN15/NN15<br>NN15/NN14<br>NN14/NN13<br>NN13</td><td>T Reticulofenestra pseudoumbilicus<br>T Amaurolithus tricorniculatus<br>B common Discoaster asymmetricus<br>T Amaurolithus primus<br>T Reticulofenestra antarctica<br>B Reticulofenestra pseudoumbilica, Discoaster ovata (subbottom)<br>T Ceratolithus acutus<br>X Ceratolithus acutus to C. rugosus (Atl.)<br>B Ceratolithus rugosus<br>T Triquetrorhabdulus rugosus</td><td><strong>3.70</strong><br><strong>3.92</strong><br><strong>4.13</strong><br>4.50<br>4.91<br>4.91<br>5.04<br>5.05<br><strong>5.12</strong><br>5.28</td></tr><tr><td>5.333<br>Messinian</td><td>CN10b<br>CN10b/CN10a<br>CN10a/CN9d<br>CN9d/CN9c<br>CN9c<br>CN9c/CN9b</td><td>NN12</td><td>B Ceratolithus larrymayeri (sp.1)<br>B Ceratolithus acutus<br>T Discoaster quinqueramus<br>T Nicklithus amplificus<br>X Nicklithus amplificus to Triquetrorhabdulus rugosus<br>B Nicklithus amplificus</td><td>5.34<br>5.35<br><strong>5.59</strong><br>5.94<br>6.79<br>6.91</td></tr><tr><td>7.246<br>Tortonian<br>Tortonian</td><td>CN9b<br>CN9b/CN9a<br>CN9a</td><td>NN11</td><td>B Amaurolithus primus, Amaurolithus spp.<br>T Discoaster loeblichii<br>B common Discoaster surculus<br>B Discoaster quinqueramus<br>B Discoaster berggrenii<br>T Minylitha convallis<br>B Discoaster loeblichii<br>B paracme Reticulofenestra pseudoumbilicus<br>T Discoaster bollii<br>B common Discoaster pentaradiatus<br>T Discoaster hamatus<br>T Catinaster calyculus<br>T Catinaster coalitus<br>B Minylitha convallis<br>X Discoaster hamatus to Discoaster neohamatus<br>B Discoaster bellus<br>X Catinaster calyculus to Catinaster coalitus<br>B Discoaster neohamatus<br>B Discoaster hamatus<br>B common Helicosphaera stalis<br>T common Helicosphaera walbersdorfensis<br>B Discoaster brouweri<br>B Catinaster calyculus<br>B Catinaster coalitus</td><td>7.42<br>7.53<br>7.79<br>8.12<br><strong>8.29</strong><br>8.68<br>8.77<br>8.79<br>9.21<br>9.37<br><strong>9.53</strong><br>9.67<br>9.69<br>9.75<br>9.76<br>10.40<br>10.41<br>10.52<br><strong>10.55</strong><br>10.71<br>10.74<br>10.76<br>10.79<br><strong>10.89</strong></td></tr><tr><td></td><td>CN9a/CN8</td><td>NN11/NN10</td><td></td><td></td></tr><tr><td></td><td>CN8</td><td>NN10</td><td></td><td></td></tr><tr><td></td><td>CN8/CN7</td><td>NN10/NN9</td><td></td><td></td></tr><tr><td></td><td>CN7</td><td>NN9</td><td></td><td></td></tr><tr><td></td><td>CN7/CN6</td><td>NN9/NN8</td><td></td><td></td></tr><tr><td></td><td>CN6</td><td>NN8</td><td></td><td></td></tr><tr><td></td><td>CN6/CN5b</td><td>NN8/NN7</td><td></td><td></td></tr></tbody></table>
<table><caption>Table T7 (continued).</caption><thead><tr><th rowspan="2">GTS2012<br>Chronostratigraphy</th><th colspan="2">Standard tropical-subtropical biozone (biochron)</th><th rowspan="2">Biohorizon (datum)</th><th rowspan="2">GTS2012 age<br>(Ma)</th></tr><tr><th>CN Zones<br>(Okada & Bukry, 1980)</th><th>NN Zones<br>(Martini, 1971)</th></tr></thead><tbody><tr><td rowspan="3">Tortonian<br>11.608</td><td rowspan="3">CN5b</td><td rowspan="3">NN7</td><td>T Coccolithus miopelagicus</td><td>10.97</td></tr><tr><td>T Calcidiscus premacintyrei</td><td>11.21</td></tr><tr><td>T common Discoaster kugleri</td><td>11.58</td></tr><tr><td rowspan="10">Serravallian</td><td rowspan="2">CN5b/CN5a</td><td rowspan="2">NN7/NN6</td><td>T Cyclicargolithus floridanus</td><td>11.85</td></tr><tr><td><strong>B common Discoaster kugleri</strong></td><td><strong>11.90</strong></td></tr><tr><td rowspan="8">CN5a</td><td rowspan="8">NN6</td><td>T Coronocyclus nitescens</td><td>12.12</td></tr><tr><td>T regular Calcidiscus premacintyrei</td><td>12.38</td></tr><tr><td>B common Calcidiscus macintyrei</td><td>12.46</td></tr><tr><td>B Reticulofenestra pseudoumbilicus</td><td>12.83</td></tr><tr><td>B Triquetrorhabdulus rugosus</td><td>13.27</td></tr><tr><td>T common Cyclicargolithus floridanus</td><td>13.28</td></tr><tr><td>B Calcidiscus macintyrei</td><td>13.36</td></tr><tr><td><strong>T Sphenolithus heteromorphus</strong></td><td><strong>13.53</strong></td></tr><tr><td>13.82</td><td>CN4</td><td>NN5</td><td></td><td></td></tr><tr><td>Langhian</td><td><strong>CN4/CN3</strong></td><td><strong>NN5/NN4</strong></td><td><strong>T Helicosphaera ampliaperta</strong></td><td><strong>14.91</strong></td></tr></tbody></table>

Pliocene/Miocene boundary an age between the Zanclean and Messinian stages (5.33 Ma), and the late/middle Miocene boundary an age between the Serravallian and Tortonian stages (11.63 Ma). For calcareous nannofossil biostratigraphy, the Pleistocene/Pliocene boundary now falls in Zone NN16 (Martini, 1971) between the LADs of *Discoaster surculus* (2.49 Ma) and *Discoaster tamalis* (2.80 Ma). The Pliocene/Miocene boundary is marked by Zone NN12 between the LAD of *Triquetrorhabdulus rugosus* (5.28 Ma) and the FAD of *Ceratolithus larrymayeri* (5.34 Ma), the latter of which can be approximated using the FAD of *Ceratolithus acutus* (5.35 Ma). The late/middle Miocene boundary is placed in Zone NN7 between the LAD of common *Discoaster kugleri* (11.58 Ma) and the FAD of common *D. kugleri* (11.90 Ma). During Expedition 385, the identification of these geological time boundaries was mostly based on recognition of these nannofossil bioevents.

Nannofossil taxonomy mainly follows that of Perch-Nielsen (1985) and Bown (1998), which are included in the Nannotax3 online database (http://www.mikrotax.org/Nannotax3; last date of retrieval 9 November 2019), except for the taxa discussed below.

Several species of the genus *Gephyrocapsa*, which are commonly used as Pleistocene biostratigraphic markers, often show a great range of variation in sizes and other morphological features, causing problems in identification (e.g., Samtleben, 1980; Su, 1996; Bollmann, 1997). Size-defined morphological groups of this genus (Young, 1998; Maiorano and Marino, 2004; Lourens et al., 2005; Raffi et al., 2006) were used as bioevent markers during shipboard study, including small *Gephyrocapsa* spp. (<3.5 µm), medium *Gephyrocapsa* spp. (≥4 µm), and large *Gephyrocapsa* spp. (≥5.5 µm).

Several *Reticulofenestra* species with different coccolith and central opening sizes have been used as Neogene and Quaternary biostratigraphic markers; however, these characteristics show considerable intra- and intertaxon variation, making species determination difficult (e.g., Young, 1998; Su, 1996). We followed the definition of *Reticulofenestra pseudoumbilicus* by Young (1998) as having a maximum coccolith length >7 µm (similar to the size of its holotype), especially for specimens from its uppermost range in the early Pliocene. We distinguished *Reticulofenestra asanoi* from the similarly sized *Pseudoemiliania lacunosa* by the absence of slits on the shield (Su, 1996).

The LAD of *Sphenolithus* spp. (3.54 Ma) in Pliocene Zone NN16 was based on the LAD of *Sphenolithus abies* and *Sphenolithus neoabies* according to Raffi et al. (2006).

### 6.2.2. Abundance and preservation classification

Calcareous nannofossil samples were prepared using standard smear slide techniques. For sandy sediments, suspended aliquots of the raw sample were utilized for analysis. Slides were mounted with Norland optical adhesive Number 61 and cured under ultraviolet light for examination.
Slides were analyzed by means of a Zeiss Axiophot microscope under cross-polarized and plane-polarized or phase-contrast light using oil immersion at 1000× magnification. All photomicrographs were taken using a SPOT Flex system with the IODP Image Capture and commercial SPOT software. A Hitachi TM3000 tabletop SEM was used to confirm the presence of small forms and the preservation state of calcareous nannofossils.

Total calcareous nannofossil abundance in the sediment (referred to as “group abundance” in DESClogik) was visually estimated at 500× magnification by referring to the particle abundance charts in Rothwell (1989) and reported using the following abundance categories (here applied to fossil tests):

* D = dominant (>90% of tests present).

* A = abundant (>50%-90% of tests).

* C = common (>10%-50% of tests).

* F = few (1%-10% of tests).

* R = rare (<1% of tests).

* B = barren (no nannofossil tests present in 100 fields of view [FOVs]).

The relative abundance of individual calcareous nannofossil taxa was based on the number of specimens per FOV at 1000× magnification and recorded as follows:

* D = dominant (>50%, or >100 specimens per FOV).

* A = abundant (10%-50%, or 10-100 specimens per FOV).

* C = common (1%-10%, or 1-10 specimens per FOV).

* F = few (0.1%-1%, or 1 specimen per 2-10 FOVs).

* R = rare (<0.1%, or <1 specimen per 10 FOVs).

* P = present (1 specimen per >100 FOVs).

Preservation of nannofossil tests was noted as follows:

* VG = very good (no evidence of dissolution and/or overgrowth, no alteration of primary morphological characteristics, and specimens are identifiable to the species level).

