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1. Expedition 381 Preliminary Report: Corinth Active Rift Development

   https://doi.org/10.14379/iodp.pr.381.2019  

   Shillington, D.J. ; McNeill, L.C. ; Carter, G.D.O. ( February 2019 , Preliminary report)

   null (Ed.)

   The primary objective of International Ocean Discovery Program Expedition 381 was to retrieve a record of early continental rifting and basin evolution from the Corinth rift, central Greece. Continental rifting is fundamental for the formation of ocean basins, and active rift zones are dynamic regions of high geohazard potential. However, the detailed spatial and temporal evolution of a complete rift system needed to understand rift development from the fault to plate scale is poorly resolved. In the active Corinth rift, deformation rates are high, the recent synrift succession is preserved and complete offshore, earlier rift phases are preserved onshore, and a dense seismic database provides high-resolution imaging of the fault network and of seismic stratigraphy around the basin. As the basin has subsided, its depositional environment has been affected by fluctuating global sea level and its absolute position relative to sea level, and the basin sediments record this changing environment through time. In Corinth, we can therefore achieve an unprecedented precision of timing and spatial complexity of rift-fault system development, rift-controlled drainage system evolution, and basin fill in the first few million years of rift history. The following are the expedition themes: • High-resolution fault slip and rift evolution history, • Surface processes in active rifts, • High-resolution late Quaternary Eastern Mediterranean paleoclimate and paleoenvironment of a developing rift basin, and • Geohazard assessment in an active rift. These objectives were and will be accomplished as a result of successful drilling, coring, and logging at three sites in the Gulf of Corinth, which collectively yielded 1645 m of recovered core over a 1905 m cored interval. Cores recovered at these sites together provide (1) a longer rift history (Sites M0078 and M0080), (2) a high-resolution record of the most recent phase of rifting (Site M0079), and (3) the spatial variation of rift evolution (comparison of sites in the central and eastern rift). The sediments contain a rich and complex record of changing sedimentation, sediment and pore water geochemistry, and environmental conditions from micropaleontological assemblages. The preliminary chronology developed by shipboard analyses will be refined and improved during postexpedition research, providing a high-resolution chronostratigraphy down to the orbital timescale for a range of tectonic, sedimentological, and paleoenvironmental studies. This chronology will provide absolute timing of key rift events, rates of fault movement, rift extension and subsidence, and the spatial variations of these parameters. The core data will also allow us to investigate the relative roles of and feedbacks between tectonics, climate, and eustasy in sediment flux and basin evolution. Finally, the Corinth rift boreholes will provide the first long Quaternary record of Mediterranean-type climate in the region. The potential range of scientific applications for this unique data set is very large, encompassing tectonics, sedimentary processes, paleoenvironment, paleoclimate, paleoecology, geochemistry, and geohazards. 

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2. Expedition 381 Scientific Prospectus: Corinth Active Rift Development

   https://doi.org/10.14379/iodp.sp.381.2017  

   McNeill, L. ; Shillington, D. ; Carter, G. ( October 2017 , Scientific prospectus)

   null (Ed.)

   Continental rifting is fundamental for the formation of ocean basins, and active rift zones are dynamic regions of high geohazard potential. However, much of what we know from the fault to plate scale is poorly constrained and is not resolved at any level of spatial or temporal detail over a complete rift system. For International Ocean Discovery Program Expedition 381, we propose drilling within the active Corinth rift, Greece, where deformation rates are high, the synrift succession is preserved and accessible, and a dense, seismic database provides high-resolution imaging, with limited chronology, of the fault network and of seismic stratigraphy for the recent rift history. In Corinth, we can therefore achieve an unprecedented precision of timing and spatial complexity of rift-fault system development and rift-controlled drainage system evolution in the first 1–2 My of rift history. We propose to determine at a high temporal and spatial resolution how faults evolve, how strain is distributed, and how the landscape responds within the first few million years in a nonvolcanic continental rift, as modulated by Quaternary changes in sea level and climate. High horizontal spatial resolution (1–3 km) is provided by a dense grid of seismic profiles offshore that have been recently fully integrated and are complemented by extensive outcrops onshore. High temporal resolution (~20–50 ky) will be provided by seismic stratigraphy tied to new core and log data from three carefully located boreholes to sample the recent synrift sequence. Two primary themes are addressed by the proposed drilling integrated with the seismic database and onshore data. First, we will examine fault and rift evolutionary history (including fault growth, strain localization, and rift propagation) and deformation rates. The spatial scales and relative timing can already be determined within the seismic data offshore, and dating of drill core will provide the absolute timing offshore, the temporal correlation to the onshore data, and the ability to quantify strain rates. Second, we will study the response of drainage evolution and sediment supply to rift and fault evolution. Core data will define lithologies, depositional systems and paleoenvironment (including catchment paleoclimate), basin paleobathymetry, and relative sea level. Integrated with seismic data, onshore stratigraphy, and catchment data, we will investigate the relative roles and feedbacks between tectonics, climate, and eustasy in sediment flux and basin evolution. A multidisciplinary approach to core sampling integrated with log and seismic data will generate a Quaternary chronology for the synrift stratigraphy down to orbital timescale resolutions and will resolve the paleoenvironmental history of the basin in order to address our objectives. 

