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  1. ; ; ( , Scientific prospectus)
    During International Ocean Discovery Program (IODP) Expedition 391, the Tristan-Gough-Walvis Ridge (TGW) hotspot track was cored in December 2021–February 2022. Its overarching objective was to recover basaltic rock from TGW edifices to understand the evolution of Walvis Ridge and related guyots. Significant cuts to the Expedition 391 operational plan were necessary as a result of lost time due to COVID-19 mitigation procedures. Because the R/V JOIDES Resolution will pass over Walvis Ridge during the transit from Cape Town, South Africa, to Lisbon, Portugal, prior to IODP Expedition 397, the 3 week transit provides an opportunity to drill one or twomore »holes that were planned but not cored during Expedition 391. The transit schedule indicates that ~7 days of ship time will be available for this effort. Coring will be attempted at one or two sites, depending on weather and operational difficulties. The first site to be cored will be proposed Site GT-6A on the flank of the Gough track ridge. If time permits, coring will also be done at proposed Site TT-3A on the Tristan track, completing the proposed transect across the three chains of the Walvis Ridge guyot province. Two operational strategies are planned to address the limited time available. First, the ~164 m thick (Site GT-6A) and ~146 m thick (Site TT-3A) sediment sections will be drilled without coring to ~20 m above basement. Primary Site GT-6A, which is ~1.1 km upslope from alternate Site GT-4A, was specifically proposed because of its reduced sediment thickness.« less
    Free, publicly-accessible full text available July 1, 2023
  2. ; ; ; ( , Proceedings of the International Ocean Discovery Program)
    Postcruise examination of the data splice for International Ocean Discovery Program Expedition 378 Site U1553, in light of new X-ray fluorescence data, revealed three cores from Hole U1553E that were misaligned. These cores have been shifted to fill in some gaps in the original splice.
    Free, publicly-accessible full text available June 30, 2023
  3. ; ( , Proceedings of the International Ocean Discovery Program)
    Outer-trench sediments offshore Sumatra were drilled at Sites U1480 and U1481 during International Ocean Discovery Program (IODP) Expedition 362. This expedition aimed to drill the thick outer-trench sediments (up to 4–5 km) to better understand the mechanisms of shallow mega-thrust slip in the Sumatra subduction system. The iodine concentration dissolved in the interstitial water collected from these sites, ~250 km southwest of the subduction zone, was determined to understand the geochemical environment and iodine origin in the outer-trench sediment. The iodine concentrations increase with depth from seawater level to ~100 µM (270 times higher than seawater). In the outer-trench sedimentsmore »offshore Sumatra, the iodine profile results from a complex process of the iodine-rich fluid derived from the basement, in situ iodine release caused by the decomposition of organic materials, and freshening due to mineral dehydration.« less
    Free, publicly-accessible full text available June 30, 2023
  4. ( , Proceedings of the International Ocean Discovery Program)
    Holes C0002Q–C0002T were drilled in the inner accretionary prism of the Nankai Trough during International Ocean Discovery Program (IODP) Expedition 358. Sample depths range 2827.5–3067.5 meters below seafloor (mbsf). This report provides the results of X-ray diffraction analyses of the clay-sized fraction (<2 µm spherical settling equivalent) from 33 specimens of bulk cuttings (1–4 mm size fraction). Four core samples from Hole C0002T were also analyzed. Mean weight percent values for common clay-sized minerals are smectite = 20.0 wt%, illite = 54.5 wt%, undifferentiated (chlorite + kaolinite) = 13.8 wt%, and quartz = 11.7 wt%. The average value of themore »illite crystallinity index is 0.64Δ°2θ. Values of expandability for smectite + illite/smectite (I/S) mixed-layer clay average 57%, and the average proportion of illite in I/S clay is 46%. Depth-dependent trends are not evident in either the clay mineral assemblages or diagenetic indicators. Significant discrepancies exist between these new results and data from the overlapping depth intervals in Hole C0002P. A total of 18 core samples from IODP Hole C0025A in the central Kumano Basin were also analyzed, covering a depth range of 406.12–571.94 mbsf. In Lithologic Unit I (lower fore-arc basin facies), the mean values are smectite = 16.5 wt%, illite = 58.4 wt%, undifferentiated (chlorite + kaolinite) = 14.8 wt%, and quartz = 10.4 wt%. The statistics are similar for Lithologic Unit II (trench-slope facies): smectite = 23.7 wt%, illite = 54.1 wt%, undifferentiated (chlorite + kaolinite) = 11.9 wt%, and quartz = 10.3 wt%. The average value of the illite crystallinity index is 0.55Δ°2θ. The expandability of smectite + I/S averages 60%, and the average proportion of illite in I/S is 20%.« less