* G = good (little dissolution and/or overgrowth, primary morphological characteristics unaltered or only slightly altered, and specimens are identifiable to the species level).

* M = moderate (some etching and/or overgrowth, primary morphological characteristics somewhat altered, and most specimens are identifiable to the species level).

* P = poor (severely etched and fragmented or with overgrowth, primary morphological characteristics largely destroyed, fragmentation has occurred, and most specimens cannot be identified at the species and/or generic level).

## 6.3. Marine diatoms

### 6.3.1. Zonal scheme and taxonomy

Marine diatom biostratigraphy followed the works of Schrader (1974) from DSDP Leg 22/23, Barron (1980) from DSDP Leg 54, Barron (1985) and Barron and Gladenkov (1995) from ODP Leg 145, and Barron (2003). Although the majority of the biostratigraphy followed the work of Barron (1985, 2003), the zonal schemes were refined as needed.

Diatom ages for zones and datum events were calibrated to the Gradstein et al. (2012) geological timescale if there were changes from the astronomically tuned Neogene timescale 2004 (ATNTS2004; Lourens et al., 2005) and also compared to other microfossil datums (Table T8). The LAD and FAD defined by Yanagisawa and Akiba (1998) and modified by Gladenkov (2003) were applied as top (T) and base (B), respectively. Diatoms were identified to the species level when possible.

### 6.3.2. Abundance and preservation classification

Diatom observations were made on every core, being based on standard smear slides prepared from core catcher or section-half samples. Strewn slides were prepared according to McKay et al. (2019) if time allowed. Additional smear/strewn slides were made from intervals within section
halves (usually the archive half) to refine particular zone assignments or for improved age control as needed. Norland optical adhesive Number 61 was placed on the coverslip, and the coverslip was then glued to the slide. The adhesive was solidified by placing it under an ultraviolet lamp for 10–15 min.

Diatom total qualitative abundance was determined at 630× magnification using phase contrast. Observations were made on the two slide transects located at the center of the slide. This slide area is where the sediment is placed before spreading; thus, it is the area with the most consistent amount of sediments between all slides. The number of transects increases if any doubt in the species or their abundance occurs.

Diatom preservation was assessed by applying the following criteria:

* G = good (majority of specimens complete with minor dissolution and/or breakage and no significant enlargement of the areolae or dissolution of the frustule rim detected; the sample generally had a high concentration of diatoms per gram).

<table><caption>**Table T8.** Diatom events and scaled ages (Gradstein et al., 2012) in the Guaymas Basin, Expedition 385. T = top/last appearance datum, B = base/first appearance datum. Download table in CSV format.</caption><thead><tr><th>Diatom zonation</th><th>Subzone</th><th>Diatom bioevent</th><th>GTS 2012 age (Ma)</th><th>Age reference</th></tr></thead><tbody><tr><td rowspan="4">Fragilariopsis doliolus</td><td rowspan="4">B</td><td><strong>T Fragilariopsis reinholdii</strong></td><td><strong>0.62</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>T Fragilariopsis fossilis</td><td>0.70</td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>T Thalassiosira plicata</td><td>0.80</td><td>Barron, 2003</td></tr><tr><td>T Rhizosolenia matuyamai</td><td>1.05</td><td>Barron, 2003</td></tr><tr><td rowspan="2">Fragilariopsis reinholdii</td><td rowspan="2">A</td><td>B Rhizosolenia matuyamai</td><td>1.18</td><td>Barron, 2003</td></tr><tr><td><strong>T Rhizosolenia praebergonii var. robusta</strong></td><td><strong>1.72</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="4">Rhizosolenia praebergonii</td><td rowspan="2">C</td><td>B Azpeitia barronii</td><td>1.80</td><td>Barron, 2003</td></tr><tr><td><strong>B Fragilariopsis doliolus</strong></td><td><strong>2.00</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="2">B</td><td><strong>T Thalassiosira convexa var. convexa</strong></td><td><strong>2.43</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>B Rhizosolenia praebergonii var. robusta</td><td>2.50</td><td>Barron, 2003</td></tr><tr><td rowspan="2">A</td><td><strong>T Nitzschia jouseae</strong></td><td><strong>2.80</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td><strong>B Rhizosolenia praebergonii</strong></td><td><strong>3.20</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="6">Nitzschia jouseae</td><td rowspan="6">B</td><td>B Thalassiosira plicata</td><td>3.30</td><td>Barron, 2003</td></tr><tr><td>T Actinocyclus ellipticus f. lanceolatus</td><td>3.40</td><td>Barron, 2003</td></tr><tr><td>B Azpeitia africana</td><td>3.80</td><td>Barron, 2003</td></tr><tr><td><strong>B Thalassiosira convexa var. convexa</strong></td><td><strong>3.80</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>B Asteromphalus elegans</td><td>4.20</td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>T Fragilariopsis cylindrica</td><td>4.90</td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="6">Thalassiosira convexa</td><td rowspan="2">C</td><td>B Nitzschia jouseae</td><td><strong>5.10</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>B Thalassiosira oestrupii</td><td>5.60</td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="2">B</td><td>T Asterolampra acutiloba</td><td>5.90</td><td>Barron, 2003</td></tr><tr><td><strong>T Thalassiosira miocenica</strong></td><td><strong>5.90</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="4">A</td><td><strong>T Fragilariopsis miocenica</strong></td><td><strong>6.10</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>T Bogorovia lancetula</td><td>6.20</td><td>Barron, 2003</td></tr><tr><td><strong>T Thalassiosira praeconvexa</strong></td><td><strong>6.20</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>B Thalassiosira miocenica</td><td>6.50</td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="2">Nitzschia miocenica</td><td rowspan="2">A</td><td><strong>B Thalassiosira convexa var. aspinosa</strong></td><td><strong>6.60</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>T Nitzschia praeinholdii</td><td>6.70</td><td>Barron, 2003</td></tr><tr><td rowspan="2">A</td><td><strong>B Thalassiosira praeconvexa</strong></td><td><strong>6.70</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td><strong>T Nitzschia porteri</strong></td><td><strong>7.10</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="4">Nitzschia porteri</td><td rowspan="2">B</td><td><strong>B Fragilariopsis miocenica</strong></td><td><strong>7.30</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td><strong>T Rossiella paleacea</strong></td><td><strong>7.60</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="2">A</td><td>T Thalassiosira grunowii</td><td>7.80</td><td>Barron, 2003</td></tr><tr><td>T Actinocyclus ellipticus var. javaicus</td><td>7.80</td><td>Barron, 2003</td></tr><tr><td rowspan="2">A</td><td><strong>T Thalassiosira burckliana</strong></td><td><strong>7.90</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>B Fragilariopsis cylindrica</td><td>8.00</td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="6">Thalassiosira yabei</td><td rowspan="2">A</td><td><strong>T Thalassiosira yabei</strong></td><td><strong>8.20</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td><strong>B Fragilariopsis fossilis</strong></td><td><strong>8.90</strong></td><td>Barron, 1985; Barron, 2003</td></tr><tr><td rowspan="4">B</td><td>T Coscinodiscus loeblichii</td><td>8.80</td><td>Barron, 2003</td></tr><tr><td>T Thalassiosira brunii</td><td>8.90</td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>B Thalassiosira eccentric</td><td>9.00</td><td>Barron, 2003</td></tr><tr><td><strong>B Thalassiosira burckliana</strong></td><td><strong>9.00</strong></td><td>Barron, 2003</td></tr><tr><td rowspan="4">A</td><td rowspan="4">B</td><td>T Coscinodiscus vetustissimus var. javanica</td><td>9.40</td><td>Barron, 1985; Barron, 2003</td></tr><tr><td>B Coscinodiscus loeblichii</td><td>9.60</td><td>Barron, 2003</td></tr><tr><td>B Coscinodiscus vetustissimus var. javanica</td><td>9.60</td><td>Barron, 1985; Barron, 2003</td></tr><tr><td><strong>T Actinocyclus moronensis</strong></td><td><strong>9.80</strong></td><td>Barron, 1985; Barron, 2003</td></tr></tbody></table>
* M = moderate (minor but common areolae enlargement and dissolution of the frustule rim with a considerable amount of breakage of specimens).

* P = poor (strong dissolution or breakage, some specimens unidentifiable, and strong dissolution of the frustule rim and areolae enlargement; the sample generally had a lower concentration of diatoms per gram).

A question mark (?) regarding preservation was used when the sample did not allow an assessment of this property.

Diatom total abundance, a qualitative measure, was based on the number of diatom valves found in one or two slide transects:

* D = dominant (>90% of valves present).

* A = abundant (50%–90% of valves).

* C = common (10%–50% of valves).

* F = few (1%–10% of valves).

* R = rare (<1% of valves).

* B = barren (no diatom valves present).

Relative abundance of individual diatom species (percentage of the total diatom valves) was based on the assemblages found in one or two slide transects and was recorded using the following categories:

* D = dominant (>30% of diatom valves in 1 or 2 slide transects).

* A = abundant (>10%–30% of diatom valves in 1 or 2 slide transects).

* C = common (>5%–10% of diatom valves in 1 or 2 slide transects).

* F = few (>1%–5% of diatom valves in 1 or 2 slide transects).

* R = rare (≤1% of diatom valves in 1 or 2 slide transects).

For the purpose of biostratigraphy and to minimize biases because of the amount of sediment placed on the smear slides, the datums are defined by the presence of at least two specimens in two slide transects. This method was chosen after considering the identification uncertainties and confidence levels discussed in Fatela and Taborda (2002) and the existence of laboratory cross contamination because of the presence of sediment derived from previous samples. Therefore, only relative diatom abundances defined as common or higher were considered for dating purposes. The number of transects was increased once any doubt had arisen regarding species identification or when only fragments of a particular species were present. The counting procedure and definition of counting units (diatom valves) followed Schrader and Gersonde (1978).

# 7. Paleomagnetism

## 7.1. Samples, instruments, and methodology

Paleomagnetic studies during Expedition 385 principally focused on measurement of the natural remanent magnetization (NRM) of archive-half sections on the superconducting cryogenic rock magnetometer (SRM) before and after alternating field (AF) demagnetization. Our aim was to produce a magnetostratigraphy to merge with paleontological datums to yield an age model for each site. Analyses of the archive halves were complemented by stepwise demagnetization and measurement of discrete cube specimens taken from the working halves; these samples were demagnetized to higher AF levels and at closer AF intervals than sections measured on the SRM (Figure F21A). Additionally, discrete samples of sills and indurated sediments were subjected to thermal demagnetization.