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3. Expedition 397 Preliminary Report: Iberian Margin Paleoclimate

   Hodell, D.A. ; Abrantes, F. ; Alvarez Zarikian, C.A. ( February 2023 , Preliminary report)

   During International Ocean Discovery Program Expedition 397, we recovered a total of 6176.7 m of core (104.2% recovery) at four sites (U1586, U1587, U1385, and U1588) from the Promontório dos Principes de Avis (PPA) (Figure F1), a plateau located on the Portuguese continental slope that is elevated above the Tagus Abyssal Plain and isolated from the influence of turbidites. The drill sites are arranged along a bathymetric transect (4691, 3479, 2590, and 1339 meters below sea level [mbsl], respectively) to intersect each of the major subsurface water masses of the eastern North Atlantic (Figures F2, F7). Multiple holes were drilled at each site to ensure complete spliced composite sections (Figure F3; Table T1), which will be further refined postcruise by a campaign of X-ray fluorescence core scanning. At Site U1586 (4691 mbsl), the deepest and farthest from shore, a 350 m sequence was recovered in four holes that extend as far back as the middle Miocene (14 Ma), which is nearly twice as old as initially predicted from seismic stratigraphy. Sedimentation rates are lower (averaging 5 cm/ky in the Quaternary) at Site U1586 than other Expedition 397 sites (Figure F4), and a few slumped intervals were encountered in the stratigraphic sequence. Despite these limitations, Site U1586 anchors the deep end-member of the bathymetric transect and provides an important reference section to study deepwater circulation, ventilation and carbon storage in the deep eastern North Atlantic. At Site U1587 (3479 mbsl), the second deepest site along the depth transect, we recovered a 567 m sequence of late Miocene to Holocene sediments that accumulated at rates between 6.5 and 11 cm/ky (Figure F4). The high sedimentation rates and long continuous record at this site will permit climate reconstruction at high temporal resolution (e.g., millennial) for the past 7.8 My. A complete Messinian Stage (7.246–5.333 Ma) was recovered, which provides a valuable opportunity to study the Messinian Salinity Crisis in an open marine setting adjacent to the Mediterranean. Site U1385 (Shackleton site) was a reoccupation of a position previously drilled during Integrated Ocean Drilling Program Expedition 339. Expedition 339 Site U1385 has yielded a remarkable record of millennial-scale climate change for the past 1.45 My (Marine Isotope Stage [MIS] 47) (Figure F6). During Expedition 397, we deepened the site from 156 to 400 meters below seafloor (mbsf), extending the basal age into the early Pliocene (4.5 Ma). Sedimentation rates remained high, averaging between 11 and 9 cm/ky throughout the sequence (Figure F4). The newly recovered cores at Expedition 397 Site U1385 will permit the study of millennial climate variability through the entire Quaternary and into the Pliocene, prior to the intensification of Northern Hemisphere glaciation. Site U1588 is the shallowest, closest to shore, and youngest site drilled during Expedition 397 and is also the one with the highest sedimentation rate (20 cm/ky). The base of the 412.5 m sequence is 2.2 Ma, providing an expanded Pleistocene sequence of sediment deposited under the influence of the lower core of the Mediterranean Outflow Water (MOW). Together with other Expedition 339 sites, Site U1588 will be important for determining how the depth and intensity of the MOW has varied on orbital and millennial timescales. In addition, it also provides a marine reference section for studying Quaternary climate variability at very high temporal resolution (millennial to submillennial). A highlight of the expedition is that sediment at all sites shows very strong cyclicity in bulk sediment properties (color, magnetic susceptibility, and natural gamma radiation). Particularly notable are the precession cycles of the Pliocene that can be correlated peak-for-peak among sites (Figure F10). These cyclic variations will be used to derive an orbitally tuned timescale for Expedition 397 sites and correlate them into classic Mediterranean cyclostratigraphy. The cores recovered during Expedition 397 will form the basis of collaborative postcruise research to produce benchmark paleoclimate records for the late Miocene through Quaternary using the widest range of proxy measurements. It will take many years to complete these analyses, but the records will lead to major advances in our understanding of millennial and orbital climate changes and their underlying causes and evolving contextuality. Outreach during Expedition 397 was highly productive, reaching a record number of students and the general public across the world through several diverse platforms, including live ship-to-shore events, webinars, social media, videos, radio pieces, blog posts, and in-person activities. 