    Free, publicly-accessible full text available May 26, 2023
  5. ; ; ; ; ; ( , Proceedings of the International Ocean Discovery Program)
    International Ocean Discovery Program (IODP) Expedition 369 recovered pelagic sediments spanning the Albian to Pleistocene at Sites U1513, U1514, and U1516. The cores provide an opportunity to determine paleoclimatic and paleoceanographic dynamics from a hitherto poorly sampled mid-high-latitude location across an ~110 My interval, beginning during the Cretaceous supergreenhouse when eastern Gondwana was still largely assembled and ending during the modern icehouse climate after the final breakup of Gondwana. Here we present ~650 bulk carbonate carbon and oxygen stable isotope data points and plot them alongside shipboard data sets to present a first broad documentation of chemostratigraphic data that revealmore »the stratigraphic position of key climatic transitions and events at Sites U1513, U1514, and U1516. These records show a pronounced long-term δ13C decrease and δ18O increase from the Albian/Cenomanian through the Pleistocene. Superimposed on this long-term trend are transient δ13C and δ18O events correlated with Oceanic Anoxic Event 2, peak Cretaceous warmth during the Turonian, Santonian to Maastrichtian cooling, the Cretaceous/Paleogene boundary, the Paleocene/Eocene Thermal Maximum, the Early Eocene Climatic Optimum, the Middle Eocene Climatic Optimum, and the Eocene–Oligocene transition. Recognizing these isotopic events confirms and refines shipboard interpretations and, more importantly, demonstrates the suitability of Sites U1513, U1514, and U1516 for future high-resolution paleoceanographic works aimed at illuminating the links between tectonic and oceanographic dynamics and global versus local environmental changes.« less
    Free, publicly-accessible full text available May 20, 2023
  6. ; ; ( , Preliminary report)
    Hotspot tracks (quasilinear chains of seamounts, ridges, and other volcanic structures) provide important records of plate motions, as well as mantle geodynamics, magma flux, and mantle source compositions. The Tristan-Gough-Walvis Ridge (TGW) hotspot track, extending from the active volcanic islands of Tristan da Cunha and Gough through a province of guyots and then along Walvis Ridge to the Etendeka flood basalt province, forms one of the most prominent and complex global hotspot tracks. The TGW hotspot track displays a tight linear age progression in which ages increase from the islands to the flood basalts (covering ~135 My). Unlike Pacific tracks,more »which are simple chains of seamounts that are often compared to chains of pearls, the TGW track is alternately a steep-sided narrow ridge, an oceanic plateau, subparallel linear ridges and chains of seamounts, and areas of what appear to be randomly dispersed seamounts. The track displays isotopic zonation over the last ~70 My. The zonation appears near the middle of the track just before it splits into two to three chains of ridge- and guyot-type seamounts. The older ridge is also overprinted with age-progressive late-stage volcanism, which was emplaced ~30–40 My after the initial eruptions and has a distinct isotopic composition. The plan for Expedition 391 was to drill at six sites, three along Walvis Ridge and three in the seamount (guyot) province, to gather igneous rocks to better understand the formation of track edifices, the temporal and geochemical evolution of the hotspot, and the variation in paleolatitudes at which the volcanic edifices formed. After a delay of 18 days to address a shipboard outbreak of the coronavirus disease 2019 (COVID-19) virus, Expedition 391 proceeded to drill at four of the proposed sites: three sites on the eastern Walvis Ridge around Valdivia Bank, an ocean plateau within the ridge, and one site on the lower flank of a guyot in the Center track, a ridge located between the Tristan subtrack (which extends from the end of Walvis Ridge to the island of Tristan da Cunha) and the Gough subtrack (which extends from Walvis Ridge to the island of Gough). One hole was drilled at Site U1575, located on a low portion of the northeastern Walvis Ridge north of Valdivia Bank. At this location, 209.9 m of sediments and 122.4 m of igneous basement were cored. The latter comprised 10 submarine lava units consisting of pillow, lobate, sheet, and massive lava flows, the thickest of which was ~21 m. Most lavas are tholeiitic, but some alkalic basalts were recovered. A portion of the igneous succession consists of low-Ti basalts, which are unusual because they appear in the Etendeka flood basalts but have not been previously found on Walvis Ridge. Two holes were drilled at Site U1576 on the west flank of Valdivia Bank. The first hole was terminated because a bit jammed shortly after penetrating igneous basement. Hole U1576A recovered a remarkable ~380 m thick sedimentary section