Demagnetization was conducted with the aim of removing magnetic overprints, which arise both naturally, particularly by the acquisition of viscous remanent magnetization, and as a result of drilling, coring, and sample preparation. Intense, usually steeply inclined overprint has been routinely described from ODP and IODP cores; it results from exposure of the cores to strong magnetic fields due to magnetization of the core barrel and elements of the BHA and drill string (Stokking et al., 1993; Richter et al., 2007). The use of nonmagnetic stainless steel core barrels
during APC, HLAPC, and RCB coring during Expedition 385 reduced the severity of this drilling-induced overprint (Lund et al., 2003).

Discrete cube samples for paleomagnetic analysis were collected where the core sections were relatively continuous and undisturbed (usually the case in APC- and HLAPC-cored intervals) or where discontinuous recovery or core disturbance made use of continuous sections unreliable (in this case, the discrete samples became the sole basis for magnetostratigraphy). We collected one to two discrete samples per core throughout all sites. We also examined the downhole variation in paleomagnetic results to determine the extent of alteration processes caused by the sill intrusions.

**7.2. Archive-half measurements**

Measurements of remanence and stepwise AF demagnetization were conducted on archive halves with the SRM, driven with the IMS SRM software, version 10.3 (Figure F21C). The SRM is a 2G Enterprises Model 760R-4K equipped with direct-current superconducting quantum interference devices (DC-SQUIDs) and an in-line automated three-axis AF demagnetizer capable of reaching a peak field of 80 mT. The spatial resolution, measured by the width at half height of the response of the pickup coils, is <10 cm for all three axes, although magnetization can be sensed over a core length of as much as 30 cm. The magnetic-moment noise level of the SRM is ~2 × 10⁻¹⁰ Am². The practical noise level, however, is affected by the magnetization of the core liner and the background magnetization of the measurement tray, resulting in a lower limit of magnetization of ~2 × 10⁻⁵ A/m, which can be reliably measured.

We measured the archive halves at 5 cm intervals, and they were passed through the sensor at a speed of 10 cm/s. A 15 cm long interval of empty track was measured before the start of the section passed the center of the pickup coils of the SQUID sensors, and an equal interval of empty

<figure><img src="image_25.png" /></figure>

**Figure F21.** A. Coordinate systems for IODP paleomagnetic samples: archive and working halves. B. Natsuraha-Giken sampling box (7 cm³) with cube coordinate system. Red hatched arrow is parallel to up arrow on sample cube and points in -z-direction. C. Coordinate system used for the SRM on JOIDES Resolution. D. Measurement positions in AGICO JR-6A dual speed spinner magnetometer. E. Example of sawn discrete cube sample and discrete sample in plastic sampling box.
track was measured after the end of the section had passed through it. These are referred to as the
header and trailer measurements and serve the dual functions of monitoring the background mag-
netic moment and enabling future deconvolution analysis. After an initial measurement of NRM,
we proceeded to demagnetize the archive halves over steps of 5, 10, 15, and 20 mT to provide
detailed data on potential drilling overprints. NRM after AF demagnetization was plotted for indi-
vidual sample points as vector plots (Zijderveld, 1967) to assess the effectiveness of removal of
overprints and to show variations with depth at individual demagnetization levels. We inspected
the plots visually to judge whether the remanence after demagnetization at the highest AF demag-
netization step reflected the characteristic remanent magnetization (ChRM) and geomagnetic
polarity sequence.

**7.3. Discrete samples**

Where the sediment was sufficiently soft, we collected discrete 7 cm³ volume samples in plastic Natsuhara Giken sampling boxes (Figure F21B). In soft sediment, these boxes were pushed into the working half of the core by hand with the “up” arrow on the box pointing upsection in the core (Figure F21E). In sills and more indurated sediment, we cut cubes with orthogonal passes of a tile saw that had two parallel blades spaced 2 cm apart (Figure F21E). We simply marked an upcore orientation arrow on the split core face of the cut cube sample. These lithified samples, without a plastic container, were available for both AF and thermal demagnetization.

**7.3.1. Remanence measurements**

We measured the NRM of discrete samples before and after demagnetization on an AGICO JR-6A dual speed spinner magnetometer (sensitivity = ~2 × 10⁻⁶ A/m). We used the automatic sample holder for measuring the plastic sampling boxes and lithified cubes without a plastic container (Figure F21D).

For sediment, progressive AF demagnetization of the discrete samples was achieved with a DTech D-2000 AF demagnetizer in three subsequent positions at intervals of 5 mT up to 30 mT followed by steps at 40, 50, and 60 mT.

For hard rock, we thermally demagnetized a subset of the lithified cube samples, an alternative method that is more effective at demagnetizing high-coercivity materials (e.g., hematite). This method is also efficient at removing the magnetization of magnetic sulfides, particularly greigite, which thermally decomposes during heating in air at temperatures of 300°-400°C (Roberts and Turner, 1993; Musgrave et al., 1995). Difficulties in thermally demagnetizing samples in plastic boxes discouraged us from applying this method to softer samples.

We demagnetized the samples in a Schonstedt TSD-1 thermal demagnetizer, initially at temperature steps of 50° to 450°C and then at steps of 25° to 600°C, and measured demagnetized NRM after each step on the spinner magnetometer. Additional 25°C steps were later added at 175°, 225°, 275°, 325°, and 375°C to better constrain the demagnetization of multidomain magnetite. Samples were held at the specified temperature for a minimum of 30 min and then cooled to room temperature by the built-in fan. To minimize the effect of any magnetism that could be acquired in any residual magnetic field while samples cooled in the oven, samples were arranged in antipodal positions between each heating step.

Demagnetization data for archive halves and all discrete samples were displayed in vector compo-
nent diagrams (Zijderveld, 1967). ChRM directions were calculated from the best fitting compo-
nent by principal component analysis (Kirschvink, 1980) using the software MacPaleomag by
Jeffrey Gee (Scripps Institution of Oceanography) ([https://earthref.org/ERDA/2203](https://earthref.org/ERDA/2203)). We ana-
lyzed the data using inclination-only statistics (Arason and Levi, 2010). In addition, the mean
destructive field and median destructive temperature were calculated at the field (for AF demag-
netization) and temperature (for thermal demagnetization) at which the NRM intensity is reduced
to 50%, which helps to determine the magnetic mineral composition present in samples and their
associated grain sizes.
**7.3.2. Liquid nitrogen treatment**

Multidomain magnetite, with grain sizes typically greater than ~1 µm, does not exhibit the simple relationship between acquisition and unblocking temperatures predicted by Néel (1949) for single-domain grains, which could potentially cause low-temperature or low-coercivity overprints. For this reason, when we had evidence that overprints in multidomain grains were obscuring the magnetostratigraphic signal (e.g., in igneous rocks), we instituted a program of liquid nitrogen cooling of the discrete samples in field-free space (Dunlop et al., 1997). This involved inserting the samples (after first drying them during thermal demagnetization at 110°C) into a bath of liquid nitrogen held in a Styrofoam container, which was then placed in a triple-layer mu-metal cylindrical can to provide a (near) zero-field environment. We then allowed the nitrogen to boil off and the samples to warm. Cooling the samples forces the magnetite below the Verwey transition; warming within field-free space above the transition enables remanence to recover in single-domain grains, but it randomizes remanence in multidomain grains. Once the samples were at room temperature, they were transferred to a smaller mu-metal can until measurement to avoid acquisition of a viscous remanence. Their remanence was measured, and then routine thermal demagnetization was continued.

**7.3.3. Anisotropy of magnetic susceptibility**

At all drill sites, we carried out magnetic fabric analysis in the form of measurements of anisotropy of magnetic susceptibility as a measure of sediment compaction. We carried this out on all discrete samples using an AGICO Kappabridge KLY 4 magnetic susceptibility meter. We calculated anisotropy as the foliation $F = K_2/K_3$ and the lineation $L = K_1/K_2$, where $K_1$, $K_2$, and $K_3$ are the maximum, intermediate, and minimum eigenvalues of the anisotropy tensor. We describe the shape of the anisotropy ellipsoid by the shape parameter *T* (Jelínek and Kropáček, 1978) where $-1.0 < T < 1.0$ indicate prolate/oblate fabrics, respectively. Additionally, we describe the strength of anisotropy using the corrected anisotropy degree *Pj* (Jelínek and Kropáček, 1978), where *Pj* = 1.0 indicates an isotropic fabric, and, for example, *Pj* = 1.05 indicates 5% anisotropy. Both the shape parameter and anisotropy degree are dependent on the relationships between the eigenvalues of the anisotropy tensor.

**7.4. Sample coordinates**

All magnetic data are reported relative to the IODP orientation conventions: +*x* is into the face of the working half, +*y* points toward the left side of the face of the working half, and +*z* points down-section. The relationship of the SRM coordinates (*x*-, *y*-, and *z*-axes) to the data coordinates (*x*-, *y*-, and *z*-directions) is as follows: for archive halves, *x*-direction = *x*-axis, *y*-direction = -*y*-axis, and *z*-direction = *z*-axis; for working halves, *x*-direction = -*x*-axis, *y*-direction = *y*-axis, and *z*-direction = *z*-axis (Figure F21A). Discrete cubes are marked with an arrow on the split face (or the corresponding face of the plastic box) in the upsection (i.e., -*z*) direction (Figure F21B, F21E).

