The Tristan-Gough-Walvis Ridge volcanic chain, located in the South Atlantic Ocean on the African plate, is one of Earth's longest linear seafloor features. However, the origin of its magmatism remains poorly understood. To better understand its formation, temporal evolution, and geochemical characteristics, six sites were drilled along the Tristan-Gough-Walvis Ridge chain by International Ocean Discovery Program (IODP) Expeditions 391 and 397T: three sites on Valdivia Bank (U1575, U1576, and U1577) and three sites in the Guyot Province (U1578, U1584, and U1585). Among these, Site U1578, located on the deep northwestern flank of a "Center track" seamount, represents the deepest basement penetration (>300 m) of both expeditions. According to preliminary geophysical and biostratigraphic constraints, the stratigraphic sections recovered from Site U1578 span >2.0 m.y. of the Paleocene (ca. 64.8-62.3 Ma). Here, we present an integrated study of major and trace element concentrations in minerals, combined with in situ Sr isotopes of plagioclase (Pl) from Site U1578 basalts. Based on the olivine-spinel (Ol-Sp) thermometry and pyMelt modeling, the calculated mantle potential temperature of the Center track is >= 1400 degrees C, which is similar to 50 degrees C higher than that of mid-ocean-ridge basalts (MORBs), most likely reflecting the influence of a mantle plume. Based on geochemical compositions and crystal textures, we identified three distinct clinopyroxene (Cpx) groups: Group 1 is characterized by high Mg# (>83.4) and elevated Ni (>200 ppm) and Cr (>5000 ppm) contents; Group 2 has intermediate Mg# (76.6-83.4), Ni (100-200 ppm), and Cr (1000-5000 ppm); and Group 3 exhibits low Mg# (<76.6) and depleted Ni (<70 ppm) and Cr (<30 ppm) contents. Multiple episodes of magma recharge and mixing in the plumbing system beneath the Center track produced a diversity of mineral textures, including normal, reverse, sector, and oscillatory zoning. Additionally, Pl from this site is isotopically heterogeneous (Sr-87/Sr-86 of 0.7038 +/- 0.0001 to 0.7046 +/- 0.0001) and broadly similar to basalts from the northern Tristan track in the Guyot Province. A shift to more radiogenic Sr isotopic signatures from the lower to the upper igneous units suggests the increasing incorporation of radiogenic materials into the mantle source with time, potentially derived from enriched mantle typically associated with basalts of the southern Gough track. These findings indicate that basaltic lavas from the Center track originate from an anomalously hot and geochemically enriched mantle source associated with a mantle plume or hotspot activity. Diverse mineral textures and chemistry record complex fractional crystallization and mixing processes during magma storage prior to eruption.

Grain size analysis of the terrigenous fraction of sediments from IODP Site U1501 was used to characterize depositional patterns in the northern South China Sea since the Middle Eocene (similar to 35 Ma). Fine sand dominates the lower sequence (similar to 457-440 m CSF-A (core depth below sea floor - A)), reflecting turbidite influence on the Chinese continental shelf (similar to 35-34 Ma). This is followed by a fining-upward trend (4-8 phi) marking the transition to hemipelagic deposition mostly devoid of turbidites. A new silt-dominated sedimentation regime became established at similar to 30 Ma, which correlates with the initial expansion of the Pearl River. The regime is accompanied by stable source geochemical proxies (e.g. Zr/TiO2 values) and remains unaffected by an unconformity (T60) and hiatus at similar to 26.8-24.36 Ma. Grain size changes with stable geochemical proxies require variable intensities of terrigenous influx, which we propose reflect the dynamics of surface buoyant plumes and their controlling factors. At similar to 16 Ma, sediment fines abruptly (4.7-7.5 phi) and grain size remains constant to the present, reflecting drier conditions in the source area that began shortly afterward. The observed patterns suggest that grain size data from hemipelagic sediments devoid of turbidites can be combined with source tracers to help reconstruct the intensity of buoyant plumes over time.