consisting mostly of chalk covering a nearly complete sequence from Paleocene to Late Cretaceous (Campanian). These sediments display short and long cyclic color changes that imply astronomically forced and longer term paleoenvironmental changes. The igneous basement yielded 11 submarine lava units ranging from pillows to massive flows, which have compositions varying from tholeiitic basalt to basaltic andesite, the first occurrence of this composition recovered from the TGW track. These units are separated by seven sedimentary chalk units that range in thickness from 0.1 to 11.6 m, implying a long-term interplay of sedimentation and lava eruptions. Coring at Site U1577, on the extreme eastern flank of Valdivia Bank, penetrated a 154 m thick sedimentary section, the bottom ~108 m of which is Maastrichtian–Campanian (possibly Santonian) chalk with vitric tephra layers. Igneous basement coring progressed only 39.1 m below the sediment-basalt contact, recovering three massive submarine tholeiite basalt lava flows that are 4.1, 15.5, and >19.1 m thick, respectively. Paleomagnetic data from Sites U1577 and U1576 indicate that their volcanic basements formed just before the end of the Cretaceous Normal Superchron and during Chron 33r, shortly afterward, respectively. Biostratigraphic and paleomagnetic data suggest an east–west age progression across Valdivia Bank, becoming younger westward. Site U1578, located on a Center track guyot, provided a long and varied igneous section. After coring through 184.3 m of pelagic carbonate sediments mainly consisting of Eocene and Paleocene chalk, Hole U1578A cored 302.1 m of igneous basement. Basement lavas are largely pillows but are interspersed with sheet and massive flows. Lava compositions are mostly alkalic basalts with some hawaiite. Several intervals contain abundant olivine, and some of the pillow stacks consist of basalt with remarkably high Ti content. The igneous sequence is interrupted by 10 sedimentary interbeds consisting of chalk and volcaniclastics and ranging in thickness from 0.46 to 10.19 m. Paleomagnetic data display a change in basement magnetic polarity ~100 m above the base of the hole. Combining magnetic stratigraphy with biostratigraphic data, the igneous section is inferred to span >1 My. Abundant glass from pillow lava margins was recovered at Sites U1575, U1576, and U1578. Although the igneous penetration was only two-thirds of the planned amount, drilling during Expedition 391 obtained samples that clearly will lead to a deeper understanding of the evolution of the Tristan-Gough hotspot and its track. Relatively fresh basalts with good recovery will provide ample samples for geochemical, geochronologic, and paleomagnetic studies. Good recovery of Late Cretaceous and early Cenozoic chalk successions provides samples for paleoenvironmental study.« less
    Free, publicly-accessible full text available May 1, 2023
  7. ; ; ; ; ; ; ( , Scientific prospectus)
    The South Atlantic Transect (SAT) is a multidisciplinary scientific ocean drilling project that will recover complete sedimentary sections and the upper ~250 m of the underlying oceanic crust along a slow/intermediate spreading rate Mid-Atlantic Ridge crustal flow line at ~31°S. These cores were originally scheduled to be collected during International Ocean Discovery Program (IODP) Expeditions 390 and 393 in October–December 2020 and April–June 2021, respectively. In 2020 and 2021, the global COVID-19 pandemic resulted in the postponement of several IODP expeditions, including Expeditions 390 and 393, chiefly because science parties were unable to travel to the R/V JOIDES Resolution. Inmore »response, the ship was used to conduct preparatory work for the postponed expeditions that did not require a science party aboard but could be carried out by the ship’s crew and a team of technicians from the JOIDES Resolution Science Operator. Two of these expeditions (390C and 395E) were in service of the SAT drilling project, to reduce the operational risks and expedite basement drilling during the rescheduled Expeditions 390 and 393. Expeditions 390C and 395E visited five of the six primary SAT sites and successfully cored a single advanced piston corer/extended core barrel hole penetrating the entire sediment section and <10 m into the underlying basalt before installing a reentry system in a second hole at each site visited. Given these accomplishments, the operations plans for the rescheduled Expeditions 390 and 393 have been revised.« less
    Free, publicly-accessible full text available May 1, 2023
  8. ; ; ( , Proceedings of the International Ocean Discovery Program)