**7.5. Core orientation**

The core orientation process determines the angular correction to apply to the archive halves' declination values as measured by the SRM. APC and HLAPC cores were oriented by means of the Icefield MI-5 core orientation tool. The Icefield orientation tool is connected to the core barrel in such a way that the double lines on the core liner are at a fixed known angle to the sensors. The Icefield orientation tool orients cores by taking orientation measurements for a short period of time just prior to when the core is taken. The orientation tool is run on the APC BHA in a non-magnetic core barrel. The drill string is kept steady while the tool measures and stores measurements (declination, inclination, total magnetic field, and temperature) from a triaxial magnetometer and a triaxial accelerometer. During Expedition 385, a measurement interval of 10 s was used. The Icefield orientation tool records an azimuth to magnetic north for each core. The sensors provide an azimuthal correction for the core barrel that, combined with the local magnetic declinations, enables the measured NRM declinations on archive halves to be transformed into true geographic coordinates. The data were processed using the in-house Inclin software.
<table><caption>**Table T9.** Age estimates for timescale of magnetostratigraphic chrons (Gradstein et al., 2012) and age and duration of magnetic excursions within the Brunhes and Matuyama Chrons (Laj and Channell, 2015) expected for IODP Expedition 385. Italics indicate poorly documented excursions. T = top, B = bottom. **Download table in CSV format.**</caption><thead><tr><th>Chron</th><th>Datum</th><th>Age (Ma)</th><th>Name</th><th>Excursion name</th><th>Estimated age (ka)</th><th>Estimated duration (ky)</th></tr></thead><tbody><tr><td colspan="7">Excursions within the Brunhes Chron (&lt;0.781 Ma)</td></tr><tr><td></td><td></td><td></td><td></td><td>Mono Lake</td><td>33</td><td>1</td></tr><tr><td></td><td></td><td></td><td></td><td>Laschamp</td><td>41</td><td>1.5</td></tr><tr><td></td><td></td><td></td><td></td><td>Norwegian-Greenland Sea</td><td>60</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>Blake</td><td>120</td><td>5</td></tr><tr><td></td><td></td><td></td><td></td><td>Iceland Basin</td><td>188</td><td>3</td></tr><tr><td></td><td></td><td></td><td></td><td>Pringle Falls</td><td>211</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>Calabrian Ridge I</td><td>260</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>Calabrian Ridge II</td><td>325</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>Calabrian Ridge III</td><td>525</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>Big Lost</td><td>560-580</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>Stage 17</td><td>670</td><td></td></tr><tr><td colspan="7">Excursions within the Matuyama Chron (0.781-2.581 Ma)</td></tr><tr><td></td><td></td><td></td><td></td><td>Kamikatsura</td><td>850</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>Santa Rosa</td><td>932</td><td>3</td></tr><tr><td></td><td></td><td></td><td></td><td>Punaruu</td><td>1115</td><td>3</td></tr><tr><td></td><td></td><td></td><td></td><td>Bjorn</td><td>1255</td><td>3</td></tr><tr><td></td><td></td><td></td><td></td><td>Gardar</td><td>1465</td><td>20</td></tr><tr><td></td><td></td><td></td><td></td><td>Gilsa</td><td>1567</td><td>8</td></tr><tr><td></td><td></td><td></td><td></td><td>Pre-Olduvai</td><td>1977</td><td>3</td></tr><tr><td></td><td></td><td></td><td></td><td>Huckleberry Ridge</td><td>2040</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>Pre-Réunion I</td><td>2236</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td>Pre-Réunion 2/Halawa</td><td>2421</td><td></td></tr><tr><td>C1n</td><td>B</td><td>0.781</td><td>Brunhes/Matuyama</td><td></td><td></td><td></td></tr><tr><td>C1r.1n</td><td>T</td><td>0.988</td><td>Jaramillo top</td><td></td><td></td><td></td></tr><tr><td></td><td>B</td><td>1.072</td><td>Jaramillo base</td><td></td><td></td><td></td></tr><tr><td>C1r.2n</td><td>T</td><td>1.173</td><td>Cobb Mountain top</td><td></td><td></td><td></td></tr><tr><td></td><td>B</td><td>1.185</td><td>Cobb Mountain base</td><td></td><td></td><td></td></tr><tr><td>C2n</td><td>T</td><td>1.778</td><td>Olduvai top</td><td></td><td></td><td></td></tr><tr><td></td><td>B</td><td>1.945</td><td>Olduvai base</td><td></td><td></td><td></td></tr><tr><td>C2r.1n</td><td>T</td><td>2.128</td><td>Reunion top</td><td></td><td></td><td></td></tr><tr><td></td><td>B</td><td>2.148</td><td>Reunion base</td><td></td><td></td><td></td></tr><tr><td>C2An.1n</td><td>T</td><td>2.581</td><td>Matuyama/Gauss</td><td></td><td></td><td></td></tr></tbody></table>

The ChRMs can also provide a reference frame to orient cores. Provided that the reference magnetic pole is known, the orientation of the paleomagnetic vector is then used to restore the azimuth of the +x core axis (e.g., Fuller, 1969).

## 7.6. Magnetostratigraphy

Expedition 385 drill sites are located between ~27°10′N and 27°40′N, far enough from the Equator to easily identify distinct changes in inclination. By considering the mean state of the Earth's magnetic field to be a geocentric axial dipole, it is possible to calculate the field inclination, *I*, as tan(*I*) = 2 tan(*lat*), where *lat* is the latitude. Hence, the time-averaged normal field at the present-day positions of Sites U1545–U1552 has a positive (downward) inclination of ~46°. Negative inclinations indicate reversed polarity. The shipboard data were correlated to the geomagnetic polarity timescale of Gradstein et al. (2012) with the aid of biostratigraphic datums. Magnetic excursions within the Brunhes Chron (C1n) and Matuyama Chron (C1r) are dated according to Laj and Channell (2015) and references therein (Table T9).

# 8. Inorganic geochemistry

## 8.1. Interstitial water collection

Inorganic geochemical data from IW profiles provide information on biogeochemical reactions, abiotic reactions, water-rock interactions, and fluid migration. During Expedition 385, IW samples were collected for onboard analysis and for a wide range of postexpedition analyses. The squeeze cakes, residual sediments after IW extraction, were also collected and distributed for postexpedition research. In addition, sediment subsampling and extraction of dissolved inorganic
nitrogen (i.e., ammonium and nitrate) for nitrogen isotope analysis of dissolved inorganic nitrogen and mineral nitrogen were performed aboard the vessel.

IW was extracted using a titanium squeezer (Manheim and Sayles, 1974) according to the following procedure. After cutting from the core liner, the surface of each whole-round core sample was carefully scraped off with a ceramic knife to remove potential contamination from seawater, drilling disturbances, and sediment smearing that may have happened along the inside of the core liners. Holes U1545C, U1546D, U1548C–U1548E, U1551B, and U1552A–U1552C were trimmed under a nitrogen-filled glove bag to minimize the oxidation of redox-sensitive elements (S, Fe, and Mo); the other holes were processed under atmospheric conditions. For APC cores, ~0.5 cm of material from the outer diameter, top, and bottom of the whole-round sample was usually removed, whereas in XCB and RCB cores, where borehole contamination may be more substantial, ~1 cm of the outer sediment and any physically disturbed layers were removed from each whole-round core section. The cleaned sediment (~150–300 cm³) was placed into a 9 cm diameter titanium squeezer that was then placed in a Carver hydraulic laboratory press (Manheim and Sayles, 1974) and squeezed at pressures no higher than ~20,000 lb (~10 MPa) to prevent water release from clay minerals during squeezing. After each use, the squeezer was cleaned with tap water, rinsed with 18 MΩ deionized water (DI), and thoroughly dried with compressed air.

The squeezed IW was filtered through a DI-prewashed Whatman No. 1 filter placed in the squeezer cell above a titanium screen. The squeezed fluids were filtered through a 0.2 µm polyethersulfone membrane disposable filter attached to the squeezing assembly and collected in a precleaned (10% HCl) high-density polyethylene (HDPE) syringe attached to the filter. Squeeze cakes were saved for separate analyses by science party members and generally frozen at –20°C unless specified otherwise.

To better understand the processes in the shallow sediment column of Sites U1547–U1549, IW was sampled using Rhizon samplers at a higher spatial resolution. This technique was previously tested and validated during Integrated Ocean Drilling Program Expedition 302 (Dickens et al., 2007). Within 10 min after cores were recovered on the core receiving platform, core sections were transported inside and holes were drilled into the plastic liner (1–2 per section). Precleaned (10% HCl) 5 cm long Rhizon samplers were inserted into holes, connected to precleaned (10% HCl) 30 mL syringes that were pulled to generate a vacuum, and held open with a spacer.

Sample distribution was determined based on the recovered IW volume and analytical priorities as well as the objectives of the expedition. Shipboard analyses were done on all IW recovered, whereas personal sampling was mainly done on holes where microbiology sampling occurred. For personal sampling, the relative priorities of geochemistry and microbiology sample distribution, as well as sample pretreatment and storage, are summarized in Table T10.

Generally, IW samples were analyzed on board following the protocols outlined by Gieskes et al. (1991), Murray et al. (2000), and the IODP user manuals for shipboard instrumentation (http://iodp.tamu.edu/labs/documentation), which were updated during this expedition. Details for specific analyses are provided below.

## 8.2. Interstitial water analysis

### 8.2.1. Salinity, alkalinity, and pH

Salinity, alkalinity, and pH were measured immediately after squeezing following the procedures in Gieskes et al. (1991). Salinity was measured using an Index Instruments Ltd. temperature-compensated digital refractometer. International Association for the Physical Sciences of the Oceans (IAPSO) standard seawater was used for salinity calibration (salinity = 35). The pH value was measured by means of a combination glass electrode, and alkalinity was determined by Gran titration with a Metrohm 794 basic Titrino autotitrator. A 3 mL sample was titrated against 0.1 N HCl at 25°C to reach an endpoint of pH = 4.2. The IAPSO standard seawater (alkalinity = 2.325 mM; certified value) as well as laboratory-made standards (20 and 40 mM of the 0.1 M KCl + 0.7 M Na₂CO₃ mixture) were used for calibration. The IAPSO standard was analyzed at the beginning and end of a set of samples for each site and after every 10 samples. Repeated measurements of IAPSO seawater for alkalinity yielded precision better than 2.5%.
## 8.2.2. Chloride concentration by titration

High-precision chloride concentrations were acquired using a Metrohm 785 DMP autotitrator. A 0.1 mL aliquot of sample was diluted with 30 mL of 90 ± 2 mM HNO₃ and titrated with 0.015 N AgNO₃. The silver nitrate (AgNO₃) solutions were calibrated against repeated titrations of the IAPSO standard seawater (~559 mM chloride). The IAPSO standard was analyzed at the beginning and end of a set of samples for each site and after every 10 samples. Repeated measurements of the IAPSO standard seawater yielded precision better than 0.4%.

## 8.2.3. Sulfate, chloride, bromide, sodium, magnesium, potassium, and calcium

Sulfate, chloride, bromide, sodium, magnesium, potassium, and calcium concentrations were analyzed by ion chromatography (Metrohm 850 Professional IC) using aliquots of 100 µL that were diluted 1:100 with DI water. For anion (Cl⁻, SO₄²⁻, and Br⁻) analyses, a Metrosep C6 column (100 mm long; 4 mm inner diameter) was used with 3.2 mM Na₂CO₃ and 1.0 mM NaHCO₃ solutions as eluents. For cation analyses (Na⁺, K⁺, Mg²⁺, and Ca²⁺), a Metrosep A supp 7 column (150 mm long; 4 mm inner diameter) was used with 1.7 mM of HNO₃ and pyridine-2,6-dicarboxylic acid (PDCA) solutions as eluents. The standards used were based on IAPSO dilutions (1:50 to 1:350) to create a 6-point calibration curve. Reproducibility was checked based on the standard IAPSO sample dilution of 1:100 run after every 10 samples. The reproducibility of chloride, sulfate, sodium, magnesium, and calcium was better than 1.5%, whereas for bromide and potassium it was better than 3.0%.