Ocean Plate Stratigraphy (OPS) represents a sequence of volcanic and sedimentary rocks of the uppermost part of an oceanic plate typically preserved in tectonic stacks of an accretionary wedge. While the characteristics of Phanerozoic OPS are generally well-known, those of Neoproterozoic OPS, especially their sedimentary components, remain underexplored. We combined field observations with petrography and geochemistry (major and trace elements, Sr-Nd isotopes) of sedimentary rocks from the Gwna Group (Mona Complex, Wales, UK) representing a well-preserved example of Neoproterozoic OPS. The rocks were subdivided into five groups: (1) red chert/jasper, (2) carbonate/dolostone, (3) black mudstone, (4) red/green mudstone, and (5) turbiditic/volcaniclastic rocks. The carbonate rock and red chert fill interpillow spaces or form less than 2-meter-thick layers above a basaltic base. These rocks formed as chemical precipitates from hydrothermal fluid (aNd = -2.4 to -1.2) or hydrothermally fluxed seawater (aNd = -8.3 to -7.4) related to magmatic activity on the seafloor. Unlike Phanerozoic OPS, the studied OPS does not include a thick bedded chert sequence resulting from the accumulation of plankton remains. The red, green, and black mudstones were deposited on the ocean floor in a pelagic or hemipelagic environment under oxygenated and anoxic conditions. They were predominantly sourced from distal mature continental crust as exemplified by their low aNd values (-11.3 to -3.5). In contrast, the turbiditic and volcaniclastic rocks (aNd = -1.9 to +0.8) that form most of the Gwna Group were sourced from an adjacent volcanic arc and deposited in a trench. We show that the OPS lithological and compositional changes relate to Neoproterozoic plate motion and increasing proximity to a subduction zone. The OPS of the Gwna Group serves as a crucial paleooceanographic and paleogeographic indicator in the Neoproterozoic.

Paleogeographic changes have significantly shaped ocean circulation and climate dynamics throughout Earth’s history. This study integrates geological proxies with climate simulations to assess how ocean gateway evolution influenced ocean salinity near the end of the Mesozoic (~66 Ma). Our modeling results demonstrate that 1) Central American Seaway shoaling reorganizes ocean currents, and 2) Arctic marine gateway restrictions, confining Arctic–Global Ocean exchange exclusively to the Greenland–Norwegian Seaway, drive Arctic Ocean surface freshening and southward outflow of buoyant, low-salinity waters. However, only the combined effect of these two factors leads to both Arctic freshening and increased water mass stratification in the Greenland–Norwegian Seaway, proto-North Atlantic, and the Western Tethys. This scenario aligns with Maastrichtian palynological, micropaleontological, and geochemical records from high- and low-latitude sites. Our findings highlight the profound impact of these latest Cretaceous paleogeographic reconfigurations in altering global salinity patterns, underscoring their role as key drivers of global climate dynamics.

Massive submarine basalt flows were sampled at five sites on the Tristan-Gough-Walvis hotspot track in the South Atlantic by International Oceanic Discovery Program Expeditions 391/397T, where the plume was interacting with a mid-ocean ridge, a setting similar to that the of modern Iceland. High resolution XRF core scans document significant internal chemical variations with depth in these flows. Some of this reflects basal olivine accumulation. However, some examples have "scallop-shaped" patterns that are interpreted to represent influxes of new magma during flow lobe inflation with successive lava injections focused toward the base of the flow unit. Olivine concentration in the deeper parts of the flow is interpreted to reflect top-down tapping of a vertically zoned magma chamber, with the upper part of the chamber erupting first, and successive eruptive pulses tapping progressively deeper levels of the stratified chamber. The occurrence of massive submarine lava flows requires high eruptive fluxes relative to pillow lava formation. Propagation of these massive flows is favored by (a) high sea water confining pressures, which inhibit vesiculation and keep effective viscosity low and dissolved volatile content high, and (b) chill zones and thick viscoelastic crusts of quenched lava on the flow tops, which effectively insulate the flow interior from ambient temperatures. The formation of a thin film of super-heated steam on the upper flow surface may similarly enhance the insulation. Evidence suggests that similar massive flows on the seafloor may extend many kilometers from their vents.