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4. Expedition 397 Scientific Prospectus: Iberian Margin Paleoclimate

   https://doi.org/10.14379/iodp.sp.397.2022  

    Hodell, D.A. ; Abrantes, F. ; Alvarez Zarikian, C.A. ( February 2022 , Scientific prospectus)

   The Iberian margin is a well-known source of rapidly accumulating sediment that contains a high-fidelity record of millennial climate variability (MCV) for the late Pleistocene. The late Sir Nicholas (Nick) Shackleton demonstrated that piston cores from the region can be correlated precisely to polar ice cores in both hemispheres. Moreover, the narrow continental shelf off Portugal results in the rapid delivery of terrestrial material to the deep-sea environment, thereby permitting correlation of marine and ice core records to European terrestrial sequences. Few places exist in the world where such detailed marine-ice-terrestrial linkages are possible. The continuity, high sedimentation rates, and fidelity of climate signals preserved in Iberian margin sediments make this region a prime target for ocean drilling. During Integrated Ocean Drilling Program Expedition 339 (Mediterranean Outflow), one of the sites proposed here was drilled to a total depth of 155.9 meters below seafloor in multiple holes. At Site U1385 (the “Shackleton site”) a complete record of hemipelagic sedimentation was recovered for the last 1.45 My corresponding to Marine Isotope Stage 47 with sedimentation rates of 10–20 cm/ky. Preliminary results from Site U1385 demonstrate the great promise of the Iberian margin to yield long records of millennial-scale climate change and land–sea comparisons. International Ocean Discovery Program (IODP) Expedition 397 will extend this remarkable sediment archive through the Pliocene and expand the depth range of available sites by drilling additional sequences in water depths from 1304 to 4686 meters below sea level (mbsl). This depth transect is designed to complement those sites drilled during Expedition 339 (560–1073 mbsl) where sediment was recovered at intermediate water depth under the influence of Mediterranean Outflow Water (MOW). Together, the sites recovered during Expeditions 339 and 397 will constitute a complete depth transect with which to study past variability of all the major subsurface water masses of the eastern North Atlantic. Because most of the mass, thermal inertia, and carbon in the ocean-atmosphere system is contained in the deep ocean, well-placed depth transects in each of the major ocean basins are needed to understand the underlying mechanisms of glacial–interglacial cycles and MCV. We have identified four primary sites (SHACK-4C, SHACK-10B, SHACK-11B, and SHACK-14A) at which multiple holes will be drilled to ensure complete recovery of the stratigraphic sections at each site, ranging in age from the latest Miocene to Holocene. Building on the success of Site U1385 and given the seminal importance of the Iberian margin for paleoclimatology and marine-ice-terrestrial correlations, the cores recovered during Expedition 397 will provide present and future generations of paleoceanographers with the raw material needed to reconstruct the North Atlantic climate at high temporal resolution for the entire Quaternary and Pliocene. 

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5. Expedition 398 Preliminary Report: Hellenic Arc Volcanic Field

   Druitt, T.H. ; Kutterolf, S. ; Ronge, T.A. ( January 2024 , Preliminary report)

   The objectives of International Ocean Discovery Program (IODP) Expedition 398, Hellenic Arc Volcanic Field (11 December 2022 to 10 February 2023), were to study the volcanic record of the central Hellenic island arc; document the links and feedbacks between volcanism/magmatism, crustal tectonics, and sea level; investigate the processes and products of shallow submarine eruptions of silicic magma; and groundtruth the seismic stratigraphy of Santorini caldera. Reconstructing the subsidence history of the southern Aegean Sea and searching for deep life inside and outside of Santorini caldera were additional objectives. The expedition drilled 10 primary and alternate sites that were originally proposed, in addition to 2 extra sites that were requested during the expedition. Outside of Santorini caldera, drilling penetrated the thick basin fills of the crustal rift system hosting the Christiana-Santorini-Kolumbo volcanic field, identifying numerous pumice and ash layers, some known from on land and others hitherto unknown, pushing back the onset of volcanism in the area into the Early Pleistocene or even Pliocene. Significant events of mass wasting into the basins, accompanied by very high sedimentation rates, were also documented. These basin sites served to groundtruth the seismic stratigraphy of the basins and to open the way to unraveling relationships between volcanic activity and crustal rift pulses. Two sites of condensed sequences on the basin margins served to sample many volcanic layers within the detailed age-depth constraints provided mainly by biostratigraphy, as diagenetic effects complicated the magnetic reversal record significantly. Drilling penetrated the Alpine basement at three basin sites northeast of Santorini, whereas in the Christiana Basin to the southwest it penetrated a thick sequence of Messinian evaporites. Drilling inside Santorini caldera penetrated to ~120 meters below seafloor (mbsf), less than planned due to hole instability issues but deep enough to groundtruth the seismic stratigraphy and to sample the different layers. One intracaldera hole yielded a detailed tephra record of the history of the Kameni Islands, as well as possible evidence for deep bacterial colonies within the caldera. Despite variable recovery in the unstable pumice and ash deposits, the expedition was a significant success that may address almost all the science objectives once the laboratory work has been done. A dense program of preexpedition and shipboard outreach during the expedition gave rise to 59 live ship-to-shore tours, reaching 6,400 people in 7 countries including many school children. A total of 51 journalists were contacted and 9 stories were written about the expedition, with a readership of almost 200,000 people. While in Santorini caldera, the ship hosted 12 documentarians and journalists, the future products of whom should include a 1.5 h documentary and a four-part TV series about Expedition 398. The expedition social media pages were active. Prior to the expedition, an exhibition, “In Search of Earth’s Secrets,” ran for a week on Santorini and was visited by more than 1,800 school children. 

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