## 8.2.4. Ammonium, phosphate, and sulfide

Concentrations of dissolved ammonium, phosphate, and sulfide were determined using an Agilent Technologies Cary Series 100 UV-Vis spectrophotometer with a sipper sample introduction system following Gieskes et al. (1991). The ammonium concentrations were determined by a colorimetric method that incorporates diazotization of phenol and subsequent oxidation of the diazo compound by Clorox to yield a blue color, measured spectrophotometrically at 640 nm. Samples were diluted prior to color development so that the highest ammonium concentration was always <1000 µM. The solution was kept at room temperature for ~6.5 h to develop color after adding the reagents. The reproducibility of the analysis was better than 2.0%.

<table><caption>**Table T10.** Summary of IW sampling distribution during Expedition 385. DIN = dissolved inorganic nitrogen, VFA = volatile fatty acid, DOC = dissolved organic carbon, DIC = dissolved inorganic carbon, LMW = low molecular weight, DON = dissolved organic nitrogen, HMW = high molecular weight, ZnAc = zinc acetate. **Download table in CSV format.**</caption><thead><tr><th>Analysis items</th><th>Sample code</th><th>Priority</th><th>Subsample container</th><th>Volume (mL)</th><th>Frequency</th><th>Pretreatment</th><th>Storage</th></tr></thead><tbody><tr><td>Shipboard salinity, pH, alkalinity, anions, cations, nutrients</td><td>IWS</td><td>1</td><td>14 mL Falcon tube</td><td>8</td><td>1 per core</td><td>None</td><td>Frozen at -20°C after analysis</td></tr><tr><td>Shipboard cations</td><td>IWICP</td><td>1</td><td>2 mL cryo vial</td><td>2</td><td rowspan="5">1 per core</td><td>10 µL HNO<sub>3</sub>/2 mL IW</td><td>Store at 4°C</td></tr><tr><td>δ<sup>18</sup>O and δD</td><td>IWKIM1</td><td>2</td><td>2 mL glass vial</td><td>2</td><td>None</td><td>Store at 4°C</td></tr><tr><td>Nontraditional isotopes (Sr, Li, Mg, etc.)</td><td>IWKIM3</td><td>2</td><td>8 mL Nalgene bottle</td><td>6</td><td>10 µL HNO<sub>3</sub>/2 mL IW</td><td>Store at 4°C</td></tr><tr><td>δ<sup>13</sup>C<sub>DIC</sub></td><td>IWTORR</td><td>2</td><td>2 mL glass vial</td><td>2</td><td>10 µL HgCl<sub>2</sub></td><td>Store at 4°C</td></tr><tr><td>δ<sup>18</sup>O and δD, Δ<sup>17</sup>O</td><td>IWASH</td><td>2</td><td>2 mL glass vial</td><td>2</td><td>No headspace/crimp with stopper and aluminum cap</td><td>Store at 4°C</td></tr><tr><td>δ<sup>15</sup>N of DIN</td><td>IWYAMA</td><td>2</td><td>5 mL cryo vial</td><td>5</td><td rowspan="5">1 per core</td><td>None</td><td>Frozen at -20°C</td></tr><tr><td>VFA</td><td>385VHIW1</td><td>2</td><td>4 mL glass vial</td><td>2</td><td>None</td><td>Frozen at -20°C</td></tr><tr><td>DOC</td><td>385VHIW2</td><td>2</td><td>4 mL glass vial</td><td>2</td><td>None</td><td>Store at 4°C</td></tr><tr><td>DIC</td><td>385VHIW3</td><td>2</td><td>2 mL glass vial</td><td>2</td><td>None</td><td>Frozen at -20°C</td></tr><tr><td>S isotopes and concentration for sulfide</td><td>IWPAST1</td><td>2</td><td>20 mL iChem glass vial</td><td>5</td><td>100 mg ZnAc/5 mL IW</td><td>Store at 4°C</td></tr><tr><td>Fe, Mo, Ni isotopes</td><td>IWPAST2</td><td>2</td><td>15 mL Nalgene bottle</td><td>10</td><td rowspan="3">Depends on temperature profile</td><td>6 µL HNO<sub>3</sub>/10 mL IW</td><td>Store at 4°C</td></tr><tr><td>DOC-LMW</td><td>IWZHUA</td><td>2</td><td>20 mL serum glass vial</td><td>6</td><td>None</td><td>Frozen at -80°C</td></tr><tr><td>Hydrocarbon</td><td>IWEDGC1</td><td>2</td><td>20 mL serum glass vial</td><td>20</td><td>Crimp with stopper and aluminum cap</td><td>Store at 4°C</td></tr><tr><td>DIC, DOC, DON</td><td>IWEDGC2</td><td>2</td><td>5 mL cryo vial</td><td>10</td><td rowspan="2">1 per core</td><td>Two 5 mL sample</td><td>Frozen at -20°C</td></tr><tr><td>Dissolved nitrate + nitrite, ammonia, phosphate</td><td>IWEDGC2</td><td>2</td><td>5 mL cryo vial</td><td>5</td><td>None</td><td>Frozen at -20°C</td></tr><tr><td>Silicon isotope</td><td>IWRAN</td><td>2</td><td>Pre-acid washed 5 mL cryo vial</td><td>5</td><td>1 per core</td><td>Add 25 µL 1 M HCl</td><td>Room temperature</td></tr><tr><td>δ<sup>33,34,36</sup>S of sulfate and sulfide</td><td>IWSEEW</td><td>3</td><td>20 mL iChem glass vial</td><td>5</td><td>1 per core</td><td>100 mg ZnAc/5 mL IW</td><td>Store at 4°C</td></tr><tr><td>DOC-HMW</td><td>IWSEID</td><td>3</td><td>30 mL Nalgene amber bottles</td><td>30</td><td>1 per core</td><td>Avoid contact with plastics or organic solvents</td><td>Frozen at -80°C</td></tr></tbody></table>
Phosphate concentrations were based on the reaction of orthophosphate with Mo(VI) and Sb(III) in an acidic solution, forming an antimony-phosphomolybdate complex that is subsequently reduced by ascorbic acid to form a blue color. The absorbance was measured spectrophotometrically at 885 nm wavelength ~30 min after adding the mixed reagent solution (Gieskes et al., 1991). Samples were diluted prior to color development so that the highest concentration was always <100 µM. The reproducibility was better than 2.0%.

For sulfide analysis ($\Sigma\text{H}_2\text{S} = \text{S}^{2-} + \text{HS}^{-} + \text{H}_2\text{S}$), exposure to air must be minimized to prevent abiotic oxidation of IW sulfide. These samples were fixed with a zinc acetate solution (100 g/L: 50 µL per 1 mL of sample) that was immediately added to freshly squeezed IW. Sulfide concentrations were measured following the Cline method (Cline, 1969; Grasshoff et al., 1999) with no dilution for concentrations ranging between 1 and 60 µM and with a dilution factor of 10 for concentrations up to 600 µM. Dilutions were made with $\text{N}_2$-purged DI water. For each dilution factor, a calibration curve was prepared with the same zinc acetate final concentrations. The absorbance was read at 670 nm. Because most of our samples had sulfide concentrations higher than 600 µM (several millimolar), we also measured high concentrations of sulfide directly using a solution containing a known excess of triiodide ($\text{I}_3^-$) (Grasshoff et al., 1999) that forms a yellow color. Sulfide reacts with triiodide to form $\text{I}^-$ and S, and therefore lowers the absorbance at 400 nm. This titration is commonly used to determine the concentration of the $\text{Na}_2\text{S}$ stock solution later used to build the standards for the Cline method.

### 8.2.5. Sample preparation for shore-based sulfur isotope analysis

While handling IW samples for sulfur isotopic analyses, prolonged exposure to air must be minimized to prevent abiotic oxidation of IW sulfide. Because of their oxygen sensitivity, these samples were processed immediately from freshly squeezed IW. Before IW sampling, sample vials were prepared as shown in Table T10.

### 8.2.6. Major, minor, and trace elements

Major and minor elements ($\text{Na}^+$, $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, $\text{K}^+$, $\text{Li}^+$, B, Si, $\text{Ba}^{2+}$, Fe, Mn, and $\text{Sr}^{2+}$) were analyzed using ICP-AES (Agilent 5110 ICP-OES instrument in ICP-AES mode with a SPS4 autosampler). The general method for shipboard ICP-AES analysis of samples is described in ODP Technical Note 29 (Murray et al., 2000) and in the user manuals for shipboard instrumentation with modifications as indicated. Samples and standards were diluted 1:10 in 2% $\text{HNO}_3$ and spiked with an internal standard to correct for atomic and ionic interferences. Specifically, 100 µL of spike solution containing 100 ppm Be, In, and Sc and 200 ppm Sb was added to 500 µL of IW sample and 4.4 mL of 2% $\text{HNO}_3$. Each batch of samples analyzed on the ICP-AES contained blanks and solutions of known concentrations. Each item aspirated into the ICP-AES was counted three times from the same dilute solution in a given sample run. Following each instrument run, the measured raw intensity values were transferred to a data file and automatically corrected for instrument drift and blank values using Agilent's ICP Expert software (version 7.3.0.1.9507).

Standardization of major cations ($\text{Na}^+$, $\text{K}^+$, $\text{Mg}^{2+}$, and $\text{Ca}^{2+}$) was achieved by successive dilution of IAPSO standard seawater (1:1 to 1:100). Analytical reproducibility was based on repeated analyses of the 1:1 dilution standard over the 2 month expedition and had the following variability ranges: $\text{Ca}^{2+} < 1.5\%$, $\text{Mg}^{2+} < 1.6\%$, $\text{Na}^+ < 1.7\%$, and $\text{K}^+ < 1.5\%$.

