Search for: All records

International Ocean Discovery Program (IODP) Expedition 378 is designed to recover the first comprehensive set of Paleogene sedimentary sections from a transect of sites strategically positioned in the South Pacific to reconstruct key changes in oceanic and atmospheric circulation. These high southern–latitude sites will provide an unparalleled opportunity to add crucial new data and geographic coverage to existing reconstructions of Paleogene climate. As the world’s largest ocean, the Pacific Ocean is intricately linked to major changes in the global climate system. Previous drilling in the low-latitude Pacific Ocean during Ocean Drilling Program (ODP) Legs 138 and 199 and Integrated Ocean Drilling Program Expeditions 320 and 321 provided new insights into the mechanisms of the climate and carbon system, productivity changes across the zone of divergence, time-dependent calcium carbonate dissolution, bio- and magnetostratigraphy, the location of the Intertropical Convergence Zone, and evolutionary patterns for times of climatic change and upheaval. Expedition 378 in the South Pacific Ocean uniquely complements this work because appropriate high-latitude records are unobtainable in the Northern Hemisphere of the Pacific Ocean. To optimize the recovery of Paleogene carbonates buried under red clay sequences at present latitudes of 40°–52°S and enable a full range of paleoceanographic proxy-based investigations, Expedition 378 will drill a transect of sites primarily situated along magnetic Anomaly 25n on ~56 Ma crust. Additional sites are located on 40 Ma crust (Anomaly 18). The drilling strategy will also redrill the sedimentary record at Deep Sea Drilling Project (DSDP) Site 277 to obtain a continuous record of a previously spot-cored, classic Paleogene high-latitude site and provide a crucial, continuous record of the shallow Subantarctic South Pacific Ocean from the Paleocene to late Oligocene. These new cores and data will significantly contribute to the challenges of the “Climate and Ocean Change: Reading the Past, Informing the Future” theme of the IODP Science Plan (How does Earth’s climate system respond to elevated levels of atmospheric CO2? How resilient is the ocean to chemical perturbations?). Furthermore, Expedition 378 will provide material from the far South Pacific Ocean in an area with no previous scientific drilling as part of a major regional slate of expeditions in the Southern Ocean to fill a critical need for high-latitude climate reconstructions. The operational plan is to occupy seven primary sites (with two proposed alternate sites) along an east–west transect to recover the most complete sedimentary succession possible, which includes coring three holes at each site with wireline logging operations at the two deepest penetration sites. Basement will be tagged in at least one of the holes at each site. 

International Ocean Discovery Program (IODP) Expedition 368X is the third of three cruises that form the South China Sea Rifted Margin program. Expeditions 367, 368, and 368X share the common key objectives of testing scientific hypotheses of breakup of the northern South China Sea (SCS) margin and comparing its rifting style and history to other nonvolcanic or magma-poor rifted margins. Four primary sites were selected for the overall program: one in the outer margin high (OMH) and three seaward of the OMH on distinct, margin-parallel basement ridges informally labeled Ridges A, B, and C from north to south. The ridges are located in the continent–ocean transition (COT) zone ranging from the OMH to the interpreted steady-state oceanic crust (Ridge C) of the SCS. The main scientific objectives include 1. Determining the nature of the basement in crustal units across the COT of the SCS that are critical to constrain style of rifting, 2. Constraining the time interval from initial crustal extension and plate rupture to the initial generation of igneous ocean crust, 3. Constraining vertical crustal movements during breakup, and 4. Examining the nature of igneous activity from rifting to seafloor spreading. In addition, sediment cores from the drill sites targeting primarily tectonic and basement objectives will provide information on the Cenozoic regional environmental development of the Southeast Asia margin. Expedition 368X was planned to reoccupy a site started during Expedition 368. Because of repeated breakdowns of the low clutch diaphragm in the drawworks, Hole U1503A was abandoned after installing casing to 991.5 m. Despite this setback to Expedition 368 and the South China Sea Rifted Margin program, Hole U1503A was completed during Expedition 368X. The overarching scientific goal of IODP Expeditions 367 and 368 was to unveil the mechanisms of continental breakup at the northern SCS margin from rifting through steady-state spreading. A key operational objective of Site U1503 was to sample the lowermost ~300 m of sediments on top of basement to constrain the age and subsidence history of the crust at this location, the timing of normal faulting, and the environment of the early half-graben fill. A second important goal was to sample at least 100 m of the igneous basement. Deep representative sampling of the igneous material at this site will provide an important reference frame for the modeling of breakup and early ocean spreading. In Hole U1503A, the sediment sequence was cored with the rotary core barrel (RCB) system from 995.1 to 1597.84 m (602.74 m penetration; 128.01 m recovered; 21%) and then the underlying basement was continuously cored from 1597.84 to 1710.1 m (112.26 m penetration; 47.91 m recovered; 43%). Although logging deeper than 991.5 m (bottom of casing) was not possible because of unstable hole conditions, Hole U1503A was logged with the Vertical Seismic Imager in the cased portion of the hole. No days were lost to waiting on weather, and the only mechanical downtime was a 1.5 h period when an electrical malfunction caused the top drive to shut down for repairs. Expedition 368X successfully completed the operational objectives in Hole U1503A that were abandoned during Expedition 368. In the SCS margin science program, material recovered during Expedition 368X will contribute toward meeting the four specific objectives of Expeditions 367 and 368. Postexpedition research on the sediments and basalt recovered from Hole U1503A will allow for determination of emplacement age and geochemical analyses of rock composition and assessment of melting processes and age of crystallization. The combination of such analyses will contribute to geochemical or thermomechanical modeling that will constrain mantle origin and melting processes leading to the formation of these basalts.