Tephra layers embedded in marine sediments can be significant in controlling submarine landslide dynamics and seafloor morphology, but their preconditioning effects on slope failure remain uncertain. Here, we study the morphology and preconditioning factors of submarine landslides from a volcanically active region, the Eastern South Korea Plateau (ESKP) using a recently acquired multibeam echosounder (MBES), high-resolution sub-bottom chirp profiler, and piston core data, together with previous geophysical data. At least 50 translational landslides were identified on the southern margin of the ESKP in an area of-470 km2, with a relatively small volume of remobilized sediment (-10 km3). The landslide headscarps are arcuate, up to 400 m in height, and lie at water depths of 980 to 2300 m. Landslides on the upper ESKP margin are more disintegrative (debris flow type) than those on the lower margin which consists largely of blocky type failures with small runouts. Landslide deposits identified in the cores consist of debris flows and slides/slumps while background deposits contain hemipelagic mud interbedded with ca. 10-cm-thick coarse-grained, poorly-sorted pumiceous tephra. Seismic and core integration indicate that the glide planes of the observed slides correspond to the pumice-rich tephra layers. These tephras are predominantly composed of fresh volcanic glass devoid of clay, indicating that the composition of the tephra did not control the formation of weak layers or slide planes. We infer therefore that the weakness of the glide planes resulted from high hydraulic (pore) pressure at the interface between some of the porous tephra layers and their overlying, relatively impermeable, hemipelagic mud. In addition to burial compaction and build-up of pore pressure in the tephra layers, fluid overpressure could have been facilitated by earthquakes causing granular convection within, and compaction of, the poorly sorted tephra. The landslide predominantly formed > ca. 84 ka ago, which suggests time-restricted triggering associated with a temporary increase in seismicity and/or sediments reaching their overpressure threshold during burial compaction. Our study suggests that regional occurrences of discrete layers of porous tephra deposits within finer grained hemipelagic sediments can potentially control the generation of landslides in subaqueous environments affected by explosive volcanism.

Developing approaches to determine the modes of transport and weathering of mafic detrital minerals in natural sedimentary environments is critical to our understanding of sediment production, dispersal and provenance, as well as carbon capture under natural and enhanced weathering regimes. We integrated the characterisation of morphological and surface textures with the surface composition of recent detrital clinopyroxene grains concentrated in a sandy coastal area from the western North Island of New Zealand and a rocky shore area of Santa Maria Island in the Azores Archipelago. Using the compactness shape descriptor, 341 grains were subdivided into elongated, elongated angular, euhedral, angular and subangular groups, with each group further characterised using morphological and microtextural indicators of abrasion, breakage and dissolution/chemical weathering. In both studied environments, the clinopyroxenes are dominated by elongated to angular shapes with flat cleavage surfaces and conchoidal fractures. This is consistent with dominant subaqueous transport by rivers and longshore currents for New Zealand, and dominant wave action with limited sediment supply by rivers along the rocky shore of Santa Maria. More abundant subabraded and abraded shapes with bulbous and elongated depression microtextures are observed in New Zealand, which indicates additional effects by aeolian transport that are not seen in Santa Maria. Consistent with semi-quantitative EDS spot analyses that document fresh clinopyroxenes surfaces, chemical weathering textures are very rare to absent. In Santa Maria, sampling of recent beach sand was complemented by similar to 125 kyr-old palaeobeach clinopyroxenes, but these yielded similar textural results without evidence for chemical weathering. However, the surface of these older clinopyroxenes includes small adhering smectite (typically <50 mu m in width and a few mu m in thickness) interpreted to reflect incipient cementation with buffering of acidic fluids by more reactive lithic fragments in the deposits. The lack of chemical weathering but pervasive evidence for mechanical breakage of clinopyroxenes indicate that, at the sand size, these minerals break faster than they dissolve due to frequent subaqueous and/or aeolian reworking in the studied high-energy environments and temperate climatic conditions. (c) 2024 Elsevier B.V. All rights reserved.