For minor and trace element concentration analyses ($\text{Li}^+$, B, Si, $\text{Ba}^{2+}$, Fe, Mn, and $\text{Sr}^{2+}$), the 1:10 dilution of the sample was not sufficient to prevent a matrix effect. Thus, standards were prepared in an acidified synthetic seawater with an ionic strength similar to seawater. A stock multielement standard solution was prepared from ultrapure primary standards (1000 ppm; SPEX CertiPrep reference standards) in a 2% $\text{HNO}_3$ solution. The stock solution was then diluted in the same 2% ultrapure $\text{HNO}_3$ solution (1:1 to 1:20). For consistency, the calibration standards were then diluted using the same method as the samples. The 1:1 standard was repeatedly analyzed with each batch of samples over the 2 month expedition as a check of analytical reproducibility. Analytical reproducibility based on repeated analyses of the minor and trace elements was $\text{Li}^+ < 1.6\%$, B < 1.6%, Si < 2.4%, $\text{Ba}^{2+} < 2.6\%$, Fe < 2.5%, Mn < 1.7%, and $\text{Sr}^{2+} < 2.2\%$.
**8.3. Extraction experiment for shore-based nitrogen isotope analysis**

Dissolved inorganic nitrogen species (i.e., ammonium and nitrate) and exchangeable ammonium within clay mineral interlayers were extracted from sediment samples (about 5 cm³ wedge samples) collected at 10–20 m depth intervals by shaking the sample in ~80 mL of 2 M KCl solution in a flask overnight. After extraction, the liquid phase was filtered with a 0.2 µm membrane filter and stored in a freezer (colder than –20°C) in plastic bottles (125 mL). The solid phase containing mineral nitrogen was washed with pure water and stored in a plastic bag and then freeze-dried. The dried samples were stored in a refrigerator at 4°C.

**8.4. Igneous rock geochemistry**

**8.4.1. Sample preparation**

Least-altered rock chips 5–10 cm³ in volume were selected from fragmented core pieces of the working-half sections of recovered sill material from Sites U1545–U1548 and U1550. Each solid rock sample was placed in a beaker containing isopropanol and agitated in an ultrasonic bath for 15 min. Upon decanting the isopropanol, the samples were then agitated twice in an ultrasonic bath in nanopure DI water (18 MΩ·cm) for 10 min. Subsequently, the clean pieces were dried for 10–12 h at 110°C. The rock samples were then crushed to <1 cm in length between two Delrin plastic disks in a hydraulic press.

Crushed rock chips were then subjected to grinding to produce a fine powder using a SPEX 8515 Shatterbox powdering system with a tungsten carbide mill. A potential contamination effect of the latter was investigated during ODP Leg 206 (Shipboard Scientific Party, 2003b). This study found contamination to be negligible for major elements and most trace elements determined aboard the vessel (Sc, V, Cr, Ni, Sr, Y, Zr, and Ba). A systematic analysis of shipboard powders from Integrated Ocean Drilling Program Expedition 304/305, however, pointed to possible Co contamination during the powdering process (Godard et al., 2009). Upon milling, the prepared powder was processed for ICP-AES measurements.

**8.4.2. Loss on ignition**

Upon powdering, a sample powder aliquot of 2.00 to 5.00 ± 0.05 g was weighed on a Mettler Toledo balance and ignited for 4 h at 1025°C for igneous rocks to determine weight loss on ignition (LOI) volatile budgets with an estimated precision of 0.02 g (0.4%).

**8.4.3. ICP-AES**

For IW measurements, the standard shipboard procedure for digestion of rocks and subsequent ICP-AES analysis is outlined in Murray et al. (2000) and the shipboard user guide for ICP-AES. Modifications as indicated in the IODP Expedition 366 methods (Fryer et al., 2018) and Expedition 369 methods (Huber et al., 2019) were applied to igneous rock analysis during Expedition 385. The analytical protocol, which is adopted from the IODP Expedition 376 methods (de Ronde et al., 2019), is summarized below.

Samples and standards were weighed on a Cahn C-29 microbalance to 100.0 ± 0.5 mg. Weighing errors are estimated to be ±0.2 mg under relatively smooth sea-surface conditions. Aliquots of ignited bulk rock powders were mixed with 400.0 ± 0.5 mg of LiBO₂ flux (preweighed on shore). An aqueous LiBr solution (10 µL of 0.172 mM) was added to the flux and rock powder mixture as a nonwetting agent prior to sample fusion to prevent the fused bead from sticking to the crucible during cooling. Samples were fused individually in Pt-Au (95:5) crucibles for ~12 min at a maximum temperature of 1050°C in an internally rotating induction furnace (Bead Sampler NT-2100).

For the subsequent digestion procedure, each bead was transferred into a 125 mL, precleaned (10% HCl) HDPE bottle and dissolved in a 50 mL solution containing 10 wt% HNO₃ (derived from Optima-grade concentrated HNO₃). To promote the dissolution, bottles with mixed beads and HNO₃ were placed in a Burrell wrist-action shaker and shaken for 1–2 h at a temperature of 7°C. After the bead was completely dissolved in HNO₃, 20 mL of each acidified sample solution was extracted and transferred through a 0.45 µm Acrodisc filter into a 60 mL Nalgene bottle to avoid any insoluble material during the ICP-AES measurement. Each filtered sample solution was then
diluted by pipetting a 0.5 mL aliquot into 4.4 mL of 10 wt% HNO₃ and 0.1 mL of internal standard solution containing Be, In (100 µg/g), and Sb (200 µg/g), applying a solution-to-sample dilution factor of 4000×.

Measurements of major and trace element contents of standards and samples were performed on an Agilent 5110 ICP-OES instrument in ICP-AES mode. Analyses of certified international rock reference materials, calibration and drift solutions, and chemical procedure blanks were processed along with the unknown samples for each measurement run (Table T11). Detection limits were calculated as 3× the standard deviation of the mean for blank solution measurements (Table T12).

The ICP-AES plasma was ignited at least 20 min prior to each sample run to enable the instrument to stabilize sufficiently. All other premeasurement preparation on the ICP-AES instrument was routinely performed using the JRSO shipboard procedures to maintain consistency between different runs. The ICP-AES data presented in the Igneous petrology sections of corresponding site chapters (i.e., Sites U1545, U1546, U1547/U1548, and U1550) were acquired using Agilent's ICP Expert software. Twenty measurements for each element define the intensity curve within the designated wavelength window. Integration of the area delineated by the baseline and the intensity curve is done by the Expert software. Each sample was analyzed three times from the same dilute solution in a given sample run. The wavelength yielding the best calibration line was identified and used to determine the concentrations for each element of unknown samples.

Estimates of accuracy of major and trace element analyses were based on analyses of seven international, certified igneous rock powder standards (Table T12). During the single ICP-AES igneous rock measurement run on Expedition 385, an international rock standard was analyzed in every fourth to fifth sample position so that each standard was measured once within the single sample run. A procedural blank solution was analyzed at the beginning and end of this run, and 35 unknown samples were analyzed. A 10% HNO₃ wash solution was run for 90 s between each sample analysis. Check standards were used to monitor and determine analytical accuracy and precision of the final data. Detection limits were obtained from blank measurements.