    During International Ocean Discovery Program Expeditions 367/368/368X, Hole U1501D was cored on the continental shelf (2846 meters below sea level) in the northern South China Sea (SCS). In Hole U1501D, sediments were recovered from 433.5 to 644.3 meters below seafloor (mbsf) and the acoustic basement was penetrated at 598.91 mbsf. The acoustic basement is a stratigraphic boundary at which late Eocene Cenozoic sediments likely unconformably overlay heterolithic Mesozoic sandstones that are intercalated with rare siltstones and subordinate conglomerate with pebble- and cobble-sized igneous clasts of proximal provenance. Here, we present major and trace elements and Sr-Nd-Pb-Hf isotope data of amore »fine-grained granite pebble, a medium-grained granite cobble, and a porphyritic volcanic pebble. The data show that these clasts are relics of the Mesozoic subduction-related magmatism that was active along the southeast Asian margin prior to the Cenozoic rifting. The Pb isotope composition of the clasts partially overlaps with the enriched Cenozoic mid-ocean-ridge basalt type and intraplate basalts of the SCS. However, the clasts are distinct from the Cenozoic basalt volcanism in Sr-Nd-Hf isotope space. Thus, Sr-Nd-Hf isotope systematics of the Cenozoic basalts might be useful in detecting traces of crustal contamination in the earliest rift basalts of the SCS that may have erupted through the Mesozoic continental basement.« less
    Free, publicly-accessible full text available April 27, 2023
  9. ; ; ; ( , Proceedings of the International Ocean Discovery Program)
    During International Ocean Discovery Program (IODP) Expedition 367/368/368X, Holes U1504A and U1504B were cored on the continental shelf (2817–2843 meters below sea level) in the northern South China Sea (SCS). A total of 106 m of metamorphic basement was penetrated that consists of greenish gray, deformed mylonitic, epidote-chlorite to calc-silicate schists containing granofels clasts ("greenschist"). Here we report bulk-rock major and trace element data from 17 greenschist samples, from which a subset of 9 samples was additionally analyzed for Pb-Nd-Hf isotope ratios. Fluid-mobile elements (U, Li, Rb, K, and Cs) behave somewhat erratically, yet tectonic discrimination and primitive mantle–normalized multielementmore »diagrams reveal signatures that are typical for enriched intraplate basalts. These include a negative Pb anomaly (Ce/Pb = 34 ± 10), relative enrichments of Nb and Ta (Nb/La = 1.5 ± 0.3; Th/Nb = 0.07 ± 0.01), and a steep rare earth element pattern (La/Sm = 3.7 ± 0.7; Ho/Lu = 2.9 ± 0.2). The high values of the uranogenic 206Pb/204Pb (21.2–25.9) and 207Pb/204Pb (15.7–16.0) and their strong correlation point to a postformation "U addition event" that took place at 329 Ma ± 2 My (late Carboniferous). 143Nd/144Nd and 176Hf/177Hf data are consistent with the origin from an enriched Paleozoic age mantle source. In summary, our data suggest that the protolith of the Site U1504 metamorphic basement was an ocean-island basalt–type igneous rock that deformed during the late Paleozoic and was part of the prerift crustal basement of the SCS Basin.« less
    Free, publicly-accessible full text available March 31, 2023
  10. ( , Proceedings of the International Ocean Discovery Program)
    Sediments deposited on the upper slope of the Hikurangi subduction margin, offshore New Zealand, are composed mostly of hemipelagic mud with interbeds of silt to sand that were modified after deposition by strong bottom currents. Some of those deposits were spot cored at Site U1519 during International Ocean Discovery Program (IODP) Expedition 375. This report provides the results of 76 X-ray diffraction analyses of the clay-sized fraction (<2 µm spherical settling equivalent). Sampling focused on the background lithology of hemipelagic mud. Normalized weight percent values for common clay-sized minerals (where smectite + illite + undifferentiated [chlorite + kaolinite] + quartzmore »= 100%) reveal unusually small amounts of scatter both within and between the two lithostratigraphic units. The mean and standard deviation (σ) values for Unit I are smectite = 44.1 wt% (σ = 3.7), illite = 34.0 wt% (σ = 2.8), undifferentiated (chlorite + kaolinite) = 10.7 wt% (σ = 1.3), and quartz = 11.2 wt% (σ = 2.2). The mean and standard deviation values for Unit II are smectite = 49.9 wt% (σ = 5.5), illite = 31.9 wt% (σ = 4.0), undifferentiated (chlorite + kaolinite) = 5.8 wt% (σ = 1.8), and quartz = 12.3 wt% (σ = 7.4). Large gaps between cored intervals preclude recognition of possible depth-dependent or age-dependent trends, but the values at Site U1519 closely match those at nearby Site U1517 (Tuaheni Landslide Complex). Two major unconformities were interpreted in seismic reflection profiles that cross Site U1519, and compositional differences across those features are trivial. Variations among indicators of clay diagenesis are also relatively small. The average value of the illite crystallinity index is 0.537Δ°2θ (σ = 0.019). The expandability of smectite + illite/smectite mixed-layer clay averages 79% (σ = 3%), and the average proportion of illite in illite/smectite mixed-layer clay is 13% (σ = 6%).« less
    Free, publicly-accessible full text available March 29, 2023