The past similar to 200 million years of Earth's geomagnetic field behavior have been recorded within oceanic basalts, many of which are only accessible via scientific ocean drilling. Obtaining the best possible paleomagnetic measurements from such valuable samples requires an a priori understanding of their magnetic mineralogies when choosing the most appropriate protocol for stepwise demagnetization experiments (either alternating field or thermal). Here, we present a quick, and non-destructive method that utilizes the amplitude-dependence of magnetic susceptibility to screen submarine basalts prior to choosing a demagnetization protocol, whenever conducting a pilot study or other detailed rock-magnetic characterization is not possible. We demonstrate this method using samples acquired during International Ocean Discovery Program Expedition 391. Our approach is rooted in the observation that amplitude-dependent magnetic susceptibility is observed in basalt samples whose dominant magnetic carrier is multidomain titanomagnetite (similar to TM60-65, (Ti0.60-0.65Fe0.35-0.40)Fe2O4). Samples with low Ti contents within titanomagnetite or samples that have experienced a high degree of oxidative weathering do not display appreciable amplitude dependence. Due to their low Curie temperatures, basalts that possess amplitude-dependence should ideally be demagnetized either using alternating fields or via finely-spaced thermal demagnetization heating steps below 300 degrees C. Our screening method can enhance the success rate of paleomagnetic studies of oceanic basalt samples. Oceanic basalts are ideal recorders of the Earth's magnetic field. To decipher magnetic histories recorded in rocks, paleomagnetists need to isolate the magnetization directions and intensities within rocks by one of two possible methods. One method typically involves progressively heating the samples to high temperatures. The other method involves exposing samples to alternating magnetic fields with increasing peak field intensities. Both of these methods are ultimately destructive to the original magnetization preserved within rocks. However, without knowledge of a given rock's magnetic mineralogy, randomly choosing thermal or alternating field demagnetization methods may result in high failure rates. We developed a pre-screening method to help decide which cleaning method will likely be more successful for a given sample based on low-field magnetic susceptibility measurements. These measurements do not affect the original magnetic information recorded in a rock, thereby permitting subsequent paleomagnetic studies on the same sample. Our technique can be performed as rapidly as 2 min per sample, is non-destructive, and does not require complicated sample preparation. Paleomagnetic studies utilize either alternating field or thermal demagnetization, but it is difficult to choose the best protocol a priori Amplitude-dependence of magnetic susceptibility measurements permits preliminary magnetic mineralogy characterization in submarine basalts Rapid amplitude-dependence measurements may aid in deciding upon the best demagnetization protocol for submarine basalt samples

Images of the outside of hard rock whole-round sections were acquired using a linescan imager (Section Half Imaging Logger [SHIL]) and a special holder that allows each 90 degree segment of the outer surface to be positioned properly. The images were taken at a resolution of 20 lines/mm (50 micropixels). JRSO staff take these quadrant images and compile them into a side-by-side rollout photograph of the section. Composite images are available as both JPG and TIF image formats. Individual quadrant images are available as JPG images only through this report; contact the IODP-JRSO Data Librarian if quadrant TIF files (~160 MB) are needed.

Glide planes, the basal surface or failure surface upon which submarine landslides initiate, commonly develop along weak, distinctive stratigraphic horizons but their lithological/mechanical characteristics and genetic mechanisms remain largely unknown. We use 2-D multi-channel seismic reflection data, integrated with multibeam bathymetry and deep drilling data from the Ulleung Basin margins, East (Japan) Sea, to: (1) identify and characterize the nature of glide planes associated with submarine landslides; (2) understand the influence of climate-modulated factors in preconditioning slope failures; and (3) document the post-failure evolution of the landslides. 24 glide planes were identified among 38 submarine slides (SL1 – SL38), which correspond to regionally continuous, positive-polarity high-amplitude seismic reflections. Well-seismic integration support ca. 340 ka – 1,200 ka ages of formation of the major glide planes in the southwestern and western margins of the basin. These glide planes developed at the interface between clay-rich sediment deposited during glacial periods and biogenic diatom-rich sediments deposited during interglacial periods. Physical, mineralogical and geochemical properties determined by density, porosity, gamma-ray, shear strength, X-ray diffraction, and X-ray fluorescence data reveal significant lithological and mechanical changes at the interface between these two lithologies. We therefore infer that these interfaces dictate the position of failure surfaces, with the diatom-rich layers acting as a weak layer. Excess pore pressure in these layers is likely due to initial high-water contents (up to 75%) and high compressibility; this is considered an important pre-condition for failure. In contrast, the glide planes along the northwestern margin of the Ulleung Basin (SL34 – 37) are older (ca. 1,200 ka – 2,140 ka). Seismic data further reveal three distinct contrasting styles of landslide post-failure behavior throughout the margins: (1) evacuated slide scars with areas of smooth seafloor; (2) slide scars with residual debris consisting of blocky sediments; and (3) slide scars with buried intact sediment blocks in front of the headwalls. Lateral variability of fluid flow, sediment composition, and mechanical properties of basal 'weak' layer(s), or the magnitude of earthquakes may have contributed to forming different types of mass-transport deposits (MTDs). Overall, these results show that landslide formation in the East (Japan) Sea result from a complex climatic, volcanic and tectonic interplay that controlled the formation of weak layers. Some of these layers extend regionally and can be identified and mapped by remote geophysical methods and targeted drilling.