<table><caption>**Table T11.** Preferred values for the rock standards used for calibration of major and trace element inductively coupled plasma atomic emission spectroscopy (ICP-AES) analyses on igneous rocks, Expedition 385. LOI = loss on ignition. — = no data. **Download table in CSV format.**</caption><thead><tr><th>Sample:</th><th>MRG-1</th><th>NIM-P</th><th>JG-1a</th><th>AGV-1</th><th>BCR-2</th><th>BHVO-2</th><th>BIR-1</th></tr><tr><th>Provider:</th><th>CCRMP</th><th>NIM (now MINTEK)</th><th>GSJ</th><th>USGS</th><th>USGS</th><th>USGS</th><th>USGS</th></tr><tr><th>Material:</th><th>Gabbro</th><th>Pyroxenite</th><th>Granodiorite</th><th>Andesite</th><th>Basalt</th><th>Basalt</th><th>Basalt</th></tr><tr><th>Location:</th><th>Mount Royal, Montreal, Canada</th><th>Critical zone of the Bushveld Igneous Complex, South Africa</th><th>Ashio Mountains, Japan</th><th>Guano Valley, Oregon, USA</th><th>Columbia River, Oregon, USA</th><th>Kilauea, Hawaii, USA</th><th>Reykjavik, Iceland</th></tr></thead><tbody><tr><td colspan="8"><strong>Major element oxide (m% [wt%]):</strong></td></tr><tr><td>SiO<sub>2</sub></td><td>39.12</td><td>51.10</td><td>72.19</td><td>58.84</td><td>54</td><td>49.6</td><td>47.77</td></tr><tr><td>TiO<sub>2</sub></td><td>3.77</td><td>0.2</td><td>0.25</td><td>1.05</td><td>2.27</td><td>2.73</td><td>0.96</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>8.47</td><td>4.18</td><td>14.22</td><td>17.15</td><td>13.48</td><td>13.44</td><td>15.35</td></tr><tr><td>Fe<sub>2</sub>O<sub>3</sub>t</td><td>17.94</td><td>12.76</td><td>2.05</td><td>6.77</td><td>13.77</td><td>12.39</td><td>11.26</td></tr><tr><td>MnO</td><td>0.17</td><td>0.22</td><td>0.06</td><td>0.09</td><td>0.2</td><td>0.17</td><td>0.17</td></tr><tr><td>MgO</td><td>13.55</td><td>25.33</td><td>0.69</td><td>1.53</td><td>3.6</td><td>7.26</td><td>9.68</td></tr><tr><td>CaO</td><td>14.7</td><td>2.66</td><td>2.13</td><td>4.94</td><td>7.11</td><td>11.4</td><td>13.24</td></tr><tr><td>Na<sub>2</sub>O</td><td>0.74</td><td>0.37</td><td>3.41</td><td>4.26</td><td>3.12</td><td>2.22</td><td>1.75</td></tr><tr><td>K<sub>2</sub>O</td><td>0.18</td><td>0.09</td><td>4.01</td><td>2.92</td><td>1.77</td><td>0.51</td><td>0.03</td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>0.08</td><td>0.02</td><td>0.08</td><td>0.49</td><td>0.36</td><td>0.27</td><td>0.05</td></tr><tr><td>LOI</td><td>1.28</td><td>0.34</td><td>0.68</td><td>1.96</td><td>0.32</td><td>0.01</td><td>0</td></tr><tr><td colspan="8"><strong>Trace element (µg/g):</strong></td></tr><tr><td>Sc</td><td>55</td><td>29</td><td>6.31</td><td>12.2</td><td>33.53</td><td>31.83</td><td>44</td></tr><tr><td>V</td><td>526</td><td>230</td><td>23</td><td>121</td><td>417.6</td><td>318.2</td><td>313</td></tr><tr><td>Cr</td><td>430</td><td>24,000</td><td>18.6</td><td>10.1</td><td>15.9</td><td>287.2</td><td>382</td></tr><tr><td>Ni</td><td>193</td><td>560</td><td>6.4</td><td>16</td><td>12.6</td><td>119.8</td><td>166</td></tr><tr><td>Zn</td><td>191</td><td>100</td><td>38.8</td><td>88</td><td>129.5</td><td>103.9</td><td>71</td></tr><tr><td>Sr</td><td>266</td><td>32</td><td>185</td><td>662</td><td>337.4</td><td>394.1</td><td>108</td></tr><tr><td>Y</td><td>14</td><td>5</td><td>31.6</td><td>20</td><td>36.1</td><td>25.9</td><td>16</td></tr><tr><td>Zr</td><td>108</td><td>30</td><td>121</td><td>227</td><td>186.5</td><td>171.2</td><td>15.5</td></tr><tr><td>Ba</td><td>61</td><td>46</td><td>458</td><td>1266</td><td>683.9</td><td>130.9</td><td>7</td></tr><tr><td colspan="8"><strong>Volatile:</strong></td></tr><tr><td>CO<sub>2</sub></td><td>1.07</td><td>0.08</td><td>—</td><td>—</td><td>—</td><td>—</td><td>—</td></tr></tbody></table>
<table><caption>**Table T12.** Analyses of international rock reference materials, Expedition 385. ND = not determined, * = certified or recommended value, diff. % = percentage of relative difference between certified/recommended and measured value of rock standard, — = not applicable. **Download table in CSV format.**</caption><thead><tr><th>Standard reference material</th><th>SiO<sub>2</sub> (wt%)</th><th>TiO<sub>2</sub> (wt%)</th><th>Al<sub>2</sub>O<sub>3</sub> (wt%)</th><th>Fe<sub>2</sub>O<sub>3</sub>t (wt%)</th><th>MnO (wt%)</th><th>MgO (wt%)</th><th>CaO (wt%)</th><th>Na<sub>2</sub>O (wt%)</th><th>K<sub>2</sub>O (wt%)</th><th>P<sub>2</sub>O<sub>5</sub> (wt%)</th><th>Sc (µg/g)</th><th>V (µg/g)</th><th>Cr (µg/g)</th><th>Ni (µg/g)</th><th>Zn (µg/g)</th><th>Sr (µg/g)</th><th>Y (µg/g)</th><th>Zr (µg/g)</th><th>Ba (µg/g)</th></tr></thead><tbody><tr><td>MRG-1 (*)</td><td>39.12</td><td>3.77</td><td>8.47</td><td>17.94</td><td>0.17</td><td>13.55</td><td>14.70</td><td>0.74</td><td>0.18</td><td>0.08</td><td>55</td><td>526</td><td>430</td><td>193</td><td>191</td><td>266</td><td>14</td><td>108</td><td>61</td></tr><tr><td>MRG-1 (measured)</td><td>39.09</td><td>3.77</td><td>8.46</td><td>17.93</td><td>0.17</td><td>13.55</td><td>14.71</td><td>0.74</td><td>0.18</td><td>0.08</td><td>55</td><td>526</td><td>430</td><td>193</td><td>191</td><td>266</td><td>14</td><td>108</td><td>61</td></tr><tr><td>MRG-1 (diff. %)</td><td>0.15</td><td>0</td><td>0.24</td><td>0.11</td><td>0</td><td>0</td><td>-0.14</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td></tr><tr><td>NIM-P (*)</td><td>51.10</td><td>0.2</td><td>4.18</td><td>12.76</td><td>0.22</td><td>25.33</td><td>2.66</td><td>0.37</td><td>0.09</td><td>0.02</td><td>29</td><td>230</td><td>24,000</td><td>560</td><td>100</td><td>32</td><td>5</td><td>30</td><td>46</td></tr><tr><td>NIM-P (measured)</td><td>51.10</td><td>0.2</td><td>4.18</td><td>12.76</td><td>0.22</td><td>25.33</td><td>2.66</td><td>0.37</td><td>0.09</td><td>0.02</td><td>29</td><td>230</td><td>ND</td><td>560</td><td>100</td><td>32</td><td>ND</td><td>30</td><td>46</td></tr><tr><td>NIM-P (diff. %)</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td></tr><tr><td>JG-1a (*)</td><td>72.19</td><td>0.25</td><td>14.22</td><td>2.05</td><td>0.06</td><td>0.69</td><td>2.13</td><td>3.41</td><td>4.01</td><td>0.08</td><td>6.31</td><td>23.0</td><td>18.6</td><td>6.4</td><td>38.8</td><td>185</td><td>31.6</td><td>121</td><td>458</td></tr><tr><td>JG-1a (measured)</td><td>72.30</td><td>0.25</td><td>14.30</td><td>2</td><td>0.057</td><td>0.69</td><td>2.13</td><td>3.39</td><td>3.96</td><td>0.08</td><td>6.21</td><td>22.7</td><td>17.6</td><td>6.91</td><td>36.5</td><td>187</td><td>32.1</td><td>118</td><td>470</td></tr><tr><td>JG-1a (diff. %)</td><td>-0.30</td><td>0</td><td>-1.13</td><td>4.88</td><td>10.00</td><td>0</td><td>0</td><td>1.17</td><td>2.49</td><td>0</td><td>3.17</td><td>2.61</td><td>10.75</td><td>-15.94</td><td>11.86</td><td>-2.16</td><td>-3.16</td><td>4.96</td><td>-5.24</td></tr><tr><td>AGV-1 (*)</td><td>58.84</td><td>1.05</td><td>17.15</td><td>6.77</td><td>0.09</td><td>1.53</td><td>4.94</td><td>4.26</td><td>2.92</td><td>0.49</td><td>12.2</td><td>121</td><td>10.1</td><td>16</td><td>88</td><td>662</td><td>20</td><td>227</td><td>1,266</td></tr><tr><td>AGV-1 (measured)</td><td>58.84</td><td>1.05</td><td>17.15</td><td>6.77</td><td>0.097</td><td>1.53</td><td>4.94</td><td>4.26</td><td>2.92</td><td>0.50</td><td>12.0</td><td>120</td><td>10.0</td><td>16</td><td>88</td><td>660</td><td>20</td><td>227</td><td>1,230</td></tr><tr><td>AGV-1 (diff. %)</td><td>0</td><td>0</td><td>0</td><td>0</td><td>-15.56</td><td>0</td><td>0</td><td>0</td><td>0</td><td>-4.08</td><td>3.28</td><td>1.65</td><td>1.98</td><td>0</td><td>0</td><td>0.60</td><td>0</td><td>0</td><td>5.69</td></tr><tr><td>BCR-2 (*)</td><td>54.0</td><td>2.27</td><td>13.48</td><td>13.77</td><td>0.2</td><td>3.60</td><td>7.11</td><td>3.12</td><td>1.77</td><td>0.36</td><td>33.53</td><td>417.6</td><td>15.9</td><td>12.6</td><td>129.5</td><td>337.4</td><td>36.1</td><td>186.5</td><td>683.9</td></tr><tr><td>BCR-2 (measured)</td><td>54.1</td><td>2.26</td><td>13.50</td><td>13.80</td><td>0.20</td><td>3.59</td><td>7.12</td><td>3.16</td><td>1.79</td><td>0.35</td><td>33</td><td>416.0</td><td>18.0</td><td>12.57</td><td>127.0</td><td>346.0</td><td>37.0</td><td>188.0</td><td>683</td></tr><tr><td>BCR-2 (diff. %)</td><td>-0.37</td><td>0.88</td><td>-0.30</td><td>-0.44</td><td>3.00</td><td>0.56</td><td>-0.28</td><td>-2.56</td><td>-2.26</td><td>5.56</td><td>3.16</td><td>0.77</td><td>-26.42</td><td>0.48</td><td>3.86</td><td>-5.10</td><td>-4.99</td><td>-1.61</td><td>0.26</td></tr><tr><td>BHVO-2 (*)</td><td>49.6</td><td>2.73</td><td>13.44</td><td>12.39</td><td>0.17</td><td>7.26</td><td>11.4</td><td>2.22</td><td>0.51</td><td>0.27</td><td>31.83</td><td>318.2</td><td>287.2</td><td>119.8</td><td>103.9</td><td>394.1</td><td>25.9</td><td>171.2</td><td>130.9</td></tr><tr><td>BHVO-2 (measured)</td><td>49.9</td><td>2.73</td><td>13.50</td><td>12.30</td><td>0.17</td><td>7.23</td><td>11.4</td><td>2.22</td><td>0.52</td><td>0.27</td><td>32</td><td>317.0</td><td>280.0</td><td>119.0</td><td>103.0</td><td>389.0</td><td>26.0</td><td>172.0</td><td>130</td></tr><tr><td>BHVO-2 (diff. %)</td><td>-1.21</td><td>0</td><td>-0.89</td><td>1.45</td><td>1.18</td><td>0.83</td><td>0</td><td>0</td><td>-3.92</td><td>0</td><td>-1.07</td><td>0.75</td><td>5.01</td><td>1.34</td><td>1.73</td><td>2.59</td><td>-0.77</td><td>-0.93</td><td>1.38</td></tr><tr><td>BIR-1 (*)</td><td>47.77</td><td>0.96</td><td>15.35</td><td>11.26</td><td>0.17</td><td>9.68</td><td>13.24</td><td>1.75</td><td>0.03</td><td>0.05</td><td>44</td><td>313</td><td>382</td><td>166</td><td>71</td><td>108</td><td>16</td><td>15.5</td><td>7</td></tr><tr><td>BIR-1 (measured)</td><td>47.96</td><td>0.96</td><td>15.50</td><td>11.30</td><td>0.175</td><td>9.70</td><td>13.30</td><td>1.82</td><td>0.03</td><td>0.02</td><td>44</td><td>310</td><td>370</td><td>170</td><td>70</td><td>110</td><td>16</td><td>18.0</td><td>7</td></tr><tr><td>BIR-1 (diff. %)</td><td>-0.80</td><td>0</td><td>-1.95</td><td>-0.71</td><td>-5.88</td><td>-0.41</td><td>-0.91</td><td>-8.00</td><td>0</td><td>120</td><td>0</td><td>1.92</td><td>6.28</td><td>-4.82</td><td>2.82</td><td>-3.70</td><td>0</td><td>-32.3</td><td>0</td></tr></tbody></table>

Data reduction consisted of initial drift correction applied to each element of all analyses, based on a linear interpolation between drift-monitoring solutions that were run every fourth analysis. Upon implementing this step and subtracting the procedural blank, a calibration line for each element was calculated through applying the results of the certified rock standards. Element contents used for the calibrations represented values compiled from the literature. They were recalculated on a volatile-free basis for those samples having LOI values >2 wt%. Total Fe oxide concentrations are reported as Fe₂O₃(t). The compiled element contents of the international rock standards are those recommended by Govindaraju (1994) and the GeoReM database (http://georem.mpch-mainz.gwdg.de; Jochum et al., 2005) (Table T11). Element abundances in the Expedition 385 igneous rock samples were then derived from the relevant calibration lines. Only those ICP-AES analyses of Expedition 385 igneous rock samples yielding a total sum of minimum 98 wt% and maximum 102 wt% (hydrous composition) were considered for data analysis and interpretation.

