Introduction 4 Lithostratigraphy and sedimentology 12 Biostratigraphy and micropaleontology 19 Geochemistry 21 Paleomagnetism 23 Physical properties 28 Downhole measurements 31 Stratigraphic correlation 34 References

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Chapter contents Background and objectives. .

Integrated Ocean Drilling Program (IODP) Expedition 346 (29 July-27 September 2013) drilled seven sites covering a wide latitudinal range in the body of water bordered by the Eurasian continent, the Korean Peninsula, and the Japanese Islands, as well as two closely spaced sites in the East China Sea. This expedition recovered 6135.3 m of core with an average recovery of 101%-a record amount of core recovered during any single IODP expedition. Expedition 346 was the first scientific drilling expedition ever to focus exclusively on the climate system in this region, which is at once so critical yet potentially vulnerable to the challenges society faces in the coming years of global climate change. With the East Asian Monsoon directly affecting the water supply of one-third of the global population, the expedition scientific results and postexpedition research that will follow have direct bearing on society's understanding of this complex atmosphereocean climate system. The high quality of materials recovered and the complete documentation of their geological, geochemical, and geophysical context will lead to an unparalleled series of future studies by the expedition Science Party as well as many other scientists over the coming decades. Cores obtained during this expedition will be used to test the hypothesis that Pliocene-Pleistocene uplift of the Himalaya and Tibetan Plateau, and the consequent emergence of the two discrete modes of Westerly Jet circulation, caused the amplification of millennial-scale variability of the East Asian summer monsoon and East Asian winter monsoon and provided teleconnection mechanism(s) for Dansgaard-Oeschger cycles.Recent and novel advances in drilling technology and newly developed analytical tools enabled collection and examination of sediment records that were impossible to acquire even a few years ago. The newly engineered half advanced piston corer enabled recovery of the deepest piston core in Deep Sea Drilling Project/ Ocean Drilling Program/IODP history (490.4 m in IODP Hole U1427A); that achievement was also the deepest continuously recovered piston cored sequence, initiated at the mudline and penetrating to ~500 m core depth below seafloor, Method A (CSF-A). Technological advances delivered a series of "new surprises" (e.g., pristine dark-light laminae from ~12 Ma sediment recovered by piston core from 410 m CSF-A at IODP Site U1425 and from 210 m CSF-A at IODP Site U1430) that will stimulate new scientific in-

Chapter contents Background and objectives. .

Chapter contents Background and objectives. .

Integrated Ocean Drilling Program (IODP) Site U1423 is in the northeastern part of the marginal sea surrounded by the Japanese Islands, the Korean Peninsula, and the Eurasian continent at 41°41.95′N, 139°4.98′E and 1785 meters below sea level. The site is ~130 km south of Ocean Drilling Program (ODP) Site 796 and 100 km northwest of the entrance of the Tsugaru Strait ( Fig. F1). Site U1423 is situated on a terrace on the middle of the slope from Oshima Island, a small volcanic island 30 km to the southeast. The site is under the direct influence of the Tsushima Warm Current (TWC) that flows further north beyond the Tsugaru Strait toward the Soya Strait (Yoon and Kim, 2009). Because the sill depth of the Soya Strait is only 55 m, the influence of the TWC on the site should have been significantly affected by glacioeustatic sea level changes during the Quaternary. Although Site U1423 is relatively close to Site 796, the tectonic setting of the two sites seems different. Site 796 has been directly influenced by west-east compression caused by incipient subduction along the nearby plate boundary between the North American and Eurasian plates (Tada, 1994). In contrast, Site U1423 seems less influenced by this compression because seismic profiles suggest conformable deposition for at least for the last ~5 m.y. (upper 300 m of sediment). Relatively low linear sedimentation rates (LSRs) are anticipated based on results from the site survey. The rates are likely to be low enough to detect the contribution of eolian dust from the Asian continent. Analyses of a site survey core confirm occasional dropstones in the upper 150 m of the sequence, suggesting its appropriateness for studies of ice-rafted debris (IRD).Site U1423 is the middle site of the northern half of the latitudinal transect targeted by IODP Expedition 346 and is also the middle depth site of the depth transect. The location of Site U1423 in the northern part of the marginal sea was selected to identify the spatial extent of IRD events and their temporal variations. Because sea ice formation in this marginal sea occurred along its northwestern margin as a result of strong winter cooling by the East Asian winter monsoon (EAWM) wind (Talley et al., 2003), we expected the intensity of the IRD events to reflect the strength of the EAWM. At Site U1423, we hoped to reconstruct the EAWM intensity through examination of IRD abundance and distribution along the northern latitudinal transect in the marginal sea. Because stronger EAWM wind produces deep water, called Japan Sea