Elemental concentration in interstitial water samples was measured by inductively coupled plasma - atomic emission spectroscopy (ICP-AES). Data are presented by element-wavelength pair (e.g., more than one calcium line may be reported). Elemental lines for which data do not exist for a particular expedition will not appear.

X-ray diffraction (XRD) is used to identify minerals and their proportions in sediment or hard rock sample powders on a Bruker AXS D4 Endeavor X-ray diffractometer. Results are returned as diffractograms in a viewable format (either PDF or PNG).

Shear strength was measured on section halves using a GEISA automated vane shear (AVS) frame and device controller. The device is suitable for sediment not affected by cementation (i.e., saturated, clay-rich, soft sediment). Shear strength measurements should be considered only approximate, particularly because the influence of pore pressure changes during the undrained experiment cannot be estimated. Report includes vane shear strength at the sample's failure point, maximum torque angle, penetration direction, and rate of vane rotation.

Abstract Valdivia Bank (VB) is a Late Cretaceous oceanic plateau formed by volcanism from the Tristan‐Gough hotspot at the Mid‐Atlantic Ridge (MAR). To better understand its origin and evolution, magnetic data were used to generate a magnetic anomaly grid, which was inverted to determine crustal magnetization. The magnetization model reveals quasi‐linear polarity zones crossing the plateau and following expected MAR paleo‐locations, implying formation by seafloor spreading over ∼4 Myr during the formation of anomalies C34n‐C33r. Paleomagnetism and biostratigraphy data from International Ocean Discovery Program Expedition 391 confirm the magnetic interpretation. Anomaly C33r is split into two negative bands, likely by a westward ridge jump. One of these negative anomalies coincides with deep rift valleys, indicating their age and mechanism of formation. These findings imply that VB originated by seafloor spreading‐type volcanism during a plate reorganization, not from a vertical stack of lava flows as expected for a large volcano.

This work investigates how the surface textures and morphology of pyroxene grains evolve during their source‐to‐sink history. This study applies to detrital clinopyroxenes concentrated in coastal dune sands of the Gulf of Mexico which were sourced in the Trans Mexican Volcanic Belt then transported and deposited in environments subject to limited chemical weathering. The composition and morphology of the pyroxenes was characterised using single‐grain geochemical analysis and surface texture imagery with a novel approach based on the compactness property to assess the shape of minerals. This reveals heterogenous diopside‐augite populations, displaying mineral morphologies dominantly controlled by impact breakage along cleavages, little physical abrasion along their edges and with limited evidence for chemical weathering. Mechanical surface textures dominate over mechanical/chemical and chemical surface textures. These mechanical surface textures are preserved primarily as flat cleavage surfaces and rounded edges inherited from fluvial‐intertidal and aeolian transport, respectively. Mechanically/chemically induced surface textures are preserved as elongated depressions. Chemical surface textures are sparse and mostly represented by mammillated textures that suggest local dissolution under subaqueous conditions. The scarcity of chemical surface textures is attributed to frequent fragmentation of the clinopyroxenes along cleavages and limited chemical weathering during transport of the observed populations. Clinopyroxene grains in the coastal dune sands primarily retain surface characteristics from fluvial transport. Although the breakage of minerals along cleavages can obscure their original morphology under a weathering‐limited erosion regime, this study shows how surface textures and morphology of pyroxene grains is used to determine episodes of transport and deposition close to volcanic environments. The use of the compactness property as a shape descriptor measurement of particles provides an alternative approach to observe how clinopyroxene remains unaltered despite the high energy conditions of the coastal area.

Digital section images were taken of the flat face of split cores on the Section Half Imaging Logger (SHIL) using a linescan camera at a resolution of 20 lines/mm (50 micron pixels). Cores were imaged as soon as possible after splitting to minimize color changes that occur through oxidation and drying. The SHIL produces TIF files as well as reduced-size JPG files. The TIF files are not kept online but users may request them from the IODP-JRSO Data Librarian.

Color reflectance data were measured on section halves using an integration sphere and a UV-VIS spectrophotometer mounted on the Section Half Multisensor Logger (SHMSL). Spectral counts are recorded in the range of 380 to 700 nm, covering the visible spectrum, and binned in ~2 nm bins. Spectral data are reduced from spectra and recorded in tristimulus XYZ values, CieLAB L*a*b* values, and other units.

A digital composite image (PNG) is made for each core comprising core sections scanned using a line-scan camera. The composite layout is equivalent to traditional core table photos. Top left is top of core; color and meter rule references are included.