## 9. Organic geochemistry

Organic geochemical data provide essential information on the cycling of carbon and other elements in marine sediments. Downhole profiles of total organic carbon (TOC) and total nitrogen (TN) are needed to quantify the sedimentary organic matter pool and to characterize the availability of substrates for microbial communities. Profiles of dissolved organic matter (DOM) and hydrocarbon gases provide insights into the microbial utilization and thermogenic alteration of sedimentary organic matter. Quantifying dissolved inorganic carbon (DIC) and molecular hydrogen (H₂) enables assessments of free energy yields for methanogenesis and other H₂-consuming reactions. Moreover, the presence of hydrocarbon gases must be monitored to prevent safety and environmental risks during drilling.

During Expedition 385, we conducted safety gas monitoring according to the routine shipboard safety and pollution prevention protocol for every site and hole (Kvenvolden and McDonald, 1986; Pimmel and Claypool, 2001). In addition, we sampled gases, IW, and the solid phase of sediments and igneous rocks for a wide range of shipboard and shore-based chemical and isotopic analyses in the holes dedicated to microbiological and geochemical investigations (Table T13). Our sampling program was closely coordinated with inorganic geochemists, microbiologists, and physical properties specialists. Organic geochemists focused on gas sampling, which included analyses of hydrocarbon gases, H₂, and CO, whereas inorganic geochemists collected corresponding IW sam-
ples in adjacent depth intervals, including those for DIC and DOM analyses (see **Inorganic geochemistry**). Adjacent to gas samples, small solid-phase samples were taken for shipboard analysis of TOC, TN, total sulfur (TS), and carbonate contents (see **Solid-phase analysis**) as well as porosity (see **Petrophysics**). In cooperation with microbiologists, whole-round core sections were collected from selected depth intervals and prepared for shipboard and shore-based incubation experiments and for shore-based analysis of sedimentary organic matter and biomarkers (see **Microbiology**).

# 9.1. Gas analysis

## 9.1.1. Gas sampling

While recovering cores with the APC and HLAPC systems, the expansion of entrapped gases can form voids in the sediments. When such voids were observed, their length was recorded before they were sampled on the core retrieval platform. Void gas (VAC) samples were collected by piercing the core liner with a custom piercing tool that allows gas to expand into a 60 mL gas-tight syringe connected to the tool. A 10 mL split of the sample was taken for immediate shipboard analyses of hydrocarbon gases, H₂, and CO, and the remaining sample was transferred into crimp-capped headspace vials prefilled with a saturated solution of NaCl for shore-based analysis of the stable isotopic composition of hydrocarbon gases and CO₂ and for methane clumped isotopologue analysis (for sample codes, see Table T13).

For safety gas monitoring, samples for hydrocarbon gas analysis were collected from each core immediately after retrieval on the core receiving platform. Samples were taken as a headspace (HS) sample: ~5 cm³ of sediment was collected from the bottom of Section 1 using a cut-off syringe for soft to semiconsolidated sediment or a metal boring tool when the sediment became more lithified. During hard rock drilling, small rock chips from igneous rocks were used when available. Sediment samples were extruded or placed into preweighed 21.5 mL glass vials and immediately sealed with a polytetrafluoroethylene/silicone septum and metal crimp cap. The vial was incubated in an oven at 70°C for 30 min to allow dissolved hydrocarbon gases to equilibrate with the headspace prior to analysis (samples identified as “HS” in Table T13 and Figure F22) following the sampling protocol of previous expeditions (Expedition 322 Scientists, 2010; Expedition 337 Scientists, 2013; Morono et al., 2017; Sun et al., 2018).

Safety gas monitoring was accompanied by shipboard analysis of H₂ and CO. Exactly 3 cm³ of sediment was collected in replicate from the bottom of Section 1 with a cut-off syringe. Sediment samples were transferred into preweighed 21.5 mL glass vials, which were subsequently filled with low-H₂ 18 MΩ water, closed with a gray butyl rubber stopper, and crimp capped. Care was taken to overfill the vials with the 18 MΩ water before closing to avoid any air contamination. Subsequently, 5 cm³ of molecular nitrogen (N₂) gas headspace was inserted into the vial using a needle with a gas-tight syringe. The N₂ gas used for the headspace injection was taken from the bypass-outlet of the reduced gas analyzer used for the analysis of H₂ and CO. This ensures low H₂ and CO contents because this gas has gone through a catalytic converter that oxidizes H₂ and CO. To

<table><caption>**Table T13.** Definitions of sample types in association with sample codes and planned analyses. **Download table in CSV format.**</caption><thead><tr><th>Sample source</th><th>Sample type</th><th>Sample code</th><th>Location of analysis</th><th>Analysis (planned or undertaken)</th></tr></thead><tbody><tr><td rowspan="6">Core Receiving Platform</td><td>Sediment</td><td>385AROM</td><td>Home institution</td><td>Organic matter diagenesis</td></tr><tr><td>Sediment</td><td>385GZH2</td><td>Shipboard</td><td>H₂</td></tr><tr><td>Sediment</td><td>385GZH2</td><td>Shipboard</td><td>H₂ (replicate)</td></tr><tr><td>Sediment</td><td>385VHBM</td><td>Home institution</td><td>Biomarkers</td></tr><tr><td>Sediment</td><td>HS</td><td>Shipboard</td><td>Hydrocarbon gas for safety gas monitoring</td></tr><tr><td>Sediment</td><td>385VHCH4</td><td>Home institution</td><td>Stable isotope (methane)</td></tr><tr><td rowspan="2">COMGAS1</td><td>Sediment</td><td>385VHCO2</td><td>Home institution</td><td>Stable isotope (CO₂)</td></tr><tr><td>Sediment</td><td>CARB</td><td>Shipboard</td><td>Inorganic carbon and total carbon/nitrogen/sulfur</td></tr><tr><td rowspan="4">COMGAS2</td><td>Sediment</td><td>385VHCH4</td><td>Home institution</td><td>Stable isotope (methane)</td></tr><tr><td>Sediment</td><td>385GZH2</td><td>Shipboard</td><td>H₂</td></tr><tr><td>Sediment</td><td>385JACH4</td><td>Home institution</td><td>Clumped isotopologue (methane)</td></tr><tr><td>Sediment</td><td>385JACH4</td><td>Home institution</td><td>Clumped isotopologue (methane—replicate)</td></tr></tbody></table>
avoid overpressurization of the sample vial during the headspace injection, an equivalent amount of water was allowed to escape the vial through a separate needle. Next, the samples were vortexed and stored upside down for 20 min to allow H₂ and CO to diffuse out of the IW and equilibrate with the headspace at room temperature.

The analysis of hydrocarbon gases, H₂, and CO relies on the nearly complete extraction of the dissolved gases into a defined headspace volume and subsequent analyses of their partial pressures in headspace gas. To determine the corresponding molar concentrations of the dissolved gases, the headspace volume, the sample volume, and the sample's water content need to be known. Therefore, in microbiology holes, a MAD sample was taken from the working half as close to the headspace sample as possible to determine sediment porosity (see Petrophysics).

During sediment sampling at sites where high-resolution sampling was desired, two 5 cm long whole-round core samples were taken as designated community gas samples referred to as COMGAS1 and COMGAS2 for shipboard and shore-based analyses (Figure F22). The samples were cut from the bottom of Sections 2 and 5 immediately after core retrieval and split into subsamples without delay. The following subsamples were taken:

* For shore-based stable carbon isotope analysis of CO₂ (δ¹³C-CO₂): ~5 cm³ of wet sediment from both COMGAS1 and COMGAS2 were placed in 20 mL glass vials (385VHCO2). Glass vials were completely filled with a saturated NaCl solution, sealed with soft gray chlorobutyl stoppers, and crimp capped. Within ~2 h after sampling, artificial headspace was introduced by replacing 5 mL of NaCl solution with pure CO₂-free N₂ gas; vials were stored upside down at 4°C (cf. Inagaki et al., 2015; Morono et al., 2017).

* For shore-based stable carbon and hydrogen isotope analysis of CH₄ (δ¹³C-CH₄ and δD-CH₄) and higher hydrocarbon gases: ~5 cm³ of wet sediment from both COMGAS1 and COMGAS2 was placed in a 20 mL glass vial containing 5 mL of 1 M NaOH solution (385VHCH4). The vial was capped with a precleaned black butyl stopper (heated to boiling with 1 M KOH for ~1 h and subsequently rinsed and left immersed with nanopure water overnight [cf. Oremland et al., 1987]) and frozen upside down at -20°C (cf. Hinrichs et al., 2006; Ertefai et al., 2010).

* For shore-based clumped isotope analysis of CH₄ (Δ¹²CH₂D₂ and Δ¹³CH₃D): two replicates of ~5 cm³ of wet sediment from COMGAS2 were placed in 20 mL glass vials containing 5 mL of 1 M NaOH solution (385JACH4). The vials were capped with a polytetrafluoroethylene/sili-

Section

<figure><img src="image_26.png" /></figure>

**Figure F22.** Sampling scheme for gas analyses, Expedition 385. Section numbers, sample codes, and whole-round dimensions are shown. Void gases (VAC), samples for safety gas monitoring (HS), and H₂ samples (385GZH2) were directly collected on the core receiving platform. Samples for gas and solid-phase analysis were collected from COMGAS whole rounds. Moisture and density samples (MAD) were taken from the split working halves. For details see text. Sample codes are defined and provided in Table T13. CC = core catcher, CARB = total carbon/inorganic carbon.